Publications

Three designs for a 4-by-4 are described for use in a spatial power-combined transmitter. The subarrays are constructed using a hybrid-circuit, tile-approach architecture and are composed of 16 cavity-backed, proximity-coupled microstrip antennas, each fed by a 0.5 watt amplifier. Both linearly and circularly polarized subarrays have been constructed for operation over a 10% band centered at 10 GHz. The linearly polarized subarray showed the following peak performance: EIRP greater than 27 dBW, effective transmitter power greater than 5 watts, dc-RF efficiency greater than 20%, and excellent graceful degradation performance.

The radiation efficiency of conventional microstrip antennas generally decreases when the substrate thickness or permittivity is increased because of loss to surface waves. However, constructing a metal cavity around the microstrip antenna prevents the surface wave propagation. Thus, the cavity backed microstrip antenna has been predicted to have increased radiation efficiency. In this paper, we compare conventional and cavity backed microstrip patch antennas on substrates with an electrical thickness of 0.067 ho and dielectric constants of ~r=2.94, 6.15, and 10.2. As one would expect, the radiation efficiency of the conventional patch decreases with increasing dielectric constant, but the efficiency remains relatively constant for the cavity backed patch. In this work, three different methods are used to measure the radiation efficiencies: a far field gain comparison, a Wheeler cap method and an input admittance method.