Progress In Electromagnetics Research Letters, Vol. 13, 139–147, 2010
A DUAL-BAND BANDPASS FILTER HAVING WIDE AND NARROW BANDS SIMULTANEOUSLY USING MULTILAYERED STEPPED IMPEDANCE RESONATORS
M.-H. Weng
Medical Devices and Opto-Electronics Equipment Department Metal Industries Research & Development Center
3F, No. 88, Luke 5th Road, Lujhu Township, Kaoshiung 82151, Taiwan S.-K. Liu
Institute of Photonics and Communications
National Kaohsiung University of Applied Sciences
Chien Kung Campus 415 Chien Kung Road, Kaohsiung 807, Taiwan H.-W. Wu
Department of Computer and Communication Kun Shan University
No. 949, Dawan Road, Yongkang City, Tainan County 710, Taiwan C.-H. Hung
Institute of Photonics and Communications
National Kaohsiung University of Applied Sciences
Chien Kung Campus 415 Chien Kung Road, Kaohsiung 807, Taiwan Abstract—Compact dual-band bandpass filter (BPF) with wide and narrow bands simultaneously is presented. By using the stepped impedance resonators (SIRs) in multilayered structure, the dual-band responses with wide and narrow bands simultaneously can be obtained. The filter has 3-dB fractional bandwidths (FBWs) of 45% and 10% for 2.4 GHz and 5.2 GHz, respectively. The circuit size is compact due to the multilayered structure. Moreover, multi-path propagation inside the multilayered structure generates transmission zeros at each skirt of the passbands for improving the passband selectivity. Measured results of the filter are in good agreement with the full-wave electromagnetic (EM) simulation.
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1. INTRODUCTION
Bandpass filters (BPFs), especially having a dual-band and charac-teristic, are popular critical components in multi-service wireless com-munication and/or wideband comcom-munication systems. When design-ing dual-band BPFs, several schemes can be used, such as cascad-ing coupled-resonators [1], combincascad-ing with the low- and high-pass cir-cuits [2] and using the coupled-resonators with open or short stubs [3]. Stepped impedance resonator (SIR) is also a well known type to re-alize dual-band BPF, by shifting its high order resonant modes to desired location [4–7]. However, filters using the above schemes cause a large size since they are fabricated on a single substrate. Moreover, when designing wideband BPFs, the schemes are different from those of dual-band BPFs. For wideband characteristics, the resonators with strong coupling or multi-modes are needed [8, 9]. Therefore, the dual-band BPFs having wide and narrow dual-bands simultaneously challenge designers to obtain the desired coupling coefficients and external qual-ity coefficients, as well as a compact size and a good dual-passband performance. 3-D multilayered structures by low temperature cofired ceramic (LTCC) technologies are well known for very high density cir-cuits [10]. Advantages of the multilayered BPFs also have benefits of strong coupling and cross-coupling effects between the resonators to achieve the desired bandwidth and provide transmission zeros for improving the passband selectivity [11].
In this paper, we present the design of the dual-band BPF with different bandwidths within two passbands by adopting the SIRs in multilayered structure. The design procedure includes the resonant characteristic of SIR, determination of the coupling coefficients and external quality coefficients. The measured results of the filter show a good agreement with the IE3D full-wave simulation [12].
2. DESIGN CONCEPT
Figure 1(a) shows the 3-D view of the multilayered dual-band BPF. The filter mainly consists of four folded SIRs and tapped input/output (I/O) lines connecting with SIR 1 and SIR 4. SIR 2 and SIR 3 are arranged on the 1st substrate, underneath the SIR 1 and SIR 4, as shown in Fig. 1(b). To reduce the circuit size, each SIR is folded. Fig. 2 shows the coupling paths of the typical and proposed coupled-resonators for dual-band BPF.
As shown in Fig. 2(a), the typical coupling structure only provides two coupling paths to introduce one transmission zero between two passbands [9]. However, the proposed coupling structure shown in
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structure. The size is around 30% reduction in comparison of the past literature [11]. Fig. 7 shows the simulated and measured frequency responses. Measured results have |S11| of 20 dB, |S21| of 0.29 dB and
FBW of 46% at 2.4 GHz; and |S11| of 15 dB, |S21| of 0.9 dB and FBW
of 12% at 5.2 GHz. The filter is four-pole based structure but the six-pole-like frequency response is shown over the frequency range. The multi-path propagation in the multilayered structure introduces several transmission zeros at each skirt of the passbands, actually improving the band selectivity.
4. CONCLUSION
The design of dual-band BPF with much different FBWs has been presented. The proposed filter has FBWs of 46% and 12% at 2.4/5.2 GHz, respectively. By tuning the impedance ratio and length ratio of the SIRs, the dual-band response can be well controlled. Wideband characteristic at single passband can be achieved by the multilayered structure. Multi-path propagation inside the multilayered structure can improve the passbands selectivity. This type of filter is actually suitable for modern mobile wireless communication systems, requiring different FBWs for the two passbands and greatly reduces the circuit size when needing strong coupling by multilayered structure. REFERENCES
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