plane, with dielectric layers between radiating and capacitor patch
and between capacitor patch and ground plane. The configuration
is defined in Fig. 1.Using the mixed potential integral expression
scheme of , the integral equations are obtained. They are solved
with a moment method procedure. The details of this procedure are
well-known [4]-[7]. It suffices to say that a subsectional expansion
scheme is used combining rooftop functions with the edge expansion
functions of [SI at the edges and in the comers. They satisfy the edge
conditions, which results in an enhancement of the convergence of
the resonant frequency in terms of the number of expansion functions.
It has to be emphasized that, due to the fact that the capacitor patch
is far from its resonance, the use of subsectional expansion functions
is much more efficient than the use of entire domain expansion
functions. The rigorous model described in [4], [9], and [lo] is used
for the coaxial feed.
In order to establish the accuracy of the model, calculated and
measured results have to be compared. Since no publications were
found with measurements of the capacitively fed microstrip patch,
we looked for other stacked patch configurations for which our
model can be used. The analysis of the thick dual patch microstrip
antenna of [l] with our model yields good agreement between
calculations and measurements. These results are already published
in [4]. Additionally, own experiments were performed. The objective
was to obtain highly accurate results suited for comparison. Since the
permittivities of dielectric substrates are known with an accuracy of
typically a few percent, the goal of high accuracy means that the use
of air as well-known dielectric was mandatory