MMW system trade-offs

A brief review is given of the current state of knowledge of atmospheric propagation and clutter characteristics at frequencies in the range of 35 GHz to 95 GHz. The performance of a 35-GHz and a 95-GHz air-to-ground fire control system are evaluated for a realistic environment based on the current state of knowledge. Representative atmospheric attenuation values of clear air, 4-mm/hr rainfall, and 10-mm/hr rainfall at 35 and 95 GHz are summarized. Figures giving compiled values of radar reflectivity data at 35 and 95 GHz for grass, crops, and snow-covered ground as a function of depression angle (measured from the horizontal) are also presented. The two radar systems were evaluated in terms of their ability to detect a 40-m² target in the presence of atmospheric attenuation and three types of clutter. Generally, the 35-GHz system performed better in terms of signal-to-noise ratio performance and in signal-to-clutter ratio performance for light clutter. In heavy clutter, the 95-GHz system performed significantly better than the 35-GHz system. For 300-m altitude and refrozen snow clutter background, neither system developed a large enough signal-to-clutter ratio to detect the target reliably