Mixed-potential integral equation technique for the characterization of microstrip antennas printed on uniaxial substrates

Many substrate materials commonly used for planar antennas exhibit uniaxial anisotropy. It is well-known also that anisotropic substrates exercise a non negligible influence on the radioelectric performances of planar circuits and antennas. Hence it is really important to quantify this influence in order to evaluate its effects on these performances. Antennas printed on uniaxial substrates have already been studied in the literature using integral equations associated to Green´s functions in spectral domain. In the present paper, the authors develop the mixed-potential formulation to analyse circuits and antennas using anisotropic materials. The Green´s functions for a multilayer structure with both electric and magnetic anisotropism are analytically determined in the space domain rather than the spectral domain. The main advantage of this formulation is to get the current distribution directly without using an inverse Fourier transform which is time consuming. As an application the effect of the anisotropic properties of a uniaxial substrate on the characteristics of a microstrip antenna is calculated and compared to the isotropic case.