Summary
International Symposium on Antennas and Propagation
2010
Session Number:4FD2
Session:
Number:4FD2-3
Design of Dual-Band Bandpass Filter with Controllable Bandwidths
Xiu Yin Zhang, Yuan Chun Li, Quan Xue, Chi Hou Chan,
pp.-
Publication Date:2010/11/23
Online ISSN:2188-5079
Summary:
Dual-band operation for RF systems has been widespread in modern wireless communication systems to enhance the functionality and capacity. In these systems, high-performance dual-band bandpass filters (BPFs) are heavily demanded to suppress unwanted signals. In response to this requirement, much research work has been conducted and various design approaches have been proposed [1]-[7]. Among them, two kinds of methods are very popular. The first category is to combine two sets of resonators with common input and output ports [1]-[3]. The passband frequencies can be easily tuned by changing the dimensions of the corresponding resonators. Using proper configurations, the required external quality factors and coupling coefficients can be simultaneously obtained at two passbands and hence the bandwidths can be independently controlled. Although it is easy to meet the performance requirement, the structures are relatively complex and the size is bulky. The second category is to make use of resonators’ fundamental resonant frequency and the second harmonic to generate two passbands [4]-[7]. A typical example is to use stepped-impedance resonators (SIRs) to design dual-band filters. By controlling the impedance and length ratios of SIRs, desirable operating frequencies can be obtained. However, it is difficult to control the bandwidth of each passband. In this letter, a novel method for designing dual-band BPFs with controllable bandwidths is proposed. The filters utilize stub-loaded resonators. The stubs, loaded at the center of open-ended microstrip lines, affect only the upper passband performance and have no impact on the lower passband behavior. Hence, the coupling path formed between the stubs only deliver signals at the upper passband frequency. The other coupling path can be used to adjust the coupling strengths at both passband frequencies. By properly controlling the coupling strength at each path, the desirable coupling coefficients at both passbands can be obtained and hence the bandwidths can be controlled. Furthermore, by using the stub-loaded resonators [7], the passband frequencies can be easily tuned. Therefore, both the frequency and bandwidth of each passband can be easily controlled. Based on the proposed idea, two BPFs are implemented. The design methodology and experimental results are presented.