Single-Layer Waveguide Feed for Uniform Plane TEM-Wave in Oversized-Rectangular Waveguide With Hard-Surface Sidewalls

A new single-layer waveguide feed is presented for excitation of the dominant quasi-TEM mode in oversized-rectangular waveguide with hard-surface sidewalls. Coupling windows are cut on the narrow wall of the waveguide feed and are cascaded on the same layer as the oversized waveguide. The feed is compact in terms of the length compared to the conventional hard horns and inhomogenious transformers. This type of waveguide feed is useful for the uniform feeding of the oversized-rectangular waveguide slot-array antenna with installed hard-surface sidewalls. Excitation of the uniform plane wave in 4lambda0wide waveguide is confirmed by the measurements on 12 GHz band model. The ripple in amplitude is less than 3 dB and in phase less than 15deg. The uniformity of the field distribution is preserved along the direction of the wave propagation. Presented waveguide feed has the 3-dB beamwidth of 12.5deg which is 4.5deg narrower than the one of the conventional waveguide feed. The bandwidth is 16.7% in terms of reflection less than -10 dB for the overall feeding structure