Conceptual reconfigurable antenna for 35 GHz high-resolution spaceborne synthetic aperture radar

An innovative Cassegrain antenna for spaceborne synthetic aperture radar (SAR) utilizes a reconfigurable feed array for scene grazing angles from 15(degree) to 70(degree) to produce the largest antenna beam footprints that are circular and to maintain high efficiency or the transmitter. The antenna has a beam waveguide input and the feed array is located in this waveguide. The feed array of transmitreceive modules is reconfigured to vary the illumination shape and area of the radiating portion of the antenna. Each transmit device operates at its full power for maximum efficiency, and the number of devices is determined by the required power. Single-point design for a 35 GHz SAR in a 700 km altitude orbit is presented to detect terrain with 0.1 m resolution. The antenna is a 19.6 m/sup 2/ elliptical reflector, the power density at the aperture is 25.5 W/m/sup 2/, and 500 W maximum average power is required. Compared to X-band, 1) the 35 GHz design requires a much smaller antenna, 2) high resolution requires less percentage bandwidth, and 3) integration requirements are less demanding. For comparison, a 9 GHz SAR point design is included for grazing angles of 15(degree) and 70(degree).