ComRad3, a multichannel direct conversion receiver for FM Broadcast Band Radar

FM Broadcast Band Radar, based on the commensal use of the narrow band emissions of the FM broadcast band (88-108 MHz) is highly attractive for developing nations. We report on a direct sampling, multichannel receiver designed to exploit the entire FM broadcast band. To allow for applications such as angle of arrival (AoA) measurements, 3 receiver channels are provided, i.e. 3 analogue stages each driving a coherently clocked analogue to digital converter (ADC). The receiver allows for the continuous, simultaneous and coherent channelisation using 16 digital down converters (DDCs). Up to 8 FM band channels can therefore be digitised simultaneously when using 2 receiver channels or up to 5 FM band channels when using 3 receiver channels. This provides redundancy against the time-fluctuating modulation bandwidth of FM broadcast band channels as well as potential robustness against undesirable propagation effects such as multipath, achievable as a result of the concurrent exploitation of multiple carrier frequencies. Application of Compressive Sensing techniques are also allowed by the multichannel architecture, spread over the whole band. The architecture, test results, and demonstration of aircraft detection are presented.