Spatial Frequency Modulation of Probing Signals from Phased Array Radar Systems

Introduction. Complex signals are widely used in radar location. The use of phased array antennas (PAA) offers additional opportunities for covert operation of radar systems by increasing their noise immunity and electromagnetic compatibility. This article compares the energy concealment of a radar system with a multi-frequency probing signal with spatial frequency modulation and that of an analogous system without additional spatial modulation.
Aim. Analysis of the energy concealment of radar operation with spatial frequency modulation of a quasicontinuous multi-frequency probing signal in a transmitting-and-receiving PAA. Materials and methods. The signal security and mutual influence was analyzed using an energy receiver (ER) with an input filter and an amplitude detector. The characteristics of signal security were obtained using a set of ambiguity functions (AF) in the temporal, frequency, and spatial domains. Signals with continuous and quasi-continuous radiation were considered.
Results. Estimates of the gain in the signal level received at the ER input at different angles of its location relative to the target are obtained. The analysis is performed when the signal spectrum matches the ER filter band. A situation with the known angular position of the ER is considered. An algorithm for adaptive formation of the PAA pattern with zero radiation in the direction of the ER is proposed. In this case, interference side lobes of a multi-dimensional spatiotemporal AF may occur, for which an inconsistent correlation processing algorithm is considered. Estimates of the loss in terms of signal/noise due to misalignment are given. The energy concealment of a radar system with spatial modulation and a conventional radar with a similar multi-frequency probing signal in terms of energy and the number of bands and an identical equidistant N-element FAA, but without additional spatial modulation, is carried out.
Conclusion. The results obtained indicate the possibility of increasing the communication security of radar operation due to additional spatial modulation of the multi-frequency probing signal. In this case, energy losses associated with the use of multi-channel spatial-frequency correlation processing are absent.

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