Synchronisation of bistatic radar systems

Bistatic radar is gaining more and more interest over the last years. It offers more freedom to deploy the transmitter and the receiver, e.g. in a way to enhance the signature of stealthy targets. Furthermore, the bi- or multistatic system can be realized without using expensive transmit/receive-modules. An additional feature of bistatic radar is that continuous wave signals can be used. A crucial problem associated with bi- and multistatic systems is the synchronisation of time and frequency at the transmitters and receivers for coherent signal processing and range measurement. Modern communications satellites and world wide accessible GPS signals allow to synchronise the time easily over a long period with a time difference of less than 1 ns. The required frequency stability depends on the baseline and may vary with application. Image generation with bistatic SAR systems requires a frequency coherence for at least the coherent integration time. For interferometric SAR systems this coherence has to be expanded over the whole processing time. The paper concentrates on the problem of time and frequency synchronisation between a bistatic transmitter and receiver pair. Possible solutions for attaining the requirements of bistatic radar systems are discussed.