Digital demodulation of DTV signals for passive radar application

A new digital receiver developed at the UW Radar Remote Sensing Lab is capable of directly sampling each of four antennas at 5 GSPS. With this receiver we are able to capture all signals below 2.5 GHz in support of our passive radar efforts in the VHF and UHF radio spectrum. For passive radar applications, we must separate the strong direct path, multipath and the weak echoes of the object of interest from the total signals. Unlike conventional DTV demodulators which may use analog phase-locking techniques to align the DTV waveform for symbol extraction, our clock rate of the receiver is fixed and is different from the DTV standard rate. Furthermore, simultaneous detection of DTV and (for instance) GPS would create conflicting demands for clock phase and frequency control. So, we have developed a completely digital process to demodulate the 8VSB signal. DTV signals have a known structure which permits recovery of the original transmitted waveform from imperfect reception. With such a nearly ideal reference signal, we are able to improve the instantaneous dynamic range to over 100 dB in about one-second coherent processing, and thus detect the weak echoes from targets of interest, such as aircraft or ionospheric field-aligned irregularities, and pave the way to angle of arrival estimates or interferometric images of these scatterers.