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As penetration depth through vegetation and ground becomes more important in active remote sensing applications, there is a shift toward using lower frequencies.To facilitate imaging of ground water, soil moisture and composition, and penetrating through forest canopies, a dual-band synthetic aperture radar (SAR) has been proposed to operate at VHF and UHF frequencies. To accommodate weekly repeat observations from LEO, a swath of roughly 350 Km is needed, requiring a 30-m long antenna aperture from the SAR design point of view. The beams of the UHF and the VHF antennas must coincide in the cross-track direction, resulting in antenna widths of 3m and 11m, respectively. A stacked, linearly dual-polarized patch array feeding a 30 meter diameter parabolic reflector is proposed for this application, which synthesizes near-rectangular effective apertures on the reflector. Using a mesh reflector technology, the mass of such an antenna configuration is about ten times smaller than a corresponding phased-array antenna. A scaled-frequency version of the feed array was initially designed, built, and tested. It was also integrated with a scaled reflector antenna to verify the performance of the overall system. The actual frequency version was then designed, built, and tested. The design of the dual-band stacked array and the power dividers will be discussed, the fabrication process explained, and the approaches used for optimizing the performance characteristics will be presented. The measurement results for return loss on both transmit and receive, isolation, and radiation pattern will be presented and shown to be in good agreement with the simulated results. 12

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Abslracl -An L-band total power receiver for use in a synthetic thinned array radiometer (STAR) is described. The total power architecture of a radiometer receiver requires special considerations to control gain fluctuations due to small temperature drifts. The STAR application requires consistent passband and stable phase between receiven. The design presented incorporates direct detection to eliminate distributed local oscillators for phase stability, distributed ceramic interference reject filters for passband consistency and temperature compensating atteuuatnrs for gain stability. The receiver is packaged in a unique "winged-hex'' shape to enable close packaging with the STAR antennas and to facilitate thermal management. The resulting low cost, compact receiver is made from COTS components.