加载倒T形并联枝节的微带低通滤波器设计

Design of micro-strip low pass filter loaded by inverse T-shape parallel branch

针对传统的高低阻抗微带低通滤波器和开路端短截线微带低通滤波器体积较大、过渡带较缓且插入损耗较大的问题,采用高阻抗传输线单元加载并联倒T形枝节方法,构成带阻滤波支路,抑制了寄生通带,减小了滤波器面积。以7阶切比雪夫低通滤波器为例进行了设计和测试。实验结果表明,倒T形并联枝节滤波器截止频率为5.06 GHz,通带内最大插入损耗小于0.95 d B,在5.61～13.6 GHz内阻带抑制超过21 d B,而滤波器的面积比传统的开路端短截线微带低通滤波器减小20%。

For the traditional high-low impedance micro-strip lowpass filter and the open-ended stubs micro-strip lowpass filter, the sizes were large, the transition bands were slow, and the insert losses were relatively large. To solve these problems, the inverted T shaped parallel branch was loaded at the side of the high-impedance transmission line unit. The inverted T shaped shunt branch provided a stop-band filter sub-circuit, which can suppress the harmonic spurious components and reduce the size of filter. Based on the 7 order Chebyshev lowpass filter, the filter was designed and implemented. The experimental results show that the cutoff frequency of the filter is 5.06 GHz, the pass-band insertion loss is less than 0.95 d B, and stop-band rejection in 5.61-13.6 GHz is more than 21 d B. Compared to the traditional micro-strip lowpass filter with open-ended stubs, the area of the presented filter is decreased by 20%.