基于枝节线加载谐振器的可调滤波器设计

Design of a Tunable Filter Based on Stub-Loaded Resonator

传统基于变容二极管的双频电可调滤波器由于外部容值的加入,该类滤波器的插损变大,同时相对带宽锐减。基于多模谐振器结构,提出了一种新型的工作频段独立、电可调的双频带通滤波器。该滤波器由短路枝节线加载谐振器和一对1/4波长谐振器组成。在各自的谐振器末端加载带有变容二极管的外部偏置电路,1/4波长谐振器构成第一通带,短路枝节线加载谐振器构成第二通带,两通带之间互不干扰,单独调节。应用奇偶模分析法及调节耦合间距的方法,确保双通带均出现两个极点,保证其带宽的稳定性。该电可调滤波器第一通带可调范围为0.7~0.85 GHz,第二通带可调范围为0.9~1.05 GHz,同时双频带的相对带宽基本保持在10%以上,较以往的双频电可调滤波器,该款滤波器的相对带宽有了较为明显的提升。

The traditional dual-band electrically tunable filter based on varactor has a bad insertion loss and a sharp decrease in fractional bandwidth due to the addition of external capacitance.Based on the multi-mode resonator,this paper proposes a novel dual-band band-pass tunable filter.The filter consists of a multi-mode resonator loaded with short-circuit branch line and a pair of quarter-wavelength resonators.At the end of each resonator,external bias circuit with varactor diode and quarter-wavelength resonator are loaded to consist the first passband,while short-circuit branch line loaded with resonator consists into the second passband,these two pass bands do not interfere with each other,they can be adjusted separately.By using the odd-even mode analysis and the method of adjusting the coupling length,two poles of each band will appear to ensure the stability of the bandwidth.The tunable range of the first passband is 0.7 ~ 0.85 GHz,the adjustable range of the second passband is 0.9 ~ 1.05 GHz.Meanwhile,the fractional bandwidth of the filter is kept above 10%.Compared with traditional dual-band filter,the proposed filter has an apparent increase of the fractional bandwidth.