Improving Orbital Angular Momentum Mode Utilization With Mode Switching Periodically in Radar Forward-Looking Imaging

The infinity and orthogonality of the orbital angular momentum (OAM) of vortex electromagnetic waves (VEMWs) provide a new degree of freedom for the modulation of information. The VEMW generated by the uniform circular array (UCA) exhibits the characteristics of the Bessel function in terms of amplitude, and there is a null amplitude region in the beam center. This characteristic is particularly obvious when the array radius is small. In practical applications, it is usually necessary to switch OAM mode to ensure the richness of the received information. This leads to a sudden drop in radiation energy when switching OAM modes, and the OAM mode cannot be fully utilized. To address this issue, this letter proposes an OAM mode switching method based on the characteristics of the intersection of the adjacent-order Bessel functions for radar forward-looking imaging. Meanwhile, this letter introduces OAM mode repetition frequency (OMRF) to indicate the “speed” of switching OAM mode. Finally, through the application in the field of forward-looking radar imaging, it is proved that the method proposed in this letter can effectively improve the OAM mode utilization rate and anti-noise ability.