- Email: [email protected]
Design of superconducting multi-pole miniaturized filters with quasi-spiral resonators for decreasing unwanted cross couplings
Physica C 469 (2009) 1649–1652
Contents lists available at ScienceDirect
Physica C journal homepage: www.elsevier.com/locate/physc
Design of superconducting multi-pole miniaturized filters with quasi-spiral resonators for decreasing unwanted cross couplings S. Ono a,*, Y. Harada b, A. Saito a, J.H. Lee a, T. Kato a, M. Uno a, M. Yoshizawa c, S. Ohshima a a
Graduate School of Science and Engineering, Yamagata University, 4-3-16 Johnan, Yonezawa 992-8510, Japan Advanced Industrial Science and Technology (AIST), Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki, 305-8568, Japan c Graduate School of Engineering, Iwate University, 4-3-5, Ueda, Morioka, Iwate, 020-8551, Japan b
a r t i c l e
i n f o
Article history: Available online 31 May 2009 PACS: 74.72.Jt 84.90.+a 85.25.Am 84.30.Vn Keywords: Quasi-spiral resonator (QSR) Miniaturized superconducting filter Bandpass filter
a b s t r a c t We designed a 5-GHz miniaturized 8-pole bandpass filter (BPF) using superconducting microstrip quasispiral resonators (QSRs) for international mobile telecommunication (IMT)-advanced receiving applications. We used the QSRs with line width and spacing equal to 10 lm for further miniaturization, and investigated a relationship between the structure of the QSR and the unloaded quality factor (Qu). The Qu of the optimized QSR of approximately 25,000 was obtained. It was difficult to design a BPF using miniaturized QSRs with high Qu because of strong cross couplings between QSRs. The kg/8-line inserted inverters were effective in decreasing the unwanted cross couplings. Using these QSR and the kg/8-line inserted inverters, 8-pole cascaded quadruplet (CQ) BPF was designed. We found that it was possible to design a miniaturized BPF with high Qu. Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction For more practical uses of superconducting filters in devices, such as a multi-channel radio frequency (RF) cryo-systems, integration of some superconducting transmitting and receiving filters into the cryo-coolers is necessary. Recently, high power transmitting superconducting bandpass filters (BPFs) with microstrip- or bulk-type resonators have been designed and fabricated, such as single mode or dual mode types [1–4]. However, it is difficult that many transmitting and receiving superconducting BPFs are packaged in cryo-cooler because of large volume of transmitting BPF. Therefore, our aim is to develop a miniaturized receiving filter with the final goal of developing an RF cryo-system for international mobile telecommunication (IMT)-advanced base stations. In previous work, we reported on a 10-pole BPF using quasi-spiral resonators (QSRs) with 40-lm lines and spacing designed and fabricated using single-sided MgB2 superconducting thin films [5]. The substrate area was 10 20 mm. The frequency performance was in close agreement with that of a simulation. In
* Corresponding author. Address: Graduate School of Science and Engineering, Yamagata University, Ohshima Lab., 4-3-16 Johnan, Yonezawa, Yamagata 992-8510, Japan. Tel./fax: +81 238 26 3289. E-mail address: [email protected] (S. Ono). 0921-4534/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2009.05.078
order to obtain the more miniaturized BPF with sharp skirt performance, the resonator using narrower line and spacing needs to keep high unloaded quality factor (Qu). Additionally, the design of miniaturized BPF needs to include not only main couplings but also cross couplings. There were control techniques of coupling between resonators which change the coupling direction of each resonator, vertically move the position of the resonator, and connecting resonators through transmission lines to effectively control couplings between resonators. Their techniques are used to improve skirt performance of BPF [6–8]. Hong et al. attained high selectivity using transmission line inserted inverters and the design technique of cascaded quadruplet (CQ) [9]. The CQ structure consists of a cascaded section of four resonators. In case of k12k23k34k14 < 0, one cross coupling can be arranged in such a way that a pair of attenuation poles is introduced at a finite frequency to improve selectivity [10]. It is very effective design method because one cross coupling normally causes one attenuation pole. In case of the BPF design using QSR, the control of unwanted cross coupling is needed. In this paper, we discussed the dependence of Qu on length ratio of c-spiral and rewound-spiral part in QSR with 10-lm lines and spacing and the decreasing of unwanted cross couplings. Also, the design of multi-pole CQ technique using QSR for use in IMT-advanced applications was presented.
1650
S. Ono et al. / Physica C 469 (2009) 1649–1652
2. Design of Chebyshev-type BPF using QSR
(a)
2.1. Design of QSR with 10-lm line and spacing
1
2.2. Design of Chebyshev-type 4-pole BPF using QSR Chebyshev-type 4-pole BPF using the QSR with 10-lm w and s was designed. The design specifications for application in the receiver systems of IMT-advanced base stations were as follows; center frequency at 5 GHz, bandwidth of 100 MHz, and less than a 0.1-dB ripple in the passband. Following the synthesis procedure described in [13], the theoretical external quality factor Qe and coupling coefficients ki,i+1 (i = 1–3) of a 4-pole Chebyshev-type BPF were derived as Qe = 55.44, and k12 = k34 = 1.66 10 2, k23 = 1.32 10 2. Fig. 2a shows equivalent circuit of 4-pole BPF. The subscripts of k were defined as the order of resonators in the filter. A 4-pole Chebyshev-type QSR BPF was designed using an
25000
20000
k23 k34
2
3
Qe
4
Z0
(b) 0 -20 Magnitude [dB]
It is important for miniaturization of resonator that the Qu has to be kept high. Inset of Fig. 1 shows the structure of a QSR. The QSR was composed of a rewound-type spiral resonator and two c-type spiral resonators [11]. The QSRs with 10-lm width (w) and spacing (s) were designed using electromagnetic simulator [12]. In this electromagnetic simulation, the conductive layer was assumed to be a zero thickness superconductor, RDC = 0, and RRF = 1.3 10 9. RDC and RRF were the DC resistance and the skin effect coefficient, respectively. The dielectric layer was to be a 0.5-mm-thick c-cut sapphire with a dielectric constant of 11.0 which was considered the effective dielectric constant included anisotropic and loss tangent of zero. The length of rewound-spiral and c-spiral were defined to l1 and l2. The simulating conditions were determined as changing the ratio of l2–l 1. Fig. 1 shows the dependence of the Qu on the l2/l1. Changing l2/l1 from 1 to 1.3, the Qu of the QSR was found approximately 25,000. The express of Qu is followed as 1/Qu = 1/Qd + 1/Qc + 1/Qr. Where Qd is a dielectric quality factor which is determined by loss of substrate, Qc is a conductor quality factor which is determined by losses of signal line and ground plane, Qr is a radiation quality factor which is determined by loss of radiation from resonator. The Qd and Qc were estimated at infinity and 400,000 under the simulating conditions, respectively [9]. In case of QSR, we found that Qu was dominant to Qr.
Unloaded quality factor Qu
k12
Z0 Qe
-40 -60 10 mm 2 4
-80 10 mm
-100
QSR 1 3
-120 4.8
4.85
4.9 4.95 5 Frequency [GHz]
5.05
5.1
Fig. 2. The equivalent circuit of 4-pole Chebyshev-type BPF and full-wave simulated performance of 4-pole QSR BPF. (a) The equivalent circuit. (b) The frequency performance of 4-pole QSR BPF. The inset shows designed layout of 4pole QSR BPF.
electromagnetic simulation with these theoretical values of Qe and k. The schematic layout of the designed 4-pole Chebyshev-type QSR BPF and simulated frequency responses are shown in Fig. 2b. In the inset of Fig. 2b, the accurate structures of QSRs with 10 lm line and space were shown as Fig. 1. After this, we also used these schematic structures of QSRs in the inset of Figs. 3–5. Although the frequency performance of in-band satisfied the design specification, asymmetrical a pair of attenuation poles was generated. It means that 4-pole QSR BPF has unwanted cross couplings between any resonators. Therefore, we investigated frequency performances of a 4-pole BPF using a coupling matrix [14,15]. It gives information about the resonant frequency of each resonator and all electromagnetic couplings between resonators. As the results, we found two important things; first, this BPF had three unwanted couplings, k13, k24 and k14. The k13 and k24 were magnetic coupling. The k14 was electrical coupling. Magnetic or electric coupling were decided by phase performance [9,16]. Second, if the k13 and k24 could be decrease, it became a cascaded quadruplet (CQ) structure. It is needed to decrease the unwanted cross couplings.
3. Control of cross couplings
15000 3.1. Decreasing of unwanted cross coupling l1
10000
5000
l2
0 0
0.2 0.4 0.6 0.8 1 l2 / l1
1.2 1.4 1.6
Fig. 1. The dependence of Qu on l2/l1. The inset shows the structure of microstrip QSR and elaborated configuration of QSR structure.
We also investigated QSRs using open-ended kg/4- or kg/8-line inserted inverters. The distance between two QSRs was 1.05 mm. The dependencies of coupling coefficient on spacing (g) between the transmission line and resonators are shown in Fig. 3. The coupling coefficient was calculated using a conventional method [16]. The coupling coefficient without a transmission line was 6.01 10 3. For the kg/4-line inserted inverter, a negative coupling coefficient was maintained as shown in Fig. 3a. For the kg/8-line inserted inverter, the coupling coefficient changed from negative to positive, as shown in Fig. 3b. When the spacing between a transmission line and resonators was approximately 0.14 mm, the
1651
S. Ono et al. / Physica C 469 (2009) 1649–1652
(a)
(a ) 0
g
Coupling coefficient k
-0.02
S
2
3
6
7
1
4
5
8
(b)
-0.04
L
λg /4-line inserted in verter
λg/4-line inserted inverter
-0.06 -0.08
10 mm
-0.1 QSR
QSR
-0.12 0
0.05
0.1 0.15 g [mm]
0.2
λg /8-line inserted inverter
0.25
(b) 0.005
10 mm
Coupling coefficient k
0.000
g
Fig. 5. Diagram of designed 8-pole CQ QSR BPF. (a) CQ topology. (b) The layout of 8pole CQ QSR BPF.
-0.005 -0.010
coupling coefficient was almost zero. This result indicates that it is possible to remove unwanted cross couplings.
λg/8-line inserted inverter
-0.015
3.2. Demonstration of deceasing unwanted cross couplings in 4-pole BPF
-0.020 -0.025 -0.030
QSR
-0.035 0.00
0.05
0.10 0.15 g [mm]
0.20
0.25
Fig. 3. Dependence of coupling coefficient on gap between lines and resonators. (a) kg/4-line inserted inverter. (b) kg/8-line inserted inverter.
We designed 4-pole BPF using kg/8-line inserted inverter. The layout of this is shown in the inset of Fig. 4. The kg/8-transmission lines were arranged between 1st (2nd) and 3rd (4th) resonators. Fig. 4 shows the frequency performance of 4-pole BPF using transmission lines. A pair of attenuation poles becomes almost symmetry. It means that the effects of unwanted couplings, k13, k24, were almost zero using kg/8-line inserted inverters. We found that it was possible to make CQ structure.
0 -10
0
S 11
-20 Magnitude [dB]
Magnitude [dB]
-20 -40 -60 10 mm 2 4
S 21 -80
-100 -120 4.8
10 mm
λg/8-line inserted inverter
QSR
-40 -50 -60 -70
13
4.85
-30
4.9 4.95 5 Frequency [GHz]
5.05
5.1
Fig. 4. Full-wave simulated performance of 4-pole QSR BPF using kg/8-line inserted inverters. The inset shows designed layout of 4-pole QSR BPF using kg/8-line inserted inverters.
-80 4.9
4.95
5 5.05 Frequency [GHz]
5.1
Fig. 6. Simulated frequency responses of 8-pole CQ QSR BPF and 8-pole Chebyshevtype circuit model. Black and broken lines indicate the frequency performances of 8-pole CQ QSR BPF and Chebyshev-type BPF, respectively.
1652
S. Ono et al. / Physica C 469 (2009) 1649–1652
4. Design of 8-pole CQ BPF
Acknowledgements
We designed 8-pole CQ QSR BPF by combined two CQ structures to improve skirt performance. The coupling topology and layout of 8-pole filter are shown in Fig. 5. The CQ structure was realized by producing two cross-couplings, k14, k58. It was easy to remove k13, k24, k35, k46, k57, and k68 using line inserted inverters, while difficult to remove k25, k36, and k47. Therefore, the desired coupling coefficient between 4th and 5th resonator was attained by setting a large distance between them and connecting line inserted inverters. The simulated results of the frequency performance of 8-pole CQ QSR BPF and the theoretical frequency performance of 8-pole Chebyshev type BPF are shown in Fig. 6. Black and broken lines indicate the frequency performances of 8-pole CQ QSR BPF and Chebyshev-type BPF, respectively. The frequency response, which met almost all specifications, was obtained. Also, the skirt performance of 8-pole CQ QSR BPF was better than that of 8-pole Chebyshev type. Although an asymmetric pair of attenuation poles should be adjusted in detail, we could present the design of multi-pole miniaturized filters having sharp skirt performance. Experimental investigations of the designed filter will be presented further papers.
This work was supported in part by Project of Japan Science and Technology Agency (JST) Iwate, and partly supported by the Ministry of Internal Affairs and Communication (MIC) Project of research and development of fundamental technologies for advanced radio frequency spectrum sharing in mobile communication systems. A part of this work was carried out in the clean room of Yamagata University.
5. Conclusions It was investigated the optimized structure of QSR. The Qu of optimized structure by varying the ratio of c-spiral and rewoundspiral part of the QSR was equal to approximately 25,000. We proposed an effective technique of decreasing unwanted couplings using kg/8-line inserted inverters. Using these QSR and the kg/8-line inserted inverters, 8-pole cascaded quadruplet (CQ) BPF was designed. We could design multi-pole miniaturized filters having high Qu and sharp skirt performance.
References [1] S. Takeuchi, M. Ohsaka, H. Kinouchi, S. Ono, A. Saito, A. Akasegawa, T. Nakanishi, A. Kawakami, K. Yamanaka, K. Kurihara, S. Ohshima, Physica C 468 (2008) 1954. [2] A. Saito, J.H. Lee, H. Teshima, S. Ono, S. Ohshima, IEEE Trans. Appl. Supercond., in press. [3] K. Yamanaka, M. Ishii, A. Akasegawa, T. Nakanishi, J.D. Baniecki, K. Kurihara, Physica C 468 (2008) 1950. [4] H. Kayano, N. Shiokawa, T. Kawaguchi, T. Hashimoto, IEICE Trans. Electron. J90C (2007) 188. [5] S. Ono, Y. Harada, T. Kato, A. Saito, J.H. Lee, H. Kinouchi, T. Oba, M. Yoshizawa, S. Ohshima, Physica C 468 (2008) 1969. [6] H. kayano, N. Shiokawa, M. Yamazaki, T. Watanabe, F. Aiga, T. Hashimoto, IEEE MTT-S Symp. Dig. (2006) 1201. [7] S. Li, J. Huang, Q. Meng, L. Sun, Q. Zhang, F. Li, A. He, X. Zhang, C. Li, H. Li, Y. He, IEEE Trans. Microwave Theory Tech. 55 (2007) 754. [8] J.-S. Hong, E.P. McElean, B. Karyamapudi, IEEE MTT-S Symp. Dig. (2005) 1467. [9] J.-S. Hong, M.J. Lancaster, Microstrip Filters for RF/Microwave Application, John Willy & Sons, Inc., America, 2001. pp. 341–350, 264–271, 325–329, 102–104. [10] R. Levy, IEEE Trans. Microwave Theory Tech. 43 (1995) 2940. [11] Z. Ma, T. Kawaguchi, Y. Kobayashi, Tech. Rep. IEICE MW 70 (2002) 1. [12] Sonnet Suite, Release 10.52, Sonnet Software, Inc., 2005. [13] I. Bahl, P. Bhartia, Microwave Solid State Circuit Design, Wiley Interscience, Canada, 2003. [14] R.J. Cameron, IEEE Trans. Microwave Theory Tech. 51 (2003) 1. [15] S. Amari, U. Roswnberg, J. Bornemann, IEEE Trans. Microwave Theory Tech. 50 (2002) 1969. [16] T. Kawaguchi, Y. Kobayashi, Z. Ma, Tech. Rep. IEICE MW 14 (2004) 75.
Contents lists available at ScienceDirect
Physica C journal homepage: www.elsevier.com/locate/physc
Design of superconducting multi-pole miniaturized filters with quasi-spiral resonators for decreasing unwanted cross couplings S. Ono a,*, Y. Harada b, A. Saito a, J.H. Lee a, T. Kato a, M. Uno a, M. Yoshizawa c, S. Ohshima a a
Graduate School of Science and Engineering, Yamagata University, 4-3-16 Johnan, Yonezawa 992-8510, Japan Advanced Industrial Science and Technology (AIST), Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki, 305-8568, Japan c Graduate School of Engineering, Iwate University, 4-3-5, Ueda, Morioka, Iwate, 020-8551, Japan b
a r t i c l e
i n f o
Article history: Available online 31 May 2009 PACS: 74.72.Jt 84.90.+a 85.25.Am 84.30.Vn Keywords: Quasi-spiral resonator (QSR) Miniaturized superconducting filter Bandpass filter
a b s t r a c t We designed a 5-GHz miniaturized 8-pole bandpass filter (BPF) using superconducting microstrip quasispiral resonators (QSRs) for international mobile telecommunication (IMT)-advanced receiving applications. We used the QSRs with line width and spacing equal to 10 lm for further miniaturization, and investigated a relationship between the structure of the QSR and the unloaded quality factor (Qu). The Qu of the optimized QSR of approximately 25,000 was obtained. It was difficult to design a BPF using miniaturized QSRs with high Qu because of strong cross couplings between QSRs. The kg/8-line inserted inverters were effective in decreasing the unwanted cross couplings. Using these QSR and the kg/8-line inserted inverters, 8-pole cascaded quadruplet (CQ) BPF was designed. We found that it was possible to design a miniaturized BPF with high Qu. Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction For more practical uses of superconducting filters in devices, such as a multi-channel radio frequency (RF) cryo-systems, integration of some superconducting transmitting and receiving filters into the cryo-coolers is necessary. Recently, high power transmitting superconducting bandpass filters (BPFs) with microstrip- or bulk-type resonators have been designed and fabricated, such as single mode or dual mode types [1–4]. However, it is difficult that many transmitting and receiving superconducting BPFs are packaged in cryo-cooler because of large volume of transmitting BPF. Therefore, our aim is to develop a miniaturized receiving filter with the final goal of developing an RF cryo-system for international mobile telecommunication (IMT)-advanced base stations. In previous work, we reported on a 10-pole BPF using quasi-spiral resonators (QSRs) with 40-lm lines and spacing designed and fabricated using single-sided MgB2 superconducting thin films [5]. The substrate area was 10 20 mm. The frequency performance was in close agreement with that of a simulation. In
* Corresponding author. Address: Graduate School of Science and Engineering, Yamagata University, Ohshima Lab., 4-3-16 Johnan, Yonezawa, Yamagata 992-8510, Japan. Tel./fax: +81 238 26 3289. E-mail address: [email protected] (S. Ono). 0921-4534/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2009.05.078
order to obtain the more miniaturized BPF with sharp skirt performance, the resonator using narrower line and spacing needs to keep high unloaded quality factor (Qu). Additionally, the design of miniaturized BPF needs to include not only main couplings but also cross couplings. There were control techniques of coupling between resonators which change the coupling direction of each resonator, vertically move the position of the resonator, and connecting resonators through transmission lines to effectively control couplings between resonators. Their techniques are used to improve skirt performance of BPF [6–8]. Hong et al. attained high selectivity using transmission line inserted inverters and the design technique of cascaded quadruplet (CQ) [9]. The CQ structure consists of a cascaded section of four resonators. In case of k12k23k34k14 < 0, one cross coupling can be arranged in such a way that a pair of attenuation poles is introduced at a finite frequency to improve selectivity [10]. It is very effective design method because one cross coupling normally causes one attenuation pole. In case of the BPF design using QSR, the control of unwanted cross coupling is needed. In this paper, we discussed the dependence of Qu on length ratio of c-spiral and rewound-spiral part in QSR with 10-lm lines and spacing and the decreasing of unwanted cross couplings. Also, the design of multi-pole CQ technique using QSR for use in IMT-advanced applications was presented.
1650
S. Ono et al. / Physica C 469 (2009) 1649–1652
2. Design of Chebyshev-type BPF using QSR
(a)
2.1. Design of QSR with 10-lm line and spacing
1
2.2. Design of Chebyshev-type 4-pole BPF using QSR Chebyshev-type 4-pole BPF using the QSR with 10-lm w and s was designed. The design specifications for application in the receiver systems of IMT-advanced base stations were as follows; center frequency at 5 GHz, bandwidth of 100 MHz, and less than a 0.1-dB ripple in the passband. Following the synthesis procedure described in [13], the theoretical external quality factor Qe and coupling coefficients ki,i+1 (i = 1–3) of a 4-pole Chebyshev-type BPF were derived as Qe = 55.44, and k12 = k34 = 1.66 10 2, k23 = 1.32 10 2. Fig. 2a shows equivalent circuit of 4-pole BPF. The subscripts of k were defined as the order of resonators in the filter. A 4-pole Chebyshev-type QSR BPF was designed using an
25000
20000
k23 k34
2
3
Qe
4
Z0
(b) 0 -20 Magnitude [dB]
It is important for miniaturization of resonator that the Qu has to be kept high. Inset of Fig. 1 shows the structure of a QSR. The QSR was composed of a rewound-type spiral resonator and two c-type spiral resonators [11]. The QSRs with 10-lm width (w) and spacing (s) were designed using electromagnetic simulator [12]. In this electromagnetic simulation, the conductive layer was assumed to be a zero thickness superconductor, RDC = 0, and RRF = 1.3 10 9. RDC and RRF were the DC resistance and the skin effect coefficient, respectively. The dielectric layer was to be a 0.5-mm-thick c-cut sapphire with a dielectric constant of 11.0 which was considered the effective dielectric constant included anisotropic and loss tangent of zero. The length of rewound-spiral and c-spiral were defined to l1 and l2. The simulating conditions were determined as changing the ratio of l2–l 1. Fig. 1 shows the dependence of the Qu on the l2/l1. Changing l2/l1 from 1 to 1.3, the Qu of the QSR was found approximately 25,000. The express of Qu is followed as 1/Qu = 1/Qd + 1/Qc + 1/Qr. Where Qd is a dielectric quality factor which is determined by loss of substrate, Qc is a conductor quality factor which is determined by losses of signal line and ground plane, Qr is a radiation quality factor which is determined by loss of radiation from resonator. The Qd and Qc were estimated at infinity and 400,000 under the simulating conditions, respectively [9]. In case of QSR, we found that Qu was dominant to Qr.
Unloaded quality factor Qu
k12
Z0 Qe
-40 -60 10 mm 2 4
-80 10 mm
-100
QSR 1 3
-120 4.8
4.85
4.9 4.95 5 Frequency [GHz]
5.05
5.1
Fig. 2. The equivalent circuit of 4-pole Chebyshev-type BPF and full-wave simulated performance of 4-pole QSR BPF. (a) The equivalent circuit. (b) The frequency performance of 4-pole QSR BPF. The inset shows designed layout of 4pole QSR BPF.
electromagnetic simulation with these theoretical values of Qe and k. The schematic layout of the designed 4-pole Chebyshev-type QSR BPF and simulated frequency responses are shown in Fig. 2b. In the inset of Fig. 2b, the accurate structures of QSRs with 10 lm line and space were shown as Fig. 1. After this, we also used these schematic structures of QSRs in the inset of Figs. 3–5. Although the frequency performance of in-band satisfied the design specification, asymmetrical a pair of attenuation poles was generated. It means that 4-pole QSR BPF has unwanted cross couplings between any resonators. Therefore, we investigated frequency performances of a 4-pole BPF using a coupling matrix [14,15]. It gives information about the resonant frequency of each resonator and all electromagnetic couplings between resonators. As the results, we found two important things; first, this BPF had three unwanted couplings, k13, k24 and k14. The k13 and k24 were magnetic coupling. The k14 was electrical coupling. Magnetic or electric coupling were decided by phase performance [9,16]. Second, if the k13 and k24 could be decrease, it became a cascaded quadruplet (CQ) structure. It is needed to decrease the unwanted cross couplings.
3. Control of cross couplings
15000 3.1. Decreasing of unwanted cross coupling l1
10000
5000
l2
0 0
0.2 0.4 0.6 0.8 1 l2 / l1
1.2 1.4 1.6
Fig. 1. The dependence of Qu on l2/l1. The inset shows the structure of microstrip QSR and elaborated configuration of QSR structure.
We also investigated QSRs using open-ended kg/4- or kg/8-line inserted inverters. The distance between two QSRs was 1.05 mm. The dependencies of coupling coefficient on spacing (g) between the transmission line and resonators are shown in Fig. 3. The coupling coefficient was calculated using a conventional method [16]. The coupling coefficient without a transmission line was 6.01 10 3. For the kg/4-line inserted inverter, a negative coupling coefficient was maintained as shown in Fig. 3a. For the kg/8-line inserted inverter, the coupling coefficient changed from negative to positive, as shown in Fig. 3b. When the spacing between a transmission line and resonators was approximately 0.14 mm, the
1651
S. Ono et al. / Physica C 469 (2009) 1649–1652
(a)
(a ) 0
g
Coupling coefficient k
-0.02
S
2
3
6
7
1
4
5
8
(b)
-0.04
L
λg /4-line inserted in verter
λg/4-line inserted inverter
-0.06 -0.08
10 mm
-0.1 QSR
QSR
-0.12 0
0.05
0.1 0.15 g [mm]
0.2
λg /8-line inserted inverter
0.25
(b) 0.005
10 mm
Coupling coefficient k
0.000
g
Fig. 5. Diagram of designed 8-pole CQ QSR BPF. (a) CQ topology. (b) The layout of 8pole CQ QSR BPF.
-0.005 -0.010
coupling coefficient was almost zero. This result indicates that it is possible to remove unwanted cross couplings.
λg/8-line inserted inverter
-0.015
3.2. Demonstration of deceasing unwanted cross couplings in 4-pole BPF
-0.020 -0.025 -0.030
QSR
-0.035 0.00
0.05
0.10 0.15 g [mm]
0.20
0.25
Fig. 3. Dependence of coupling coefficient on gap between lines and resonators. (a) kg/4-line inserted inverter. (b) kg/8-line inserted inverter.
We designed 4-pole BPF using kg/8-line inserted inverter. The layout of this is shown in the inset of Fig. 4. The kg/8-transmission lines were arranged between 1st (2nd) and 3rd (4th) resonators. Fig. 4 shows the frequency performance of 4-pole BPF using transmission lines. A pair of attenuation poles becomes almost symmetry. It means that the effects of unwanted couplings, k13, k24, were almost zero using kg/8-line inserted inverters. We found that it was possible to make CQ structure.
0 -10
0
S 11
-20 Magnitude [dB]
Magnitude [dB]
-20 -40 -60 10 mm 2 4
S 21 -80
-100 -120 4.8
10 mm
λg/8-line inserted inverter
QSR
-40 -50 -60 -70
13
4.85
-30
4.9 4.95 5 Frequency [GHz]
5.05
5.1
Fig. 4. Full-wave simulated performance of 4-pole QSR BPF using kg/8-line inserted inverters. The inset shows designed layout of 4-pole QSR BPF using kg/8-line inserted inverters.
-80 4.9
4.95
5 5.05 Frequency [GHz]
5.1
Fig. 6. Simulated frequency responses of 8-pole CQ QSR BPF and 8-pole Chebyshevtype circuit model. Black and broken lines indicate the frequency performances of 8-pole CQ QSR BPF and Chebyshev-type BPF, respectively.
1652
S. Ono et al. / Physica C 469 (2009) 1649–1652
4. Design of 8-pole CQ BPF
Acknowledgements
We designed 8-pole CQ QSR BPF by combined two CQ structures to improve skirt performance. The coupling topology and layout of 8-pole filter are shown in Fig. 5. The CQ structure was realized by producing two cross-couplings, k14, k58. It was easy to remove k13, k24, k35, k46, k57, and k68 using line inserted inverters, while difficult to remove k25, k36, and k47. Therefore, the desired coupling coefficient between 4th and 5th resonator was attained by setting a large distance between them and connecting line inserted inverters. The simulated results of the frequency performance of 8-pole CQ QSR BPF and the theoretical frequency performance of 8-pole Chebyshev type BPF are shown in Fig. 6. Black and broken lines indicate the frequency performances of 8-pole CQ QSR BPF and Chebyshev-type BPF, respectively. The frequency response, which met almost all specifications, was obtained. Also, the skirt performance of 8-pole CQ QSR BPF was better than that of 8-pole Chebyshev type. Although an asymmetric pair of attenuation poles should be adjusted in detail, we could present the design of multi-pole miniaturized filters having sharp skirt performance. Experimental investigations of the designed filter will be presented further papers.
This work was supported in part by Project of Japan Science and Technology Agency (JST) Iwate, and partly supported by the Ministry of Internal Affairs and Communication (MIC) Project of research and development of fundamental technologies for advanced radio frequency spectrum sharing in mobile communication systems. A part of this work was carried out in the clean room of Yamagata University.
5. Conclusions It was investigated the optimized structure of QSR. The Qu of optimized structure by varying the ratio of c-spiral and rewoundspiral part of the QSR was equal to approximately 25,000. We proposed an effective technique of decreasing unwanted couplings using kg/8-line inserted inverters. Using these QSR and the kg/8-line inserted inverters, 8-pole cascaded quadruplet (CQ) BPF was designed. We could design multi-pole miniaturized filters having high Qu and sharp skirt performance.
References [1] S. Takeuchi, M. Ohsaka, H. Kinouchi, S. Ono, A. Saito, A. Akasegawa, T. Nakanishi, A. Kawakami, K. Yamanaka, K. Kurihara, S. Ohshima, Physica C 468 (2008) 1954. [2] A. Saito, J.H. Lee, H. Teshima, S. Ono, S. Ohshima, IEEE Trans. Appl. Supercond., in press. [3] K. Yamanaka, M. Ishii, A. Akasegawa, T. Nakanishi, J.D. Baniecki, K. Kurihara, Physica C 468 (2008) 1950. [4] H. Kayano, N. Shiokawa, T. Kawaguchi, T. Hashimoto, IEICE Trans. Electron. J90C (2007) 188. [5] S. Ono, Y. Harada, T. Kato, A. Saito, J.H. Lee, H. Kinouchi, T. Oba, M. Yoshizawa, S. Ohshima, Physica C 468 (2008) 1969. [6] H. kayano, N. Shiokawa, M. Yamazaki, T. Watanabe, F. Aiga, T. Hashimoto, IEEE MTT-S Symp. Dig. (2006) 1201. [7] S. Li, J. Huang, Q. Meng, L. Sun, Q. Zhang, F. Li, A. He, X. Zhang, C. Li, H. Li, Y. He, IEEE Trans. Microwave Theory Tech. 55 (2007) 754. [8] J.-S. Hong, E.P. McElean, B. Karyamapudi, IEEE MTT-S Symp. Dig. (2005) 1467. [9] J.-S. Hong, M.J. Lancaster, Microstrip Filters for RF/Microwave Application, John Willy & Sons, Inc., America, 2001. pp. 341–350, 264–271, 325–329, 102–104. [10] R. Levy, IEEE Trans. Microwave Theory Tech. 43 (1995) 2940. [11] Z. Ma, T. Kawaguchi, Y. Kobayashi, Tech. Rep. IEICE MW 70 (2002) 1. [12] Sonnet Suite, Release 10.52, Sonnet Software, Inc., 2005. [13] I. Bahl, P. Bhartia, Microwave Solid State Circuit Design, Wiley Interscience, Canada, 2003. [14] R.J. Cameron, IEEE Trans. Microwave Theory Tech. 51 (2003) 1. [15] S. Amari, U. Roswnberg, J. Bornemann, IEEE Trans. Microwave Theory Tech. 50 (2002) 1969. [16] T. Kawaguchi, Y. Kobayashi, Z. Ma, Tech. Rep. IEICE MW 14 (2004) 75.