A post-wall center-feed waveguide consisting of T-junctions is proposed for reducing the slot-free area of a parallel plate slot array antenna. The width of the slot-free area is reduced from 2.6 λ0 to 2.1 λ0. A sidelobe level in the E-plane is expected to be suppressed lower than that of the conventional center-feed antenna using cross-junctions. The method of moments with solid-wall replacement designs initially the T-junctions and HFSS including the post surfaces modifies only the reflection cancelling post. We have designed and fabricated a 61.25 GHz model antenna with uniform aperture illumination. The sidelobe level in the E-plane is suppressed to -9.5 dB while that of a conventional cross-junction type is -7.8 dB. Also, we suppress it to -13.8 dB by introducing a -8.3 dB amplitude tapered distribution in the array of the radiation slot pairs.

The results of experiments on the effect of the height and diameter of the cup on cup microstrip antennas are presented. The results show that the optimum height of the cup for the narrowest beamwidth and the highest gain is about 1/3 λ, and that the beamwidth decreases and the gain increases as the diameter of the cup increases.