紧凑型多陷波超宽带滤波器的设计

针对传统带阻单元构成滤波器存在陷波深度不足和阻带抑制较差的问题，提出一种加载开路枝节的多陷波超宽带滤波器。基于开路枝节线和阶跃阻抗谐振器理论，通过在超宽带滤波器多模谐振器上引入一对折叠开路枝节线产生2个陷波频段，这种特殊枝节实现的陷波抑制能力更强；在超宽带结构下方耦合阶跃阻抗谐振器产生第3个陷波频段，陷波深度更好。最终实现超宽带带通滤波器的中心频率为6.6 GHz，陷波频段相对带宽约为134%。仿真与实测结果表明，该滤波器工作带宽为2.2~11.2 GHz，实现了2.8~4.4 GHz,6.2~6.8 GHz和8.8~9.8 GHz 3个频段的陷波特性，可有效滤除C波段和WLAN频段信号对超宽带通信系统的干扰。满足超宽带系统对陷波滤波器插入损耗和带外抑制的要求。

Design of a compact UWB filter with multi-band notched characteristics

Aiming at the problem that the notched depth is insufficient and the stop band suppression is bad in the filter composed by traditional band stop units, a multi-band notched characteristics ultra-wideband(UWB) filter structure with open circuited stub is proposed. Based on the theories of open circuited stub and step impedance resonator, two notch bands are produced by adding a pair of folded open circuited stub on the multi-mode resonator of the UWB filter. The special stub can realize stronger notch suppression capability. The third notched band is produced by coupling a step impedance resonator below the UWB structure, which makes the depth of the notched band preferable. Ultimately, the center frequency of UWB bandpass filter is 6.6 GHz, the relative bandwidth of the notched band is about 134%. Simulated and measured results show that the filter has a working bandwidth of 2.2 GHz~11.2 GHz, it realizes band notched characteristics of triple frequency bands at 2.8 GHz~4.4 GHz, 6.2 GHz~6.8 GHz and 8.8 GHz~9.8 GHz, which can efficiently eliminate the interfere of C band and WLAN band signals on UWB communication systems. It meets the requirements of insertion loss and out of band rejection of notch filter in UWB system.