V. A. Nikolaev - Dr.Sc. (Eng.), Leading Research Scientist, JSC «Distant Radiocommunication Scientific Research Institute» (Moscow) E-mail: nikolaev@niidar.ru O. A. Bakurova - Engineer, JSC «Distant Radiocommunication Scientific Research Institute» (Moscow) E-mail: obakurova@niidar.ru D. V. Botov - Engineer, JSC «Distant Radiocommunication Scientific Research Institute» (Moscow) L. G. Miklashevskaya - Engineer, JSC «Distant Radiocommunication Scientific Research Institute» (Moscow)

The shortcomings of the existing receiving antenna for over-the-horizon surface-wave radar with switching of the vibrators to obtain the required directional diagram in the azimuth and elevation planes have been considered. The existing antenna contains a significant amount beam formers, switches, and high frequency connectors which reduce reliability. This antenna requires a ground reflector to reduce the impact of high-frequency cables on external characteristics. The proposed new structure of the digital receiving antenna as a linear antenna array consisting of self-supporting vibrators do not contain a large number of radio elements and does not require using of a ground-based reflector, which significantly reduces its cost and increases reliability. The new antenna provides operation in the whole specified range of operating frequencies without division into subranges. To assess need of a ground reflector for the existing antennas, as well as the degree of influence of high-frequency cables on external characteristics, we measured the radiation pattern in the elevation plane. As the test model a shortened vertical vibrator has been used because its radiation pattern is known. The experimental results confirmed a strong influence of the reflector and cables located on the earth surface, expressed in the growth of radiation in the area of the circumzenithal angles and the appearance of the additional maximum of the radiation pattern. A new receiving antenna consists of a single row of vibrators, matched by external noises. The use of non-directional in the azimuth plane antenna elements is possible because the transmitting antenna is unidirectional, and the reception of signals from the land will be severely weakened due to large losses of surface wave during its propagation over land. Thus, the number of vibrators in the new antenna is reduced four times. Application of the aerial two wire feeders instead of high-frequency cables allows to eliminate the labour-intensive procedure of phasing, and also to use two independent types of waves - anti-phase and in-phase one. Anti-phase wave is excited by currents flowing in the vibrator shoulders. In-phase wave is generated due to the direct receiving of the useful signal with parallel polarization by the feeder wires. Joint processing of two orthogonal signals allows (within certain limits) to regulate the elevation directivity pattern. The directivity patterns of the antenna element with two wire feeder have been presented. The diagram of the new antenna element consisting of a vibrator, a two-wire feeder, a feeder length delimiter on the in-phase wave and a signal divider has been given. For comparison, the antenna element of the existing antenna contains 4 vibrators, 3 beamforming circuits and 7 high-frequency cables with connectors. Thus, the proposed receiving antenna has high reliability and low cost thanks to its simple structure and the lack of ground-based reflector. The new antenna allows the joint processing of two signals of orthogonal polarizations, which substantially increases the re-sistance to ionospheric disturbance.

 

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