Anarbitrarily shaped microstrip patch antenna excited by a three-dimensional electric point-source is examined. The metallic patch resides on a biisotropic chiral grounded slab. The analysis is based on the integral equation approach. The Green functions for the layered medium are used to formulate a coupled set of integral equations for the patch induced current. The layered medium Green dyadic function is expressed in terms of spectral TE and TM waves and of Sommerfeld-type integrals. The Sommerfeld-type integrals are expressed in a new and original way which greatly reduces the computational effort. Simulation results for structures in various high frequency configurations are presented.