UWEE Tech Report Series

An investigation of a distributed passive radar system


John D. Sahr

passive radar, passive coherent location,


We present a basic modelling investigation of a distributed passive radar observing communications and broadcast transmitters at VHF and UHF. This investigation is intended to provide a basis for predicting the level of performance required to achieve a useful detection for tracking aircraft. We also present some basic analytic scaling arguments, motivated by the numerical studies, that indicate the performance level in a way more convenient for system design. Some basic assumptions go into this modelling effort. Many receivers or transmitters will be used; the individual receivers will be of modest performance; the receivers will not be carefully sited. Because it is anticipated that the receivers will not be particularly sensitive, we will not attempt to implement a quality propagation model (with terrain). This is reasonable for "not very mountainous terrain." We do account for "Lloyds Mirror" propogation phenomena, but neglect any attempt to model propagation loss in excess of free space (such as through foliage, or buildings). Because we are interested in the scatter associated with aircraft, much of the expected propagation path is above foliage or buildings. Finally, at VHFand low UHF wavelenghts, we neglect any absorption associated with rainfall. The simulation works by flying a 1 dBsm target above a region which is filled with a distribution of transmitters or receivers. The target flies with velocity 200 m/s, and in a straight line. Although this isn't a very interesting trajectory, it behaves like a trajectory in the sense that the times serial nature of the data permits one to ask questions about consecutive detection by particular FM broadcast (100 MHz) with many receivers, and cell phone (900 MHz) with a very few. From a propagation point of view, these situations are approximately duals. However there are logistic differences which are important. In particular, we conclude that a transmitter-rich system will work as well as a receiver-rich system, and will cost less and be easier to operate.

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