Bistatic SAR Flight Demonstration Using Agile Frequency Waveforms to Achieve Orthogonal Sidelobe Axes

Bistatic synthetic aperture radar (SAR) transfer functions have skewed passband regions when traditional wave-forms are used. The impulse responses that correspond to these skewed shapes have sidelobes distributed along sets of non-orthogonal axes. Many SAR applications require orthogonal sidelobe axes. Inscribing a rectangular shape within a skewed passband archives orthogonal axes by sacrificing resolution. Alternatively changing the waveform's frequency from pulse to pulse can manipulate the shape of the passband forcing the axes to be orthogonal. This agile frequency waveform method was proven with a bistatic SAR demonstration using an airborne transmitter and a stationary receiver. The transmitter and receiver had a bistatic angle of 35 degrees between them relative to the image scene. Using standard waveforms, the sidelobe axes were measured to be 74.6 degrees apart. The ideal separation is 90 degrees. Using agile frequency waveforms sidelobe axes were measured to be 88.5 degrees apart.