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A Yagi–Uda antenna, or simply Yagi antenna, is a directional antenna consisting of two or more parallel resonant antenna elements in an end-fire array; [1] these elements are most often metal rods (or discs) acting as half-wave dipoles. [2]
The most common monopole is a vertical, 1 / 4 wave tall, which is the minimum size for it to self-resonate. [ n ] A one-quarter wave monopole has a gain of 5.12 dBi when mounted over a good ground plane .
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.
Moxon antenna for the 20-meter band.The antenna is the faint rectangle of wires held in tension by the bent X-shaped support frame. Moxon antenna for the 2-meter band. The Moxon antenna or Moxon rectangle is a simple and mechanically rugged two-element parasitic array, single-frequency antenna. [1]
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 be expensive due to the need to ensure precision of the reflecting surface (typically less than 1 / 100 λ RMS surface accuracy) and to ...
Adding a reflector to a dipole, to make a 2 element Yagi, increases the gain by about 5 dB over the dipole. Adding a director to this, to give a 3 element Yagi, gives a gain of about 7 dB over a dipole. As a rule of thumb, each additional parasitic element beyond this adds about 1 dB of gain. [2]
It is used to receive the VHF terrestrial television bands, consisting in the US of 54–88 MHz and 174–216 MHz , with wavelengths of 5.5–1.4 m. Since this frequency range is much wider than a single fixed dipole antenna can cover, it is made with several degrees of adjustment.
A turnstile antenna, or crossed-dipole antenna, [1] is a radio antenna consisting of a set of two identical dipole antennas mounted at right angles to each other and fed in phase quadrature; the two currents applied to the dipoles are 90° out of phase. [2] [3] The name reflects the notion the antenna looks like a turnstile when mounted ...