Circular Polarization and Mode Reconfigurable Wideband Orbital Angular Momentum Patch Array Antenna

Abstract

A circular polarization (CP) and mode reconfigurable wideband orbital angular momentum (OAM) patch array antenna is presented. The proposed design is based on a reconfigurable feed network (RFN), a direct current (dc) bias circuit, and a $2 \times 2$ patch array. By changing the dc bias voltages of p-i-n didoes, the operating state of the antenna can be reconfigured between the left-hand CP with a mode $l = +1$ and right-hand CP (RHCP) with a mode $l = -1$ , over the wide impedance bandwidth of 21%. For the two states, the measured peak gains are larger than 5.3 and 5.2 dBi, and the axial ratios in half-power main beam directions are lower than 1.29 and 1.05 dB, respectively. Different from existing OAM antennas, the diversities of polarization, frequency, and mode, as well as the CP with inherently high cross-polarization discrimination are simultaneously integrated in the proposed antenna, which serves as a good basis for improving the capacity and spectral efficiency of radio systems. In addition, the antenna features single-external input port, a simple RFN occupying a small number of diodes, and a compact size of $1.28 \times 1.28 \times 0.07 \lambda _{0}^{3}$ ( $\lambda _{0}$ is the free-space wavelength at center frequency), all of which ease implementation and reduce fabrication cost. Therefore, the proposed antenna is very promising for modern high-speed and large capacity wireless communication systems.