Bengin-Crnojevic, V.

Budimir, D.

WestminsterResearch

     University of Westminster Eprints http://eprints.wmin.ac.uk    Novel compact resonators with multiple 2-D Hilbert fractal curves.  V. Bengin-Crnojevic Djuradj Budimir  School of Informatics    This is an electronic version of a paper presented at the 35th European Microwave Conference, 04-06 Oct 2005, Paris, France.  © EuMA.      The Eprints service at the University of Westminster aims to make the research output of the University available to a wider audience.  Copyright and Moral Rights remain with the authors and/or copyright owners. Users are permitted to download and/or print one copy for non-commercial private study or research.  Further distribution and any use of material from within this archive for profit-making enterprises or for commercial gain is strictly forbidden.        Whilst further distribution of specific materials from within this archive is forbidden, you may freely distribute the URL of the University of Westminster Eprints (http://eprints.wmin.ac.uk).   In case of abuse or copyright appearing without permission e-mail wattsn@wmin.ac.uk. PROOF PDF @ 2005 EuMW 2005                                                                                                EuMW 2005 Novel Compact Resonators with Multiple 2-D Hilbert Fractal Curves V. Crnojevic-Bengin, and D. Budimir University of Westminster, Department of Electronic Systems, Wireless Communications Research Group,  115 New Cavendish Street, W1W 6UW, London, UK   Abstract  — A novel capacitively coupled microstrip resonators with multiple 2-D Hilbert curves embedded in and under the microstrip are presented in this paper. The proposed resonators achieve length reduction of over 84% when compared to the conventional resonators. By using the proposed resonators, a compact bandpass filter is designed to work in the GPS frequency band while exhibiting very high attenuation in the neighbouring 1.8 GHz GSM band.  I. INTRODUCTION Recently, there has been much interest in the field of photonic bandgap (PBG) engineering. Microstrip lines with periodic elements etched in the ground plane have been found to behave like PBG a structure, [1]. A number of different PBG structures have been proposed in order to increase the slow-wave effect and improve the performances [2]-[4]. Fractal curves are well known for their unique space-filling properties. Recently, a number of applications of different fractal shapes emerged: fractal-shaped planar resonators revealed superiority of the two-dimensional (2-D) fractal structures over the conventional non-fractal ones, [5], while multilayer resonators with embedded three-dimensional (3-D) fractal curves outperformed equivalent planar structures, [6]. Fractal curves were also used to form a multilayer PBG structure, [7] or high impedance surfaces, [8]-[9]. In this paper, multiple 2-D Hilbert fractal curves were embedded in and under the microstrip resonator, to foster the PBG effect. The proposed structures were simulated using values typical for standard Thick-film (TF) technology and the results were compared to the conventional capacitively coupled resonator.  To illustrate the results, a narrow-band bandpass filter incorporating the proposed resonator was designed to work in the GPS frequency range, while demonstrating high attenuation in the neighbouring 1.8 GHz GSM range. II. RESONATOR CONFIGURATIONS Resonators presented in this paper are based on the traditional capacitively coupled microstrip resonator with 50-Ohm feeding microstrip lines and gaps equal to 200 um. The resonators are constructed on a 625 um thick Alumina substrate having relative dielectric constant εr=9.6 and dielectric loss tangent equal to 0.0006.  In the single-layer variant, the conventional microstrip resonator is replaced with N 2-D Hilbert curves having the line width and spacing equal to 100 um, Fig. 1.   1 2  Fig. 1. Single-layer resonator comprising of N=4 2-D Hilbert lines.  In the multilayer variant, N 2-D Hilbert curves are placed under the microstrip, Fig. 2. Conductors in different layers are separated by the 50 um thick dielectric layers, having εr=9.6 and dielectric loss tangent 0.0006.   1 2  Fig. 2. Two-layer resonator with N=4 2-D Hilbert lines embedded under the microstrip.  PROOF PDF @ 2005 EuMW 2005                                                                                                EuMW 2005 III. SIMULATION RESULTS Performances of the resonators were determined by EMSight, EM simulator in Microwave Office. All material characteristics and dimensions were kept within boundaries of widely available standard TF procedure. The proposed configurations were analysed for different values of N and compared to conventional capacitively coupled microstrip resonator in terms of dimensions and unloaded and loaded Q-factor.  Simulation results for both configurations and various values of N are shown in Tables I and II, where L denotes the resonator length, while s210 denotes insertion loss at resonant frequency.   TABLE I. SIMULATION RESULTS FOR SINGLE-LAYER RESONATOR COMPRISING OF N  2-D HILBERT CURVES   N 6 5 4 3 L, [mm]  9.45 7.9 6.3 4.7 fr, [GHz] 1.827 2.162 2.646 3.403 s210, [dB] -4.41 -3.32 -2.4 -1.65 QL 716 569 441 315 QU 1123 1065 1038 997  TABLE II. SIMULATION RESULTS FOR RESONATORS WITH  N  2-D HILBERT CURVES EMBEDDED UNDER THE MICROSTRIP  N 6 5 4 3 L, [mm]  9.45 7.9 6.3 4.7 fr, [GHz] 0.96 1.148 1.428 1.884  s210, [dB] -16.6 -13.5 -11 -8  QL 1433 1400 1231 1047 QU 1467 1465 1337 1244  By comparing values in Tables I and II, it can be seen that placing multiple 2-D Hilbert curves under the microstrip offers more potential for size reduction of the resonator, as well as a significant improvement of unloaded Q-factor. However, due to the higher energy loss induced this way, this approach generates higher insertion loss. In Table III, simulation results for two-layer 2-D Hilbert resonators presented above are compared to those of conventional capacitively coupled resonators tuned to the same resonant frequency. It can be seen that incorporating multiple 2-D Hilbert curves under the microstrip results in length reduction of more then 84% when compared to the conventional case, while the unloaded Q-factor remains approximately the same.  IV. BANDPASS FILTER DESIGN  The proposed resonator with multiple 2-D Hilbert curves embedded under the microstrip was used to design a bandpass filter operating in the GPS range and having high attenuation in the neighbouring GSM range. The specifications used are given in Table IV.  TABLE IV. BANDPASS FILTER SPECIFICATIONS  Center Frequency 1.575 GHz Bandwidth 2 MHz Max. passband ripple  0.3 dB Attenuation from 1.75GHz to 2GHz > 60 dB  Designed filter is of second order, Fig. 3, and it was constructed on a 9.7 Alumina having dielectric loss tangent 0.0006. Dielectric layers between the feeding lines, resonators and multiple 2-D Hilbert curves are 50 um thick. Lengths of the resonators were simultaneously tuned to achieve specified center frequency. There is no gap in the direction of the X-axes between the feeding lines and the resonator, while the gap between the two resonators is equal to 1400 um.    Fig. 3. A 3-D view of the designed bandpass filter.  Filter performances were determined by full-wave EM simulations. Simulation results are shown in Fig. 4, with the inset showing the passband. It can be seen that the filter complies with the specifications very well, achieving low passband ripple and attenuation of more then 100 dB in the unwanted GSM frequency band.      PROOF PDF @ 2005 EuMW 2005                                                                                                EuMW 2005  TABLE III. COMPARISON WITH THE CONVENTIONAL CAPACITIVELY COUPLED RESONATORS  fr, [GHz] QUHilb QUconv LHilb, [mm] Lconv, [mm] Length reduction 0.96 1467 1520 9.45 61.7 84.6 % 1.148 1465 1469 7.9 51.5 84.6 % 1.428 1337 1364 6.3 41.3 84.7 % 1.884 1244 1239 4.7 31.3 85 %                   Fig. 4. Bandpass filter response; Inset: a passband detail.   Fig. 4. Bandpass filter response; Inset: a passband detail V. CONCLUSION This paper has presented a novel compact resonators with multiple 2-D Hilbert curves embedded in and under the resonator. Performances of the proposed resonators were determined for different number of Hilbert curves (N) and compared to those of the conventional capacitively coupled microstrip resonator. Incorporating multiple 2-D Hilbert curves under the microstrip resulted in length reduction of more then 84% when compared to the conventional case, while the unloaded Q-factor remains approximately the same.   A bandpass filter was designed to work in the GPS range, using the proposed resonator with multiple 2-D Hilbert curves embedded under the microstrip. Simulation results conformed to specifications well, showing attenuation of more then 100 dB in the 1.8 GHz GSM range.   REFERENCES [1] V. Radisic, Y. Qian, R. Coccioli, and T. Itoh, “Novel 2-D photonic bandgap structure for microstrip lines,” IEEE Microwave Guided Wave Lett., vol. 8, , pp. 69-71, February 1998. [2] F. Yang, K. Ma, Y. Qian, and T. Itoh, “A uniplanar compact photonic-bandgap (UC-PBG) structure and its applications for microwave circuits,” IEEE Trans. on Microwave Theory and Tech., vol. 47, no. 8, pp. 1509-1514, August 1999. [3] M. A. G. Laso, T. Lopetegi, M. J. Erro, D. Benito, M. J. Garde, and M. Sorolla, “Multiple-frequency-tuned photonic bandgap microstrip structures,” IEEE Microwave and Guided Wave Lett., vol. 10, no. 6, pp. 220-222, June 2000. [4] T. Kim, C. Seo, “A novel photonic bandgap structure for low-pass filter of wide stopband,” IEEE Microwave and Guided Wave Lett., vol. 10, no. 1, pp. 13-15, January 2000. [5] Fractalcoms Final Report, Project No. IST-2001-33055, www.tsc.upc.es/fractalcoms [6] V. Crnojevic-Bengin, and D. Budimir, “Novel microstrip resonators with embedded 3-D curves,” Asia-Pacific Microwave Conference APMC 2004, New Delhi, India, December 2004. [7] H. Liu, X. Sun, and Z. Li, “A low-pass filter of wide stopband with a novel multilayer photonic bandgap structure,” Microwave and Optical Technology Lett., vol. 40, no. 5, pp. 431-432, March 2004. [8] J. McVay, N. Engheta, and A. Hoorfar, “High impedance metamaterial surfaces using Hilbert-curve inclusions, ” IEEE Microwave and Wireless Components Lett., vol. 14, no. 3, pp. 130–132, March 2004. [9] S. Tse, B. Sanz Izquierdo, J. C. Batchelor, and R. J. Langley, “Reduced size cells for electromagnetic bandgap structures,” Electronics Lett., vol. 39, no. 24, November 2003. 1.5 1.6 1.7 1.8 1.9 2Frequency (GHz)-150-100-500DB(|S[2,1]|)1.573 1.575 1.577Frequency (GHz)-13-11-9 DB(|S[2,1]|)

Novel compact resonators with multiple 2-D Hilbert fractal curves

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Novel compact resonators with multiple 2-D Hilbert fractal curves

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