The goal of this thesis is to develop a digital signal processing module, capable of compensating the inherent distortions found in a multi-channel passive radar. The radar's receiver has a dedicated RF stage for each of its channels, with each of these RF stages having a different frequency response due to them being distinct physical components. As a result, the signals received on the individual channels are amplitude and phase shifted to varying amounts which interferes with algorithms relying on phase differences, such as direction-of-arrival and beamforming. In this document I examine a method for measuring the differences between the frequency responses and present the results of one such measurement. To counteract the effects of the mentioned distortion, a FIR-filter based compensating stage was implemented for FPGA. For the calculation of appropriate FIR coefficients based on the desired frequency response, an algorythm is described and implemented.
A purpose-made simulation environment was developed in MATLAB for the software-based verification of the implemented compensating stage. The simulation generatetes a stimulus signal to be fed into the input of the compensating stage. This stimulus is a close approximation of the received signal during real operation. The correct operation of the compensating stage was confirmed through analysis of its response to the given stimulus.
Correct operation was further confirmed by a successful field test, the results of which can be found at the end of this document.