Frequency-Independent Antenna

Frequency-Independent Antenna

 

an antenna with primary electrical characteristics that vary insignificantly with frequency over an extremely wide range; the various types of such antennas constitute a group of broadband antennas for which the ratio of maximum operating frequency to minimum ranges to 20:1 or more. The theoretical and technological foundations for frequency-independent antennas were established between 1957 and 1965 by the American scientists V. H. Rumsey, D. Dyson, and others.

The weak dependence of the antennas’ characteristics (the shape of the directive pattern, the front-to-rear ratio, the input impedance, and so on) on frequency stems from the fact that the radiation field is created by currents distributed over a finite portion of the antenna surface, known as the active region, beyond whose limits the currents decrease sharply; as the frequency varies, the active region changes in such a way that its relative dimensions expressed in terms of the wavelength λ corresponding to the frequency remain unchanged. The lower wavelength limit λmax of the antenna’s operating range is determined by the frequency at which the active region is shifted to the edge of the antenna. The antenna’s operating range can, in principle, be extended toward the shorter wavelengths as far as desired, but in practice the limit is determined by a number of incidental factors, such as the cross-sectional dimensions of the power feeder that are acceptable for given values of the losses introduced, the breakdown voltage, the transmitted power, and so on.

The most common frequency-independent antennas are in the form of two-arm spiral and conical helical antennas, log-periodic antennas, and sickle-shaped dipoles. There are also multiarm spiral and helical antennas that have several independent inputs; a well-known type is in the form of a conical dipole with an ultra-wide range of input impedances.

Frequency-independent antennas are used for shortwave radio communications, telemetry, and radio astronomy. During the 1970’s lightweight types of relatively simple design were developed for various frequency ranges: log-periodic wire antennas were developed for decameter waves, and spiral and helical antennas were created for centimeter and millimeter waves from strip conductors deposited on a fiberglass substrate by a photochemical process. Highly directional frequency-independent antennas are being designed as horn antennas with walls having transverse ribs and antenna arrays composed of log-periodic or conical helical radiators positioned along radii in a specific sector of a circle.

REFERENCES

Benenson, L. S. “Slabonapravlennye shirokodiapazonnye antenny.” In the collection Sovremennye problemy antenno-volnovodnoi tekhniki. Moscow, 1967.
Rumsey, V. H. Chastotno-nezavisimye antenny. Moscow, 1968. (Translated from English.)
Fiks, M. E. “Rupornye antenny s rebristymi stenkami” (survey). Informatsionnyi biull. NIIEIR: Radioelektronika sa rubezhom, 1976, issue 10.

L. S. BENENSON

References in periodicals archive ?
A multi-layer structure was introduced in [9-11] using an electromagnetically coupled overlaid patch array for the design of wideband arrays based on frequency-independent antenna principles.
Although many frequency-independent antenna designs meet these requirements, the current literature suggests that a printed, low profile antenna design may be best, due to its ease of fabrication and its robust overall structure [5-9].
In 1983, Randtron Antenna Systems (Menlo Park, CA), a division of L-3 Communications (New York, NY), developed the dual-polarized sinuous antenna (DPSA), a common-aperture, frequency-independent antenna with performance equal to or better than a spiral antenna of the same size and capable of simultaneously responding to all polarizations, including orthogonal circular, elliptical and linear.
The in-depth research proves that the Archimedean spiral is not a frequency-independent antenna structure because the spacing between the arms is specified by a constant, not an angle [25].
It is also known from antenna theory that a frequency-independent antenna can be obtained when its geometry has certain scalability properties.
Representative of a frequency-independent antenna is the dual-polarized sinuous antenna produced by Loral Randtron (Menlo Park, CA).
Mayes, "New circularly-polarized frequency-independent antennas with conical beam or omnidirectional patterns," IRE Trans.
In general, the geometry of frequency-independent antennas is evidenced by a multiplicity of adjoining cells, where each cell is scaled in dimensions relative to the adjacent cell by a factor [tau] that remains fixed throughout the antenna.
Band notching on frequency-independent antennas has also been presented such as on TEM horn, log-periodic and Vivaldi antennas [16-18], but to the best of author's knowledge, a spiral antenna with band notch characteristics has not yet been reported in the open literature.
Scherer of Loral Randtron Systems to expand Chapter 14, which details frequency-independent antennas.
His research has included low-profile antennas, numerical electromagnetic analysis, microwave transmission lines and frequency-independent antennas.

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