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A PLANAR-TYPE DIELECTRIC RESONATOR AND FILTER USING LTCC PROCESS Jounghyun Yim, 1 Daehyun Kang, 1 Seokho Son, 2 and Bumman Kim 1 1 Department of Electrical Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Korea 2 RN2 Technologies Ltd., 137–5, Okum-ri, Tanhyun-myun, Paju-si, Kyunggi-do, Korea Received 28 July 2006 ABSTRACT: A new structure planar-type dielectric resonator (PDR) with high Q has been developed using an LTCC process. The PDR con- sists of two different dielectric constant materials, a hollow patch center ground plane in the middle of the cavity layer and shielded cavity met- als. The realized PDR shows a high unloaded-Q factor of about 1920 at 34.3 GHz. We also developed a dual mode band-pass filter using the pro- posed PDR, demonstrating a compact filter at a millimeter-wave band. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 578 –581, 2007; Published online in Wiley InterScience (www.interscience.wiley. com). DOI 10.1002/mop.22206 Key words: DR; filter; LTCC; PDR 1. INTRODUCTION Recently, the planar type dielectric resonator (PDR) has been studied extensively because of the high Q factor and ease of integration with MICs or MMICs [1–5]. The requirements of the dielectric resonator for filters and low phase noise oscillators are high Q, small size, low insertion loss, high temperature stability, and low cost. Dielectric resonators, including PDR, require a cavity wall to reduce radiation loss and high dielectric disk or sphere to confine a mode, and an air gap to form an evanescent field region. Within this complicated structure, the dielectric disk or sphere should be placed accurately for proper operation. The cavity provides good performances but the technique is very expensive because of the complicated structure. In this article, we have proposed a new PDR that can meet most of the above requirements. Our PDR, fabricated with LTCC, has strong merits at low cost and manufacturability because it does not require a separate air gap or metal cavity. Instead, it is filled with a low dielectric material replacing the air gap and a deposited metal layer on the outer surface functions as a cavity wall. All alignments are placed by LTCC process. The proposed LTCC PDR has only one hollow patch ground plane located in the middle of the high dielectric layer and the structure reduces the metal loss enhancing the Q factor about twice compared with the conven- tional PDRs. Furthermore, it can be coupled easily to other circuits or structures using a microstrip-line coupler. Using the proposed resonator, we have demonstrated a dual mode band-pass filter [4] for millimeter-wave applications. 2. PLANAR DIELECTRIC RESONATOR FORMED BY LTCC PROCESS The Q factor of dielectric resonator is described by Eq. (1), where Q u is the unloaded Q factor of the resonator, Q r is Q for radiation loss, Q c is for conductivity loss, and Q d is due to dielectric loss [5]. 1 Q u  1 Q r  1 Q c  1 Q d  1 Q c  1 Q d , (1) Q r is negligible when the dielectric resonator is surrounded by a metallic wall cavity and Q u depends mainly on Q c and Q d . For a high quality factor dielectric resonator, the material should have a low loss tangent and its structure should support low conductivity loss characteristics. The configuration of the general PDR is depicted in Figure 1(a). It consists of a high dielectric plate having a ground plane with a hollow patch on both the up and down-side surfaces and a metal cavity. The ground plane can be located on one side of the dielectric plate shown in Figure 1(b) [3]. Our proposed PDR has been fabricated using a high dielectric LTCC placed in the middle of two low dielectric LTCC layers. It has only one ground plane at the center of the high dielectric LTCC, as shown in Figure 1(c). In the PDR, the outer cavity and inner ground plane form a partially loaded waveguide with a cutoff region against outside propagating wave in a horizontal direction. So, it has a tightly confined mode inside of the hollow patch and can provide a good quality factor. Figure 1 Configuration of PDRs. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com] TABLE 1 Configuration of PDR Radius (m) 1250 1400 1600 F (GHz) Q factor F (GHz) Q factor F (GHz) Q factor Two-side GND 36.43 2259.2 34.09 2714.6 31.58 2882.2 One-side GND 34.38 3425.0 32.53 3409.5 30.54 3864.0 Center GND 35.29 6388.8 33.16 5716.8 30.95 5510.7 578 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 49, No. 3, March 2007 DOI 10.1002/mop