V.B. Bakeev, M.A. Minkin

It is beyond the question now that use of active phased circular arrays in systems of broadband radio communication, radio monitoring and passive radiolocation in RF, VHF and UHF regions is very promising. Such a multiinput circular array, depending on its function, can include up to 32 and more of partial antenna arrays (PAA), and each of them includes from 3 to 16 and more of active antenna elements (AE). Number of receive (processing) chains is determined by overall number of AEs and can reach several hundreds and more. Lengths of feeder cables should be minimal as far as possible in order to lower antenna feed chain noise factor and to increase a station sensitivity. Given this, when using circular arrays, it is most practical to install pattern-generating and radio engineering equipment of station in an underground or ground construction in a centre of the ring, that is not always possible and may require expensive construction work, especially for an underground facility. At the same time, using of existing ground constructions usually situated nearby to antenna fields even if they are 300...500 meters far, assumes drastic increase of high-frequency feeders lengths that makes, considering their quantity, using of mentioned structures impossible. The only possible alternative to a use of a phase-stable high frequency feeder and thus a solution of this problem is a use of an optical feeder. Technology of analog signal of mentioned ranges transmission by optic fiber is not new but it was not widely adopted and had a limited commercial use until recently. Advantages of optical fiber as an environment for analog signal transmission were studied and substantiated quite enough. Although, the second component of an optic fiber transmission link (FOTL), namely receiving and transmitting modules that provide transmission and receive of analog high frequency signal by optic fiber, virtually is not covered in literature. In this work an attempt to evaluate a possibility of optic fiber technologies practical application when developing multi-element circular arrays based stations was made. Survey of modern foreign and domestically produced receiving and transmitting modules was made. Analysis of FOTL parameters impact on sensitivity and dynamic range of circular array based receiving station was carried out. It was shown that due to embedding of a low-noise amplifier directly into a circular array antenna module, replacement of phase-stable high frequency cable with optic fiber leads to insignificant lowering of station sensitivity (0.15 dB). And at the same time decreasing of dynamic range by intermodulation does not exceed 5 dB. It was noticed in the article that even now application of optic fiber technologies in construction of multi-element circular arrays is a quite expensive solution, mostly because of optic receive and transmitting modules high cost. Although use of them, with a whole of capital and long-term maintenance costs as well as increased station reliability taken into account, appear to be quite justified.