Inter Mode Interference in Circular Antenna Arrays for Orbital Angular Momentum (OAM) Based Communication

Abstract

Optimization of antenna arrays is essential to achieve high data rates in modern communication systems. One promising array used in future communication systems is the uniform circular array (UCA) carrying orbital angular momentum (OAM) modes. In a UCA, the array elements are arranged in a circle with uniform angular spacing. The OAM modes are defined by the excitation of an array, i.e. an OAM mode is excited by exciting each element with equal amplitude and a phase increasing linearly around the array. When one OAM mode is excited and another OAM mode is received, this is called inter mode interference (IMI). Within an array this could be caused by a non-symmetrical array structure. In this paper, the IMI of non-symmetrical UCAs operating OAM waves is explored with comparison to the symmetrical UCA. It is shown, that change in geometric deviation along the array can be used to determine the dominant IMI, which allows the prediction of the IMI when designing an OAM array. These predictions are validated using an elliptical array and an array with misaligned elements. Knowledge of the IMI caused by a geometrical deviation can be used in the future to prevent or correct this IMI.