Passive Multistatic Radar Imaging Using an Ofdm Based Signal of Opportunity Thesis

The existence of non-radar radio frequency (RF) signals in the environment possessing radar-like characteristics make them ideal candidates for use in radar applications such as synthetic aperture radar (SAR). The orthogonal frequency division multiplexing (OFDM) specific Worldwide Interoperability for Microwave Access (WiMAX) waveform is one such example. Research at the Air Force Institute of Technology (AFIT) is focused on exploiting commercial WiMAX signals for radar applications, and an experimental OFDM radar has been developed to support research in this area. Research objectives of this work focus on achieving a proof-of-concept in using WiMAX signals within a passive, multistatic radar construct to generate simulated SAR images. Two signal processing methods have been proposed to create phase history data. The first exploits the assumption of frequency orthogonality between two transmit signals and uses this to separate the two signals to perform parallel processing of the individual signals. The second method combines two individual reference signals to produce a single phase history in an attempt to utilize a wider signal bandwidth and therefore improve the image range resolution. To support derivations of the signal processing methods, a software model has been created within MATLAB to simulate a SAR collection scenario. To validate the software model, experimental data collections were achieved using the OFDM radar, and the same signal processing models applied to generate experimental phase history data. Based on the software and experimental data collections, SAR images are created using a modified convolution-based filtered backprojection (FBP) algorithm. The images generated from both experimental and simulated data were observed iv to be consistent with each other, and with expectations in terms of target resolution. Coherent image addition results in improved image resolution due to the geometric and frequency diversity of the multistatic scenario compared to the individual bistatic pairs.