Continuous-Aperture OAM Communication Systems: An Electromagnetic Information Theory Perspective

We present a novel continuous-aperture orbital angular momentum (CAP-OAM) communication system, which can be regarded as an asymptotic generalization of existing (discrete) uniform circular array-based OAM (UCA-OAM) systems. We first derive the current distribution that generates OAM mode in the CAP-OAM transmitter and specify the resulting radiated electric field. We characterize a closed-form equivalent discrete wireless channel model of the CAP-OAM system, which rigorously captures the effect of various system parameters, including path loss, carrier frequency, antenna aperture size, transmission distance, polarization interferences, etc. We also define the effective degrees of freedom (DoF) and mathematically analyze the achievable rate of CAP-OAM systems. Through computer simulations, we confirm that the CAP-OAM system significantly outperforms the classical UCA-OAM system in terms of achievable rates and effective DoF. To the best of our knowledge, CAP-OAM communication systems have not been investigated from the perspective of electromagnetic information theory.