Practical implementation of stripmap Doppler imaging

Doppler imaging is a technique that can generate fine two-dimensional (2D) imagery in the absence of large bandwidths. Radar imaging has traditionally consisted of combining wide bandwidth waveforms with aperture synthesis. Wide bandwidth waveforms provide high resolution in down-range (line-of-sight), whereas aperture synthesis enables high resolution in the orthogonal direction. However, in today´s increasingly congested spectral environment, using wide bandwidths waveforms is becoming less and less attractive. Consequently, imaging techniques that require only narrow bandwidth waveforms offer very attractive and practical advantages. An approach, examined here, is to use phase in conjunction with aperture synthesis to achieve high resolution in down-range while using narrowband waveforms. This method has the added benefit of using the same collection geometry as traditional stripmap synthetic aperture radar imaging. Therefore Doppler imaging is compatible with use in spectrally congested environments where wide bandwidth waveforms might be prohibited. In this study, the basic Doppler imaging concept is explained, a simple framework for its operation is introduced and resolution limits are examined. Results are presented from both simulations and full-scale experiments, which demonstrate range resolutions as fine as 23 cm using an 8.9 GHz CW waveform and 2 m long synthetic aperture.