It has been demonstrated that a microstrip antenna excited in a non-degenerate resonant mode has a driving point impedance which can be modeled as a resonant parallel R-L-C circuit in series with the an inductor. The latter is an inductance which can be associated with the feeding probe or microstrip line feed of the antenna. This paper investigates the variation with feed location of this inductive component both experimentally and by a full modal expansion of the field using the “cavity model”. The results demonstrate that the simple, feed position-independent formula for this inductive component is inadequate for certain applications involving loaded microstrip elements. The results also show that the cavity model can predict the variation of feed inductance with feed location reasonably well except near the edge of the patch. The physical mechanism for the variation of this inductive component as well as the physical reason why the cavity model overestimates this parameter with feeds near the edge are presented. A rigorous model of a coaxial feed is studied in which the primary exciting field is assumed to be an incident TEM wave in the cable. It is found that for elements thin enough for the cavity model to be applicable, use of the probe current distribution alone as the primary source yields impedances which differ only slightly from those provided by the rigorous model. However, other results are obtained which indicate the limits of such a simple feed model as the element thickness increases.