Abstract
In this letter, a helical slot antenna for generating multiple orbital angular momentum (OAM) modes is proposed. The proposed antenna consists of four concentric helical slot array antennas, which are excited by an annular microstrip line. The number of each helical slot, and length of microstrip feed are chosen to create circularly polarized OAM modes of 0, −1, −2, and −3 at 3.5 GHz frequency with more than 10% fractional bandwidth. The final multimode antenna has 89 mm in diameter and 19.1 mm in height. A prototype of the proposed compact antenna is fabricated. From the simulation and measurement results, prominent spiral phase planes are observed at all antenna ports. Both the measurement and simulation results show that the proposed compact antenna has valuable features to produce different vortex modes.
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