A Concept of Advanced Design Governed by Theoretically Predicted Current Distributions on the Ground Plane Beneath an Aperture-Fed Microstrip Antenna

This work addresses a concern of aperture coupled microstrip patch which is commonly overlooked. Such feeding configuration is typically believed to be immune to high cross-polar (XP) radiations, which indeed is a paradox. It actually offers considerably low XP only across H-plane, but concerning high XP over its diagonal or skewed planes (azimuth $\approx 45^{\circ }$ -70°). An aperture feed, therefore, hardly reveals any advantageous feature in terms of the overall XP discrimination. Such a major shortcoming of aperture-fed microstrip, to the best of our knowledge, has been addressed and successfully resolved in this article for the first time. It explores a way of mitigating near field issues based on theoretical analysis and has proposed a simple strategic approach to reform the same for a rectangular patch. A representative design, theoretical justification, and experimental studies with an S-band prototype have been presented. XP suppression by 11dB has been experimentally achieved in the diagonal (D-) plane with no considerable changes in its H- or E-plane. That eventually attains an overall XP discrimination by nearly 27dB from the perspective of 3D radiation scenario. The proposed technique hardly affects the co-polar radiations or gain of its traditional design. Moreover, this is satisfactorily functioning for a $2\times 2$ sub-array with a remarkable co-to-cross isolation by about 34dB over the entire radiation planes.