The application of lumped element equivalent circuits approach to the design of single-port microstrip antennas

A simple method for inverting negative resistances of nonphysical circuits generated from approximating rational functions through vector fitting is proposed. This technique is applied to three resonant antenna structures. The challenge of applying this method to these structures lies in the accurate modeling of the ways in which the different resonant modes are excited, some via coaxially feeding a rectangular patch along the diagonal, while others via capacitively coupling energy from the driven patch to a parasitic patch. The equivalent circuits of these designs produce scattering parameter results that are consistent with the fitted functions: This methodology of resistance invertibility is a great tool that can be used to model antenna designs with low order equivalent circuits, drastically reducing the design time. In addition, valuable information that could aid in the optimization of microstrip antennas can be quickly ascertained through these techniques.