Generation of Higher-Order OAM Waves With Single-Point Fed Circular Microstrip Antenna Using Bifurcated Cylindrical Harmonics

EM waves with finite orbital angular momentum (OAM) have shown potential for a dramatic increment in the RF channel capacities. Generation of OAM waves using microstrip antennas makes the most economical configuration and thus can further boost the research toward realization of RF OAM channels. So far, all such microstrip configurations that generate OAM waves require more than one feed, especially for modes higher than the fundamental. This article gives a new and simple OAM antenna design method for radiating OAM waves of desired topological charge using a direct single point feed connected to a circular microstrip antenna (CMA) for corresponding mode. The presented method manipulates cylindrical harmonics using tiny modifications in the CMA. Subsequently, a generalized equivalent circuit model has been given for the same. Additionally, the presented method has also been qualitatively extended to annular ring microstrip antennas (ARMAs). Simulated and measured results have been presented to corroborate the proposed concept.