264 MHz HTS Lumped Element Bandpass Filter

Transcription

1 IEICE SAITO TRANS. et al: 264 ELECTRON., MHz HTS LUMPED VOL. E83-C, ELEMENT NO. 1 JANUARY BANDPASS 2 FILTER 15 PAPER Special Issue on Superconductive Devices and Systems 264 MHz HTS Lumped Element Bandpass Filter Kenshi SAITO a), Nobuyoshi SAKAKIBARA, Yoshiki UENO,Yoshio KOBAYASHI, Daisuke YAMAGUCHI, Kei SATO, and Tetsuya MIMURA, Members SUMMARY A 5-pole lumped element bandpass filter (BPF) of center frequency MHz and fractional bandwidth (FBW).76% is designed and fabricated using YBa 2 Cu 3 O 7-d (YBCO) thin films deposited on both sides of a MgO substrate(4 mm 4 mm.5 mm). The return loss, minimum insertion loss and ripple were measured to be 2. db, less than.1 db and less than.1 db at 7 K, respectively. These results verify both the compactness and low loss characteristics in the VHF band. The simulated frequency response, where the frequency dependences of inductance (L) and capacitance (C) elements and housing effect are taken into account, is in good agreement with the measured frequency response. key words: high-temperature superconductor, microstrip line, lumped element circuit, bandpass filter 1. Introduction Lumped element circuits could be fabricated to be smaller than distributed circuits. In particular, the reduction of size is very attractive in lower frequency ranges such as the UHF or VHF bands. However, the insertion loss of a RF lumped element filter fabricated from a normal conductor greatly increases because of large conductor loss. If a superconductor is used instead of the normal conductor, this insertion loss can be kept very low. Due to the reason mentioned above, several high-temperature superconductor (HTS) microwave microstrip line lumped element bandpass filters (BPF) have been reported recently [1] [4]. For use in the VHF band, the circuit design procedure and the performance of low-temperature superconductor (LTS) filters using Nb films were reported [5] [8]. In this paper, we describe the design and experimental results of a VHF band.76% fractional bandwidth (FBW) 5- pole HTS lumped element BPF. 2. Filter Design A design of the microstrip line lumped element BPF has already been reported [5] [8]. Figure 1 shows the equivalent circuit of a 5-pole Chebyshev BPF with center frequency Manuscript received May 2, Manuscript revised July 23, The authors are with Advanced Mobile Telecommunication Technology Inc., Nisshin-shi, Japan. The authors are with the Department of Electrical and Electronics Engineering, Saitama University, Urawa-shi, Japan. The authors are with NTT Mobile Communications Network Inc., Yokosuka-shi, Japan. a) saito@ngo.amtel.co.jp MHz, 3 db-fractional bandwidth (FBW).76% and passband ripple.1 db, respectively. Figure 2 shows the calculated frequency response of the equivalent circuit. Next, we design the layout, based on the equivalent circuit. We used a microwave linear circuit simulator (HP-MDS) to realize this design. The microstrip line lumped element filter is composed of inductance (L) and capacitance (C) elements fabricated on a microstrip line. Here, we chose the meander pattern for L elements. Figure 3 shows the equivalent circuit of the L and C elements. Measured values of relative dielectric constant (e r =9.685) and the substrate thickness (t=495 µm) were used. Each L and C element was simulated by the electromagnetic simulator (HP-MOMENTUM) at the center frequency of the filter. Then the series L, C and shunt C values were obtained using a simple -type equi valent circuit (PI) model. The inductor dimensions were optimized manually to obtain the desired series inductance. The parasitic capacitance of the inductor was subtracted from the desired shunt capacitance of the adjacent capacitor. The capacitors were then designed by comparing the computed C value to that of the equivalent circuit at the center frequency. Figure 4 shows the filter layout. The width of the transmission line (w=48 µm) was determined by the characteristic impedance of 5 Ω. The line width of the L element was selected as w=9 µm, from the viewpoint of power-handling capability and mask accuracy. Considering the restriction of film size, 4 mm 4 mm, the elements were arranged in two symmetrical rows connected by L3, as shown in the Fig. 4. In this arrangement, the 1st and 5th resonators were coupled to each other. The 2nd and 4th resonators were also coupled. Because of this extra cross-coupling, it was predicted that the transmission zero would be located at either the lower or higher side of the passband depending on whether the crosscoupling was inductive or capacitive. When the lumped element layout is simulated using an electromagnetic simulator, the analysis mesh should be considerably smaller than that used for analysis of a distributed circuit, in order to obtain a precise calculation result [7]. (L and C elements were calculated using a mesh of less than 1/ 15 of the wavelength) Therefore, the calculation of whole circuits was difficult under the hardware limitations. Therefore, we calculated the filter response by cascading the L and C values simulated by each L and C element.

2 Insertion Loss [db] 4mm 16 IEICE TRANS. ELECTRON., VOL. E83-C, NO. 1 JANUARY pF 45.nH.2145pF 45.nH.1323pF 45.nH.1323pF 45.nH.2145pF 45.nH 1.899pF RA RB 6.421pF 12.76pF 17.97pF 15.91pF 16.5pF 16.2pF Fig. 1 Equivalent circuit of a microstrip 5-pole Chebyshev BPF of center frequency MHz, 3 db-fractional bandwidth (FBW).76% and passband ripple.1 db Fig. 2 Frequency response calculated for the BPF in Fig Return Loss [db] center 16.2pF 16.5pF 15.91pF 17.97pF 12.76pF 6.421pF L1 C1 C2 C3 C1 C2 C3 L1 4mm L3 Fig. 4 Layout of a microstrip lumped element 5-pole BPF. C2 C1 C3 C1 C3 Fig. 3 (a) L element (b) C element Equivalent circuit of L and C elements on microstrip line. Fig. 5 Photograph of the microstrip lumped element 5-pole BPF mounted on the housing. The substrate size is 4 mm 4 mm. 3. Filter Fabrication The filter was fabricated using 4 mm 4 mm YBa 2 Cu 3 O 7- d (YBCO) thin films deposited on both sides of a.5-mm-thick MgO substrate. The YBCO films on both sides of the MgO substrate had a thickness of about 5 nm. The patterned surface of the YBCO film was coated with a 5-nm-thick CeO 2 film and the back surface with a 5-nm-thick Au film. After fabrication, the filter was encased in a copper housing coated with gold. The filter in the housing is shown in Fig Measurement and Result The frequency responses of the filter were measured using a HP872C VNWA (vector network analyzer) at 7 K. The

3 Insertion Loss [db] Insertion Loss [db] Insertion Loss [db] SAITO et al: 264 MHz HTS LUMPED ELEMENT BANDPASS FILTER 17 calibration was carried out at the connector of the filter housing at room temperature. The difference of the cable loss in the cryocooler between 7 K and 3 K was approximately.5 db. Figure 6 (a) shows the frequency responses near the passband. Figures 6(b) and (c) show the expanded and (a) (b) (c) Fig. 6 (a) Measured frequency response of the microstrip lumped element 5-pole BPF. (b) Measured frequency response of the microstrip lumped element 5-pole BPF (expanded view). (c) Measured frequency response of the microstrip lumped element 5-pole BPF (wide-band view). -2 Return Loss [db] wide-band responses, respectively. The measured center frequency was MHz, 3 db- FBW was.8%, return loss was 2. db and the minimum insertion loss and passband ripple were under.1 db. The tuning was necessary because of a variation in the substrate thickness that affected the performance of the filter. It had a spurious free response up to 9 MHz. This is an advantage over quarter- or half-wavelength line-resonator-type filters. Comparing the designed and measured frequency responses, an extra transmission zero located near the higher passband edge, and the increase of the BW could be seen. (a) (b) Fig. 7 (a) Frequency dependence of C3 element (The value at MHz indicate 1%). (b) Frequency dependence of L1 element (The value at 264.5MHz indicate 1%).

4 18 IEICE TRANS. ELECTRON., VOL. E83-C, NO. 1 JANUARY 2 The extra transmission zero is considered to be caused by the cross-coupling between nonadjacent resonators [6] [8]. Then, we investigated causes of the BW increasing. For filters based on a distributed circuit, we can design it at the center frequency, because frequency dependences of the circuit constants such as guiding wavelength on the substrate and the coupling coefficient, can be ignored. Contrary to this, for the case of the lumped element filter, it has been reported that the BW of the measured response becomes wider than that of the simulated response when the L and C elements are designed at the center frequency [1], [4]. We consider two possible causes to be as follows. One is the frequency dependences of the L and C elements and the other is the housing effect. First, we calculated the frequency dependences of the L and C elements. Some of the results are shown in Figs. 7(a) and (b). Figure 7(a) shows the frequency dependences of C3 (a PI equivalent circuit consists of C31, C32, C33) elements; the variation of series capacitance C32 was the largest. The percentage of variation between the passband was.3%. Figure 7(b) shows the frequency dependences of L1 (a PI equivalent circuit consists of C11, L12, C13) elements; the variation of series capacitance L12 was the largest. The percentage of variation between the passband was.23%. Next, we simulated the frequency response, taking the frequency dependences of the L and C elements into account. The frequency dependences of L and C values were assumed to be linear at the upper and lower passband edges. Then, we simulated the frequency response, taking the housing effect into account. The distance between the substrate and lid (h=14 mm) was considered in an electromagnetic simulation. The measured and simulated frequency responses are shown in Fig. 8. The center frequencies of these responses were not the same so they were adjusted, and the horizontal-axis indicates the frequency shift from the center frequency. In Fig. 8, Fig. 8 Measured and simulated frequency responses. (a) measured response (at 7 K). (b) simulated response (L and C element frequency dependence and housing effect were not taken into account). (c) simulated response where housing effect was taken into account. (d) simulated response where both L and C element frequency dependence and housing effect were taken into account. curve (a) indicates the measured response at 7 K and curves (b), (c) and (d) indicate simulated responses. Curve (b) is a simulated response, where both the frequency dependences of the L and C elements and the housing effect are not taken into account. Curve (c) is a simulated response, where only the housing effect was taken into account. Curve (d) is a simulated response, where both the frequency dependences of the L and C elements and the housing effect are taken into account. The simulated frequency response (d) is in good agreement with the measured frequency response (a). It is clear that the effect of frequency dependences of the L and C elements is greater than the housing effect. 5. Conclusion A 5-pole lumped element bandpass filter has been designed and fabricated using 4 mm 4 mm YBCO thin films deposited on both sides of a.5-mm-thick MgO substrate. The return loss, minimum insertion loss and passband ripple were measured to be 2. db, less than.1 db and less than.1 db, respectively at 7 K. This result verifies both the compactness and low loss characteristics of this filter in the VHF band. Subsequently, we compared the increase of the measured BW against the simulated BW. The simulated frequency response, where the frequency dependences of the L and C elements and housing effect are taken into account, is in good agreement with the measured frequency response. Acknowledgment The authors thank G.Tsuzuki and M. Suzuki for useful discussion and technical assistance in circuit design, device fabrication and adjustment. References [1] D.G.Swanson, Jr., R.Forse, and B.J.L.Nilsson, A 1GHz thin film lumped element high temperature superconductor filter, IEEE MTT-S Digest, pp , [2] S.Ye and R.R.Mansour, Design of manifold-coupled multiplexers using superconductive lumped element filters, IEEE MTT- S Digest, pp , [3] D.Zhang, G.-C.Liang, C.F.Shih, and R.S.Withers, Narrowband lumped-element microstrip filters using capacitively-loaded inductors, IEEE MTT-S Digest, pp , [4] D.Zhang, G.-C.Liang, C.F.Shih, M.E.Johansson, and R.S.Withers, Narrowband lumped-element microstrip filters using capacitively-loaded inductors, IEEE Trans. Microwave Theory & Tech., vol.43, no.12, pp , Dec [5] K.Nomura and Y.Kobayashi, Study on design of microstrip lumped-element bandpass filter, IEICE Technical Report, MW96-84, pp.19-24, Sept [6] D.Yamaguchi, et al., Design of a 264 MHz superconductive thin film microstrip lumped element bandpass filter, 1998 Electronics Society Conf. of IEICE, SC-4-3, pp , Oct [7] D.Yamaguchi, et al., Design of a 264 MHz superconductive thin film lumped element bandpass filter using MDS, IEICE Technical Report, MW98-14, Dec [8] Y.Kobayashi, et al., Design of a 264 MHz superconductive thin film lumped element filter, 1998 Asia-Pacific Microwave Conf. Proc., pp , Dec

5 SAITO et al: 264 MHz HTS LUMPED ELEMENT BANDPASS FILTER 19 Kenshi Saito was born in Aichi, Japan, in He received the B.E. and M.E. degrees in electrical engineering from Tokyo Metropolitan University in 1985 and 1987, respectively. In 1987, he joined DENSO CORPO- RATION and was engaged in the design of microwave circuit. He joined Advanced Mobile Telecommunication Technology Inc., in Since then, he has been engaged in the design of High-Tc superconductor microwave filters. Nobuyoshi Sakakibara was born in Aichi, Japan, in He received B.E. and M.E. degrees from Nagoya University in 1979 and 1981, respectively. In 1981, he joined DENSO CORPORATION and was engaged in researches on electronic devices. He received Dr. Eng. degree from Nagoya Institute of Technology in Since 1993, he has been engaged in researches on high-tc superconducting microwave filters in Advanced Mobile Telecommunication Technology Inc. He is a member of Japan Society of Applied Physics. Yoshiki Ueno was born in Nara, Japan, in He received the B.E. degree in electrical engineering from Osaka University, Osaka, Japan, in He joined DENSO CORPO- RATION, Aichi, Japan, in He has been engaged in the research of crystal growth of compound semiconductors and development of millimeter wave MMIC. Since 1993, he has been also researching on high-tc superconducting microwave filters in Advanced Mobile Telecommunication Technology Inc. He is a member of Japan Society of Applied Physics and the Institute of Electrical and Electronics Engineers. Daisuke Yamaguchi was born in Hokkaido, Japan, on October 14, He received the B.E. and M.E. degrees in electrical engineering from Saitama University, Saitama, Japan, in 1997 and 1999, respectively. In 1999, he joined Mitsubishi Electric Corporation, Kamakura, Japan. Kei Sato received the B.E. and M.E. degrees in Electrical Engineering from Tohoku University, Sendai, Japan, in 199 and 1994, respectively. He joined NTT Tohoku Mobile Communications Network Inc. in He is currently a Research Engineer of Wireless Laboratories at NTT Mobile Communications Network Inc. and developing a cryogenic receiver system for cellular base stations. Tetsuya Mimura received the B.E. and M.E. degrees from Shinshu University, Nagano, Japan, in 1991 and 1993, respectively. He joined NTT Mobile Communications Network Inc. in 1993, where he engaged in research on circuit technologies. He is currently a Research Engineer of Wireless Laboratories and developing a cryogenic receiver system for cellular base stations. Yoshio Kobayashi was born on July 4, He received the B.E., M.E., and D.Eng. degrees in electrical engineering from Tokyo Metropolitan University, Tokyo, Japan, in 1963, 1965, and 1982, respectively. He joined Saitama University, Urawa, Saitama, Japan in 1965, where he is presently a Professor of electrical and electronic engineering. His current research interests are in dielectric resonators and filters, measurement of microwave characteristics of dielectric and superconducting materials, and passive device applications of high-tc superconductors in the microwave region. He served as the Chair of the Technical Group on Microwaves, IEICE, from 1993 to 1994, as the Chair of Technical Committee on Millimeter-wave Communications and Sensing, IEE Japan from 1993 to 1995, and as the Chair of the IEEE MTT-S Tokyo Chapter from 1995 to He also served as the Chair of Steering Committee, 1992 Microwave Workshops and Exhibition (MWE 92). and as the Chair of Steering Committee, 1998 Asia Pacific Microwave Conference (APMC 98) held in Yokohama, Japan. Dr. Kobayashi is a member of the IEE of Japan and was elected to the grade of IEEE Fellow in He received The 2 th H. Inoue Award from Research Development Corporation of Japan in 1995.