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This article explores signal processing architectures for disturbance cancellation and range-Doppler map evaluation in orthogonal frequency division multiplexing (OFDM) radar. The signal processing chain of an OFDM radar typically encompasses a disturbance cancellation stage followed by the range-Doppler map evaluation, which can be in turn decomposed into a range compression stage performed at OFDM symbol level and a Doppler processing across symbols. In this article, we use a reciprocal filter (RF) to perform the range compression and we deepen the understanding of the RF properties with particular reference to their impact on the other processing stages of the signal processing scheme, above all disturbance cancellation. By exploiting this understanding, we show that it is possible to create synergies between different processing stages, even swapping their order, with the aim to improve the performance of the system while keeping limited its complexity. Thanks to this strategy, alternative versions of existing disturbance cancellation algorithms can be considered that would not be feasible in conventional architectures. Moreover, this article makes it possible to include within the same interpretative framework approaches that seem to be very distant from each other in terms of processing techniques thus allowing their throughout comparison both in terms of target detection performance and in terms of computational complexity. The performance of different solutions is investigated and compared against simulated and experimental data for the case of an OFDM radar that parasitically exploits DVB-T signals of opportunity.

With the rapid and growing spread of automotive radar systems in modern vehicles, the problem of their mutual interference is becoming a major safety concern. This article considers the use of receive-only sensors onboard the vehicles, which exploit an external illumination source to provide automotive radar functionalities. The passive radar paradigm would solve the problem of mutual interference, allowing different systems to share the same transmitted signal. A preliminary analysis of the feasibility of this concept is carried out, exploiting real-world transmitters of opportunity. The potentialities offered by both satellite and ground-based illuminators are investigated and the expected performance is evaluated in terms of achievable coverage and spatial resolution. Aiming to enable a practical implementation of the proposed concept, an appropriate signal processing scheme is proposed to obtain maps of the observed scene. A Doppler beam sharpening approach is adopted to discriminate and localize stationary scatterers in azimuth based on the differences in their relative Doppler shift. The problem of left/right ambiguity arising from the forward-looking geometry is tackled by exploiting an array of few antenna elements on receive. Specifically, an ambiguity removal approach is proposed, based on digital beam pattern adaptation, designed to maximise the response in the desired direction and suppress unwanted echoes from the corresponding ambiguous one. The effectiveness of this approach is further improved by cascading an apodization technique that prevents the undesirable increase in the noise level. Moreover, some criteria are introduced for the design of the antenna layout, resorting to non-uniform linear array configurations. The proposed system is tested against a simulated environment, where the multi-channel signal processing, combined with a properly designed array layout, is shown to provide an unambiguous mapping of the observed scene over wide angular sectors, even operating with few antenna elements on receive.