Dual-Band Bandpass Filter With Controllable Stopband Bandwidth

Nan Wang,Haokun Wei,Xiting Ruan,Shuangyang Liu,Qian Xu,Kun Gao,Anxue Zhang,Xiaojian Chen,Qian Yang

doi:10.3389/fphy.2021.809752

Abstract

A novel dual-band bandpass filter (BPF) is proposed with independently controllable transmission zeros (TZs) which can realize widely tunable stopband bandwidth (BW). The planar microstrip filter consists of a three-degree L-C ladder lowpass filter loaded with two unsymmetrical shorted stubs which are used to produce different TZs. By tuning the parameters of the two unsymmetrical shorted stubs, the TZs can be independently controlled. Therefore, the BPF has independent controllable center frequencies (CFs), passband bandwidths, and stopband bandwidths between adjacent passbands. All the L-C values in the equivalent circuit of the proposed filter are optimized to fulfill the design specifications. For demonstration, a dual-band BPF is designed. The measured results show good agreement with the simulated ones.

Highlights

Modern wireless communication systems need high performance filters which have controllable center frequencies (CFs), passband bandwidths, stopband bandwidths, and sharp rejection
The parameter La1 of the shorted stub 1 can tune TZ1 and TZ4, which means the first passband CF and stopband bandwidth can
Since the position of the last transmission poles (TPs) is near that of TZ3, the upper stopband performance is effected by the move of TZ3

Summary

INTRODUCTION

Modern wireless communication systems need high performance filters which have controllable CFs, passband bandwidths, stopband bandwidths, and sharp rejection. Signal-interference principles [4,5,6] are applied to design single- or dual-band BPFs with broad stopband bandwidths by creating multiple TZs. To design high performance filters with multiple passbands, the method of multiple monofrequency resonators coupling to a non-resonating node is proposed in [7]. This study presents a novel BPF loaded with two unsymmetrical shorted stubs to introduce two different TZs in the stopband to realize the controllable stopband bandwidth. The parameter La1 of the shorted stub 1 can tune TZ1 and TZ4, which means the first passband CF and stopband bandwidth can TABLE 1 | Optimized L-C values for a dual-band BPF (L unit in nH, C unit in pF). Since the position of the last TP is near that of TZ3, the upper stopband performance is effected by the move of TZ3

RESULTS

CONCLUSION

DATA AVAILABILITY STATEMENT