Practical design of rectangular waveguide filters with a capacitive building block providing an extra transmission zero

This paper faces up the practical design of a class of rectangular waveguide filters using a recently proposed capacitive coupling scheme. Such a coupling scheme creates an E-plane stub in the waveguide resonator, and provides an extra transmission zero. First, a novel 2D building block including the capacitive window and the stub is identified. A parametric analysis of this block is then carried out to evaluate its performance, and also to obtain design guidelines for its use in practical applications. Finally, such guidelines are illustrated with the EM-based design of a novel constant-width filter topology of order 5, which provides 4 transmission zeros without cross-couplings and non-resonating nodes. The designed filter is fully validated with measurements of a manufactured prototype.