A Single-Layer Series-Fed SIW Slot Array Antenna Generating Two Orbital Angular Momentum Modes

A low-profile antenna capable of generating two coaxially propagating orbital angular momentum (OAM) modes is presented. It consists of two series-fed traveling-wave uniform circular arrays of sequentially rotated radiating slots and operates at 10 190 MHz. The smaller and larger radius arrays, with 4 and 8 radiating elements, produce OAM modes with indices
l^OAM
= 0 and +1, respectively. They are designed using a unique simulation-based step-by-step technique and implemented on a single layer of the substrate-integrated waveguide, resulting in a simple structure. The antenna's performance is evaluated using simulations and measurements, with a high agreement between the results. Both modes work in left-hand circular polarization, with the first mode having a gain and axial ratio measured bandwidth of about 5.9 and 3.9%, respectively. In addition, the measured impedance bandwidth for the first and second modes is around 8.2 and 7.9%, correspondingly. Also, the orthogonality bandwidth of two identical antennas set 28 cm apart in front of each other is roughly 4.5%. The antenna's far-field and near-field radiation patterns are also investigated.