Abstract
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.
Highlights
As communication technology evolves rapidly, the contradiction between finite electromagnetic spectrum resources and continuously increasing bandwidth requirements has become increasingly prominent [1], [2]
In 2015, [21] proposed the concept of plane spiral orbital angular momentum waves at the first time whose 3D radiation pattern has the characteristics of side-fire, which is far more convenient for receiving and multiplexing in practical applications
The microstrip Yagi uniform circular array antenna generating plane spiral orbital angular momentum (PSOAM) wave fed by a self-designed 1-to-8 Wilkinson power divider is designed, fabricated, and measured
Summary
As communication technology evolves rapidly, the contradiction between finite electromagnetic spectrum resources and continuously increasing bandwidth requirements has become increasingly prominent [1], [2]. In 2015, [21] proposed the concept of plane spiral orbital angular momentum waves at the first time whose 3D radiation pattern has the characteristics of side-fire, which is far more convenient for receiving and multiplexing in practical applications This means that compared with OAM waves transmitting along the main axis, the plane spiral OAM propagates along the transverse direction, which can be used as an effective method to solve the problem of beam divergence existing in OAM. Where Jl(2π aλ sin θ ) is the lth-order Bessel function of the first kind, aλ = a/λ, λis the working wavelength of CAA in vacuum, and k = 2π/λ is wave number It can be derived from (6) that the field radiation pattern factor contains the vortex phase factor ejlφ, which demonstrates that vortex beams carrying OAM can be generated by controlling the excitation phase of the array element.
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