Integration of Millimeter-Wave Post-Wall Waveguide-Fed Parallel Plate Slot Array with Planar RF Circuits

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Various sizes of 76-Ghz post-wall waveguide-fed parallel plate slot arrays are designed and manufactured. 40-50 % efficiency has been obtained for various sizes from 26 mm x 24 mm to 104 mm x 100 mm. Sidelobe suppression is demonstrated for car radar applications. Measured sidelobes are below -22 dB for one-dimensional Taylor tapering while those for two-dimensional Taylor distribution are below -18 dB. A new configuration of three slots is proposed to radiate a 45-degree linearly polarized wave. A good cross-polarization level below -25 dB is achieved in the boresight.The internal fields and the aperture illumination are effectively approximated in an oversized rectangular slotted array. Excitation coefficient of the radiation unit is assumed by introducing the perturbation ratio, which is defined by the ratio of unit-incident fields in terms of that in the linear array design model of periodic boundary waveguide. This ratio is varied over the two-dimensional aperture of the array and explains the perturbation of slots and narrow walls. The measured aperture illumination shows the good agreement with the prediction by the proposed method.A single layer structure consisting of a 4-way Butler matrix and a waveguide slot array in the post wall waveguides is proposed. Each one of four input ports generates different linear phase distribution over the elements, and results in different main beam directions. Butler matrix generally needs cross-junctions in three-dimensional structure. The single-layer structure is realized by introducing short slot directional couplers. A 26 GHz model is designed and manufactured. Switching operation has been confirmed.