High quality factor cold sintered LiF ceramics for microstrip patch antenna applications

Cold sintering is adopted to pre-densify LiF ceramics, where the relative density increases significantly from 72.1 % at 125 MPa to 88.9 % at 500 MPa. The following post-annealings at 800 °C lead to further optimizations of densification, and near-full densifications with relative densities of 95.6 % and 97.6 % are achieved at 375 and 500 MPa, respectively. Qf value increased with increasing uniaxial pressure until it reaches the maximum value of 134,050 GHz at 375 MPa, which is 1.82 times higher than that via conventional sintering (73,800 GHz). ε_r and τ_f are mainly determined by the relative density, and the optimum microwave dielectric properties are obtained as follows: ε_r = 8.45, Qf = 134,050 GHz, τ_f =–135 ppm/°C. A microstrip patch antenna is designed and fabricated using the LiF ceramic as the substrate, which gives an S11 of –20.3 dB, a simulated high efficiency of 90.5 %, and a gain of 4.25 dB at the resonant frequency of 6.81 GHz.