3. S. Watanabe, O. Hashimoto, and M. Makida, Temperature distribution analysis of heated material put in microwave oven using FDTD-HTE method, IEICE Trans Commun J84-B (2001), 1103–1106 (in Japanese). 4. L. Catarinucci, P. Palazzari, and L. Tarricone,Human exposure to the near field of radiobase antennas-a full-wave solution using parallel FDTD, IEEE Trans Microwave Theory Tech 51 (2003), 935–940. 5. R. Suga, T. Takatomi, T. Ijuin, O. Hashimoto, S. Watanabe, and A. Watanabe, Fundamental study on uniform sterilization of foods by using microwave heating, Jpn J Food Eng 7 (2006), 25–30. © 2007 Wiley Periodicals, Inc. A CPW LINEAR RESONATOR METHOD FOR THE MICROWAVE CHARACTERIZATION OF HIGH DIELECTRIC CONSTANT FILMS Luciene S. Demenicis, 1 Rodolfo A. A. Lima, 2 Luiz Fernando M. Conrado, 2 Walter Margulis, 3 and Maria Cristina R. Carvalho 2 1 Instituto Militar de Engenharia (IME), Rio de Janeiro, Brazil 2 Centro de Estudos em Telecomunicac ¸o ˜ es, Pontifı ´cia Universidade Cato ´ lica do Rio de Janeiro (PUC-Rio), Rua Marque ˆ s de Sa ˜ o Vicente, 225–22453-900 Rio de Janeiro, Brazil 3 ACREO, Stockholm, Sweden Received 28 July 2006 ABSTRACT: A coplanar waveguide linear resonator technique for the experimental characterization of the dielectric properties of films in the microwave frequency range at room temperature is proposed. The ap- proach is simple to implement as it consists of a film with unknown high dielectric constant deposited over the resonator, printed on standard alumina substrate using conventional photolithography process. The technique is illustrated by the measurement of the dielectric constant and losses of various ceramic screen-printed thick films: BaTiO 3 (BTO), CaCu 3 Ti 4 O 12 (CCTO), and a BTO(x)–CCTO(1 - x) composite with differ- ent concentrations (x = 0.2, 0.5, and 0.8). © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 521–524, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop. 22176 Key words: very high dielectric constant; coplanar waveguide; micro- wave resonator; thick film 1. INTRODUCTION The increasing demand for broadband and mobile wireless com- munication systems has created a strong motivation for small-size microwave component development. For these applications, the use of ceramic substrates with very high dielectric constant be- comes attractive. The wavelength corresponding to a particular frequency is significantly reduced in these materials, allowing the construction of smaller packaged devices without deteriorating the electrical performance [1, 2]. Progress in this area will rely upon the identification of new microwave dielectric materials with en- hanced quality. High dielectric constant ceramic films have been widely inves- tigated for use in small-sized microwave planar circuits [3]. Thin film capacitors, phase shifters for phased array antennas, filters, resonators, and impedance transformers are some successful ex- amples of this promising technology [4 – 8]. Recently, an uncon- ventional multilayered CPW structure obtained by deposition of high dielectric constant thin films over the conductors printed on conventional bulk substrates has been proposed [9]. Using this pattern, the lines have both simple cross-sections and very com- fortable transversal dimensions, leading to cheaper manufacture. However, the dielectric properties of the films at microwave fre- quencies must be carefully controlled for such applications. The material of choice for the film in this configuration must present high dielectric constant and low-loss tangent in this frequency range. Materials such as Ta 2 O 3 , SrTiO 3 (STO), and BaSrTiO 3 (BST) have been investigated for this purpose because of their high dielectric constant in bulk form. However, their properties in film formation are very sensitive to fabrication method [10]. Besides depending on many variables associated to the manufacture pro- cess, the dielectric properties are also strongly dependent on the operation frequency range, and temperature. Thus, the accurate design of high-frequency devices requires the development of RF characterization techniques, capable of measuring dielectric con- stant and loss tangent of the related films at microwave frequen- cies. Recently, some techniques to measure the electrical properties of bulk substrates using transmission line resonators in T [11] and ring [12] configurations have been proposed. These approaches could also be extended to the characterization of dielectric films. In this article, a coplanar waveguide linear resonator technique for the experimental characterization of the dielectric constant and losses of films in the microwave frequency range is proposed. It consists of a film with unknown high dielectric constant deposited over a CPW linear resonator printed on standard alumina substrate. The resulting effective dielectric constant of the structure takes into account the contribution of both dielectrics and the geometry of the resonator. Comparison between experimental and theoretical results of transmission characteristics of the resonator with fre- quency allows the determination of the dielectric properties of the film. The technique presented and described herein is useful for the measurement of dielectric properties for both thick and thin films. It allows the measurement of the material dielectric characteristics as a film applied to the microwave structure in the same frequency range and temperature of the operation conditions. Using this technique, the dielectric constant and losses in microwave frequencies were investigated for the following ce- ramic screen-printed thick films: BaTiO 3 (BTO), CaCu 3 Ti 4 O 12 (CCTO), and a composite BTO–CCTO material. 2. TECHNIQUE DESCRIPTION The CPW-film configuration proposed in this work is depicted in Figure 1. It consists of a film with very high relative dielectric constant ( r2 ) deposited over a CPW linear resonator printed on alumina substrate ( r1 ). The length of the central strip inner section determines the resonant frequency. The technique is based on the resonance properties of a half- wavelength long CPW resonator. The structure resonates when its length is an integer multiple of half a guide wavelength. The fundamental and higher-order resonance of a series of loosely Figure 1 Perspective view of the CPW linear resonator covered with thick film DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 49, No. 3, March 2007 521