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 (ε_r=10.8) to synthesize a localized low dielectric-constant environment (ε_r=2.3). The measured radiation efficiency of a microstrip antenna on a micromachined 635-μm thick ε_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