A Series of Ultra-low Permittivity ALaP<sub>4</sub>O<sub>12</sub> (A = Li, Na, K) Metaphosphate Microwave Dielectric Ceramics for Ultra-wideband Dielectric Resonant Antenna Application
Jian Bao, Kaiheng Zhang, Wei Wang, Ziyang Liu, Zhen Fang, Xin Wang, Chang-Hao Wang, Yuchun Li, Guoqiang He, Tao Zhou, Di Zhou
Abstract
The employment of ultra-low permittivity materials in the configuration of antennas has been demonstrated to augment the antenna bandwidth and diminish signal delay effectively. This study presents three ultra-low permittivity metaphosphate microwave dielectric ceramics (MWDCs). The ALaP 4 O 12 (A = Li, Na, K) metaphosphate ceramics, which all belong to the monoclinic crystal system, exhibit extremely low permittivity (ε r ≈ 5) and excellent quality factor ( Q · f > 10,000 GHz) at a low sintering temperature ( T < 950 °C). Terahertz time-domain spectroscopy indicates that the ε r of ALaP 4 O 12 at terahertz frequencies is comparable to that observed in the microwave band and its value remains stable over an extensive frequency range. Furthermore, the relationship between the crystal structure and the dielectric properties of ALaP 4 O 12 has been analyzed through the lens of chemical bond theory. The highest Q · f value observed for LiLaP 4 O 12 can be attributed to the high chemical bond strength and stability of its crystal structure. The lowest ionic polarizability per unit volume is exhibited by NaLaP 4 O 12, which results in the lowest pore-corrected permittivity. The thermal expansion of the chemical bonds within KLaP 4 O 12 is considerable, resulting in the highest coefficient of thermal expansion. Finally, the performance of a LiLaP 4 O 12 -based dielectric resonator antenna (DRA) excited by slot-coupled microstrip lines was designed and optimized by using different ceramic radius-to-height (RH) ratios. It was found that when the RH ratio of DRA reached 1.85, both the fundamental mode (HEM 11δ ) and the higher-order mode (HEM 12δ ) of DRA were simultaneously excited. The two modes overlap significantly, resulting in an ultra-wideband (UWB) of 46.8% (bandwidth = 7.93 GHz). Concurrently, the maximum radiation efficiency and gain of the DRA, obtained from the simulation, are 97.9% and 7.92 dBi, respectively. The findings of this study may inform the investigation of ultra-low permittivity phosphorus-based MWDCs and UWB DRAs.