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Orbital angular momentum (OAM) waves with different modes usually perform different divergence angles, leading to a big challenge and high complexity for signal receiving. To address this issue, this letter presents a novel antenna array generating four-mode OAM waves with equal divergence angle. In the proposed antenna, a center patch antenna and three concentric uniform circular arrays (UCAs) are employed to carry 0, -1, -2, and -3 OAM modes from center to outer rings, respectively. Each UCA is carefully optimized to control the different mode OAM waves to propagate along the same divergence angle. To validate the design, a C-band prototype generating 0, -1, -2, and -3 modes is fabricated and measured. Measured results show that the proposed four-mode OAM waves can be well generated. More importantly, the equal divergence angle for -1, -2, and -3 mode OAM waves is obtained as expected. This antenna array can provide equal divergence angle multimode OAM waves, which simplifies the receiving side in an OAM wireless communication system.
Qin et al. (Mon,) studied this question.