Crystal structure, microwave dielectric properties, and dielectric resonant antenna studies of novel low-permittivity CoAl 2 O 4 spinel ceramics.

CoAl 2 O 4 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 CoAl 2 O 4 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 CoAl 2 O 4 ceramics towards microwave antennas. The CoAl 2 O 4 -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 CoAl 2 O 4 ceramics were promising candidates for wireless communication devices operating at the Ku -band, provided τ f can be further tuned toward zero.