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This study presents a novel radial uniform circular array (UCA) antenna for quad‐mode orbital angular momentum (OAM) multiplexing in the 5.2 GHz band. The antenna can simultaneously generate four OAM modes (±1, ±2) using two radial UCAs printed concentrically on a single substrate. Each UCA is connected to an individual dual‐mode feeding network, and generates a pair of complementary OAM modes. The feeding network for each UCA consists of one quadrature hybrid coupler and two circular feedlines, and they can be integrated onto a single substrate. The measured radiation patterns and helical phase wavefronts show the successful generation of four OAM modes by the proposed antenna. The quad‐mode OAM transmission test was performed using two prototypes of the proposed antenna, and good isolations >13.7 dB were obtained between four OAM mode channels, which demonstrates that the antenna can be successfully used for OAM multiplexing.

We propose a new concept millimetre‐wave patch antenna that integrates the functions of an antenna and a capacitive proximity sensor to detect the hand grip state for 5G mobile terminals and compensate for the hand effect. The proposed antenna has the structure of a proximity‐coupled fed patch and functions as a proximity sensor by using the capacitance change of the patch that occurs when the user's hand approaches the patch. By observing the capacitance change at the centre of the patch operating in the TM01 mode, it is possible to simultaneously perform the functions of antenna and sensor without mutual interference. The proposed antenna is implemented as a 1 × 4 array. The experimental results show that it has a stable gain of 8.3 to 10.1 dBi at 26.5 to 29.5 GHz and can operate as a proximity sensor with a capacitance change of 200 fF according to the proximity of the hand.

In this paper, we propose a uniform circular array antenna with a simple feeding structure operating in the 5.2 GHz band for orbital angular momentum (OAM) mode multiplexing. The proposed antenna can generate simultaneously two types of OAM modes (l=±2) using eight radiating patches and a feed circuit consisting of one hybrid coupler and two concentric series-parallel feedlines. Because the two feedlines are designed concentrically with different radii, they do not intersect each other in the same plane, thus having the advantage of being spatially efficient. The successful creation of the two OAM modes was confirmed through the measured radiation pattern and helical phase distribution. The dual-mode OAM transmission test shows that the proposed antenna can be successfully employed for OAM mode multiplexing by obtaining >12.4 dB of isolation between the two OAM mode channels.

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