ACKNOWLEDGMENTS This work is supported by the National Science Council of the R.O.C. under Contracts NSC95-2221-E-260-032 and NSC-095- SAF-I-564-630-TMS. The authors are also very grateful for the support from National Chip Implementation Center (CIC), Tai- wan, for chip fabrication and high-frequency measurements, and National Nano-Device Laboratory (NDL), Taiwan, for high-fre- quency measurements. REFERENCES 1. K.T. Chan, C.Y. Chen, A. Chin, J.C. Hsieh, J. Liu, T.S. Duh, and W.J. Lin, 40-GHz coplanar waveguide bandpass filters on silicon substrate, IEEE Microwave Wireless Compon Lett 12 (2002), 429 – 431. 2. C.H. Doan, S. Emami, and A.M. Niknejad, Millimeter-wave CMOS sign, IEEE J Solid State Circ 40 (2005), 144 –155. 3. W.S. Tung, H.C. Chiu, and Y.C. Chiang, Implementation of millime- ter-wave and pass filter with MMIC technology, IEE Electron Lett 41 (2005), 744 –745. 4. H.H. Lin, W.S. Tung, J.C. Cheng, and Y.C. 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COMPACT MULTILAYER DUAL-BAND FILTER USING SLOT COUPLED STEPPED-IMPEDANCE-RESONATORS STRUCTURE A. Djaiz, 1 M. Nedil, 2 A. M. Habib, 1 and T. A. Denidni 1 1 INRS-EMT, University of Que´ bec, Montre´ al, QC, Canada H5A 1K6; Corresponding author: djaiz@emt.inrs.ca 2 University of Que´ bec in Abitibi-Temiskamingue, LRCS, Underground Communication Research, Val-d’Or, QC, Canada J9P 1S2 Received 19 October 2008 ABSTRACT: In this article, a new miniaturized configuration of single- input-single-output dual-band bandpass filter operating at ISM 2.45 GHz and UNII 5.8 GHz frequency bands using a multilayer structure with stepped-impedance resonators is presented. A coupling aperture is intro- duced in a common ground to ensure the coupling between the two resona- tors located in the upper layer and the lower one. The use of stepped-im- pedance resonators allows tuning the two bands at desired frequencies. Finally, a design prototype was fabricated to validate the proposed con- cept. The insertion loss and return loss at the central frequency are 1.35 dB and 17 dB for 2.45 GHz band, and 0.98 dB and 13 dB for the 5.8 GHz band, respectively. There is a good agreement between experimental and full-wave electromagnetic simulation re- sults. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1635–1638, 2009; Published online in Wiley InterScience (www. interscience.wiley.com). DOI 10.1002/mop.24417 Key words: dual-band filter; stepped-impedance-resonators; miniatur- ization; multilayer structures 1. INTRODUCTION Dual-band bandpass filters have become attractive components for wireless communication applications. Several standards have been approved for operating in ISM, UNII, and MMDS (point-to- multipoint distribution services) wireless frequency band, includ- ing blue-tooth IEEE 802. 11 a/b/g. For this issue, dual-band filters have been proposed [1–5]. Basically, a dual-band filter is a com- bination of two different single-band filters [1]. This solution suffers from high insertion loss and large overall size in its result- ant filter block. Thus, mono-circuit filter structure with dual-band characteristic is highly desired. Lately, Tsai and Hsue [2] inserted a stopband into a broadband to form dual-bands by cascading a broadband passband filter with a narrowband stopband filter. Unfortunately, the size of this dual- band filter is comparatively large. Dual-band filters realized by resonators consisting of three open stubs in parallel have also been proposed [3], where three transmission zeros are created by the open stubs to separate the two passbands. Recently, various approaches have been proposed based on stepped-impedance resonators SIR [4 – 6], this is due of the fact of its compact size. Furthermore, by using the properties of a stepped- impedance microstrip resonator, the first-harmonic frequency is adjusted by changing the impedance ratio to construct the upper passband. However, this kind of dual-band filter is implemented on a single layer substrate, so their dimensions remain large and need to be reduced. To further minimize the size as usually requested, a novel compact dual-band microstrip bandpass filter is constructed and implemented in this article. In this aspect, a multilayer topology with stepped-impedance resonators configuration is presented and designed. The coupling between the upper resonator and the lower one is achieved by introducing one coupled aperture in the com- mon ground plane located between the two layers. To verify the DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 51, No. 7, July 2009 1635