digital synthetic aperture radar (SAR)
The modern airborne air-to-surface RADAR systems have very high characteristics first of all because of using synthetic aperture techniques. It provides the possibility to get the near to optic quality images. Following essential step in SAR systems improving is an introduction of multistatic modes, where the bistatic mode (BSAR) is a special case. It allows to get high quality SAR image directly ahead of flight, to possess the raised noise protection and better reserve of work and to provide an anti-stealth technology feature. The analysis of bistatic mode problem in time synchronization of the transmitter and receiver is discussed in this article. Some math formulas are provided, which shows the requirements of stability to the internal generators as function of resolution and coherent summarizing. Four methods of time synchronization are discussed:
Appropriate synchronization is provided by using generators with very high stability. The dependence of resynchronization time upon generators stability is introduced.
The synchronization is provided by using special radio communication channel between active and passive parts of BiSAR.
The third method is based on receiving the transmitted by active part of BiSAR signal on its passive part.
It is offered not to synchronize the receiving strobe on the passive SAR. In this case the receiver is unlocked all the time and the received signal is continuously written in the digital memory. After that the receiving strobe start time is determined adaptively or manually.
In the last part of the article the conclusion was made that, despite of all the arising complexities connected with realization of such mode, at modern development of technologies such mode can be realized.