Double-OAM-mode resistor loaded microstrip antenna with a top dielectric layer

Abstract

A double-Orbital-Angular-Momentum (OAM)-mode microstrip antenna is designed, simulated, fabricated and measured, which generates OAM with mode number l=2 and 3 on 5GHz by two resistor loaded microstrip rings respectively. For existing OAM antennas, structures like circular array, parabolic reflector and electromagnetic meta-surface are widely adopted, which are electrically large and hard to be integrated. However, the proposed antenna has a compact size and a low profile, which can be integrated in RF circuit as a component. To solve the problem of low gain in microstrip OAM antenna, parameters are optimised and a top dielectric layer is adopted, and its measured peak gain reaches 1.5dB for l=2 and 1.8dB for l=3. The measured frequency band, on which a near field vortex phase is observed and orbital angular momentum is generated, is 4.65-5.25GHz for l=2, and 4.5-5.2GHz for l=3. Besides, this antenna can multiplex more OAM modes by adopting more microstrip rings.