IEEE MTT-S 2008 International Microwave Symposium Technical Program

Session: WE4A	Planar Filter II
Chair:	Jeff Pond, Naval Research Lab.
Co-Chair:	Raafat Mansour, University of Waterloo
Abstract:	The session deals with realization of miniature microstrip filters as well as the realization of filter with improved spurious performance. A paper is also included on the use of the non-resonating nodes concept in planar filters.

WE4A-01	Parallel-Coupled Microstrip Filters with Periodic Floating-Conductors on Coupled-Edges for Spurious Suppression
1154	T. Yamaguchi¹, T. Fujii², T. Kawai¹, I. Ohta¹, ¹University of Hyogo, Himeji, Japan, ²Fujitsu Limited, Kawasaki, Japan
	This paper presents a new technique for suppressing the spurious response of parallel-coupled microstrip bandpass filters at twice the design frequency. Floating conductors loaded into periodic slots on the inner edges of each coupled section are employed to compensate the difference between even- and odd-mode phase velocities. This technique is marked by maintenance of planar structure and ease of design due to the symmetrical coupled line section. The designed filter has a satisfactory suppression level of about 40 dB and a symmetrical frequency response of the pass band. The validity of the design concept is confirmed both numerically and experimentally.

WE4A-02	A Miniaturized Microstrip Ring Resonator Lowpass Filter with Sharp Attenuation
1292	T. Wuren, I. Sakagami, M. Fujii, M. Tahara, University of Toyama, Toyama-shi, Japan
	A miniaturized circuit of a microstrip ring resonator lowpass filter with sharp attenuation is investigated in this paper. The miniaturization of the circuit is realized by using a simple specific transmission line with two open stubs. The ratio of the original ring length and miniaturized ring length is 3:2. However the miniaturized circuit is equivalent to the original circuit at three frequencies f0, 1.5f0 and 2f0. Thus, the width of the stopband is maintained as for the original circuit. Therefore, the filter characteristic is not distorted after miniaturization. The theoretical result of a miniaturized circuit shows a broader stopband and a sharper cut off frequency response than the original one, though it also shows smaller minimum attenuation in stopband and larger maximum attenuation in passband compared to the original one. Experimental result is shown for verification of the present study.

WE4A-03	Design of Dual- and Triple-Passband Bandpass Filters With Interdigital Resonators
1087	C. Tang, L. Lu, C. Shen, J. Wu, National Chung Cheng University, Chia-Yi, Taiwan
	The novel dual- and triple-passband bandpass filters are proposed in this paper. With the interdigital resonators embedded into the half-wavelength resonators, the bandpass filter with multiple passbands can be obtained easily. Moreover, by adopting the method of interdigital resonators, the passband with broader bandwidth on the higher frequency band can be obtained easily. Theoretical analyses are also described in this paper. The measured results of fabricated filters match well with the electromagnetic simulation; therefore, the feasibility of the proposed filters is approved.

WE4A-04	Design Procedure of Low Cost Substrate Microstrip Filters based on Nonresonating Nodes
1509	S. Cogollos¹, V. Boria¹, R. J. Cameron², R. R. Mansour³, ¹Universidad Politecnica de Valencia, Valencia, Spain, ²COMDEV, Cambridge, Canada, ³University of Waterloo, Waterloo, Canada
	A complete design procedure of microstrip filters with high electrical performance using non-resonating nodes (NRN) is proposed. Such design procedure, based on a distributed model with frequency dependent inverters, allows the flexible allocation of transmission zeros in order to obtain high selectivity filtering responses, as well as the reduction of their frequency sensitivity. We have successfully validated this novel strategy with the design of a high performance microstrip filter, making use of a low cost substrate (i.e. with a low dielectric constant) and considering losses effects.

WE4A-05	Improvement of Stopband Performance in Parallel-Coupled Bandpass Filters Using Quasi-Lumped Elements
1207	V. Zhurbenko, V. Krozer, P. Meincke, Technical University of Denmark, Kgs. Lyngby, Denmark
	This paper is aimed at improving the rejection level as well as overcoming the bandwidth limitations for classical coupled-line filters. A planar microwave coupled-line filter employing a quasi-lumped element resonator considerably improving the stopband characteristics is presented. The proposed bandpass filter has a compact footprint, and exhibits good stopband rejection with no repeated passband at twice the center frequency in comparison with the traditional coupled-line filter. By introducing the quasi-lumped element resonator, two transmission zeros at upper and lower stopbands are created, with adjustable locations of transmission zeros for desired performance. The device is fabricated in standard thick-film manufacturing technology. Based on parallel-coupled line theory, the impedance inverter model for this device is developed. The passband filter centered at 5.5 GHz with a 3 dB relative bandwidth of 60 % is implemented with an area of approximately λ/6 x λ/4.

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