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On the Prospects of In-band Full-Duplex Radios as Monostatic Continuous-Wave Noise Radars

Future full-duplex (FD) radios simultaneously transmit and receive (STAR) on the same frequency band. This improves spectral efficiency and enables multiple new applications in the military context. One of such applications is the use of FD technology for a continuous-wave (CW) monostatic noise radar in which a wideband noise-like waveform is simultaneously transmitted and received. The main challenge in full-duplex communication systems is the strong self-interference (SI), i.e., direct leakage, between the transmitter and the receiver. In a noise radar, this problem is even more challenging as the required bandwidth is wider and transmit power levels are higher than in typical communications applications. This paper explores the feasibility of applying current full-duplex radio technology for a noise radar, targeting a system with a bandwidth of 500 MHz and transmit power in the kilowatt range. This is challenging compared to typical 5 to 80 MHz bandwidths and 0.1 to 2 W transmit powers supported previously in FD demonstrators. The obtainable SI suppression levels are estimated in terms of passive antenna isolation, analog cancellation and digital cancellation. In addition, the effect and tolerance of very-near environmental reflections are studied. It is concluded that, while high enough SI cancellation for a noise radar is feasible using state-of-the-art technology, the available transmit power limits performance.