Transformed mathematical model of square microstrip antennas for non-sinusoidal harmonic response

In this paper, square microstrip antennas (SMSAs) are presented from a new perspective. Instead of a special case of a rectangular microstrip antenna, SMSAs are described as an independent configuration with exclusive characteristics. Based on the location of the feed point, the nature of the harmonics of SMSAs is transformed from sinusoidal to cylindrical, wherein the harmonics are not an integral multiple of a fundamental frequency. The non-sinusoidal response obtained from the SMSAs is described by a mathematical model, and an expression for the resonance frequency of cylindrical harmonics is derived. A method is proposed to achieve two different types of responses from SMSAs, depending upon the feed point location. The accuracy of the proposed theory and expression is validated with simulated and measured results.