基于电磁带隙结构的平衡五频带滤波器设计

Design of balanced quint-band filter based on electromagnetic bandgap structure

为满足现代微波滤波器高噪声抑制和多功能的性能需求,将电磁带隙结构(EBG)与微带线结构相结合,设计了一款具有高共模抑制的可调谐五频带平衡带通滤波器(BPF)。所提出的BPF结构由多对EBG谐振腔及平衡微带-槽线转换结构(MSTS)所组成,采用嵌套环型槽线来减小器件的插入损耗(IL),通过调节EBG结构中间金属柱半径和顶层槽线来实现对耦合系数Ki和外部品质因数Qe的控制。BPF的通带可调谐特性可以通过改变电容C的大小实现,所提出的BPF在整个频带范围内表现出出色的(CM)抑制特性。为验证理论的有效性,加工制作了一款频率范围在2~4.2 GHz的平衡五频带带通滤波器,五个频带的中心频率依次为2.15,2.49,2.94,3.46,3.95 GHz,测试结果显示在2~4.2 GHz的范围内滤波器的CM抑制超过-40 dB,滤波器整体尺寸为0.69λg×0.95λg。测试结果与仿真结果具有良好的一致性。

To satisfy the demand of high noise suppression and multifunction for modern microwave filters,a tunable quint-band balanced bandpass filter(BPF)was proposed with high common-mode(CM)suppression,which combined the electromagnetic bandgap(EBG)and the microstrip line structure.The proposed BPF consists of multiple pairs of EBG resonators and balanced microstrip-slotline transition structures(MSTS).The insertion loss(IL)of the device can be reduced by using multi-ring slotline.The tunable property of the proposed BPF can be achieved by changing the value of the capacitances.The proposed BPF exhibits configurable performance under differential-mode(DM)operation as well as a high CM suppression level over the entire frequency band.Finally,a quint-band balanced filter operating at 2-4.2 GHz was fabricated and measured.The central frequencies of the five bands were 2.15,2.49,2.94,3.46 GHz and 3.95 GHz.Measurement results show that the CM suppression of the filter exceeds-40 dB from 2 GHz to 4.2 GHz,and the overall size is 0.69λg×0.95λg.The experimental measurements agreed with the simulation of the designed band-pass filter.