Theoretical design of high‐performance microstrip ultra‐wideband bandpass filters with controllable transmission zeros

Abstract

AbstractThis paper presents an efficient design of high‐performance microstrip ultra‐wideband (UWB) bandpass filters (BPFs) consisting of stepped‐impedance resonators (SIRs) and two‐section open‐ended SIR stubs. An analytical study is conducted on the proposed filter prototype to show its theoretical mechanism when an exact elliptical function synthesis technique is not available. Instead, a pseudo‐elliptical filter design scheme is successfully proposed for filter. As an example, a UWB BPF with a fractional bandwidth (FBW) of 110% (BW: 3.1–10.6 GHz) is then synthesized, simulated, fabricated, and measured. The measured frequency responses of the UWB filter compare very well with the predicted ones and successfully satisfy the outdoor specifications of the Federal Communications Commission (FCC). The fabricated filter also exhibits an easily fabricated structure (no via holes and a minimum gap size of 0.16 mm), a compact size, low insertion loss, a flat group delay, and good stopband characteristics as well. It should be noted that, in terms of the proposed design scheme, the proposed filter prototype can also be used to realize a UWB filter with a given FBW of even greater than 110%. © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.