MM wave/FIR twin slot antenna structures

A twin slot antenna fed by a microstrip line for the millimeter-wave/far-infrared range is investigated. The twin slots couple incident power into a microstrip feed line which consists of microstrip low-pass filters and a microbolometer detector. An advantage of this structure is that the feed lines are isolated from the incident radiation by the slot ground plane. Several antennas were built and tested between 90 and 94 GHz. Measurements are compared with theory for the twin slots on a quartz-air-quartz stack at 90.5 GHz. Although the shape of the beam patterns agrees closely with theory, the measured gain is about 10 dB less than calculated. This discrepancy exists because the theory does not account for the various losses. It is noted that it should be possible to obtain better beam patterns by using GaAs as the outer dielectric instead of quartz.<>