Antenna array characterisation and signal processing for an FM radio-based passive coherent location radar system

The design of passive coherent location radar, which exploits broadcasting transmitters of opportunity in the very high frequency (VHF) radio bandwidth, is presented. Here, the authors primarily focus on the system set-up and on the digital pre-processing steps. Emphasis is given to the antenna section analysis. The eight-element circular array, which is used for the signal acquisition, is analysed by means of simulations and measurements. Compensation for the mutual coupling effect between the different channels is achieved by applying a technique in the digital domain. An innovative digital beamforming algorithm is introduced to reduce the sidelobe level of the circular array pattern. Direct path interference suppression, range/Doppler data processing, greatest-of constant false alarm rate algorithm and range/Doppler-time plots extraction provide the final output of the processing chain. Experimental validation of the processing architecture is presented and the final detection results are compared with an automatic dependent surveillance broadcast data set.