Broadband and Compact Coupled Coplanar Stripline Filters With Impedance Steps

Novel broadband and compact stepped-impedance coupled coplanar stripline bandpass filters are presented, analyzed theoretically, and demonstrated experimentally. These filters are based on impedance step, capacitive gap, broadside coupling, and inductive shorted strip discontinuities, which are modeled in terms of impedance ($K$-) and admittance ($J$-) inverters. Broadside coupled coplanar stripline is analyzed for the first time by the even-/odd-mode decomposition technique using the finite-element method. The broadband and compact nature of the filters is explained from the discontinuities and the coupled line structures. Specifically, cross coupling is used to enhance the selectivity of both the low and high cutoffs, leading to triplet and quadruplet cross-coupled broadband filters with finite-frequency transmission zeroes. Due to their broad bandwidth, compact size, differential configuration, and low fabrication cost, the proposed filters represent excellent solutions for codesigned RF and microwave systems such as ultra-wideband transceivers.