Ultra Compact Inline $E$ -Plane Waveguide Bandpass Filters Using Cross Coupling

This paper presents novel ultracompact waveguide bandpass filters that exhibit pseudoelliptic responses with the ability to place transmission zeros on both sides of the passband to form sharp rolloffs. The filters contain E-plane extracted pole sections (EPSs) cascaded with cross-coupled filtering blocks. Compactness is achieved by the use of evanescent mode sections and closer arranged resonators modified to shrink in size. The filters containing nonresonating nodes are designed by means of the generalized coupling coefficients' extraction procedure for the cross-coupled filtering blocks and EPSs. We illustrate the performance of the proposed structures through the design examples of third- and fourth-order filters with center frequencies of 9.2 and 10 GHz, respectively. The sizes of the proposed structures suitable for fabricating using the low-cost E-plane waveguide technology are 38% smaller than ones of the E-plane extracted pole filter of the same order.