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Traveling wave antennas are notably one of the few types of antennas that are normally not self resonant: Electrical waves induced by received radio waves travel through the antenna wire in the direction that the arriving RF signals are travelling. Only electrical waves traveling toward the feedpoint are collected; waves traveling away from the ...
The gain and input impedance of the antenna is dependent on the length of the whip element, compared to a wavelength, but also on the size and shape of the ground plane used (if any). A quarter wave vertical antenna working against a perfectly conducting, infinite ground will have a gain of 5.19 dBi and a radiation resistance of about 36.8 ohms.
The first full scale beam waveguide antenna was the 64 meter antenna at the Usuda Deep Space Center, Japan, built in 1984 by the Japan Aerospace Exploration Agency. [6] After the Jet Propulsion Lab (JPL) tested this antenna and found it better than their conventional 64-meter antennas, [ 7 ] they too switched to this method of construction for ...
Patch antenna gain pattern. A directional antenna or beam antenna is an antenna which radiates or receives greater radio wave power in specific directions. Directional antennas can radiate radio waves in beams, when greater concentration of radiation in a certain direction is desired, or in receiving antennas receive radio waves from one specific direction only.
Umbrella antennas are good ground wave antennas, and are used as radio broadcasting antennas in the MF and LF bands. The gain of an umbrella antenna over perfectly conducting ground, like other electrically short monopole antennas, is approximately 3.52 dBi if it is significantly shorter than 1 4 λ . {\displaystyle {\tfrac {1}{4}}\lambda ~.}
The 2-meter band (144-148 MHz) lies within cable channel 18, but at 4 MHz wide, it is too narrow to fit the full 6 MHz bandwidth of an NTSC analog channel; its audio carrier lies outside the band. To be used as a television frequency, some narrow-bandwidth format incompatible with most televisions must be used and converted.
An advantage of traveling wave antennas is that since they are nonresonant they often have a wider bandwidth than resonant antennas. Common types of traveling wave antenna are the Beverage antenna, axial-mode helical antenna, and rhombic antenna. Traveling-wave antennas fall into two general categories: slow-wave antennas, and fast-wave antennas.
Often random wire antennas are also (inaccurately) referred to as long-wire antennas.There is no accepted minimum size, but actual long-wire antennas must be greater than at least a quarter-wavelength ( 1 / 4 λ) or perhaps greater than a half ( 1 / 2 λ) at the frequency the long wire antenna is used for, and even a half-wave may only be considered "long-ish" rather than "truly ...
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