Compact Leaky SIW Feeder Offering TEM Parallel Plate Waveguide Launching

A planar and low-cost parallel-plate waveguide (PPW) launcher based on substrate integrated waveguide (SIW) technology is proposed. It can launch the fundamental TEM mode with a collimated wave front into a PPW structure while also being low profile and easy to fabricate. The launcher is implemented using a network of SIW transmission lines and its design is based on the leaky-wave (LW) theory. In our proposed structure, a selection of the SIW lines is made to leak power into the desired PPW region by means of a partially reflective surface, enabling planar wave front propagation of the TEM mode where efficiency values of over 90% are achieved. Measurements of a fabricated prototype are also reported at 15 GHz to demonstrate the design procedure and validate structure operation. When compared with similar co-axial and metallic waveguide launchers, our proposed SIW structure represents a compact, integrated, and unique design solution which may be useful to feed planar parallel-plate slot arrays and end-fire antennas. In addition, our novel and simple approach for PPW excitation can also be applied to other parallel-plate-based guides, low-cost transitions, and compact dividing/combining circuits for a new antenna and non-radiating LW feed systems at microwave and millimeter-wave frequencies.