Chung-Hwa Wu, Chi-Hsueh Wang, and Chun Hsiung Chen, Stopband-Extended Balanced Bandpass Filter Using Coupled Stepped-Impedance Resonators IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS, VOL. 17, NO. 7, JULY 2007 Chung-Hwa Wu, Chi-Hsueh Wang, and Chun Hsiung Chen, Adviser : Hon Kuan Min-Hang Weng Reporter : Yi-Hsin Su Date : 2010/4/28

Outline Introduction Balanced Filter Structure Design Of The Stopband-Extended Balanced Filter Filter Responses Differential-Mode Response Common-Mode Response Conclusion

Balanced Circuits Balanced circuits play an important role in building a modern communication system. Balanced circuits with differential operation show higher immunity to environmental noise A well-designed balanced bandpass filter (BPF) should exhibit the desired differential-mode frequency response and should also be capable of reducing the common-mode signal at the same time.

Introduction Recently, a fourth-order balanced coupled-line BPF using parallel-coupled-line structures was proposed, which presents both high selectivity and good common-mode rejection within the differential-mode passband. However, This filter still has several drawbacks, such as requiring via-hole process. A novel fourth-order balanced BPF based on λ/2 stepped-impedance resonators is proposed to realize the desired differential-mode characteristics in addition to overcoming the shortcomings C.-H.Wu, C.-H.Wang, and C. H. Chen, “Novel balanced coupled-line bandpass filters with common-mode noise suppression,” IEEE Trans. Microw. Theory Tech., vol. 55, no. 2, pp. 287–295, Feb. 2007.

Balanced Filter Structure The proposed fourth-order balanced filter is composed of four symmetric λ/2 SIRs, The proposed balanced filter has used the balanced feed structure This balance BPF is designed and fabricated on FR4 substrate having a thickness of 1mm, a dielectric constant of 4.4, and a loss tangent of 0.02. Physical layout of the proposed fourth-order balanced filter using symmetric=λ/2 SIRs.

Balanced Filter Structure Under differential-mode operation, a virtual-short (PEC) would appear along the symmetric-line, therefore each resonator, resonating at , may be treated as a shorted λ/4 SIR. Under common-mode operation, a virtual-open (PMC) would present along the symmetric-line, thus each resonator, resonating at ( ), may be treated as a λ/2 resonator. ＞ differential-mode common-mode

Design Of The Stopband-Extended Balanced Filter differential-mode and common-mode external quality factors against the tap position of I/O resonators. mixed coupling ( =1GHz and 3-db FBW=10%)

Design Of The Stopband-Extended Balanced Filter ( =1GHz and 3-db FBW=10%)

Filter Responses The differential-mode response, the center frequency is at 1.02 GHz, with a minimum insertion-loss of 3.51 dB and a bandwidth of 12%. The differential-mode spurious passband has been pushed up to 5.65 .

Filter Responses The common-mode signal is suppressed with a level of -34.46 dB around ,and almost below 30 dB from 0.5 to 6 GHz. This spurious response has been suppressed due to the relatively weak signal along the main path and the poor common-mode external quality factor value associated with I/O resonators.

Conclusion In this letter, a novel fourth-order balanced BPF using symmetric λ/2 SIRs is proposed. To obtain the desired differential-mode frequency response and also to avoid the undesired via-hole process. The open stub associated with tap position Lt has created an additional. transmission zero