Antennas
Antennas
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Array Antennas
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 currents from the individual antennas combine in the receiver with the correct phase relationship to enhance signals received from the desired directions and cancel signals from undesired directions. More sophisticated array antennas may have multiple transmitter or receiver modules, each connected to a separate antenna element or group of elements.
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Cassegrain Antennas
In telecommunications and radar, a Cassegrain antenna is a parabolic antenna in which the feed antenna is mounted at or behind the surface of the concave main parabolic reflector dish and is aimed at a smaller convex secondary reflector suspended in front of the primary reflector. The beam of radio waves from the feed illuminates the secondary reflector, which reflects it back to the main reflector dish, which reflects it forward again to form the desired beam. The Cassegrain design is widely used in parabolic antennas, particularly in large antennas such as those in satellite ground stations, radio telescopes, and communication satellites.
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Dual Polarized Antennas
Dual polarized horn antennas are offered as both standard and custom models with rectangular waveguide interfaces for both horizontal and vertical ports. These dual polarized horn antennas support both linear and elliptical polarized waveforms. When the antenna receives a circular polarized waveform, equal amplitude linear polarized waveforms are output at both horizontal and vertical ports. When two equal amplitude linear polarized waveforms are input into the vertical and horizontal ports, the antenna will transmit a circular polarized waveform. The listed models offer 15 dB nominal gain and 33/28 degrees typical half power beamwidth at the center frequency of the band. They also exhibit 40 dB typical port isolation and 35 dB nominal cross polarization. These antennas cover full waveguide bandwidths within the frequency range of 8.2 to 110 GHz. In addition to the models listed below, models with 10, 20, 23 and 25 dB gain and other frequency bands are also available.
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Horn Antennas
A horn antenna or microwave horn is an antenna that consists of a flaring metal waveguide shaped like a horn to direct radio waves in a beam.
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Lens Antennas
A lens antenna is a directional antenna that uses a shaped piece of microwave-transparent material to bend and focus microwaves by refraction, as an optical lens does for light.[1] Typically it consists of a small feed antenna such as a patch antenna or horn antenna which radiates radio waves, with a piece of dielectric or composite material in front which functions as a converging lens to collimate the radio waves into a beam.[2] Conversely, in a receiving antenna the lens focuses the incoming radio waves onto the feed antenna, which converts them to electric currents which are delivered to a radio receiver. They can also be fed by an array of feed antennas, called a focal plane array (FPA), to create more complicated radiation patterns.
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Omnidirectional Antennas
In radio communication, an omnidirectional antenna is a class of antenna which radiates equal radio power in all directions perpendicular to an axis (azimuthal directions), with power varying with angle to the axis (elevation angle), declining to zero on the axis.[1][2] When graphed in three dimensions (see graph) this radiation pattern is often described as doughnut-shaped. Note that this is different from an isotropic antenna, which radiates equal power in all directions, having a spherical radiation pattern. Omnidirectional antennas oriented vertically are widely used for nondirectional antennas on the surface of the Earth because they radiate equally in 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.
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Probe Antennas
Probe antennas are offered as both standard and custom models with a rectangular waveguide interface. Probe antennas can only support linear polarization. These antennas are often used to measure the gain of other antennas by comparing the signal levels of the probe antenna and antenna under testing. The standard models operate across the full waveguide band and offer 6.5 dB nominal gain and 115 and 60 degrees half power beamwidth at center frequency. The below standard offering covers the frequency range of 8.2 to 170 GHz.
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Sector Antennas
A sector antenna is a type of directional microwave antenna with a sector-shaped radiation pattern. The word "sector" is used in the geometric sense; some portion of the circumference of a circle measured in degrees of arc. 60°, 90° and 120° designs are typical, often with a few degrees 'extra' to ensure overlap and mounted in multiples when wider or full-circle coverage is required (see photos below). The largest use of these antennas is as antennas for cell phone base-station sites. They are also used for other types of mobile communications, for example in Wi-Fi networks. They are used for limited-range distances of around 4 to 5 km.
