Accurate circuit models of CPW coupling elements for the design of compact quarter-wavelength band-pass filters

Abstract

Accurate equivalent-circuit models of several types of coplanar waveguide (CPW) coupling elements are presented and their parameters are derived by employing the so-called short-open calibration (SOC) technique into the full-wave method of moments (MoM). Our brief description is firstly made on the formulation of this MoM-SOC for modeling a generalized two-port CPW discontinuity in terms of its circuit network, that is, the Z- or Y-matrix. Afterwards, three sets of J- or K-inverter parameters versus frequency are extracted and obtained in order to demonstrate the comparative coupling degree of lumped-capacitive and inductive gap-coupling, as well as distributed overlapped-coupling, structures. Next, these coupling elements are utilized together in the design of compact quarter-wavelength CPW band-pass filters via a simple cascaded network topology. Our optimized results are reasonably validated by ADS simulation and both exhibit good passband behavior with broadened bandwidth of more than 20% at 5.8 GHz and an ultra-broad upper stop-band of 6.4 to 15.9 GHz. © 2004 Wiley Periodicals, Inc. Int J RF and Microwave CAE 14: 453–461, 2004.