一种高抑制电调滤波器的设计与实现

针对超外差接收机中前端预选宽频段、低损耗与高带外抑制度的需求,文中在电感耦合方式的LC电调滤波器基础上,增加了寄生通带抑制滤波器,设计了一款基于20~800 MHz调谐范围的电调滤波器。通过实际测试得到在调谐范围内,滤波器插入损耗<1.5dB,1 dB相对带宽约20%~30%,输入输出端口驻波<1.5,二倍频处抑制度>40 dBc,寄生通带抑制滤波器能将二次谐波和三次谐波寄生通带的抑制度分别提高40 dBc和30 dBc以上,从而利于滤波器在预选部分实现中频、镜频和本振反向等抑制作用。

Design and Implementation of an Electrically Tunable Filter with High Suppression

For the demand of wide frequency band, low loss and high external restriction in the front preselection of superheterodyne receiver, a filter was increased to suppress the spurious band behind the LC electrically tunable filter with inductance coupling method in the article, designing an electrically tunable filter on account of 20~800 MHz . Actual test showed that in the tuning range, insertion loss of the filter was less than 1.5 dB, 1 dB bandwidth was about 20%~30%, VSWR of input and output ports were less than 1.5, suppression on the second harmonic frequency was more than 40 dBc. The suppression on the spurious band was increased more than 40 dBc in the second frequency and more than 30 dBc in the third harmonic frequency after applying this filter. All these benefited to the filter with the intermediate frequency suppression, mirror frequency suppression, the reverse leakage of vibration suppression, and so on.