多带外传输零点微带带通滤波器设计

设计了一种梳状微带平行耦合线窄带带通滤波器，仅应用两腔结构就实现了带外5个传输零点。通过微带线开路枝节，平行耦合线结构，以及馈电位置和两个梳状线谐振器之间的耦合，在通带附近引入了3个传输零点；四分之一波长平行耦合线接地短路结构，在带外高频产生额外两个传输零点，进而可有效抑制零点频率附近的杂波干扰。实测结果表明，设计的滤波器中心频率为238 GHz，相对带宽45%，对低频抑制大于22 dB，带外5个零点位置与计算仿真结果吻合很好。该新型滤波器结构简单紧凑，带外抑制高。

Design of a microstrip bandpass filter with multiple transmission zeros

A microstrip hairpin parallel coupled narrow band bandpass filter(BPF) is proposed, which uses only two coupled resonators to realize five transmission zeros. Due to the open circuited stubs, the open circuited parallel coupled lines, tapped feeding position and coupling between two hairpin resonators, three transmission zeros in the vicinity of the passband are introduced. Two quarter wavelength parallel coupled lines sharing the same via hole grounding can contribute two additional transmission zeros beyond the passband, which can suppress the frequency interference near the zero points. Measured results show that the filter has the fractional bandwidth of 4.5% with the center frequency of 2.38 GHz and a minimum out band loss of 22 dB in the lower band. The measured positions of the five transmission zeros agree well with the analytical model and numerical simulations. The proposed bandpass filter has such advantages as compact size, simple structure and high selectivity in the stopband.