Green’s functions for planar structures: Frequency domain versus time domain

A proper construction of Green´s functions for planar electromagnetic structures is the foremost task in the numerical analysis of microstrip antennas using integral equation techniques. In the paper, Green´s functions for a planar structure are formulated in the frequency domain and in the time domain. In the frequency domain, Sommerfeld type integrals are involved, and in the time domain, the Cagniard-de Hoop method is applied. In order to reduce high computational demands, approximate Green´s functions are frequently used. Near-field approximations of Green´s functions are presented and compared with rigorous Green´s functions to check their accuracy.