A Novel Millimeter-Wave Ultra-Wideband Bandpass Filter Using Microstrip Dual-Mode Ring Resonators Loaded with Open Tuning Stubs of Different Lengths

Abstract

In this paper, a millimeter-wave ultra-wideband (UWB) bandpass filter is developed by cascading two microstrip dual-mode ring resonators loaded with lambda0/4 and 3lambda0/4 open tuning stubs, respectively. The ring resonators are analyzed by using the even-and odd-mode method, and closed-form formulas are derived to facilitate the design of transmission zeros of these resonators. The filter has a midband frequency of 25.5 GHz and a 3-dB bandwidth of 5 GHz (20%). Due to the multiple transmission zeros produced in both the lower and upper stopbands, the filter exhibits sharp attenuations near the passband and very wide stopbands. Over 13-35 GHz, the Federal Communications Commissions indoor limit is satisfied quite well.