Design and Fabrication of a C-Band Dielectric Resonator Antenna with Novel Temperature-Stable Ce(Nb_{1- x}V_x)NbO₄(x = 0-0.4) Microwave Ceramics

Vanadium(V)-substituted cerium niobate [Ce(Nb_1-xV_x)O₄, CNVx] ceramics were prepared to explore their structure-microwave (MW) property relations and application in C-band dielectric resonator antennas (DRAs). X-ray diffraction and Raman spectroscopy revealed that CNVx (0.0 ≤ x ≤ 0.4) ceramics exhibited a ferroelastic phase transition at a critical content of V (x_c= 0.3) from a monoclinic fergusonite structure to a tetragonal scheelite structure (T_F-S), which decreased in temperature as a function of x according to thermal expansion analysis. Optimum microwave dielectric performance was obtained for CNV0.3 with permittivity (ϵ_r) of ∼16.81, microwave quality factor (Qf) of ∼41 300 GHz (at ∼8.7 GHz), and temperature coefficient of the resonant frequency (TCF) of ∼ -3.5 ppm/°C. ϵ_ris dominated by Ce-O phonon absorption in the microwave band; Qf is mainly determined by the porosity, grain size, and proximity of T_F-S; and TCF is controlled by the structural distortions associated with T_F-S. Terahertz (THz) (0.20-2.00 THz, ϵ_r∼12.52 ± 0.70, and tan δ∼0.39 ± 0.17) and infrared measurements are consistent, demonstrating that CNVx (0.0 ≤ x ≤ 0.4) ceramics are effective in the sub-millimeter as well as MW regime. A cylindrical DRA prototype antenna fabricated from CNV0.3 resonated at 7.02 GHz (|S₁₁| = -28.8 dB), matching simulations, with >90% radiation efficiency and 3.34-5.93 dB gain.