Design and Fabrication of a Satellite Communication Dielectric Resonator Antenna with Novel Low Loss and Temperature- Stabilized (Sm1-XCaX) (Nb1-XMoX)O4 (X=0.15-0.7) Microwave Ceramics

Phase transition-structure-dielectric properties in microwave band correla-tions were determined for the (Sm1-xCax) (Nb1-xMox)O4 (SNCMo@x) system. X-ray and Raman analyses along with selected-area electron diffraction indicated that SNCMo@x (0.15 <= x < 0.375) ceramics crystallize in the I2/a space group (monoclinic fergusonite), whereas the I41/a space group (tetragonal scheelite) best describes SNCMo@x (0.375 <= x <= 0.7), suggesting that the increased ionic radius of the A-site effectively contributed to the ferroelastic phase transition and ensures the stability of the scheelite phase. The SNCMo@x ceramic materials exhibit composition-dependent permittivity (epsilon r) with a distribution between 12.0 and 17.7. The distortion and deformation of the [BO] polyhedra should be responsible for the shift from negative to positive temperature coefficient of resonant frequency (TCF) and the irregular behavior of the quality factor (Q x f). An optimum microwave dielectric performance was achieved for SNCMo@0.18 (epsilon r similar to 17.1, Q x f similar to 52, 800 GHz at similar to 8.80 GHz, and TCF similar to -1.4 ppm/degrees C). This work demonstrates the important role of simultaneous substitution of A/ B cations on [BO] polyhedral distortion and deformation in RENbO4 materials and its significant effect on the microwave dielectric properties. Also, the SNCMo@0.18 ceramic has been designed as a cylindrical dielectric resonator antenna with a high simulated radiation efficiency (97.1%) and gain (5.96 dBi) at the center frequency (7.75 GHz), indicating its promising application in X-band satellite communication (7.62-7.89 GHz) because of its adjustable permittivity, low loss, and good temperature stability.