Aperture coupled waveguide feeds for microstrip antennas and microstrip couplers

While it is often desirable to select planar antennas and circuitry for their advantages in terms of cost, low-profile, and compatibility with microwave integrated circuits, there are still many applications where it is necessary to combine such components with rectangular waveguides. This is especially true at millimeter wave frequencies, where waveguide circuitry must often be connected to planar antennas, or planar circuitry must be combined with waveguide feeds. Traditional waveguide-to-microstrip transitions have used either wire probe coupling, machined matching step sections, or fin-line type transitions, but each of these suffers from several disadvantages in terms of manufacturing or fabrication complexity, cost, or an inconvenient physical configuration. This paper describes and discusses several broadwall and endwall waveguide-to-microstrip transitions that rely on aperture coupling techniques, and are thus well-suited for low-cost high-volume production for commercial millimeter wave applications. Five different waveguide-to-microstrip transitions have been analyzed using a full-wave moment method procedure, with experimental results for the more interesting designs.