| Summary: | In this paper, a water antenna has been designed to generate tunable orbital angular momentum (OAM) vortex wave. With a revisiting theoretical analysis about radiation characteristic of the shorted ring patch fed by two probes, a frequency dependent single shorted ring water antenna is designed. With the increase of the operating frequency, the single-ring water antenna can radiate the OAM waves with the changeable modes. Furthermore, a dual shorted ring water antenna is proposed. With a tunable feeding network, the OAM waves with the reconfigurable modes including the l = 1, l = 2 and mixed modes can be radiated by adjusting ON/OFF states of the PIN diode. The prototype of the dual-ring water antenna is fabricated and measured. Good agreement between the simulation and the measurement demonstrates that the overlapped bandwidth for three states covers 2.35~2.55 GHz with a good mode purity.
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