2010 IEEE MTT-S International Microwave Symposium Technical Program

Session: WE2B	Novel Techniques for Planar Filter Design
Chair:	Christopher Galbraith, MIT Lincoln Laboratory
Co-Chair:	Chi Wang, Orbital Sciences Corp.
Abstract:	This session highlights recent advances in planar filter design. Results include a synthesis procedure for lossy filters with uniform Q, several techniques for designing dual-band planar filters, a method for improving matching and isolation in a bandpass filter balun, and a reconfigurable bandstop filter using RF-MEMS-loaded split ring resonators.

WE2B-1	Synthesis of 4th order lossy filters with uniform Q distribution
10:10 AM-10:30 AM	J. Mateu¹, A. Padilla¹, C. Collado¹, M. Martinez-Mendoza², E. Rocas¹, C. Ernst², J. M. O'Callaghan¹, ¹Universitat Politecnica de Catalunya, Castelldefels, Spain, ²ESA, Noordwijk, Netherlands
(1297)	This paper outlines the synthesis procedure for obtaining the folded coupling matrix of lossy filters of 4th order with uniform Q distribution. The method is applied to Butterworth, Chebyshev and Chebyshev with a single pair of symmetrical transmission zeros responses. Closed-form expressions to relate a prescribed insertion loss and filter bandwidth with the required resonator quality factor for an infinite Q flatness filter responses have been obtained. Experimental results on a Chebyschev microstrip filter coincide with the theoretical predictions.

WE2B-2	Design of Dual-Band Net-Type Bandpass Filter
10:30 AM-10:50 AM	C. Tseng, H. Shao, National Taiwan University of Science and Technology, Taipei, Taiwan
(1370)	In this paper, a new dual-band net-type bandpass filter is designed, fabricated, and experimentally verified using dual-band and single-band net-type resonators. The dual-band net-type resonator is designed to operate at two closely specified resonant frequencies, f1 and f2. Then incorporating with single-band net-type resonators, a dual-band filter can be implemented using the design concept of adding extra coupled resonators. To reduce the circuit size, two types of resonators are further folded to become a square box shapes. The measured results of the developed filter are in a good agreement with the simulated results by full-wave electromagnetic simulator. Moreover, the developed filter not only has an excellent mid-band rejection, but also provides a wide stopband suppression.

WE2B-3	New Dual-Mode Dual-Band Bandpass Filter With Quasi-Elliptic Function Passbands and Controllable Bandwidths
10:50 AM-11:10 AM	T. Lin¹, U. Lok¹, J. Kuo², ¹National Chiao Tung University, Hsinchu, Taiwan, ²Chang Gung University, Taoyuan, Taiwan
(1162)	New dual-mode dual-band bandpass filters with quasi-elliptic function responses are devised based on a single stepped-impedance resonator. The center of the resonator is grounded through a short high-impedance section which is equivalent to an inductor for providing coupling between the resonant modes. In addition, in order to increase the degree of freedom for the dual-band design, an interdigital capacitor is introduced so that both center frequencies and bandwidths of the two passbands can be controlled. Moreover, with the aid of source-load coupling, two extra transmission zeros can be created close to the passband edges and hence greatly improve the filter selectivity between the two passbands. Two filters are fabricated and measured to validate the proposed idea. The measured results show good agreement with the simulation.

WE2B-4	Application of Generalized Bagley-Polygon Four-Port Power Dividers to Designing Microwave Dual-Band Bandpass Planar Filters
11:10 AM-11:30 AM	R. Gomez-Garcia, M. Sanchez-Renedo, University of Alcala, Alcala de Henares, Spain
(1276)	A new type of microwave dual-band bandpass planar filter based on signal-interference techniques is reported. The described filter approach consists of transversal filtering sections made up of generalized Bagley-polygon four-port power dividers. This transversal section, by exploiting feedforward signal-interaction concepts, enables dual-band bandpass filtering transfer functions with several transmission zeros to be obtained. A set of closed formulas and guidelines for the analytical synthesis of the dual-passband transversal filtering section are derived. Moreover, its practical usefulness is proven with the development and testing of a 2.75/3.25-GHz dual-band microstrip prototype.

WE2B-5	Lumped Isolation Circuits for Improvement of Matching and Isolation in Three-Port Balun Band-Pass Filter
11:30 AM-11:40 AM	T. Yang², P. Chi¹, T. Itoh¹, ¹University of California, Los Angeles, Los Angeles, United States, ²University of Electronic and Science Technology of China, Chengdu, China
(1392)	A method of improving the output impedance and isolation characteristics of the balun filter is presented in the paper. By introducing the so-called isolation network to the outputs of the balun filter, both the isolation and matching at the output ports of the balun filter, which is derived from a symmetrical four-port network, are improved to a large degree. Two isolation networks including the microstrip-line based and high-pass lumped-element based networks are proposed and implemented on the given balun filter. Compared to the standalone balun filter, the measured output isolation and return loss improvements of the balun filter with the isolation networks are more than 25 dB and 18 dB, respectively, at the center frequency of the output S-parameters. Furthermore, the proposed high-pass lumped-element based network is considerably miniaturized compared to the first microstrip-line based network. Only one-tenth of the length of the corresponding microstrip line is required.

WE2B-6	Reconfigurable 4 Pole Bandstop Filter based on RF-MEMS-loaded Split Ring Resonators
11:40 AM-11:50 AM	D. Bouyge¹, A. Crunteanu², A. Pothier², P. Martin², P. Blondy², A. Velez¹, J. Bonache¹, J. Orlianges³, F. Martin¹, ¹Cimitec, Bellaterra (Cerdanyola del Vallès), Spain, ²XLIM Research Institute - CNRS, Limoges, France, ³SPCTS Research Insitute - CNRS, Limoges, France
(1528)	A reconfigurable four-pole bandstop filter based on the combination of the split ring resonators (SRRs) and RF-MEMS switches, operative at the X frequency band, is presented for the first time. The fabricated device consists on a microstrip line loaded with four pairs of SRRs, exhibiting four different resonance frequencies, with two capacitive ON/OFF switches placed between the inner and outer ring of each SRR. Through their electrostatic actuation, the resonance frequency of each SRR can be shifted and as a result filter bandwidth can be digitally controlled, or even suppressed. Good agreement between theory and experiment is achieved.

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