ABSTRACT

This paper presents a design of a compact tri-band bandpass filter simply using a pair of the uniform impedance resonator loaded with an open-circuited stub. By introducing the variable impedance of the open-circuited stub, the proposed design has additional design parameter of the impedance ratio to adjust the resonant modes of the used resonator, so as to more easily achieve the different frequency bands. The resonant frequencies of the oddmode and evenmode of the used resonator are analyzed first in this study. A tri-band filter example is designed at the center frequencies of 1.9, 3.58, and 5.75 GHz, which can be used in 4 G system, 5 G communication system, and wireless local area network, respectively. The designed filter is simulated, fabricated, and then measured. The measurement shows that the insertion loss |S₂₁|, return loss |S₁₁|, and 3 dB fractional bandwidth for the three passbands are less than 0.25/0.37/0.9 dB, larger than 30/15/15 dB, and 17.5/12.2/8.9%, respectively. Moreover, by using the interdigital coupling of the used resonator, four transmission zeros are generated near the passband edges at 1.47, 2.56, 4.05, and 6.48 GHz, realizing high selectivity and high isolation. The measurement is consistent with the simulation, confirming the design concept.

摘要

本文介绍了一种紧凑型三频带通滤波器的设计，该滤波器仅使用一对加载有开路短截线的均匀阻抗谐振器。通过引入开路短截线的可变阻抗，所提出的设计增加了阻抗比的设计参数来调整所使用的谐振器的谐振模式，从而更容易地实现不同的频带。本研究首先分析了所用谐振器奇模和偶模的谐振频率。在1.9、3.58和5.75 GHz的中心频率设计了一个三频滤波器示例，分别可用于4G系统、5G通信系统和无线局域网。设计的滤波器经过模拟、制造和测量。测量表明，插入损耗|S ₂₁|、回波损耗|S ₁₁ | 和三个通带的3 dB 分数带宽分别小于0.25/0.37/0.9 dB、大于30/15/15 dB 和17.5/12.2/8.9%。此外，通过使用所用谐振器的叉指耦合，在1.47、2.56、4.05和6.48 GHz的通带边缘附近产生四个传输零点，实现了高选择性和高隔离度。测量与模拟一致，证实了设计理念。