提出一种新型的电容可调的微带带通滤波器, 由两个双模开环谐振器组成. 由于该谐振器的两种模式(奇模和偶模)之间不存在耦合的特性, 因此可使用一个简单的直流偏置电路来分别调节谐振器的奇模和偶模频率, 最终实现通带频率可调. 通过对谐振器模型的耦合矩阵分析, 在通带的边缘会产生传输零点, 从而大大提高了滤波器的频率选择性. 该滤波器在0.871.03 GHz(GSM 900)范围内可调, 通带内回波损耗大于20 dB, 且仿真曲线形状基本不变. 滤波器的测试结果与仿真结果基本吻合.
This paper proposes a novel varactor-tuned microstrip bandpass filter consisting of two dual-mode open-loop resonators. No coupling exists between the two operating modes, odd-mode and even-mode. Based on this feature, a simple DC bias circuit has been used to tune the resonator’s odd and even mode frequency respectively to realize tunable passband frequency. Analysis of the coupling matrix of the resonator model shows that a transmission zero is produced at the edge of the passband, which greatly improves frequency selectivity of the filter. This filter is tuned from 0.87 to 1.03 GHz (GSM 900) with return loss of more than 20 dB and nearly constant frequency response. Performance of a fabricated filter shows good agreement with the simulation results.
[1] Peng W W, Hunter I C. A new class of low-loss high-linearity electronically reconfigurable microwave filter [J]. IEEE Transactions on Microwave Theory and Techniques, 2008, 58(8):
1945-1953.
[2] Houssini M, Pothier A, Crunteanu A, et al, A 2-pole digitally tunable filter using local one bit varactors [C]//Microwave Symposium Digest, 2008 IEEE MTT-S International. 2008: 37-40.
[3] Wei L T, Lok U H, Kuo J T. New dual-mode dual-band bandpass filter with quasi-elliptic function passbands and controllable bandwidths [C]//Microwave Symposium Digest (MTT),
2010 IEEE MTT-S International. 2010: 576-579.
[4] Wolff I. Microstrip bandpass filter using degenerate modes of a microstrip ring resonator [J]. Electron Lett, 1972, 8(12): 302-303.
[5] Hong J S, Lancaster M J. Bandpass characteristics of new dualmode microstrip square loop resonators [J]. Electron Lett, 1995, 31(11): 891-892.
[6] Matsuo M, Yabuki H, Makinoto M. Dual-mode stepped impedance ring resonator for bandpass filter applications [J]. IEEE Trans Microw Theory Tech, 2001, 49(7): 1235-1240.
[7] Hong J S, Li S. Theory and experiment of dual-mode microstrip triangular patch resonators and filters [J]. IEEE Trans Microw Theory Tech, 2004, 52(4): 1237-1243.
[8] Hong J S, Shaman H, Chun Y H. Dual-mode microstrip openloop resonators and filters [J]. IEEE Trans Microw Theory Tech, 2007, 55(8): 1764-1770.
[9] Hong J S. Lancaster M J. Couplings of microstrip square openloop resonators for crosscoupled planar microwave filters [J]. IEEE Trans Microw Theory Tech, 1996, 44(12): 2099-2109.
[10] Chun Y H, Hong J S. Electronically reconfigurable dual-mode microstrip open-loop resonator filter [J]. IEEE Microwave and Wireless Components Letters, 2008, 18(7): 449-451.
[11] Guang W X, Cho Y H, Yun S W. A tunable combline bandpass filter loaded with series resonator [J]. IEEE Trans Microw Theory Tech, 2012, 60(6): 1569-1576.
[12] Amari S, Rosenberg U. Adanced coupling matrix synthesis techniques for microwave filters [J]. IEEE Trans Microw Theory Tech, 2003, 51(1): 1-10.
[13] Huang X G, Feng Q Y, Xiang Q F. Bandpass filter with tunable bandwidth using quadruplemode stub-loaded resonator [J]. IEEE Microwave and Wireless Components Letters, 2012, 22(4): 176-178.
