This paper presents a five pole Chebyshev bandpass filter using high temperature superconducting
(HTS) thin films which employed the symmetrical TM010 mode of a circular patch resonator. The
filter is designed with centre frequency of 12 GHz with fractional bandwidth of 0.45%. The design
is fabricated using double sided YBCO thin films on a sapphire wafer of size
(0.33×22.5×39.0)mm3. The achieved unloaded Q-factor of the resonators in the fabricated filter is
about 6,500 giving the filter an insertion loss of about 0.8 dB at centre frequency of 12.14 GH

Lancaster, Michael J.

Yeo, Kenneth S.K.

UEL Research Repository at University of East London

  University of East London Institutional Repository: http://roar.uel.ac.uk   This paper is made available online in accordance with publisher policies. Please scroll down to view the document itself. Please refer to the repository record for this item and our policy information available from the repository home page for further information.  Author(s): Yeo, Kenneth S. K; Lancaster, Michael J; Hong, Jia-Sheng Article title: 5-pole High-Temperature Superconductor Bandpass Filter at 12 GHz using High Power TM010 mode of Microstrip Circular Patch Year of publication: 2000 Citation: Yeo, K.S.K, Lancaster, M.J. and Hong, J.S. (2000) "5-pole High-Temperature Superconductor Bandpass Filter at 12 GHz using High Power TM010 mode of Microstrip Circular Patch", Proc. of Asia Pacific Microwave Conference, Sydney, Australia, Dec. 3rd-6th, 2000 pp. 596 - 599 Link to published version: http://dx.doi.org/10.1109/APMC.2000.925905  DOI: 10.1109/APMC.2000.925905  5-POLE HIGH-TEMPERATURE SUPERCONDUCTING BANDPASS FILTERAT 12 GHZ USING HIGH POWER TM010 MODE OF MICROSTRIP CIRCULARPATCHK. S. K. YEOThe University of BirminghamSchool of Electronic and Electrical EngineeringEdgbastonBirmingham B15 2TT, UKE-mail: K.S.K.Yeo@bham.ac.ukM. J. LANCASTERThe University of BirminghamSchool of Electronic and Electrical EngineeringEdgbastonBirmingham B15 2TT, UKE-mail: M.J.Lancaster@bham.ac.ukJ. S. HONGThe University of BirminghamSchool of Electronic and Electrical EngineeringEdgbastonBirmingham B15 2TT, UKE-mail: hongjs@eee.bham.ac.ukThis paper presents a five pole Chebyshev bandpass filter using high temperature superconducting(HTS) thin films which employed the symmetrical TM010 mode of a circular patch resonator. Thefilter is designed with centre frequency of 12 GHz with fractional bandwidth of 0.45%. The designis fabricated using double sided YBCO thin films on a sapphire wafer of size(0.33×22.5×39.0)mm3. The achieved unloaded Q-factor of the resonators in the fabricated filter isabout 6,500 giving the filter an insertion loss of about 0.8 dB at centre frequency of 12.14 GHz..1 IntroductionLow power HTS filters [1-4] have been widely reported since the discovery of HTS materials [5] in1986. The low power HTS filters give very promising performance for receive filters incommunication systems working at frequencies ranging from 800 MHz to 5 GHz. The HTS thin filmsare not very popular for high power handling devices because of the limited surface current density onHTS thin films. To increase the power handling of HTS filters, Chaloupka [6] has proposed the TM010mode of circular patch resonator to eliminate the edge current. A 2-pole [7] and 4-pole [8] have beenprevious reported which employed the edge-current free, TM010 mode, resonators. Here, we show thata higher order filter using the TM010 can be achieved. We demonstrated this by designing a 5 poleChebyshev filter with centre frequency of 12 GHz on a double sided YBCO on sapphire substrate.2 Filter Design, Fabrication and MeasurementFig. 1 shows the layout of the designed 5-pole HTS bandpass filter which comprises of high powerTM010 mode resonators. The number in resonators denotes the resonators sequence. The first and thefifth resonators are rotated by 68° from the centre coupling line of the 2nd, 3rd and 4th resonators. Thisrotation will reduce the length of the filter significantly. Because the TM010 mode is a symmetricalmode, the charge and current distributions of the TM010 are symmetrical about the centre of the disk.Therefore, the coupling between the 1st and 2nd resonators is the similar type of coupling between the2nd and 3rd resonators even though they are rotated by 68°.The input and output couplings are achieved by tapping the input and output lines into the circulardisk. More discussion about this input/output coupling will be presented in the next section. Thecoupling spacing between resonators are obtained through full-wave electromagnetic (EM) [9]simulator.The filter was fabricated using YBa2Cu3O7 thin film material deposited onto a sapphire substrate. Thesapphire substrate has a dimension of (0.33×22.5×39.0)mm3 with dielectric constant of 9.6 at theprinciple axis plane. The fabricated filter is mounted onto a gold plated titanium carrier which is thenassembled into a test housing. The housing lid accommodates seven tuning screws.Figure 1: Layout of a high power HTS using TM010 resonators on a Sapphire substrate with athickness of 0.33mm.The filter was cooled down to 60K using closed cycle cryostat and the performance of the filter wasmeasured using HP8720 network analyser. Fig. 2 shows the measured results after tuning. Themeasured centre frequency of the filter is at 12.14 GHz with fractional bandwidth of about 0.55%. Thepassband minimum insertion loss is measured at 0.8dB which corresponds to an unloaded Q-factor of6,500.The measured results show a slight increase in the bandwidth. This can be accounted for by the slightinaccuracy of the EM simulation used to determine the coupling coefficients. A single real frequencytransmission zero is obtained in the measured response. This transmission zero is due to unwantedcross-coupling between non-adjacent resonators. This unwanted cross-coupling is yet to be modelled.Due to the present of this unwanted transmission zero, the filter response is not symmetrical. It hasalso cause the low side band to roll off at much slower pace than the theoretical response as shown inFig. 2.Frequency / GHz12.00 12.05 12.10 12.15 12.20 12.25|S21| / dB-60-50-40-30-20-100|S11| / dB-50-40-30-20-10010Theoreticalwith Qu = 6,500S21 - ExpS11 - ExpFigure 2: The measured |S21| and |S11| of the tuned HTS five pole filter at about 60K and thetheoretical |S21| with unloaded Q-factor of 6,500.3 Input/Output CouplingThe input/output of this filter is achieved by tapping into the circular patch microstrip resonator. Fig. 3shows the normalised surface current distribution of the TM010 mode of a circular patch microstripresonator with radius of 9.2mm. The maximum (short circuit) surface current are found at about onehalf of the radius of the disk and minimum (open circuit) are at the edge and the centre of the disk.Therefore, by varying the tap location from the edge to the half radius of the disk, an increasingexternal Q-factor can be obtained.YZ0.00500.0050.010.00500.0050.0100.250.50.7510coupling location axisXFigure 3: 3D plot of the normalised surface current for TM010 mode of circular disk.The advantage of this tap input/output coupling over the gap coupling [10] is the relationship betweenthe external Q-factor and the coupling location. For the gap coupling, the external Q-factor decreaseswith the increase of coupling location. Note that the coupling location is referred to the radial distancefrom the edge of the disk as shown in Fig. 3. To achieve strong coupling using the gap coupled, thecoupling location is relatively large whereas for the tap coupling, the coupling distance is relativelysmall. Therefore, the tap coupling can achieve strong input/output coupling without distorting toomuch of the circular disk structure. It must be pointed out that this input/output coupling is onlyapplicable on the TM010 mode of the circular disk resonator due to the radial surface currentdistribution.4 ConclusionWe have shown a new HTS five pole bandpass filter using the high power TM010 mode of a circularpatch resonators on a sapphire substrate. We have described the filter design, fabrication andexperiment. We have also discussed a new way of implementing the input/output coupling for TM010mode circular disk resonator. This new input/output coupling can achieve the required input/outputcoupling for narrowband filter with minimum distortion of the circular disk structure. This filter is alsoshown a promising results for satellite communication system applications at 12 GHz with hugereduction in size and maintaining the high unloaded Q-factor of the resonators.References[1] D. Zhang, G.-C. Liang, C. F. Shih, Z. H. Lu, and M. E. Johansson, "A 19-Pole Cellular BandpassFilter Using 75-mm-Diameter High Temperature Superconducting Thin Films," IEEE Microw.Guilded Wave Lett., vol. 5, pp. 405-407, 1995.[2] G. L. Matthaei and G. L. Hey-Shipton, "Novel Staggered Resonator Array Superconducting 2.3-GHz Bandpass Filter," IEEE Trans. Microwave Theory and Tech., vol. MTT-41, No. 12, pp.2345-2352, 1993.[3] J. S. Hong, M. J. Lancaster, D. Jedamzik, and R. B. Greed, "8-Pole Superconducting Quasi-Elliptic Function Filter for Mobile Communications Application," IEEE MTT-S Intl. MicrowaveSymp. Digest, vol. 1, pp. 367-370, 1998.[4] S. H. Talisa, M. A. Janocko, C. K. Jones, B. R. McAvoy, J. Talvacchio, and G. R. Wagner,"Microwave Superconducting Filters," IEEE Trans. Mag., vol. 27, pp. 2544-2547, 1991.[5] J. G. Bednorz and K. A. Muller, "Possible high Tc Superconductivity in the Ba-La-Cu-OSystem," Z. fur Phys., vol. 64, p. 189, 1986.[6] H. Chaloupka, M. Jeck, B. Gurzinski, and S. Kolesov, "Superconducting Planar Disk Resonatorsand Filters with high power handling capability," Electron. Lett., vol. 32, pp. 1735-1737, 1996.[7] S. Kolesov, H. Chaloupka, A. Baumfalk, F.-J. Goertz, and M. Klauda, "High TemperatureSuperconducting Disk Resonator Filters with High Power Handling Capability," ISEC, vol. 6, pp.272-274, 1997.[8] A. Baumfalk, H. Chaloupka, M. Klauda, S. Kolesov, and C. Neumann, "HTS Power Filters forOutput Multiplexers in Satellite Communications," Appl. Supercond. Conf., 1998.[9] None, EM User's Manual. : Sonnet Software, Inc., 1993.[10] T. Hayashi, T. Mikazuki, N. Suzuki, and Y. Nagai, "Coupling Structure for Superconducting DiskFilters," Electron. Lett., vol. 30, pp. 1424-1425, 1994.

5-pole High-Temperature Superconductor Bandpass Filter at 12 GHz using High Power TM010 mode of Microstrip Circular Patch

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5-pole High-Temperature Superconductor Bandpass Filter at 12 GHz using High Power TM010 mode of Microstrip Circular Patch

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