KOBRA, a high resolution millimeterwave radar for the evaluation of targets and background signatures

Existing experimental instruments have approached resolutions of about 10 to 20 cm. The effort described here, however, should exceed this limit to be able to test the necessity of extremely high resolution in radar images. The range resolution of radar is determined by its instantaneous bandwidth. At higher millimetre wave bands even moderate relative bandwidths are equivalent to high absolute bandwidths. For the development of related processing algorithms, an experimental, polarimetric radar operating at 10 GHz, 35 GHz, 94 GHz and 220 GHz has been developed using a FM/CW waveform with a bandwidth of 4000 MHz (8000 MHz at 220 GHz) resulting in a resolution better than 4 cm (2 cm at 220 GHz). The radar has been evaluated using the method on Inverse Synthetic Aperture in tower-/turntable geometry. A second approach was tested to derive scattering centre distributions in ground based SAR configuration with a static target and the radar mounted on a sliding platform moving along a rail over a distance of a few meters. The paper describes the hardware approach, which is based upon broad band monolithically integrated GaAs components and most recent signal generation and processing hardware. The ISAR and the SAR algorithms are discussed and representative examples of highly resolved radar images are shown.