A microwave dielectric material for microstrip patch antenna substrate
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High quality factor and near-zero temperature coefficient of resonant frequency (sf) are the two key issues for a certain microwave dielectric material system used in microstrip patch antennas. ZnTiO3-based ceramics is a promising candidate for microstrip patch antennas. On inhibiting the decomposition of ZnTiO3 by adding sufficient amount of MgO, high quality factor microwave dielectric material (Zn0.7Mg0.3)TiO3 was obtained. The deviations between theoretical and observed dielectric polarizabilites, the packing fraction, and bond valence were calculated to analyze correlation between structure and properties of (Zn0.7Mg0.3)TiO3. TiO2 was added to adjust sf of (Zn0.7Mg0.3)TiO3, and 0.82(Zn0.7Mg0.3)TiO3–0.18TiO2 with an er of 28.5, a Qf of 125,050 GHz, and a near-zero sf which satisfied the requirement as a substrate material for microstrip patch antenna was obtained at 1100 °C. In addition, a dielectric microstrip antenna was designed and fabricated using the proposed dielectric materials. The microstrip patch antenna exhibited a 34.96 dB return loss and a 1.05 voltage standing wave ratio at 2.5 GHz.
I. INTRODUCTION
Dielectric microstrip antennas, due to their small size, high radiation efficiency, and ease of excitation, have received much attention in recent microwave telecommunications.1,2 The important characteristics required for a dielectric material used in microstrip antennas are: (i) high quality factor to achieve high radiation efficiency since the quality factor is representative of the antenna losses. Typically, there are radiation, conduction, dielectric, and surface wave losses. Since the dielectric microstrip antenna has a very low dielectric loss and has no metallic loss, it offers very high radiation efficiency; (ii) high dielectric constant (er) to reduce the size of the antenna because the wavelength (k) in a dielectric is inversely pffiffiffiffi proportional to e of the wavelength (k0) in vacuum r pffiffiffiffi (k ¼ k0 = er ); and (iii) near-zero temperature coefficient of resonant frequency (sf) for high temperature stability.3–5 ZnTiO3-based ceramics was one of materials suitable for the applications at microwave frequencies because of its high Qf value and low sintering temperature (1100 °C).6,7 But as reported by Kim et al.,6,7 ZnTiO3 would decompose to TiO2 and cubic Zn2TiO4 at above 945 °C which has a rather low quality factor. According to their report, single-phase ZnTiO3 can be successfully synthesized by applying a sol–gel process and a semichemical route combined with vigorous milling using zirconia beads. Adding glass–sol or B2O3 is useful to enhance sinterability of it. The a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.281 J. Mater. Res., Vol. 26, No. 19, Oct 14, 2011
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microwave dielectric properties of the specimens sintered at 875 °C with B2O3 (0.5 wt%) additions were: e 5 29–31, Qf 5 56,000–69,000 GHz, and sf 5 10 to +10 ppm/°C.8 Moreover, their further research indicated that adding sufficient
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