Equivalent Circuit Models of Finite Slot Antennas

We present a systematic approach to describe planar slot antennas embedded in generic stratified media. An equivalent transmission line model for the slot is proposed, based on a spectral domain analysis. First, we introduce a method of moments solution to model semiinfinite or finite slots, fed by a delta-gap excitation. The solution entails only two basis functions, one located at the feed and the other at the termination. The latter basis function is chosen to properly account for the field diffractive behavior at the antenna end points. An approximate circuit model is then introduced, which describes the main mode propagating along the slot as an equivalent transmission line. Lumped impedances are extracted to accurately describe the source and the end points: the reactances account for the reactive nature of the feed and the termination, while the resistances represent the radiated space waves, emerging from both the feed and the end points. This procedure can be used to derive the input impedance of planar slot antennas with arbitrary length in generic layered media or the interaction between multiple feeds within the same slot.