Bistatic radar

Keywords radar bistatic radar multistatic radar ambiguity function parasitic radar forward scatter Babinet s principle passive coherent location netted radar. 

A particular variant on the bistatic and multistatic themes is Passive Coherent Location (PCL). This is normally taken to mean a system where transmissions are provided by a third party and only the receiver is formerly part of the design. This is sometimes also referred to as a hitch hiking mode of operation. It is also usually referred to as an example of bistatic radar although, as we shall see later, many transmissions can be used from a variety of transmitter sites thus making an example of multistatic radar. 

In this section we review the fundamental building blocks of bistatic radar emphasising similarities and differences with the more usual monostatic counterpart. Figure 1 shows a typical bistatic geometry with clear separation of the transmitter and receiver. 

When a target crosses the baseline of a bistatic radar the RCS can be greatly enhanced. This is due to the forward scatter phenomenon or Babinets principle. Here the RCS of a target at the bistatic baseline is calculated from... 

There are also some important differences in the technology required to realise bistatic radar. In monostatic radar synchronisation between transmission and reception is done via a stable source, usually a local oscillator. In bistatic radar the separation of transmitter and receiver makes this much more difficult. An equivalent situation has to be achieved and this is done either via synchronised atomic clocks, a signal such as GPS or by reception of a reference signal received directly from the transmitter. The latter technique is typically used in PCL systems and we shall return to this later. 

Thus we have seen that PCL is a particular form of bistatic radar that has a number of attractive characteristics. It should not be thought of as a mature technology but more as an emerging one and extant systems are evidence of this. 

Assume the transmitted signal is a coherent train comprised of three rectangular pulses. The first example refers to the case where the target is close to the baseline Or = —80°) of one of the two bistatic pairs. For a simple bistatic radar it is well known that this scenario is detrimental to its resolution performance. The two baselines are set to lOOfcm and the target is stationary with Rr = 50km. 

Other degrees of freedom that can be varied are the baselines Li. Returning to the geometry of the first example, where Or = —80°, the additional transmitter is placed in the position of the receiver, thus having a combination of monostatic and bistatic radar. In this way topologies can be tailored to meet application needs. However, it is most important to note that this must be balanced against the increased complexity of... 

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