Crystal structure, microwave dielectric properties, and dielectric resonant antenna studies of novel low-permittivity CoAl₂O₄ spinel ceramics

CoAl₂O₄ spinel ceramics were prepared via a standard solid-state reaction method, and their crystal structure, microwave dielectric properties, and dielectric resonant antenna applications were systematically investigated in this study. X-Ray diffraction patterns and Raman spectra confirmed that CoAl₂O₄ belongs to the Fd-3 m space group with cubic crystal symmetry. ε_r and Qf values increased with the increasing sintering temperature, where an ever-improving microstructure was also observed from the scanning electron micrographs. The optimal microwave dielectric properties were achieved as follows: ε_r = 9.34, Qf = 30,500 GHz, and τ_f = −54 ppm/^°C. Moreover, a dielectric resonant antenna was designed and simulated to demonstrate the application prospects of CoAl₂O₄ ceramics towards microwave antennas. The CoAl₂O₄-based antenna resonating at 14.33 GHz exhibited a high return loss of −40.9 dB, a wide impedance bandwidth of 940 MHz, and an exceptionally high total efficiency of 96.6%. The remarkable antenna performances suggested that CoAl₂O₄ ceramics were promising candidates for wireless communication devices operating at the Ku-band, provided τ_f can be further tuned toward zero.