司马卫武

摘 要：微带滤波器由于其轻便，体积小和易于制造等优异的特点而得到了广泛的应用。但是经过Richards变换和黑田规则得到的低通滤波器由于变换函数的周期性在高频段出现了严重的寄生通带，且采用的切比雪夫模型在过渡带的性能可以得到进一步的改进。本文采取高低阻抗变换得到的椭圆函数低通滤波器，加入叉指结构的谐振单元后相比于以前的滤波器有更好的过渡带性能和高频段的寄生通带的寄生能力，三倍频处的正向电压传播系数仍抑制在-40dB以下，且其匹配性能在通带内的驻波比最大为1.5，基本符合滤波器设计要求。

关键词：宽阻带；椭圆函数；高低阻抗；叉指结构

Abstract：Microstrip filter has been widely used due to its outstanding characteristics such as lightweight，small size，easiness to manufacture and so on.But the lowpass filter gotten by Richards transformation and Kuroda rule has serious parasitic passband due to the periodic character of transform function.Furthermore，transition band of filters transformed from Chebyshev model can be further improved.This article focuses on the elliptic lowpass filter gotten by high and low impedance transformation，which has better performance of transition band and restraint capacity for parasitic passband at higher frequency after adding pectinate resonant unit.Forward voltage transmission coefficient at three times frequency can be still restrained under -40dB，with standing wave ratio within passband up to 1.6 which indicates good matching performance.It can be concluded that the design requirement of filter have been basically fulfilled.

Key words：Wide stopband；elliptic function；high and low impedance；pectinate structure

1 理論依据

叉指型结构：在传统枝节型微带低通滤波器中引入了一种叉指型结构，在没有影响带内特性的情况下，有效抑制了寄生通带，拓展了阻带。叉指型结构可以看作是高阻抗线电感和叉指耦合电容的组合，具有带阻特性。

2 设计与仿真

2.1 所用介质基材和铜膜信息

实验所用基材为Taconic公司的RF-35系列基材，RF-35是一种层压在Taconic产品中的ORCER系列材料中的有机玻璃。它基于编织纹的加固型玻璃。可以查到在1.9GHz下的相对介电常数和介电损耗角分别为0.35和0.0018，介质厚度为0.76mm，铜膜厚度为0.035mm。

2.2 HFSS对叉指型结构谐振响应的仿真

叉指型结构的谐振频率与叉指型结构的长度和缝宽度有关，可以在HFSS中对叉指型结构进行建模，以其长度和缝宽度为变量，找到能够有效抑制寄生通带的谐振频率相关的长度和缝宽度。……