新型宽阻带双通带滤波器设计

Novel dual-band bandpass filter with wide upper stopband performance

传统的双通带滤波器设计一般使用两个或多个谐振器构成,电路尺寸较大.为了减小谐振器尺寸,提出了一种新型的枝节加载方环四模谐振器.根据谐振器结构的对称性,两次应用奇偶模方法分析了该结构的谐振特性.该谐振器的4个谐振模式的等效电路均为1/4波长谐振器,实现了谐振器的小型化,且一次谐波为基频的3倍.每个模式对应的谐振频率都是独立可控的,利用其设计的双通带滤波器,也具有独立可控的通带中心频率和带宽.设计并采用了1/4波长弯钩形馈电线,为两个通带提供了合适外部耦合,也产生了两个新的传输零点,进一步改善了滤波器的选择性,获得了更宽的阻带特性;最后,设计并加工了一款微带双通带滤波器,测试与仿真结果吻合良好.

In traditional design of the dual-band bandpass filter （BPF）, two or more resonators need to be utilized, which leads to a relatively large circuit size. For miniaturization, a novel stub-loaded square loop quad-mode resonator is proposed in this paper. Due to the symmetry of the structure, the even-odd-mode method is applied twice to analyze its resonance characteristics. All the four mode equivalent circuits are quarter-wavelength resonators, so the resonator has a compact size and the first harmonic is three times the fundamental one. The resonant frequency of each mode can be tuned freely by changing the corresponding physical dimensions, and the passband frequencies and bandwidths of the designed dual-band filter using the proposed resonator are independently controllable. To improve the selectivity and achieve a wide upper stopband, quarter wavelength hook-shape feedlines are designed to provide appropriate external coupling. Two new transmission zeros are generated by the feedlines. Finally, a microstrip dual-band bandpass filter （BPF） centering at 1.5 and 2.4GHz with a 3dB fractional bandwidth （FBW） of 10.7% and 9.6% is designed and fabricated. The measured and simulated results which are in good agreement are presented.