Filtering Microstrip to Waveguide Launcher

This paper presents a novel synthesis-based co-design of a filtering microstrip-to-waveguide launcher. The proposed design is intended to replace the waveguide low-pass filter generally placed between the common port of the diplexer and the antenna port in FDD communication systems. The launcher is truly considered part of the filter since it acts as the last resonator of its prototype model. The overall frequency behavior is then completed with microstrip stubs (extracted-poles) connected through suitable transmission lines. A methodological design procedure is presented for this purpose together with a practical implementation centered in the X-band (8 – 12 GHz). Full-wave simulations and measurements are in agreement and they validate the proposed design with clear advantages in terms of out-of-band performance and reduced system complexity.