Microwave Materials with High Q and Low Dielectric Constant for Wireless Communications.

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Microwave Materials with High Q and Low Dielectric Constant for Wireless Communications. Hitoshi Ohsato, Materials Science and Engineering, Shikumi-College, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan ABSTRACT Microwave dielectrics with high Q and low εr are expected for millimeterwave applications. In this paper the preparation and properties of some candidates for microwave dielectrics such as forsterite, willemite, alumina, corundum-type compounds, green phase of Y2BaCuO5 are presented. High purity forsterite has low εr of 7.0 high Q·f of 270000 GHz and τf of -65ppm/˚C. Willemite also has low εr of 6.5, and high Q·f of 160000 GHz. Alumina has ultra high Q·f of 680000GHz with εr of 10.05, and τf of -60 ppm/˚C. Mg4(Nb2-xTax)O9 which belongs to corundum group has εr of 11.5, Q·f of 350000 GHz, and τf of -70ppm/˚C. Y2Ba(Cu1/4Zn3/4)O5 which belongs to green phase group has εr of 15.4, Q·f of 220000 GHz. The τf’s of these materials, which are an important property for millimeterwave applications, have been adjusted to zero ppm/˚C by the addition of rutile, or adjustment of solid solution composition. INTRODUCTION The wireless communications have been tremendously developed in recent ubiquitous age [1]. The utilizable region for the frequency is expanding to millimeterwave region because of shortage of the radio frequency (RF) resource. A high frequency would be expected for ultra high speed LAN, ETS and car anti-collision system on the intelligent transport system (ITS) and so on. In the range of ultra high frequency, microwave dielectric ceramics which can be used in every frequency are more available than Surface Acoustic Wave (SAW) filter and film bulk acoustic resonator (FBAR) filter, which have limitation of usage at 5 GHz and 10 GHz, respectively [2]. The dielectrics for ultra high frequency are expected to have low dielectric constant εr and high quality factor Q. Dielectric loss increases with increase of frequency as shown in figure. 1. In the case of high frequency, the number of polarity change increases with frequency. So, dielectric materials with high Q are desirable. Low εr reduces time delay (TPD) according to following equation [3]: TPD = √εr /c Where εr is the dielectric constant and c is the velocity of light. The εr of silicates such as forsterite and cordierite is lower than that of alumina as shown in figure.2. At present, the candidates for millimeterwave application include silicates such as forsterite [4] and willemite [5], corundum group compounds such as alumina [6, 7] and Mg4(Nb2-xTax)O9 [8], and green phases such as Y2Ba(Cu1/4Zn3/4)O5 [9]. Temperature coefficients of resonant frequency τf of these materials are almost worth with large minus values around -60 ppm/˚C. It is expected that the τf should be improved for millimeter applications. In this paper, we report the preparation and properties of microwave dielectric ceramics with low εr and high Q developed in our Laboratory in collaboration with Prof. Ogawa and Dr. Kan for ultra high frequency app