Electromagnetic characteristics of low-permittivity ceramics as substrates for mushroom-like high impedance surfaces

The electromagnetic characteristics of low-permittivity ceramics, including silica, willemite, forsterite and alumina, as substrates for a mushroom-like high impedance surface (HIS) for enhancing microstrip patch antenna (MPA) performance from 1 to 6 GHz have been explored based on a parametric study evaluating the effects of ceramic substrate thickness and permittivity on resonance frequency and bandwidth of the HIS using the derived equations. To inhibit surface waves, the maximum thicknesses allowed for silica, willemite, forsterite and alumina substrates were determined for the first time when the resonance frequency of HIS matched with the operating frequency of MPA. For silica, willemite, forsterite and alumina, the thicknesses are 7.25, 5.57, 5.49 and 4.53 mm at 1 GHz, respectively, and decrease with increasing frequency in the range of 1 to 6 GHz. High impedance surfaces supported by silica, willemite, forsterite and alumina substrates exhibit bandwidths of 15.19%, 11.68%, 11.50% and 9.49%, respectively, independent of frequency. Silica, willemite and forsterite are good substrates for HISs with sufficient bandwidths. An alumina-supported HIS possesses a slightly smaller bandwidth but a more compact configuration which is favorable for antenna miniaturization. The use of low-permittivity ceramic substrates for the HIS can provide desirable electromagnetic properties while maintaining the proper dimensions to prevent surface waves.