Single and dual band bandpass filters using complementary split ring resonator loaded half mode substrate integrated waveguide

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High performance microwave bandpass filters with low insertion loss, high selectivity, compact size and multiple bands are widely used for wireless and satellite communication systems [1]. During the years, bandpass waveguide filters have used all
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  Single and Dual Band Bandpass Filters Using Complementary Split Ring Resonator Loaded Half Mode Substrate Integrated Waveguide David E. Senior, Xiaoyu Cheng, Melroy Machado and Yong-Kyu Yoon   Electrical Engineering, University at Buffalo, the State University of New York Buffalo, NY, 14260, USA E-mail: des27@buffalo.edu Introduction High performance microwave bandpass filters with low insertion loss, high selectivity, compact size and multiple bands are widely used for wireless and satellite communication systems [1]. During the years, bandpass waveguide filters have used all kinds of metallic and non-metallic insertions in order to improve performance and reduce size [2]. Since the first experimental demonstrations of metamaterial particles exhibiting either negative permeability such as the split ring resonators (SRR), or negative permittivity such as the complementary split ring resonators (CSRR), different implementations combining waveguide with such structures have been widely investigated for bandpass filters [3-4], mainly motivated by their extraordinary property of generating backward wave transmission below the waveguide cutoff frequency. On the other hand, the need for new applications and integration with digital circuitry is the motivation for proposing and implementing planar microwave filters with performances similar to those provided by the bulky waveguide filters. The substrate integrated waveguide (SIW) and the half mode substrate integrated waveguide (HMSIW) [5-6] have been selected as the key wave guiding structures for the implementation of low loss, high quality factor and improved selectivity waveguide bandpass filters on printed circuit board (PCB) technology. In addition, taking into account the possibility of having forward wave propagation below the waveguide cutoff frequency, the substrate integrated waveguide has been combined with complementary split ring resonators (CSRR) for the implementation of compact size and high selectivity bandpass filters [7]. In this work, the half mode substrate integrated waveguide (HMSIW) and the complementary split ring resonators (CSRR) are used to implement single and dual band bandpass filters working with forward wave propagation below the waveguide cutoff frequency. The half mode substrate integrated waveguide allows additional size reduction compared to that provided by the substrate integrated waveguide (SIW) and more flexibility in the control of the quality factor, since no complicated microstrip to HMSIW transition is needed. Proposed Single Band and Dual Band HMSIW-CSRR Resonators The proposed unit cells for the HMSIW-CSRR filters are presented in Fig. 1. All designs are implemented on the substrate Arlon Diclad 880 with a thickness of 0.508mm, a dielectric constant of 2.2 and a loss tangent of 0.0009. A row of metalized vias with a diameter d   of 0.7mm and a separation from center to center  s  of 1.4mm are used to provide the electric sidewall of the waveguide. The 978-1-4244-4968-2/10/$25.00 ©2010 IEEE  waveguide cutoff frequency is selected to be 8.2GHz, which is achieved with an optimized width w  of 6mm for HMSIW implementations. The complementary split ring resonator is etched on the metallic surface of the waveguide. A 50 ohm microstrip line with a width w 1  of 1.547mm is connected directly to the waveguide with no transition. The position t   of the microstrip feeding line and the location l   of the complementary split ring resonator in the unit cell control the external quality factor (Q). In this work, all designs use t = 0. The distance  p  from the top of the waveguide does not significantly affect the behavior of the resonator. Out of four possible CSRR orientations, the proposed configuration shows the best transmission response. In Fig. 1b, the CSRR is modified with a meander line structure for the internal loop in order to reduce the second intrinsic resonance frequency of the CSRR and achieve dual band operation below the waveguide cutoff frequency. Thus, the resonance frequencies can be arbitrarily selected by modifying the dimensions of the CSRR. Selected resonance frequencies and the dimensions of the unit cells are summarized in Table I. Full wave structure simulations are performed using High Frequency Structure Simulator (HFSS, Ansys Inc.).   (a)   (b) Fig.1 Unit cell of half mode surface integrated waveguide (HMSIW) resonator with a series of vias for electric walls and complementary split ring resonator (CSRR) on the top surface: (a) single band, (b) dual band.   Table I. Dimensions of the proposed HMSIW-CSRR resonators Resonator  g=a=b=c c 1 c 2  p   Single band at 5.25 GHz 0.25mm 3.85mm 3.85mm 0.77mm Dual band at 3.5 and 5.85 GHz 0.25mm 6mm 4.5mm 0.57mm Two Pole Filter Implementation and Measurement Results Fig. 2 shows the layout of the single and a dual band two pole filters designed  by using the coupled resonator design procedures [1]. The external quality factor of the unit cell is calculated for a doubly loaded resonator as Q=2f  o  /BW  3dB  [1], where  f  o  is the resonance frequency and  BW  3dB   is the 3dB bandwidth for S 21 . The coupling coefficient between resonators, which is controlled by the distance l  r  , is calculated as  M  =(  f  12 - f  22 )/ (  f  12 + f  22 ) [1], where  f  1   and  f  2  are the lower and higher resonance frequency of the two adjacent resonators. For example, a two pole single band Chebyshev filter for 5.25GHz with a fractional bandwidth of 5% and a two pole dual band Chebyshev filter for 3.5GHz and 5.85GHz with a fractional  bandwidth of 5.7% and 7.5%, respectively, are designed and implemented. Table II summarizes the calculations and dimensions.   w  g a b c l  s  p t w 1 c 1 c 2 a b d   (a)   (b) Fig.2 Two pole bandpass filters: (a) single band, (b) dual band. Table II. Calculations and dimensions of the two pole HMSIW-CSRR filters Filter Q M l l  r Single band at 5.25GHz 14.16 0.0756 1.4mm 9mm Dual band at 3.5GHz 11.6 0.094 0.3mm 8.6mm Dual band at 5.85GHz 8.6 0.127 Fig. 3 shows the measurement and simulation results. The fabricated HMSIW-CSRR unit cells and filters are shown in Fig. 4. Measurements are performed using HP8510C vector network analyzer after standard short-open-load-through (SOLT) calibration in the frequency range of 2 GHz to 10GHz.   (a)   (b) (c) (d) Fig.3. Measurement and simulation results: (a) single band resonator, (b) single  band two pole filter, (c) dual band resonator, (d) dual band two pole filter.   l  r   l  p l  r 2 3 4 5 6 7 8 9 10-45-40-35-30-25-20-15-10-50Frequency (GHz)    S   2   1   a   n   d    S   1   1   (   d   B   ) 2 3 4 5 6 7 8 9 10-70-60-50-40-30-20-100Frequency (GHz)    S   1   1   a   n   d    S   2   1   (   d   B   )   2 3 4 5 6 7 8 9 10-40-35-30-25-20-15-10-50Frequency (GHz)    S   1   1   a   n   d    S   2   1   (   d   B   ) 2 3 4 5 6 7 8 9 10-70-60-50-40-30-20-100Frequency (GHz)    S   1   1   a   n   d    S   2   1   (   d   B   ) Simulation Measurement Simulation Measurement Simulation Meas. Simulation Measurement S 21 S 11 S 21 S 11 S 21 S 11 S 21 S 11   (a)   (b) Fig.4. Fabricated resonators and filters: (a) single band, (b) dual band. Conclusion Single and dual band resonators are implemented using half mode substrate integrated waveguide (HMSIW) loaded with complementary split ring resonators (CSRR). Forward wave propagation is achieved below the characteristic cutoff frequency of the waveguide due to the evanescent wave transmission properties of the CSRR. Since no transition is needed, very compact size is achieved. Single and dual band two pole filters are implemented by using the theory of coupled resonator filters. Full wave simulations are in good agreement with measurements.   Acknowledgment This work is sponsored by National Science Foundation (ECCS 0748153). David E. Senior is also supported by Fulbright, Universidad Tecnológica de Bolívar and COLCIENCIAS (Colombia).   References [1]   J.S. Hong and M.J. Lancaster,  Microstrip Filters for RF/Microwave  Applications , New York: Wiley, 2001.   [2]   V.E. Boria and B. Gimeno, "Waveguide Filters for Satellites,"  IEEEMicrowave Magazine, vo1.8, no. 5, pp.60-70, October 2007. [3]   R. Marques et al  , “Left handed media simulation and transmission of EM waves in subwavelength split ring resonator loaded metallic waveguides,”  Phys. Rev. Lett., vol. 89, no. 18, pp. 183901-183904, Oct. 2002. [4]    N. Ortiz et al  , “Complementary split ring resonator for compact waveguide filter design,”  Microw. Opt. Technol. Lett. , vol. 46, no.1, pp.88-92, May. 2005. [5]   D. Deslandes and K. Wu, “Single substrate integration technique of planar  circuits and waveguide filters,”  IEEE Trans. Microw. Theory Tech. , vol. 51, no. 2, pp. 593-596, Feb. 2003. [6]   Y.Q. Wang et al  , “Half mode substrate integrated waveguide (HMSIW)  bandpass filter,”  IEEE Microw. Wireless Compon. Lett. , vol. 17, no. 4, pp. 265-267. April 2007. [7]   Y. D. Dong, T. Yang, and T. Itoh, “Substrate integrated waveguide loaded by complementary split-ring resonators and its applications to miniaturized waveguide filters,”  IEEE Trans. Microw. Theory Tech. , vol. 57, no. 9, pp. 2211-2222, Sept. 2009. 
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