receiving circular antenna array
A.L. Buzov, M.A. Buzova, A.P. Trofimov, V.V. Yudin
This work is dedicated to research of superdirectional receiving circular arrays energetics. In classical antenna synthesis theory, superdirectivity is referred to an area of false solutions. It is caused by that on traditional beliefs a superdirectional antenna. In particular, in receive antennas the effect of a superdirectivity leads to drastic worsening of sensitivity and reduction of the effective area. Another aspect of a problem is a drastic toughening of requirements to accuracy of received signals processing.
In practice, whereas, as it is fairly underlined in article, it is not infrequently when a need in realization of superdirectivity effect (to some extent) arises, so to say, in a natural manner. It is a question of the radio systems working in wide ranges of frequencies. Antenna arrays in such systems, having "the normal" sizes on the top frequency of a range, become electrically small on the bottom frequency.
The modern level of digital signal processing development substantially diminished the difficulty of high accuracy processing. As to sensitivity, development of low-noise amplifier technology has a high profile for it. The second and more essential moment is that the requirement for sensitivity is defined by interference environment. At high level of interference (in a low-frequency part of a range) high sensitivity is not claimed, but the high directivity is just rather useful. And the effect of a superdirection has quantitative measurement and it always can be restricted to some extent. In the article questions of such restriction realization for circular arrays are considered. Hence, there is a possibility to change a degree of the superdirectivity effect realization accordingly to interference environment for the purpose of a “signal/(noise+interference)” ratio maximization. Research performed in this work is aimed to resolution of this problem.
The research technique is based on electrodynamic modeling of receiving circular array illuminated by distantly situated vibrator followed by modeling of processing taking into account the amplifier-noise parameters provided by modern element base.
During research, following devices were considered: 16-element HF array, full-sized on frequency of 30 MHz; 32-element HF array constructed on a basis of electrically small elements and having the diminished sizes on frequency of 30 MHz; 16-element circular array of 0.1...1 GHz range presenting an analog of the first array but with the diminished sizes by a principle of a moving-conductor similarity. Three processing logics surveyed, one of which allows to implement the effect of superdirectivity. As a result of calculations the frequency dependences of sensitivity, directivity factor and prize of a superdirectional mode under the ratio «signal / (noise + interference)» are obtained.
The obtained results confirm the conjectures of possibility and expediency of restricted implementation of superdirectivity effect at high enough level of exterior interferences, and also that at usage of modern low-noise amplifiers such possibilities are considerably dilated. Anyhow, all this does not call doubts for circular arrays of a HF region, full-sized on frequency of 30 MHz.
As to a small-sized array of the same range and array of a range 0.1...1 GHz (where an interference level is much less), the prize of a superdirectional mode, though less noticeable, is observed for them too. Allowing temporal fluctuation of interference level, it is possible to maintain that in these cases it is expedient to have possibility to use the superdirectivity effect too.