Processing ISAR and spotlight SAR data to very high resolution

Processing techniques are presented which provide for increased range resolution in ISAR and spotlight SAR imagery without the need for increased bandwidth. It is shown that cross-pass combination of orthogonal data sets provides one method of increasing resolution, but that impulse response functions formed in this way suffer from grating lobe interference effects. Wide angle synthetic aperture processing is shown to be a natural extension of the cross-pass combination method, and does not suffer the same deficiencies. Studies show that with a continuous 180 degree aperture, quarter wavelength range resolutions are theoretically possible. Resolutions of the order of half a wavelength are demonstrated for simulated and real ISAR point targets at X-band with reduced aperture angles. Wide angle synthetic aperture ISAR images are compared with high bandwidth images and the effects of target cross section variation are addressed. Spotlight SAR imagery, obtained using a high bandwidth (2 GHz) polarimetric X-band SAR mounted on a helicopter platform, is presented. The images have demonstrable resolutions of the order of 6 cm. The effects of increased resolution upon the nature of SAR clutter are examined