query: antennas that transmit an equal amount of energy in the horizontal direction are called

pos: Antenna (radio) to move back and forth, creating oscillating currents in the antenna. Antennas can be designed to transmit and receive radio waves in all horizontal directions equally (omnidirectional antennas), or preferentially in a particular direction (directional or high gain antennas). An antenna may include parasitic elements, parabolic reflectors or horns, which serve to direct the radio waves into a beam or other desired radiation pattern. The first antennas were built in 1888 by German physicist Heinrich Hertz in his pioneering experiments to prove the existence of electromagnetic waves predicted by the theory of James Clerk Maxwell. Hertz placed dipole antennas at

pos: Antenna (radio) classified as omnidirectional, radiating energy approximately equally in all directions, or Directional, where energy radiates more along one direction than others. (Antennas are reciprocal, so the same effect occurs for reception of radio waves.) A completely uniform omnidirectional antenna is not physically possible. Many important antenna types have a uniform radiation pattern in the horizontal plane, but send little energy upward or downward. A "directional" antenna usually is intended to maximize its coupling to the electromagnetic field in the direction of the other station. One example of omnidirectional antennas is the very common "vertical antenna" or whip antenna consisting of

pos: Omnidirectional antenna radiator, horizontal loop antenna (sometimes known colloquially as a 'circular aerial' because of the shape) and the halo antenna. Higher-gain omnidirectional antennas can also be built. "Higher gain" in this case means that the antenna radiates less energy at higher and lower elevation angles and more in the horizontal directions. High-gain omnidirectional antennas are generally realized using collinear dipole arrays. These consist of multiple half-wave dipoles mounted collinearly (in a line), fed in phase. The coaxial collinear (COCO) antenna uses transposed coaxial sections to produce in-phase half-wavelength radiators. A Franklin Array uses short U-shaped half-wavelength sections whose radiation cancels in

pos: Omnidirectional antenna all horizontal directions, while the power radiated drops off with elevation angle so little radio energy is aimed into the sky or down toward the earth and wasted. Omnidirectional antennas are widely used for radio broadcasting antennas, and in mobile devices that use radio such as cell phones, FM radios, walkie-talkies, wireless computer networks, cordless phones, GPS, as well as for base stations that communicate with mobile radios, such as police and taxi dispatchers and aircraft communications. Common types of low-gain omnidirectional antennas are the whip antenna, "Rubber Ducky" antenna, ground plane antenna, vertically oriented dipole antenna, discone antenna, mast

neg: Antenna (radio) location) of the antenna's currents when such a direction can be defined. For instance, a vertical whip antenna or Wi-Fi antenna vertically oriented will transmit and receive in the vertical polarization. Antennas with horizontal elements, such as most rooftop TV antennas in the United States, are horizontally polarized (broadcast TV in the U.S. usually uses horizontal polarization). Even when the antenna system has a vertical orientation, such as an array of horizontal dipole antennas, the polarization is in the horizontal direction corresponding to the current flow. The polarization of a commercial antenna is an essential specification. Polarization is the sum

neg: Whip antenna horizontal directions, falling monotonically to zero on the axis. Antennas longer than a quarter wavelength have patterns consisting of several conical "lobes"; with radiation maxima at several elevation angles; the longer the electrical length of the antenna, the more lobes the pattern has. Vertical whip antennas are widely used for nondirectional radio communication on the surface of the Earth, where the direction to the transmitter (or the receiver) is unknown or constantly changing, for example in portable FM radio receivers, walkie-talkies, and two-way radios in vehicles. This is because they transmit (or receive) equally well in all horizontal directions, while

neg: Antenna array The parasitic elements function as resonators, absorbing radio waves from the driven element and reradiating them with a different phase, to modify the radiation pattern of the antenna, increasing the power radiated in the desired direction. Since these have only one driven element they are often called "antennas" instead of "arrays". Antenna array An antenna array (or array antenna) is a set of multiple connected antennas which work together as a single antenna, to transmit or receive radio waves. The individual antennas (called "elements") are usually connected to a single receiver or transmitter by feedlines that feed the power to

neg: Antenna array are linked together into an antenna array, to achieve higher resolution. Using the technique called aperture synthesis such an array can have the resolution of an antenna with a diameter equal to the distance between the antennas. In the technique called Very Long Baseline Interferometry (VLBI) dishes on separate continents have been linked, creating "array antennas" thousands of miles in size. Most array antennas can be divided into two classes based on how the component antennas' axis is related to the direction of radiation. There are also arrays (such as phased arrays) in which the direction of radiation is at

neg: MIMO radar placement vector of the virtual array is equal to the convolution of formula_10 and formula_11: Picture above shows the examples of antenna geometry to form a virtual array. In the first example, two uniformly distributed antenna arrays form a 5-element virtual array despite having 6 antennas in total. In the second example, a nine-element virtual array is obtained by increasing the distance between the transmit antennas, implying that a better spatial resolution can be achieved. <br>To estimate the Direction of arrival of the targets according to the N*M signals, methods like MUSIC (algorithm) and Maximum likelihood estimation are commonly used

neg: Spark-gap transmitter Marconi tried longer antennas, which radiated lower frequency waves, probably in the MF band around 2 MHz, he found that he could transmit further. Another advantage was that these vertical antennas radiated vertically polarized waves, instead of the horizontally polarized waves produced by Hertz's horizontal antennas. These longer vertically polarized waves could travel beyond the horizon, because they propagated as a ground wave that followed the contour of the Earth. Under certain conditions they could also reach beyond the horizon by reflecting off layers of charged particles (ions) in the upper atmosphere, later called skywave propagation. After failing to interest

neg: Space–time block code transmits. This means that the signal does not have a constant envelope and that the power each antenna must transmit has to vary, both of which are undesirable. Modified versions of this code that overcome this problem have since been designed. Two straightforward codes for 4 transmit antennas are: These codes achieve rate-1/2 and rate-3/4 respectively, as for their 3-antenna counterparts. formula_26 exhibits the same uneven power problems as formula_24. An improved version of formula_26 is which has equal power from all antennas in all time-slots. One particularly attractive feature of orthogonal STBCs is that maximum likelihood decoding can be

neg: Loop antenna all antennas, smaller antennas are less efficient radiators than larger antennas. However, small loops become practical at lower frequencies where wavelengths are tens to hundreds of meters long, or greater, and full-size loops (the most efficient) and half-wave straight-wire antennas (next-most efficient) become infeasibly large. A common distinguishing feature of small loops is that their direction of maximum transmission or reception is within the plane of the loop – the opposite of large loops, whose maximum is perpendicular to the plane. In the direction that large loops produce their strongest signals in both transmit and receive, small loops have a

neg: 4G at the receiver. Independent streams can then be transmitted simultaneously from all the antennas. This technology, called MIMO (as a branch of intelligent antenna), multiplies the base data rate by (the smaller of) the number of transmit antennas or the number of receive antennas. Apart from this, the reliability in transmitting high speed data in the fading channel can be improved by using more antennas at the transmitter or at the receiver. This is called "transmit" or "receive diversity". Both transmit/receive diversity and transmit spatial multiplexing are categorized into the space-time coding techniques, which does not necessarily require the channel

neg: Channel state information the least-square estimator (also known as the minimum-variance unbiased estimator) is where formula_30 denotes the conjugate transpose. The estimation Mean Square Error (MSE) is proportional to where formula_32 denotes the trace. The error is minimized when formula_33 is a scaled identity matrix. This can only be achieved when formula_34 is equal to (or larger than) the number of transmit antennas. The simplest example of an optimal training matrix is to select formula_35 as a (scaled) identity matrix of the same size that the number of transmit antennas. If the channel and noise distributions are known, then this a priori information

neg: Telecommunications cable Telecommunications cable Telecommunications cables are a type of guided transmission mediums. Cables are usually known to transmit electric energy (AC/DC); however, cables in telecommunications fields are used to transmit electromagnetic waves; they are called "electromagnetic wave guides". Telecommunications are based on transmitting modulated waves/signals through a medium and receiving them. When the distance between the transmitter and receiver is far, or an unguided medium transmission is used, antennas are used; otherwise, telecommunications cables are used in guided medium transmission. There are several types of telecommunications cable: Telecommunications power cable products, as described in Telcordia GR-347, consist of a stranded copper

neg: Telecommunications cable and analysis criteria and QMS programs are given in GR-347 for telecommunications power cables for telecommunications equipment in COs and within OSP facilities. Telecommunications cable Telecommunications cables are a type of guided transmission mediums. Cables are usually known to transmit electric energy (AC/DC); however, cables in telecommunications fields are used to transmit electromagnetic waves; they are called "electromagnetic wave guides". Telecommunications are based on transmitting modulated waves/signals through a medium and receiving them. When the distance between the transmitter and receiver is far, or an unguided medium transmission is used, antennas are used; otherwise, telecommunications cables are used in guided

neg: Near vertical incidence skywave the antenna. One source says that a single ground wire can provide antenna gain in the 3–6 dB range. Another source indicates 2 dB for a single wire and nearly 4 dB for multiple ground wires. Ground wires are more necessary when using lower dipoles over poor soils as without them considerable energy goes into heating the ground. Depending on the specific requirements, various antennas (i.e. Sloper, T2FD, Dipole) can be used for NVIS communication, with horizontal dipoles or inverted V dipoles at about 0.2 wavelengths above ground giving the best results on transmit and at about 0.16 wavelengths on

neg: Adcock antenna officer in the British Expeditionary Force in wartime France at the time he filed his invention—solved this problem by replacing the loop antennas with symmetrically inter-connected pairs of vertical monopole or dipole antennas of equal length. This created the equivalent of square loops, but without their horizontal members, thus eliminating sensitivity to much of the horizontally polarized distortion. The same principles remain valid today, and the Adcock antenna array and its variants are still used for radio direction finding. In the late 1920s, the Adcock antenna was adopted for aerial navigation, in what became known as the low frequency radio

neg: Antenna (radio) analog television transmissions are usually horizontally polarized, because in urban areas buildings can reflect the electromagnetic waves and create ghost images due to multipath propagation. Using horizontal polarization, ghosting is reduced because the amount of reflection in the horizontal polarization off the side of a building is generally less than in the vertical direction. Vertically polarized analog television have been used in some rural areas. In digital terrestrial television such reflections are less problematic, due to robustness of binary transmissions and error correction. Current circulating in one antenna generally induces a voltage across the feedpoint of nearby antennas or antenna

neg: Fixed wireless antennas are generally larger than those seen in Wi-Fi setups and are designed for outdoor use. Several types of radio antennas are available that accommodate various weather conditions, signal distances and bandwidths. They are usually selected to make the beam as narrow as possible and thus focus transmit power to their destination, increasing reliability and reducing the chance of eavesdropping or data injection. The links are usually arranged as a point-to-point setup to permit the use of these antennas. This also permits the link to have better speed and or better reach for the same amount of power. These antennas

neg: Non-line-of-sight propagation very low bandwidth, so this type of communication is not widely used. A tropospheric scatter NLOS link typically operates at a few gigahertz using potentially very high transmit powers (typically 3 kW to 30 kW, depending on conditions), very sensitive receivers and very high gain, usually fixed, large reflector antennas. The transmit beam is directed into the troposphere just above the horizon with sufficient power flux density that gas and water vapour molecules cause scattering in a region in the beam path known as the scatter volume. Some components of the scattered energy travel in the direction of the receiver

neg: Carnot cycle its integral over any closed loop is zero and it follows that the area inside the loop on a T-S diagram is equal to the total work performed if the loop is traversed in a clockwise direction, and is equal to the total work done on the system as the loop is traversed in a counterclockwise direction. Evaluation of the above integral is particularly simple for the Carnot cycle. The amount of energy transferred as work is The total amount of thermal energy transferred from the hot reservoir to the system will be and the total amount of thermal energy

neg: Conical scanning two signals are multiplexed inside a waveguide device that has a rotating vane. The output of the multiplex device is a single RF signal and two position signals that indicate left/right and up/down. The COSRO technique does not transmit any signals that indicate the position of the rotating vane. RF receive signals from multiple transmit pulses are combined mathematically to create a vertical and horizontal signal. The vertical signal is created by adding RF samples when the vane/feedhorn is in the up direction and subtracting RF samples when the vane/feedhorn is in the down direction. The horizontal signal is created

neg: Magnetic domain it creates a domain wall between the domains, where magnetic dipoles (molecules) with magnetization pointing in different directions are adjacent. The exchange interaction which creates the magnetization is a force which tends to align nearby dipoles so they point in the same direction. Forcing adjacent dipoles to point in different directions requires energy. Therefore, a domain wall requires extra energy, called the domain wall energy, which is proportional to the area of the wall. Thus the net amount that the energy is reduced when a domain splits is equal to the difference between the magnetic field energy saved, and the

neg: Isotropic radiator is a calibrated radio receiver with an antenna which approximates an isotropic reception pattern; that is, it has close to equal sensitivity to radio waves from any direction. It is used as a field measurement instrument to measure electromagnetic sources and calibrate antennas. The isotropic receiving antenna is usually approximated by three orthogonal antennas or sensing devices with a radiation pattern of the omnidirectional type formula_6, such as short dipoles or small loop antennas. The parameter used to define accuracy in the measurements is called isotropic deviation. In optics, an isotropic radiator is a point source of light. The sun

neg: Naval Radio Transmitter Facility (NRTF) Niscemi Communications System (HFGCS) and a US Navy MUOS Ground Station. The surrounding antenna field supports one 827 foot LF antenna, 44 HF (3–30 MHz) antennas, three MUOS Earth Terminal parabolic antennas, and 2 UHF Directional Helical antennas for satellite direction finding. Several different types of HF antenna are installed, though the majority are no longer in use. 116 Antenna towers are installed which hold aloft 35 antenna transmission lines. Antenna types include four Horizontal Log Periodic (HLPA) with 2 tall towers each, four rotatable log periodic (RLPA), seven Horizontal Omnidirectional Broadband (HOBA) each with 4 antenna towers, seven High Take-Off

neg: Glossary of video terms in a distance equal to picture height. The details that can be distinguished on the television screen. Vertical resolution refers to the number of horizontal black and white lines that can be resolved in the picture height. Horizontal resolution refers to the black and white lines resolved in a dimension equal to the vertical height and may be limited by the video amplifier bandwidth. The amount of resolvable detail in the vertical direction in a picture. It is usually expressed as the number of distinct horizontal lines, alternately black and white, which can theoretically be seen in a picture. Also

neg: Dipole antenna the conductor, falling to zero in the axial direction, thus implementing an omnidirectional antenna if installed vertically, or (more commonly) a weakly directional antenna if horizontal. Most antennas in use can be seen as based on the dipole. Although they may be used as standalone low-gain antennas, they are also employed as driven elements in more complex antenna designs such as the Yagi antenna and driven arrays. Dipole antennas (or such designs derived from them, including the monopole) are used to feed more elaborate directional antennas such as a horn antenna, parabolic reflector or corner reflector. Engineers analyze vertical (or

neg: ALLISS to transmit shortwave broadcasts by Radio France International (RFI), along with other broadcast services. General category Applicable related technologies Broadcasters using ALLISS modules Technology portals (non-Thales) <br> ALLISS ALLISS is a fully rotatable antenna system for high power shortwave radio broadcasting in the 6 MHz to 26 MHz range. An ALLISS module is a self-contained shortwave relay station that is used for international broadcasting. ALLISS is a special design case of HRS type antennas. True ALLISS systems have solid radiators (horizontal radiating elements) versus tensioned flexible (open) radiators found with all other variations of ITU HRS type antennas systems. The

neg: Side lobe are called ""side lobes"", and usually represent unwanted radiation in undesired directions. The side lobe in the opposite direction (180°) from the main lobe is called the back lobe. In transmitting antennas, excessive side lobe radiation wastes energy and may cause interference to other equipment. Classified information may be picked up by unintended receivers. In receiving antennas, side lobes may pick up interfering signals, and increase the noise level in the receiver. The power density in the side lobes is generally much less than that in the main beam. It is generally desirable to minimize the sidelobe level (SLL), which

neg: Vivaldi antenna arranged in orthogonal direction – for transmitting / receiving both polarization orientations. If fed with 90-degree phase-shifted signals, orthogonal devices can transmit/receive circular-oriented electromagnetic waves. Vivaldi antennas are useful for any frequency, as all antennas are scalable in size for use at any frequency. Printed circuit technology makes this type antenna cost effective at microwave frequencies exceeding 1 GHz. Advantages of Vivaldi antennas are their broadband characteristics (suitable for ultra-wideband signals ), their easy manufacturing process using common methods for PCB production, and their easy impedance matching to the feeding line using microstrip line modeling methods. The MWEE collection of

neg: Stargate (video game) forth), the planet (and all its 10 Humanoids) is restored. As well as the points gained by killing aliens, scores are also awarded for the following: By default, the player receives an extra life, smart bomb, and Inviso energy every 10,000 points. This amount can be overridden when the machine is in maintenance mode. The control system of "Stargate" expands on that of the Defender arcade game. It has a joystick to move up and down, a 'Reverse' button to toggle the player's horizontal direction, and a 'Thrust' button to move in that direction. There is also a Fire button

neg: Yaw drive Yaw drive The yaw drive is an important component of the horizontal axis wind turbines' yaw system. To ensure the wind turbine is producing the maximal amount of electric energy at all times, the yaw drive is used to keep the rotor facing into the wind as the wind direction changes. This only applies for wind turbines with a horizontal axis rotor. The wind turbine is said to have a yaw error if the rotor is not aligned to the wind. A yaw error implies that a lower share of the energy in the wind will be running through the

neg: Polarization (waves) the other lens (of the closed eye) will have the correct circular polarization allowing the closed eye to be easily seen by the open one. All radio (and microwave) antennas used for transmitting or receiving are intrinsically polarized. They transmit in (or receive signals from) a particular polarization, being totally insensitive to the opposite polarization; in certain cases that polarization is a function of direction. Most antennas are nominally linearly polarized, but elliptical and circular polarization is a possibility. As is the convention in optics, the "polarization" of a radio wave is understood to refer to the polarization of its

neg: Antenna (radio) the above example. The radiation pattern of an antenna is a plot of the relative field strength of the radio waves emitted by the antenna at different angles in the far-field. It is typically represented by a three-dimensional graph, or polar plots of the horizontal and vertical cross sections. The pattern of an ideal isotropic antenna, which radiates equally in all directions, would look like a sphere. Many nondirectional antennas, such as monopoles and dipoles, emit equal power in all horizontal directions, with the power dropping off at higher and lower angles; this is called an omnidirectional pattern and when

neg: Altazimuth mount Altazimuth mount An altazimuth or alt-azimuth mount is a simple two-axis mount for supporting and rotating an instrument about two perpendicular axes – one vertical and the other horizontal. Rotation about the vertical axis varies the azimuth (compass bearing) of the pointing direction of the instrument. Rotation about the horizontal axis varies the altitude (angle of elevation) of the pointing direction. These mounts are used, for example, with telescopes, cameras, radio antennas, heliostat mirrors, solar panels, and guns and similar weapons. Several names are given to this kind of mount, including altitude-azimuth, azimuth-elevation and various abbreviations thereof. A gun turret

neg: Tropospheric scatter consequently only a tiny proportion of the radio energy is collected by the receiving antennas. Frequencies of transmission around 2 GHz are best suited for tropospheric scatter systems as at this frequency the wavelength of the signal interacts well with the moist, turbulent areas of the troposphere, improving signal to noise ratios. Historically, high gain dish or billboard antennas were required for tropospheric scatter systems as the propagation losses are very high; only about one billion-billionth (1 x 10) of the transmit power is available at the receiver. Paths were established at distances over 1,000 km. They required antennas ranging

neg: Air interface or antennas), or aerial, is an electrical device which converts electric power into radio waves, and vice versa.[1] It is usually used with a radio transmitter or radio receiver. In transmission, a radio transmitter supplies an electric current oscillating at radio frequency (i.e. a high frequency alternating current (AC)) to the antenna's terminals, and the antenna radiates the energy from the current as electromagnetic waves (radio waves). An antenna focuses the radio waves in a certain direction. Usually, this is called the main direction. Because of that, in other directions less energy wil be emitted. The gain of an antenna,

neg: Helical antenna (anti-clockwise) for an observer looking in the direction of propagation" Thus a right-handed helix radiates a wave which is right-handed, the electric field vector rotating clockwise looking in the direction of propagation. Helical antennas can receive signals with any type of linear polarisation, such as horizontal or vertical polarisation, but when receiving circularly polarized signals the handedness of the receiving antenna must be the same as the transmitting antenna; left-hand polarized antennas suffer a severe loss of gain when receiving right-circularly-polarized signals, and vice versa. The dimensions of the helix are determined by the wavelength λ of the radio waves

neg: Radial (radio) be absolutely straight nor absolutely horizontal. Although they provide an electrical "ground", they do not require any actual contact with the surrounding earth, even though advisable. When the radials are mechanically incorporated into the structure of a small antenna it is called a "ground plane antenna". For these antennas the radials slope off at an angle and are also called a "skirt". Similar radiating wires can be placed on the top of antennas (instead of at the base) that serve an almost identical electrical function, but in that case the structure of radial wires at the top end of the

neg: Polarization (waves) electric field, with the magnetic field being at a 90 degree rotation with respect to it for a linearly polarized wave. The vast majority of antennas are linearly polarized. In fact it can be shown from considerations of symmetry that an antenna that lies entirely in a plane which also includes the observer, can "only" have its polarization in the direction of that plane. This applies to many cases, allowing one to easily infer such an antenna's polarization at an intended direction of propagation. So a typical rooftop Yagi or log-periodic antenna with horizontal conductors, as viewed from a second

neg: Eglin AFB Site C-6 shifter attached, through which the current from the antenna must pass to get to the receiver. The currents from the separate antennas add together in the receiver with the correct phase that the receiver is sensitive to waves coming from only one direction. By altering the phase of the receiving antennas, the computer can steer the receiving pattern (main lobe) of the antenna to the same direction as the transmitted beam. The radar beam can be deflected up to 60° from its central boresight axis, allowing it to scan an azimuth (horizontal angle) of 120° and an elevation range from

neg: Synthetic-aperture radar (S) to identify the scattering behavior of objects after an interaction with electromagnetic wave. The matrix is represented by a combination of horizontal and vertical polarization states of transmitted and received signals. formula_33 where, HH is for horizontal transmit and horizontal receive, VV is for vertical transmit and vertical receive, HV is for horizontal transmit and vertical receive, and VH – for vertical transmit and horizontal receive. The first two of these polarization combinations are referred to as like-polarized (or co-polarized), because the transmit and receive polarizations are the same. The last two combinations are referred to as cross-polarized because

neg: Impedance matching and on the load side formula_27 where formula_28, formula_29, formula_30, formula_31, formula_32, formula_33, and formula_34 are phasors. At a boundary, voltage and current must be continuous, therefore All these conditions are satisfied by where formula_41 the reflection coefficient going from the transmission line to the load. The purpose of a transmission line is to get the maximum amount of energy to the other end of the line (or to transmit information with minimal error), so the reflection is as small as possible. This is achieved by matching the impedances formula_43 and formula_15 so that they are equal (formula_45). At the

neg: Transmit diversity Transmit diversity Transmit diversity is radio communication using signals that originate from two or more independent sources that have been modulated with identical information-bearing signals and that may vary in their transmission characteristics at any given instant. It can help overcome the effects of fading, outages, and circuit failures. When using diversity transmission and reception, the amount of received signal improvement depends on the independence of the fading characteristics of the signal as well as circuit outages and failures. Considering antenna diversity, in many systems additional antennas may be expensive or impractical at the remote or even at the base

neg: Sauropod neck posture The approximate conclusion was that an about equal amount of energy would have been used up. Elongated cervical ribs are skeletal evidence for a strong core to support the neck and limit its movement when walking. The study supports the idea that during times of drought and famine, an upright neck was crucial for these sauropods to survive. Sauropod neck posture Sauropod neck posture is a subject occasionally debated among scientists, with some favoring postures closer to horizontal whilst others a more upright posture. Research has looked at various avenues of evidence and analysis including: attempting to reconstruct the neutral

neg: Spatial correlation Spatial correlation Theoretically, the performance of wireless communication systems can be improved by having multiple antennas at the transmitter and the receiver. The idea is that if the propagation channels between each pair of transmit and receive antennas are statistically independent and identically distributed, then multiple independent channels with identical characteristics can be created by precoding and be used for either transmitting multiple data streams or increasing the reliability (in terms of bit error rate). In practice, the channels between different antennas are often correlated and therefore the potential multi antenna gains may not always be obtainable. This is called

neg: Shear mapping three shear mappings (horizontal, vertical, then horizontal again) to rotate a digital image by an arbitrary angle. The algorithm is very simple to implement, and very efficient, since each step processes only one column or one row of pixels at a time. The oblique type can be thought of as normal text under a shear. Shear mapping In plane geometry, a shear mapping is a linear map that displaces each point in fixed direction, by an amount proportional to its signed distance from a line that is parallel to that direction. This type of mapping is also called shear transformation,

neg: Null (radio) Null (radio) In radio electronics, a null is an area or vector in an antenna's radiation pattern where the signal cancels out almost entirely. This can be an advantage, as nulls in the horizontal plane can be used to protect other transmitters from interference. If not carefully planned however, nulls can unintentionally prevent reception of a signal. Null fill in the vertical plane is used to prevent this. Also, some directional antennas have very narrow, sharp nulls. These antennas when used for direction finding are aimed away from the signal of interest until the antenna's null is pointed at the

neg: Null (radio) signal, and the signal cannot be detected. Null (radio) In radio electronics, a null is an area or vector in an antenna's radiation pattern where the signal cancels out almost entirely. This can be an advantage, as nulls in the horizontal plane can be used to protect other transmitters from interference. If not carefully planned however, nulls can unintentionally prevent reception of a signal. Null fill in the vertical plane is used to prevent this. Also, some directional antennas have very narrow, sharp nulls. These antennas when used for direction finding are aimed away from the signal of interest until

neg: Antenna (radio) current waves travel in one direction, instead of bouncing back and forth to form standing waves as in resonant antennas. They have linear polarization (except for the helical antenna). Unidirectional traveling wave antennas are terminated by a resistor at one end equal to the antenna's characteristic resistance, to absorb the waves from one direction. This makes them inefficient as transmitting antennas. The following two antenna types do not quite properly fit in any of the sections above, or fit into several, depending on the wavelength to antenna-length ratio. Ground reflections is one of the common types of multipath. The radiation

neg: Precoding Precoding Precoding is a generalization of beamforming to support multi-stream (or multi-layer) transmission in multi-antenna wireless communications. In conventional single-stream beamforming, the same signal is emitted from each of the transmit antennas with appropriate weighting (phase and gain) such that the signal power is maximized at the receiver output. When the receiver has multiple antennas, single-stream beamforming cannot simultaneously maximize the signal level at all of the receive antennas. In order to maximize the throughput in multiple receive antenna systems, multi-stream transmission is generally required. In point-to-point systems, precoding means that multiple data streams are emitted from the transmit antennas

neg: Shear mapping Shear mapping In plane geometry, a shear mapping is a linear map that displaces each point in fixed direction, by an amount proportional to its signed distance from a line that is parallel to that direction. This type of mapping is also called shear transformation, transvection, or just shearing. An example is the mapping that takes any point with coordinates formula_1 to the point formula_2. In this case, the displacement is horizontal, the fixed line is the formula_3-axis, and the signed distance is the formula_4 coordinate. Note that points on opposite sides of the reference line are displaced in opposite

neg: Reconfigurable antenna distribution of the radiation pattern. Beam steering is the most extended application and consists of steering the direction of maximum radiation to maximize the antenna gain in a link with mobile devices. Pattern reconfigurable antennas are usually designed using movable/rotatable structures or switchable and reactively-loaded parasitic elements.. In the last 10 years, metamaterial-based reconfigurable antennas have gained attention due their small form factor, wide beam steering range and wireless applications. Polarization reconfigurable antennas are capable of switching between different polarization modes. The capability of switching between horizontal, vertical and circular polarizations can be used to reduce polarization mismatch losses in

neg: Solar power in Armenia Solar power in Armenia Solar energy is widely available in Armenia due to its geographical position and is considered a developing industry. According to the Ministry of Energy Infrastructures and Natural Resources of Armenia, Armenia has an average of about 1720 kilowatt hour (kWh) solar energy flow per square meter of horizontal surface annually and has a potential of 1000 MW power production. In the capital Yerevan, the average solar energy flux is equal to 1642 kWh/m. Armenia's area cannot be considered as homogeneous from the perspective of available solar energy: the difference between the amount of solar energy reaching

neg: Space–time block code full diversity with "linear" processing at the receiver. Earlier proposals for transmit diversity required processing schemes which scaled "exponentially" with the number of transmit antennas. Furthermore, it was the first open-loop transmit diversity technique which had this capability. Subsequent generalizations of Alamouti's concept have led to a tremendous impact on the wireless communications industry. Tarokh et al. discovered a set of STBCs that are particularly straightforward, and coined the scheme's name. They also proved that no code for more than 2 transmit antennas could achieve full-rate. Their codes have since been improved upon (both by the original authors and by

neg: International broadcasting cases counteracts the lesser effects of jamming. International stations generally use special directional antennas to aim the signal toward the intended audience and increase the effective power in that direction. Use of such antennas for international broadcasting began in the mid-1930s and became prominent by the 1950s. By using antennas which focus most of their energy in one direction, a modern station may achieve the equivalent, in that direction, of tens of millions of watts of radio power. Some international broadcasters have become available via Digital Audio Broadcasting (DAB) in Europe in the 1990s, and in a similar limited way

neg: Loop antenna RFID tags and readers interact by induction rather than transmission waves, and so are not antennas. The use of coupling coils for inductive (magnetic) transmission systems including LF and HF (rather than UHF) is outside the scope of this article. These systems do operate at radio frequencies, and do involve the use of small loops which are called "antennas" in the trade. Although these small loops are sometimes indistinguishable from the small loop antennas discussed here, such systems are not designed to transmit or receive signal waves (electromagnetic waves), and can only operate over short distances. They are near field

neg: Transmit diversity station. In these cases, transmit diversity can be used to provide diversity benefit at a receiver with multiple transmit antennas only. With transmit diversity, multiple antennas transmit delayed versions of a signal, creating frequency-selective fading, which is equalized at the receiver to provide diversity gain. Since transmit diversity with N antennas results in N sources of interference to other users, the interference environment will be different from conventional systems with one transmit antenna. Thus even if transmit diversity has almost the same performance as receive diversity in noise-limited environments, the performance in interference-limited environments will differ. Transmit diversity Transmit diversity

neg: Multi-user MIMO traffic adaptive scheduling is called dynamic single frequency networks (DSFN). CO-MIMO is a technique useful for future cellular networks which consider wireless mesh networking or wireless ad hoc networking. In wireless ad hoc networks, multiple transmit nodes communicate with multiple receive nodes. To optimize the capacity of ad hoc channels, MIMO concepts and techniques can be applied to multiple links between the transmit and receive node clusters. Contrasted to multiple antennas in a single-user MIMO transceiver, participating nodes and their antennas are located in a distributed manner. So, to achieve the capacity of this network, techniques to manage distributed radio

neg: Raised-cosine filter a matched filter is used in the receiver, due to the effects of white noise. For zero ISI, it is the net response of the transmit and receive filters that must equal formula_33: And therefore: These filters are called root-raised-cosine filters. Raised-cosine filter The raised-cosine filter is a filter frequently used for pulse-shaping in digital modulation due to its ability to minimise intersymbol interference (ISI). Its name stems from the fact that the non-zero portion of the frequency spectrum of its simplest form (formula_1) is a cosine function, 'raised' up to sit above the formula_2 (horizontal) axis. The raised-cosine filter

neg: Antenna array Antenna array An antenna array (or array antenna) is a set of multiple connected antennas which work together as a single antenna, to transmit or receive radio waves. The individual antennas (called "elements") are usually connected to a single receiver or transmitter by feedlines that feed the power to the elements in a specific phase relationship. The radio waves radiated by each individual antenna combine and superpose, adding together (interfering constructively) to enhance the power radiated in desired directions, and cancelling (interfering destructively) to reduce the power radiated in other directions. Similarly, when used for receiving, the separate radio frequency

neg: MIMO radar MIMO radar MIMO radar is an advanced type of phased array radar employing digital receivers and waveform generators distributed across the aperture. MIMO radar signals propagate in a fashion similar to Multistatic radar. However, instead of distributing the radar elements throughout the surveillance area, antennas are closely located to obtain better spatial resolution, Doppler resolution, and dynamic range. MIMO radar may also be used to obtain Low-probability-of-intercept radar properties. In a traditional Phased array system, additional antennas and related hardware are needed to improve spatial resolution. MIMO radar systems transmit mutually orthogonal signals from multiple transmit antennas, and these waveforms

neg: Square-lattice Ising model In a general case, the horizontal coupling "J" is not equal to the coupling in the vertical direction, "J*". With an equal number of rows and columns in the lattice, there will be "N" of each. In terms of where formula_5 where "T" is absolute temperature and "k" is Boltzmann's constant, the partition function formula_6 is given by The critical temperature formula_8 can be obtained from the Kramers–Wannier duality relation. Denoting the free energy per site as formula_9, one has: where Assuming there is only one critical line in the (K,L) plane, the duality relation implies that this is given

neg: Spatial correlation said to degrade the performance of multi antenna systems and put a limit on the number of antennas that can be effectively squeezed into a small device (as a mobile phone). This seems intuitive as spatial correlation decreases the number of independent channels that can be created by precoding, but is not true for all kinds of channel knowledge as described below. In a narrowband flat-fading channel with formula_1 transmit antennas and formula_2 receive antennas (MIMO), the propagation channel is modeled as where formula_4 and formula_5 are the formula_6 receive and formula_7 transmit vectors, respectively. The formula_6 noise vector is

neg: Arg e Bam Bam area has an underground made of a series of faults. The main one called Bam Fault had been inactive for a very long time. Though the earthquake was on the southern part of Bam, the main direction of the horizontal motion of the waves was East-West and was perpendicular to the direction of the main fault located around 3 km East of Bam. It seems that the Bam Fault channeled the energy of the earthquake in its direction, North-South, but in the same time it acted like a boomerang or amplifier by sending back the energy on an East-West

neg: Sector antenna narrow in the vertical direction. According to the radiation patterns depicted, typical antennas used in a three-sector base station have 66° of horizontal beamwidth. This means that the signal strength at the ±33° directions is half (3 dB down) from its peak value at the center. At the ±60° directions, it is suggested to be a border of a sector and antenna gain is negligible there. Vertical beamwidth is not wider than 15°, meaning 7.5° in each direction. Unlike antennas for commercial broadcasting - AM, FM and television for example - which must achieve line-of-sight over many miles or kilometers,

neg: Atom quantum states, are responsible for atomic spectral lines. The amount of energy needed to remove or add an electron—the electron binding energy—is far less than the binding energy of nucleons. For example, it requires only 13.6 eV to strip a ground-state electron from a hydrogen atom, compared to 2.23 "million" eV for splitting a deuterium nucleus. Atoms are electrically neutral if they have an equal number of protons and electrons. Atoms that have either a deficit or a surplus of electrons are called ions. Electrons that are farthest from the nucleus may be transferred to other nearby atoms or shared

neg: Radiation pattern antenna in which the objective is to direct the radio waves in one particular direction, the lobe in that direction is larger than the others; this is called the ""main lobe"". The axis of maximum radiation, passing through the center of the main lobe, is called the ""beam axis"" or "boresight axis"". In some antennas, such as split-beam antennas, there may exist more than one major lobe. A minor lobe is any lobe except a major lobe. The other lobes, representing unwanted radiation in other directions, are called ""side lobes"". The side lobe in the opposite direction (180°) from the

neg: Introduction to quantum mechanics the maximum energy that can be imparted to the electron. To explain the threshold effect, Einstein argued that it takes a certain amount of energy, called the "[[work function]]" and denoted by , to remove an electron from the metal. This amount of energy is different for each metal. If the energy of the photon is less than the work function, then it does not carry sufficient energy to remove the electron from the metal. The threshold frequency, , is the frequency of a photon whose energy is equal to the work function: If is greater than , the energy

neg: Work (physics) the same weight twice the distance. Work is closely related to energy. The work-energy principle states that an increase in the kinetic energy of a rigid body is caused by an equal amount of positive work done on the body by the resultant force acting on that body. Conversely, a decrease in kinetic energy is caused by an equal amount of negative work done by the resultant force. From Newton's second law, it can be shown that work on a free (no fields), rigid (no internal degrees of freedom) body, is equal to the change in kinetic energy formula_8 of

neg: Peak ground acceleration Peak ground acceleration Peak ground acceleration (PGA) is equal to the maximum ground acceleration that occurred during earthquake shaking at a location. PGA is equal to the amplitude of the largest absolute acceleration recorded on an accelerogram at a site during a particular earthquake. Earthquake shaking generally occurs in all three directions. Therefore, PGA is often split into the horizontal and vertical components. Horizontal PGAs are generally larger than those in the vertical direction but this is not always true, especially close to large earthquakes. PGA is an important parameter (also known as an intensity measure) for earthquake engineering, The

neg: Radiation properties Therefore, the gray and diffuse approximation methods are commonly used to perform radiation calculations. A gray surface is characterized by having properties independent of wavelength, and a diffuse surface has properties independent of direction. If the amounts of radiation energy absorbed, reflected, and transmitted when radiation strikes a surface are measured in percentage of the total energy in the incident electromagnetic waves, the total energy will be divided into three groups. They are called absorptivity (α), reflectivity (ρ) and transmissivity (t). A body is considered transparent if it can transmit some of the radiation waves falling on its surface. If

neg: Mass–energy equivalence is to put the observer in a frame where the photons have equal energy and are moving directly away from each other. In this frame, the observer is now moving in the same direction and speed as the center of mass of the two photons. The total momentum of the photons is now zero, since their momenta are equal and opposite. In this frame the two photons, as a system, have a mass equal to their total energy divided by . This mass is called the invariant mass of the pair of photons together. It is the smallest mass and

neg: Fan-beam antenna latter send back in space a highly focused parallel beam that one can describe as pencil shape. When one removes a section of the paraboloid, rays coming from that section are lost. In keeping the antenna only in the horizontal or the vertical, only the rays at right angle to the remaining antenna section will be focused and thus create a narrow beam in that direction while being wide in the other direction. Fan beam antennas are used in radar sets. Primary radar in airport have often fan-beam with the section of antenna oriented horizontally to give a narrow beam

neg: Channel sounding element and each receiver element, engineers transmit a broadband multi-tone test signal. The transmitter's continuous periodic test sequence arrives at the receiver, and is correlated with the original sequence. This impulse-like auto correlation function is called "channel impulse response (CIR)". By obtaining the transfer function of CIR, we can make an estimation of the channel environment and improve the performance. Based on multiple antennas at both transmitters and receivers, a MIMO vector channel sounder can effectively collect the propagation direction at both ends of the connection and significantly improve resolution of the multiple path parameters. Engineers model wave propagation as

neg: Peak ground acceleration areas with expected PGA values higher than 0.36"g" are classed as "Zone 5", or "Very High Damage Risk Zone". Peak ground acceleration Peak ground acceleration (PGA) is equal to the maximum ground acceleration that occurred during earthquake shaking at a location. PGA is equal to the amplitude of the largest absolute acceleration recorded on an accelerogram at a site during a particular earthquake. Earthquake shaking generally occurs in all three directions. Therefore, PGA is often split into the horizontal and vertical components. Horizontal PGAs are generally larger than those in the vertical direction but this is not always true, especially

neg: Hosaholalu rectangular moldings of equal width which run all around the temple. The six horizontal mouldings are intricately sculptured and are called friezes. Seen from top to bottom; the first frieze depicts birds ("hansa"), the second depicts aquatic monsters ("makara"), the third frieze has depictions of Hindu epics and other mythological and puranic stories narrated in the clockwise direction (direction of devotee circumambulation), the fourth frieze has leafy scrolls, the fifth and sixth friezes have a procession of horses and elephants respectively. In the frieze that depicts the epics, the Ramayana starts from the western corner of the southern shrine and

neg: Solar energy (power) in Azerbaijan by semitropical anticyclone systems causes generation of the air current. This factor influences on each zone in falling solar radiation distribution. In open air in Azerbaijan average annual index of direct solar radiation falling onto the horizontal surface increases from the direction of the northern to the south beginning from the sea level. On the mountainous regions solar radiation amount is higher than other places. For Azerbaijan region the direct solar radiation (2 /mW) falling onto the horizontal surface in open air and half cloudy weather. Average annual amount of diffuse solar radiation in open air consists of 2 /3530

neg: Electrically small antenna from the antenna and increases the effective size, whereas the lossy choke (e.g. ferrite bead) technique introduces losses that should be considered. Electrically small antenna An electrically small or electrically short antenna is an antenna much shorter than the wavelength of the signal it is intended to transmit or receive. Electrically short antennas are generally less efficient and more challenging to design than longer antennas such as quarter- and half-wave antennas, but are nonetheless common due to their compact size and low cost. Technically, an electrically short antenna has length 2h, such that formula_1formula_2, where λ is the free space

neg: Semiconductor detector produces free electrons and holes. The number of electron-hole pairs is proportional to the energy of the radiation to the semiconductor. As a result, a number of electrons are transferred from the valence band to the conduction band, and an equal number of holes are created in the valence band. Under the influence of an electric field, electrons and holes travel to the electrodes, where they result in a pulse that can be measured in an outer circuit, as described by the Shockley-Ramo theorem. The holes travel in the opposite direction and can also be measured. As the amount of

neg: Cooperative MIMO for increased computational processing. Above a certain transmission distance threshold, Cooperative MIMO has been shown to achieve overall energy savings. Various techniques have been developed for handling timing and frequency offsets, which is one of the most critical and challenging issues in Cooperative MIMO. Recently, research has focused on developing efficient MAC protocols. In this section, we describe precoding using a system model of a Cooperative-MIMO downlink channel for a CoMP system. A group of BSs employs an aggregate "M" transmit antennas to communicate with "K" users simultaneously. User "k", ("k" = 1,… , "K"), has "N" receive antennas. The

neg: Plasma antenna off and are good for stealth and resistance to electronic warfare and cyber attacks. Ionized gas plasma antennas can be nested such that the higher frequency plasma antennas are placed inside lower frequency plasma antennas. Higher frequency ionized gas plasma antenna arrays can transmit and receive through lower frequency ionized gas plasma antenna arrays. This means that the ionized gas plasma antennas can be co-located and ionized gas plasma antenna arrays can be stacked. Ionized gas plasma antennas can eliminate or reduce co-site interference. Smart ionized gas plasma antennas use plasma physics to shape and steer the antenna beams without

neg: Electrically small antenna Electrically small antenna An electrically small or electrically short antenna is an antenna much shorter than the wavelength of the signal it is intended to transmit or receive. Electrically short antennas are generally less efficient and more challenging to design than longer antennas such as quarter- and half-wave antennas, but are nonetheless common due to their compact size and low cost. Technically, an electrically short antenna has length 2h, such that formula_1formula_2, where λ is the free space wavelength. The far-field radiation pattern of an antenna is the sum of its near-field spherical modes, expressed using Legendre functions and spherical

neg: Mars Reconnaissance Orbiter launch and Mars Orbit Insertion. These antennas do not have focusing dishes and can transmit and receive from any direction. They are an important backup system to ensure that MRO can always be reached, even if its main antenna is pointed away from the Earth. The K-band subsystem was used for demonstration purposes. Due to lack of spectrum at 8.41 GHz X-band, future high-rate deep space missions will use 32 GHz K-band. NASA Deep Space Network (DSN) implemented K-band receiving capabilities at all three of its complexes (Goldstone, Canberra and Madrid) over its 34-m beam-waveguide (BWG) antenna subnet. During the

neg: MIMO of all formula_1 paths between the formula_2 transmit antennas at the transmitter and formula_3 receive antennas at the receiver. Then, the receiver gets the received signal vectors by the multiple receive antennas and decodes the received signal vectors into the original information. A narrowband flat fading MIMO system is modelled as: where formula_5 and formula_6 are the receive and transmit vectors, respectively, and formula_7 and formula_8 are the channel matrix and the noise vector, respectively. Referring to information theory, the ergodic channel capacity of MIMO systems where both the transmitter and the receiver have perfect instantaneous channel state information is

neg: Antenna (radio) a metal rod. A dipole antenna is similar but consists of two such conductors extending in opposite directions. Dipoles are typically oriented horizontally in which case they are weakly directional: signals are reasonably well radiated toward or received from all directions with the exception of the direction along the conductor itself; this region is called the antenna blind cone or null. Both the vertical and dipole antennas are simple in construction and relatively inexpensive. The dipole antenna, which is the basis for most antenna designs, is a balanced component, with equal but opposite voltages and currents applied at its two

neg: Parabolic antenna conducted to the receiver through cheaper coaxial cable. This is called a low-noise block downconverter. Similarly, in transmitting dishes, the microwave transmitter may be located at the feed point. An advantage of parabolic antennas is that most of the structure of the antenna (all of it except the feed antenna) is nonresonant, so it can function over a wide range of frequencies, that is a wide bandwidth. All that is necessary to change the frequency of operation is to replace the feed antenna with one that works at the new frequency. Some parabolic antennas transmit or receive at multiple frequencies

neg: Invertible matrix simulations. Examples include screen-to-world ray casting, world-to-subspace-to-world object transformations, and physical simulations. Matrix inversion also plays a significant role in the MIMO (Multiple-Input, Multiple-Output) technology in wireless communications. The MIMO system consists of N transmit and M receive antennas. Unique signals, occupying the same frequency band, are sent via N transmit antennas and are received via M receive antennas. The signal arriving at each receive antenna will be a linear combination of the N transmitted signals forming a NxM transmission matrix H. It is crucial for the matrix H to be invertible for the receiver to be able to figure

neg: Photovoltaic mounting system at the same angle as the latitude of array's location to maximize the annual energy yield of module. For example, rooftop PV module at the tropics provides highest annual energy yield when inclination of panel surface is close to horizontal direction. A study in the tropics showed that the orientation of low-slope rooftop PV has negligible impact on annual energy yield, but in the case of PV external sunshade applications, east façade and panel slope of 30–40° are the most suitable location and inclination. Photovoltaic mounting system Photovoltaic mounting systems (also called solar module racking) are used to fix solar

neg: Posturography are able to detect the tiny oscillations of the body. Dynamic posturography differentiates from static posturography generally by using a special apparatus with a movable horizontal platform. As the patient makes small movements, they transmit in real time to a computer. The computer is also used to command electric motors which can move the forceplate in the horizontal direction (translation) as well as to incline it (rotations). Thus, the posturography test protocols generate a sequence of standardized motions in the support platform in order to desequilibrate the patient's posture in an orderly and reproducible way. The platform is contained within

neg: Nuclear weapon whether they are for peaceful purposes or not. Nuclear weapon A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission bomb) or from a combination of fission and fusion reactions (thermonuclear bomb). Both bomb types release large quantities of energy from relatively small amounts of matter. The first test of a fission ("atomic") bomb released an amount of energy approximately equal to . The first thermonuclear ("hydrogen") bomb test released energy approximately equal to . A thermonuclear weapon weighing little more than can release energy equal to more than . A nuclear

neg: POVM photons, each of which is polarized along either the horizontal direction or at 45 degrees. On average there are equal numbers of horizontal and 45 degree photons. The projective strategy corresponds to passing the photons through a polarizer in either the vertical direction or -45 degree direction. If the photon passes through the vertical polarizer it must have been at 45 degrees and vice versa. The success probability is formula_33. The POVM strategy for this example is more complicated and requires another optical mode (known as an ancilla). It has a success probability of formula_34. Quantum t-designs have been recently

neg: Antenna array use multiple antennas which are fed from the same transmitter or receiver; this is called an array antenna, or antenna array. If the currents are fed to the antennas with the proper phase, due to the phenomenon of interference the spherical waves from the individual antennas combine (superpose) in front of the array to create plane waves, a beam of radio waves traveling in a specific direction. In directions in which the waves from the individual antennas arrive in phase, the waves add together (constructive interference) to enhance the power radiated. In directions in which the individual waves arrive out

neg: Traffic collision avoidance system the TCAS directional antenna to assign a bearing to other aircraft, and thus be able to generate a horizontal maneuver (e.g. turn left or right). However, it was judged by the industry to be unfeasible due to limitations in the accuracy of the TCAS directional antennas. The directional antennas were judged not to be accurate enough to generate an accurate horizontal-plane position, and thus an accurate horizontal resolution. By 1995, years of testing and analysis determined that the concept was unworkable using available surveillance technology (due to the inadequacy of horizontal position information), and that horizontal RAs were unlikely to

neg: Spatial correlation denoted formula_9. The formula_10th element of the formula_11 channel matrix formula_12 describes the channel from the formula_13th transmit antenna to the formula_14th receive antenna. When modeling spatial correlation it is useful to employ the Kronecker model, where the correlation between transmit antennas and receive antennas are assumed independent and separable. This model is reasonable when the main scattering appears close to the antenna arrays and has been validated by both outdoor and indoor measurements. With Rayleigh fading, the Kronecker model means that the channel matrix can be factorized as where the elements of formula_16 are independent and identically distributed as

neg: Amelia Earhart not designed to work above 2000 kHz. When operated above their design frequency, loop antennas lose their directionality. "Itasca" had its own RDF equipment, but that equipment did not work above 550 kHz, so "Itasca" could not determine the direction to the Electra's HF transmissions at 3105 and 6210 kHz. The Electra had been equipped to transmit a 500 kHz signal that "Itasca" could use for radio direction finding, but some of that equipment had been removed. The equipment originally used a long trailing wire antenna. While the plane was in flight, the wire antenna would be paid out at

neg: MIMO radar can be extracted from each of the receive antennas by a set of matched filters. For example, if a MIMO radar system has 3 transmit antennas and 4 receive antennas, 12 signals can be extracted from the receiver because of the orthogonality of the transmitted signals. That is, a 12-element virtual antenna array is created using only 7 antennas by conducting Digital signal processing on the received signals, thereby obtaining a finer spatial resolution compared with its phased array counterpart. Picture above shows a M-by-N MIMO radar system. Suppose that a target is located at u, the formula_1 transmit antenna

neg: Delta-v orbit, gravitational slingshot, and Interplanetary Transport Network. It is also notable that large thrust can reduce gravity drag. Delta-"v" is also required to keep satellites in orbit and is expended in propulsive orbital stationkeeping maneuvers. Since the propellant load on most satellites cannot be replenished, the amount of propellant initially loaded on a satellite may well determine its useful lifetime. From power considerations, it turns out that when applying delta-"v" in the direction of the velocity the specific orbital energy gained per unit delta-"v" is equal to the instantaneous speed. This is called the Oberth effect. For example, a satellite

neg: Antenna (radio) be classified in various ways. The list below groups together antennas under common operating principles, following the way antennas are classified in many engineering textbooks. Isotropic: An isotropic antenna (isotropic radiator) is a "hypothetical" antenna that radiates equal signal power in all directions. It is a mathematical model that is used as the base of comparison to calculate the gain of real antennas. No real antenna can have an isotropic radiation pattern. However "approximately" isotropic antennas, constructed with multiple elements, are used in antenna testing. The first four groups below are usually resonant antennas; when driven at their resonant frequency