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The CATR is used for microwave and millimeter wave frequencies where the far-field distance is large, such as with high-gain reflector antennas. The size of the range that is required can be much less than the size required for a full-size far-field anechoic chamber, although the cost of fabrication of the specially-designed CATR reflector can ...
As these antennas are made shorter (for a given frequency) their impedance becomes dominated by a series capacitive (negative) reactance; by adding an appropriate size "loading coil" – a series inductance with equal and opposite (positive) reactance – the antenna's capacitive reactance may be cancelled leaving only a pure resistance.
This will often be a half-wave dipole, a very well understood and repeatable antenna that can be easily built for any frequency. The directive gain of a half-wave dipole with respect to the isotropic radiator is known to be 1.64 and it can be made nearly 100% efficient.
The lowest frequencies used for radio communication are limited by the increasing size of transmitting antennas required. [6] The size of antenna required to radiate radio power efficiently increases in proportion to wavelength or inversely with frequency. Below about 10 kHz (a wavelength of 30 km), elevated wire antennas kilometers in diameter ...
It is used at VHF and UHF frequencies where antenna sizes are feasible. Often used for satellite communication, which uses circular polarization because it is insensitive to the relative rotation on the beam axis. [ae] Not to be confused with a "rubber ducky" antenna (normal mode helix), which is much smaller. [p]
The electrical length of an antenna, like a transmission line, is its length in wavelengths of the current on the antenna at the operating frequency. [1] [12] [13] [4]: p.91–104 An antenna's resonant frequency, radiation pattern, and driving point impedance depend not on its physical length but on its electrical length. [14]