1. 1 Design of the Compact Dual-Band Bandpass Filter With High Isolation for GPS/WLAN Applications Adviser : Hon Kuan Reporter : Yi-Hsin Su Student ID : M98L0210 Date : 2010/3/2 IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS, VOL. 19, NO. 12, DECEMBER 2009 Yu-Chi Chang, Chia-Hsiung Kao, Min-Hang Weng and Ru-Yuan Yang

2. 2 Outline  Introduction  Design Procedure  Fabrication And Measure Results  Conclusion

3. 3 Introduction  Recently, the development of multi-service mobile wireless communication systems has become attractive for commercial products especially in the combination of global position system (GPS) and wireless local area network (WLAN), global system for mobile communications (GSM)and GPS or GSM and WLAN.  Most of the reported dual-band BPFs only provide the dual passband performance in a single-service system, especially in WLAN with IEEE 802.11 a/b standard.  This paper develop a very simple structure to realize a compact and high performance dual-band BPF with a high isolation loss of 55 dB between the two passbands of GPS/WLAN and a wide upper stopband.

4. 4 Design Procedure  The schematic of the dual-band BPF basically consisting of two asymmetric SIRs and a pair of I/O ports.  This dual-band BPF is designed and fabricated on Duroid 5880 substrate having a thickness of 0.787 mm, a dielectric constant of 2.2, and a loss tangent of 0.0009.  the structural parameters: L 1 =15.02mm,L 2 =4.45mm,L 3 =15.5 3mm,L 4 =15.02mm,L 5 =0.29mm,L 6 =9.16mm,W 1 =0.2mm,W 2 =0.2mm, W 3 =3.7mm,S 1 =0.5mm,S 2 =0.1mm,S 3 =1.18mm,S 4 =0.1mm,S 5 =1.96m m Practical layout of the designed dual-band BPF.

5. 5 Design Procedure  The proposed asymmetric SIR with one step discontinuity is different from the conventional SIR with two step discontinuities.  The asymmetric SIRs are composed of a high- impedance section(Z 1 =1/Y 1 ) and a low-impedance section(Z 2 =1/Y 2 ). Schematic of the asymmetric SIR.

6. 6 Design Procedure  The impedance ratio R is defined as R=Z 2 /Z 1, θ t is defined as the total wavelength of the asymmetric SIR.  It is known that the resonance conditions of the proposed asymmetric SIR is determined when Y in =0.  The length ratio (α) of asymmetric SIR is also varied to adjust the higher order resonant modes over a wide frequency range.

7. 7 Design Procedure  That normalized ratios of the second resonant frequency(f 1 ) to the fundamental resonant frequency(f 0 ) for an asymmetric SIR with R=0.25,0.45,0.65 and 1.  Some higher order resonant modes are very close to the fundamental resonant mode; thus it is possible to shift different resonant modes to form a dual-band performance  The length ratio α can be explicitly determined as 0.625 for obtaining the dual-band response when considering the asymmetric SIR with R=0.25 Normalized ratios of the second resonant frequency to the fundamental resonant frequency for an asymmetry SIR with R=0.25,0.45.0.65 and 1.

8. 8 Design Procedure M ij is the coupling coefficient that M 23 = FBW*j 2 /g 2, M 14 = FBW*j 1 /g 1 and M 12 = M 34 =FBW*(g 1 g 2 ) 1/2.  The 3-dB fractional bandwidths (FBW) of the two passband are set as FBW1 of 6% for the first passband and FBW2 of 4% for the second passband with the same passband ripple of 0.01 dB.  From the filter specifications, the lumped circuit element values of the low-pass prototype filter are found to be g 0 =1,g 1 =1.3782,g 2 =1.2693, j 1 =-0.2492, and j 2 =0.9772.

9. 9 Design Procedure  The coupling coefficients that are calculated. The coupled spacing can be tuned to satisfy the coupling degree between the adjacent resonators Coupling coefficient of (a) M23, (b) M12 and m34for first passband and second passband simultaneously. (a)(b)

10. 10 Fabrication And Measure Results  The two passbands of the fabricated dual-band BPF in detail. The measured results have a return loss greater than 30 dB, an insertion loss less than 0.9 dB, and a FBW of 6% for 1.575 GHz, and the measured results have a return loss greater than 20 dB, an insertion loss less than 1.1 dB, and a FBW of 3.8% for 2.4 GHz.  It is also clearly found that the isolation level is around 55 dB between the two passbands and the upper stopband is from 2.7 to 5.3 GHz at the average attenuation level of 38 dB. (a) Simulated and measured frequency responses of the fabricated dualband BPF and (b) two passbands in detail.] (Insert is the photograph).

11. 11 Conclusion  A novel compact dual-band BPF at 1.575 and 2.4 GHz using two asymmetric SIRs with low loss, wide stopband and high isolation.  The two passbands can be properly tuned by controlling the resonant modes of the proposed asymmetric SIR, which are discussed as functions of the impedance ratio and physical length ratio.  The circuit size is reduced greatly about 60%compared with the dual-band BPF using the conventional SIRs with the same specifications.  The isolation is greater than 55 dB, introducing a high isolation between the two passbands.  The average attenuation level of 38 dB is obtained to achieve a wide upper stopband from 2.7 to 5.3 GHz.