Ip. Theron et Jh. Cloete, ON THE SURFACE IMPEDANCE USED TO MODEL THE CONDUCTOR LOSSES OF MICROSTRIP STRUCTURES, IEE proceedings. Microwaves, antennas and propagation, 142(1), 1995, pp. 35-40
In the numerical analysis of microstrip structures their finite conduc
tivity is often modelled by using an equivalent surface impedance to r
elate the nonzero tangential electric field on the conductor surface t
o an equivalent electric surface current. The fields on top and below
the patch are not necessarily the same and to account for this discont
inuous tangential electric field a strict equivalence formulation shou
ld include magnetic surface currents. However, it is common practice t
o neglect them, presumably because they considerably complicate the su
rface integral equation and its numerical solution. Here it is shown t
hat this practice leads to the use of an incorrect, although conservat
ive, surface impedance. A basic assumption is that delta much-less-tha
n DELTA much-less-than lambda, with delta the skin depth, DELTA the co
nductor thickness, and lambda the free space wavelength.