Compact UWB BPF With Broad Stopband Based on Loaded-Stub and C-Shape SIDGS Resonators

Jiacheng Xie,Xun Luo,Yiyang Shu,Deshan Tang

doi:10.1109/lmwc.2021.3136561

Abstract

In this letter, two types of substrate-integrated defected ground structure (SIDGS) resonators (i.e., loaded-stub and C-shape resonators) are proposed for the ultra-wideband (UWB) bandpass filter (BPF) design. Coupled SIDGS resonators can generate four transmission poles to achieve the UWB response with low insertion loss in a compact size. Besides, the spurious cancellation with a broad stopband is achieved by mutual suppression of separated harmonics from the SIDGS resonators. In addition, the lowpass units (LPUs) embedded in the microstrip feed-lines are utilized to further improve the BPF stopband rejection. To verify the mechanism, a compact BPF operating at 6.85 GHz (i.e., the passband center frequency <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{0}$ </tex-math></inline-formula> ) with 0.6-dB insertion loss and 3-dB fractional bandwidth (FBW) of 114% is implemented and fabricated. The measured stopband extends to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$9.7f_{0}$ </tex-math></inline-formula> with a rejection level more than 26 dB.

Highlights

I N MODERN wireless system, the ultra-wideband (UWB) bandpass filters (BPFs) with wide stopband and low radiation loss are developed rapidly [1]
The broad stopband is achieved by staggering the harmonics of two types of resonators and inserting lowpass units (LPUs) into the feed-lines
The BPF consists of two loaded-stub substrate-integrated defected ground structure (SIDGS) resonators, two C-shape SIDGS resonators, and two microstrip T-stubs with embedded LPUs

Summary

INTRODUCTION

I N MODERN wireless system, the ultra-wideband (UWB) bandpass filters (BPFs) with wide stopband and low radiation loss are developed rapidly [1]. To improve the passband performance, the substrate-integrated waveguide (SIW) resonators [26]–[28] are proposed with low insertion loss and flat group delay. Substrate-integrated defected ground structure (SIDGS) filters [36]–[37] are developed with low insertion loss, wide stopband, and wideband low radiation loss, simultaneously. The design of compact UWB BPF with enhanced passband and stopband performance for flexible integration remains challenges. The loaded-stub SIDGS resonators with C-shape SIDGS resonators are applied for the UWB BPF. The simplified equivalent model of the loaded-stub resonator is shown, while the even-mode and odd-mode models are derived in Fig. 2(c) and (d), respectively.

Ultra-Wideband BPF

FABRICATION AND MEASUREMENT

Findings

CONCLUSION