Broad-band U-slot patch antennas loaded by chiral material

The analysis of wide band microstrip/slot antennas residing in cavities with arbitrary patch shapes and in presence of both isotropic and chiral materials is proposed in this paper. The theoretical approach is based on the variational formulation and the numerical solution is carried out by applying a combined Finite Element-Boundary Integral (FE-BI) Method. Such an approach already known in the literature only for isotropic and anisotropic media is extended also to the case of biisotropic dielectrics, including chiral materials. A numerical code based on the new theory here presented ha's been developed and it is employed in order to investigate, the main features of chiral materials as substrates for cavity backed microstrip antennas. This numerical code allows to study also antennas loaded by isotropic substrates as particular cases when imposing the chiral admittance to vanish. To test this capability the design of an U-slot microstrip antenna printed on a conventional isotropic dielectric for wide band applications is proposed. Finally, it is shown how the employment of chiral substrates instead of isotropic ones reduces the antenna size for a fixed working frequency and improves the impedance bandwidth, without decreasing too much the other radiating properties.