Design and Implementation of Compact Hybrid Four-Mode Bandpass Filter With Multi-Transmission Zeros

Abstract

Abstract-This paper presents a novel compact microstrip hybrid four-mode bandpass filter (BPF) with good selectivity and multitransmission zeros. By adding an external resonator to a triplemode stub-loaded resonator, four modes are generated in the desired passband and a hybrid four-mode BPF is implemented. Odd-and even-mode theory is introduced to investigate the mode characteristics of triple-mode resonator in detail. Circuit model and coupling matrix are built to further explain the proposed methodology. A microstrip BPF with central frequency of 3.4 GHz for wireless communication was designed and fabricated. Three transmission zeros are obtained at 3.2 GHz, 3.55 GHz and 3.73 GHz, which improve selectivity and outof-band rejection of the filter. The measured results of the fabricated filter represent good in-band and sharp sideband characteristic, which match well with simulated results.

Tri-Band Bandpass Filter Using Open Loop Resonator Loaded by One Stub with Three Branches

“…For even-mode excitation, the equivalent circuit is as Fig. 1d, which is similar to the equivalent one in [7]. The input admittance Z in,even of the even-mode resonator is expressed as:…”

A Novel Triple-Mode Bandpass Filter Based on a Dual-Mode Defected Ground Structure Resonator and a Microstrip Resonator

“…Multimode filters can also be realized by using dual-mode resonator doublets [14]. In our previous work [15], a four-mode BPF is achieved by combination of two dual-mode microstrip resonators. By setting two stub-loaded dual-mode resonators in parallel, a BPF with four poles is realized.…”