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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 algorithm has proven reliable (likely to converge to a solution) and accurate (likely to produce results comparable to measured performance) at modeling thin-element structures like Yagi antennas and radiating towers. The NEC engine provides support for modeling patch antennas as well.
A quad is a Yagi–Uda antenna ("Yagi") made from loop elements instead of dipoles: It consists of a driven element and one or more parasitic elements; however in a quad, each of the loop elements may be square, round, or some other shape. It is used by radio amateurs on the HF and VHF amateur bands.
However, a Yagi with the same number of elements as a log-periodic would have far higher gain, as all of those elements are improving the gain of a single driven element. In its use as a television antenna, it was common to combine a log-periodic design for VHF with a Yagi for UHF, with both halves being roughly equal in size.
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.
Multiple Yagis The "double Yagi" (upper right) and the "Tri-Boom" (lower left) have multiple Yagi arrays that are tuned to different portions of the band, giving the combined antenna wide BW. The "double Yagi" is really two Yagis side-by-side; each parasitic element is two rods insulated from each other in the center. The "Tri-Boom" is three Yagis.
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]
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.