Circular superdirective receive antenna arrays

Abstract

Systems and methods are described for circular superdirective receive antenna arrays. A method includes calculating an minimum array efficiency of the superdirective circular receive array, calculating a maximum superdirective gain of the superdirective circular receive array, determining an amplitude weight or a phase weight for an array element in the superdirective circular receive array based on the minimum array efficiency and the maximum superdirective gain, and determining number of array elements in the superdirective circular receive array and a radius of the superdirective circular receive array.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates generally to the field of radars. More particularly, the invention relates to radar receive antenna arrays. Specifically, a preferred implementation of the invention relates to an optimized design for radar receive antenna arrays. 2. Discussion of the Related Art MF (medium frequency) / HF (high frequency) / VHF (very high frequency) radars and radios remain in demand even with the advent of satellites that extend the range of communication to global scales. HF signals have the advantage of spanning distances beyond the horizon limits of UHF and higher-frequency signals. Two modes account for this. Reflection of HF signals from the ionosphere is called the skywave mode, and permits radio signals to traverse half way around the world. In the surface-wave mode, the spherical earth diffracts vertically polarized signals beyond the visible horizon—even in the absence of an atmosphere or ionosphere. For surface w...

AI Technical Summary

Benefits of technology

According to yet another aspect of the invention, an apparatus for an antenna system includes a plurality of dipole elements located in a circular arrangement of a radius that is less than a detected wavelength to receive a plurality of analog signals, an analog-to-digital converter to convert the plurality of analog signals to a plurality of d...

Problems solved by technology

The drawback of MF / HF / VHF systems is the large antenna size needed for high gain and / or efficiency.

However, the efficiency of these arrays is low.

Thus, while the directive gain is high, the power gain is low.

This has been the primary source of criticism and lack of acceptance of superdirective arrays in practice.

These very intense echoes destroy the ability to see surface targets at the same ranges as the layer heights.

Although many receive antenna systems employ vertical dipole or monopole antennas that theoretically have an overhead null, in practice this is not nearly enough to eliminate all vestiges of the intense overhead echo.

Another undesirable feature of conventional phased array antennas is the variation and degradation of pattern characteristics as one steers the beam to different bearings.

In linear phased arrays, for example, steering more than 45° from the optimal broadside direction results in unacceptable main-beam broadening and increase in sidelobe levels.

However, such techniques were applied to single antenna elements only, and an implementation of the theory has not been realized for antenna arrays.

Accordingly, the requirements of a compact antenna array that possesses the signal-to-noise ratio of the arrays of the prior art (or similar thereto) have not been fully met.

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