| Summary: | Compared with the orbital angular momentum (OAM) wave whose 3D radiation pattern is a central-hollowed cone, the plane spiral orbital angular momentum (PSOAM) wave propagates along the transverse direction, which is far more convenient for practical applications. In this paper, traditional microstrip Yagi antennas are formed into a uniform circular array (UCA) to radiate PSOAM electromagnetic waves, which has the outstanding advantage of a flat structure. Firstly, the fundamentals of generating PSOAM by microstrip Yagi antenna array is introduced. Secondly, a circular microstrip Yagi PSOAM antenna array fed by a self-designed Wilkinson feeding network is designed, fabricated and measured. Eight microstrip Yagi antenna elements and its feeding network are printed on the upper and lower substrate, respectively. The profile of the proposed antenna is only $0.16\lambda _{0} $ , lower than other PSOAM antennas, which is convenient for integration with wireless communication systems. Both simulation and measurement results depict that it is capable of generating PSOAM with mode number $l=3$ on 3.43GHz. From 3.15GHZ to 3.65GHZ, the vortex electromagnetic wave of $l=3$ can be observed. The proposed microstrip Yagi antenna based on UCA provides a new way for the research of practical PSOAM antennas, has broad prospect in the future of the reconfigurable field.
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