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The discone antenna has a useful frequency range of at least 10 to 1. [2] [3] When employed as a transmitting antenna, a properly constructed discone is just as efficient as an antenna designed for a more limited frequency range. The extra bandwidth comes from the controlled taper and large termination radius of the cone.
Although the name is similar to the folded unipole, the two antennas are electrically different: The folded monopole is a much simpler antenna. Discone antenna The discone is a monopole version of a biconical antenna. The name of the antenna describes its shape: A metal disk above a metal cone.
Omnidirectional radiation patterns are produced by the simplest practical antennas, monopole and dipole antennas, consisting of one or two straight rod conductors on a common axis. Antenna gain (G) is defined as antenna efficiency (e) multiplied by antenna directivity (D) which is expressed mathematically as: =.
The following example of a complete input deck models a log-periodic antenna, like those used for VHF television reception: This 16-element log-periodic design is similar to the 12-element one being modeled in the example deck. CM TESTEX5 CM 12 ELEMENT LOG PERIODIC ANTENNA IN FREE SPACE CM 78 SEGMENTS. SIGMA=O/L RECEIVING AND TRANS. PATTERNS.
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. This resulted in much higher gain for UHF, typically on the order of 10 to 14 dB on the Yagi side and 6.5 dB for the log-periodic. [5]
It is the only type of directional antenna that is directional ("beam" antenna) over its entire working range. discone antenna The discone is omnidirectional, vertically polarized, and has a gain similar to a dipole. It is equally efficient as a monopole and is exceptionally wideband, offering a frequency range ratio of up to approximately 10:1 .
The two-element design gives modest directivity (about 2.0 dB) with a null towards the rear of the antenna, yielding a high front-to-back ratio: Gain up to 9.7 dBi can be achieved at 28 MHz. [3] Because the placement and size of the parasitic reflector both depend highly on wavelength, each Moxon antenna functions properly on the frequency band ...
A one-octave antenna might cover 100 to 200 MHz, and a two-octave antenna might cover 100 to 400 MHz. A 10:1 antenna would cover 100 to 1000 MHz. See Octave band for further details about octave-based calculation. And see the discussion of ratio bandwidths in the Bandwidth article.
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