This paper gives a feasible and simple solution of generating OAM-carrying radio beams. Eight Vivaldi antenna elements connect sequentially and fold into a hollow cylinder. The circular Vivaldi antenna array is fed with unit amplitude but with a successive phase difference from element to element. By changing the phase difference at the steps of 0, ±45°, ±90°, ±135°, and 180°, the OAM radio beam can be generated with mode numbers 0, ±1, ±2, ±3, and 4. Simulations show that the OAM states of ±2 and ±3 are the same as the traditional states, while the OAM states of 0, ±1, and 4 differ at the boresight. This phenomenon can be explained by the radiation pattern difference between Vivaldi antenna and tripole antenna. A solution of distinguishing OAM states is also proposed. The mode number of OAM can be distinguished with only 2 receivers.

A low-cost beam-steerable antenna operating at 28 GHz is presented for 5G mobile terminal applications. The proposed array has a sandwich-like stack structure, including ten patch elements, a ground plane with two rows of slots, and a long microstrip transmission feed line. The radiators and the transmission line are placed at the two sides of the ground plane, which provides great flexibility in designing the radiating pattern and the feed network. Switches are added on the transmission line to construct periodic distributed phase shifters for beam steering. 2-bit phase shifter with phases of 0°, 90°, 180°, 270° is formed without using phase delay lines. Continuous beam steering is achieved, and the steerable angle is 121° in the upper hemisphere. Two location configurations of the proposed array in 5G mobile terminals are analyzed and the angular coverage range is evaluated. The array can cover 38.8% of the hemispherical space with a gain threshold of 10 dBi.

In this paper, a dual-polarized 2-bit electronically reconfigurable reflectarray (RRA) is proposed for 5G beam scanning applications. By introducing two parallel transmission lines and a T-junction, only two p-i-n diodes are used to generate 2-bit phase quantization is analyzed and verified. Based on this concept, a novel 2-bit dual-polarized RRA element is presented that makes use of an aperture-coupled patch and microstrip delay lines behind its ground plane. Only two p-i-n diodes are loaded on each delay line to realize the 2-bit phase quantization. Two orthogonal linear polarizations are independently controlled by deploying two perpendicular coupling slots and two delay lines. A 16×16 RRA prototype is fabricated and tested at 3.6 GHz. The measurement and simulation results show good agreement. Both polarizations can provide a ±60° 2-D beam scanning range with a maximum scanning gain drop of 2.75 dB. The maximum measured gain is 23.11 dBi, which corresponds to an aperture efficiency of 40.56%. A 1-dB measured gain bandwidth of 8.06% is also achieved.

A high efficiency mobile terminal antenna with small ground clearance is presented in this paper. It consists of a chassis ground, an unbroken metal bezel, and two connecting metal strips. The theory of characteristic modes is applied to analyze the eigenmodes of the design in the frequency range of 600–3000 MHz. All the resonant modes are clearly tracked and identified. Each mode of the bezel has the even and odd states and can be illustrated by a two-slot model. The multiple modes of the bezel can be effectively excited by a simple probe. By changing the locations of the connecting strips and feeder and introducing an inductor, two fundamental modes and four higher order modes of the bezel are merged, providing sufficient bandwidth for mobile communication. The measured −6 dB bandwidths are 805–995 and 1340–2870 MHz, and the measured radiation efficiency is above 65% in both bands.