Dual-Mode Microstrip Patch Bandpass Filters With Generalized Frequency Responses

Qing Liu,Yi Zhang,Dong-Fang Zhou,Dei-Wei Zhang,Da-Long Lu

doi:10.1109/access.2019.2952403

Abstract

A basic two-pole bandpass filter based on the dual-mode square patch resonator is presented and analyzed to realize generalized frequency responses in terms of two finite transmission zeros (FTZs). The feeding lines of the dual-mode filter are deviated from the center position of the patch resonator to realize different strength of main coupling paths. And then, a novel four-pole patch bandpass filter based on a multilayer dual-mode structure is proposed and analyzed in detail. The input and output ports are designed on the upper substrate layer. The lower dual-mode patch resonator is coupled to the upper one using four coupling apertures in the middle metal layer. The multilayer dual-mode patch filter can be modeled by a dual-extended doublet scheme with source-load coupling. Generalized frequency responses in terms of four FTZs can be achieved. Several design examples using the proposed multilayer dual-mode patch filter are presented to illustrate the high degree of flexibility of FTZs. To verify the proposed structure, two examples were fabricated and measured. The measured results agree well with simulated ones.

Highlights

Microstrip bandpass filters (BPFs) are widely studied and used in the model RF/microwave circuits and systems [1]–[6]
A dual-mode patch resonator can realize a quasi-elliptic filtering response with two transmission poles (TPs) and two finite transmission zeros (FTZs), which is more advanced than the filter using two coupled single-mode patch resonators
In [18], we propose a new triplemode patch filter, which can realize high selectivity because three FTZs are produced

Summary

INTRODUCTION

Microstrip bandpass filters (BPFs) are widely studied and used in the model RF/microwave circuits and systems [1]–[6]. Flexible frequency responses in terms of two FTZs based on a dual-mode patch resonator are realized for the first time. Several design examples using the proposed multilayer dual-mode patch filter are presented to illustrate the high degree of flexibility of four FTZs. To verify the proposed structure, two four-pole dualmode patch filters with the center frequency of 3.5 GHz were fabricated and measured. THE PROPOSED DUAL-MODE PATCH FILTER Fig. 1(a) shows the layout of the proposed dual-mode square patch bandpass filter with one perturbation slot, which can be etched on the direction of the diagonal line T1T2 or P1P2. The evanescent fields of the dc and higher-order modes can provide an equivalent S-L coupling, and the sign of S-L coupling is negative which is similar to the case of filters in [18], [26]

EXTRACTED EXTERNAL QUALITY FACTORS AND S-L

EXPERIMENTAL RESULTS

CONCLUSION