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A report is presented on results achieved with an FM band commensal radar system in which the surveillance and reference antennas are widely separated, making use of common view, Global Positioning System disciplined oscillators to maintain timing synchronicity. The proposed configuration allows greater DPI suppression by means of terrain shielding and independent selection of the surveillance receiver position to enhance target visibility.
Introduction: We use the term Commensal Sensor for all sensor systems that use the facilities (typically transmissions) of an existing system without degrading in any way the performance of the other system.
Commensal radars, often referred to as passive bistatic radars (PBRs) or passive coherent location (PCL) radars, traditionally consist of a single, multichannel receiver device at each receiver site, to record surveillance and reference signals [1 -10]. Clearly the reference and surveillance channels of the system are easily set up to be phase coherent as they are typically driven from a common oscillator. This design has a drawback in that a line of sight (LoS) reference of the transmitted signal must be available at the chosen receiver site. This makes suppression of the DPI practically very difficult with achievable antenna null and backlobe performance.
Furthermore, given a multi-site commensal system, a reference antenna and receiver channel are required at each receiver site which raises overall equipment costs. We propose a new configuration, where the surveillance and reference channels can be separated so that a single reference antenna ( per exploited transmitter) can be placed at a site where there is a clear LoS to the transmitter, where multipath effects are minimised. The surveillance antennas can be placed at sites where the DPI is at a minimum due to shielding by terrain and/or structures. The channel synchronicity is provided by Global Positioning System disciplined oscillators (GPSDOs). This design will be termed the separated reference configuration. We address the issue of distributing the narrow band recorded reference for signal processing.
This Letter gives a system overview with regard to hardware and processing and then discusses some data networking aspects related to reference distribution. Some initial results are presented, along with intended future work and conclusions.
System overview: Architecture: The current implementation of the separate reference configuration operates offline. Some thought shows that...