Microwave Properties of (Ba1-xSrx)Sm2Ti4O12 Ceramics and Its Application in Dielectric Resonator Antenna

In the (Ba1-x Sr x )Sm2Ti4O12 (BSST, 0≦x≦0.1) system SrO is used to substitute BaO to improve the microwave dielectric properties of BSST ceramics. As the amount of SrO increases from 0 to 0.06 mol%, the dielectric constant (ε r) of BSST ceramics decreases from 82.3 to 72.3 and the temperature coefficients of the resonant frequency (τf) change from -21.1 to -2.36 ppm/°C, but the quality values (Q * f) show no apparent change with the variation of the x value. In the BSST system, the (Ba0.98Sr0.02)Sm2Ti4O12 ceramic reveals the maximum Q * f value. With the loading of a (Ba0.98Sr0.02)Sm2Ti4O12 dielectric resonator (DR), a circular polarization (CP) design of a DR antenna is fabricated through crossed slot of unequal arm lengths in the ground plane of a microstrip line. The proposed CP design results in the excitation of two near-degenerate orthogonal modes of near-equal amplitudes and a 90° phase difference. For the proposed design applied to the low-profile square-cross-section DR antenna of very high permittivity studied here, a large CP bandwidth, determined from the 3 dB axial ratio of as high as 2.39%, is also obtained.