基于工字型双模谐振器的恒定带宽调频滤波器的设计

Design of Constant Bandwidth Frequency Modulation Filter Based on I-shaped Dual-mode Resonator

为提高可调滤波器的带外抑制度和频率选择性,提出一种基于工字型双模谐振器结构的二阶拓扑结构恒定带宽调频滤波器。对工字型双模谐振器进行奇偶模方法分析,揭示了带宽恒定和带外传输零点引入机理,通过二阶拓扑结构布局及独立分立元件加载,增加了滤波器外部品质因数,进一步提高了滤波器带外抑制度和频率选择性。所实现的调频通滤波器电路尺寸为30 mm×25 mm,保持400 MHz绝对带宽恒定,中心频点从1.4~2.0 GHz连续可调,通带内最大损耗为4.5 dB,阻带有三个传输零点。该滤波器具有可调频点范围广、带宽恒定、带外抑制度和频率选择性较高的优点。

In order to improve the stopband rejection and selectivity of a constant bandwidth frequency modulation filter,a second-order topology based on an I-shaped double-mode resonator is proposed.Characteristics of the I-shaped double-mode resonator are analyzed by using the odd-even mode,and the introduction mechanism of bandwidth constant and out band transmission zero is revealed.By loading second-order topological structure layout and independent discrete component,the external quality factors of the filter are increased,and out stop band rejection and frequency selectivity of the filter are further improved.The effective size overall size is 30 mm×25 mm.The 400MHz bandwidth can be adjusted while the center frequency changes from 1.4 to 2.0 GHz.The minimum insertion loss is 4.5 dB.There are independently adjustable zero points to widen the stop band.The filter has the advantages of wide range of adjustable frequency,high out-of-band rejection and high selectivity.