Microstrip antennas on synthesized low dielectric-constant substrates

Micromachining techniques using closely spaced holes have been used underneath a microstrip antenna on a high dielectric-constant substrate (epsilon(r) = 10.8) to synthesize a localized low dielectric-constant environment (epsilon(r) = 2.3). The measured radiation efficiency of a microstrip antenna an a micromachined 635-mu m thick epsilon(r) = 10.8 Duroid 6010 substrate increased from 48 +/- 3% to 73 +/- 3% at 12.8-13.0 GHz (including 3,3-cm feed line losses). We believe that this technique can be applied to millimeter-wave antennas (microstrip, dipoles, slots, etc,) on silicon and GaAs substrates to result in relatively wideband (3-6%) monolithic microwave integrated circuits (MMIC) active antenna modules for phased-arrays and collision-avoidance systems.