Realization specifics of multi-beam exposure modes with beams frequency separation in spaceborn synthetic aperture radar based on active phased-array antenna

Radiolocation and radio navigation


Bulygin M. L.

Scientific Research Institute of Precision Instruments, 51, Str., Dekabristov, Moscow, 127490, Russia



Multi-beam SAR modes allow increase imaging parameters (such as swath, resolution) in AESA-based spaceborne SAR systems. An example is a multi-beam SAR mode with azimuth DBF with frequency separation of beams at the receiver.

However, multi-frequency echo-signal receiving by analog AESA is leads to frequency dispersion of AESA on receiving. This effect leads to additional deviation of each beam in elevation and additional amplitude losses. As a result, it leads to deterioration in multi-beam SAR modes performance: the swath shortens, and energy performance decreases.

AESA frequency dispersion effect while receiving can be slightly reduced in multi-beam spotlight mode, where this effect reduces swath. It can be achieved by antenna pattern extension in elevation.

AESA frequency dispersion on receiving leads to omissions in milti-beam ScanSAR imaging, which is unacceptable. In milti-beam ScanSAR this effect’s compensation is possible in two ways.

The first one is special alternation of current frequency values between the beams. This option does not increase the azimuth sector to which the beams are directed. But it can be applied in multi-beam ScanSAR only when the beams number is equal to the number of partial strips of scanning.

The second one is implemented by operative control of multi-beam pattern azimuth position. The multi-beam pattern is being redirected in azimuth through switching to the next partial strip. This option increases more than twice the azimuth sector in which the beams are directed. But it can be used at an arbitrary number of beams and partial strips of scanning.

Increasing the number of partial scanning strips weakens the AESA frequency dispersion effect on the swath on receiving in multi-beam modes, since it affects only the first and the last partial strips.

In this way suggested ways of compensating the effect of AESA frequency dispersion on receive allows reduce the effect of this impact on imaging characteristics. Moreover, an algorithm of inter-beam current frequency values alternation uses less azimuth sector in which beams are directed than an algorithm of operative control of multi-beam pattern azimuth position. It may be important in spaceborne SAR systems where AESA beam deviation in azimuth capability is limited.


synthetic aperture radar, active phased-array antenna, multi-beam exposure modes


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