In the last five years or so, there has been a great interest in RF OAM to address the contradiction between the lack of wireless spectrum resources and the continually growing demands of the bandwidth. Recent developments and technological advancements in antenna design, material science, and integrated circuits have enabled miniaturized, multiple modes, tunable in radio frequency (RF) orbital angular momentum (OAM) antenna designs. From conventional methods such as spiral phase plate and reflector antenna to antenna array and metasurface, the working principle and structures are introduced. To improve the performance of RF OAM antennas, several innovative physical concepts have been explored for the designs of RF OAM antenna designs. In this paper, we present an up-to-date survey on the development of RF OAM antenna technologies. Open issues and development trends are explored as a source of inspiration towards the future better outcome of RF OAM antenna designs.

Microwave radomes exhibiting bandpass behavior are highly desirable for antenna systems. However, most of these radomes are not frequency switchable owing to their fixed structures. Here, a switchable metasurface based on complementary diamond-ring-shaped resonators is proposed for radomes. The microwave properties of the metasurface are investigated via simulations and experiments at X-band. By adjusting the rotation angle θ from 0° to 90°, the bandpass frequency is switched from 11.0 to 9.4 GHz. Two passbands appear for 0° <; θ <; 90°. In addition, the bandwidth can also be tuned by adjusting the rotation angle. This approach paves the way for designing switchable microwave radomes.

In this paper, we propose a wideband F-shaped microstrip antenna. The proposed antenna is compact with a dimension of 18×22×1 mm3, which is a benefit for the miniaturization of the antenna system. The electromagnetic properties of the antenna are analyzed with the software CST microwave studio and the measurements are performed by using a vector network analyzer. By means of a structural parameters optimization, a 15 to 19 GHz frequency range for a reflection coefficient less than -10 dB is obtained. In addition, an antenna array is designed and fabricated. The experimental results demonstrate that the proposed antenna array has a good performance in generating orbital angular momentum beam.

The dependency on feed horn of the metasurface leads to an increased physical profile and energy dissipation, posing challenges to system miniaturization and integration. To tackle this problem, a metasurface antenna with low profile, fast programmability, and flexible wavefronts reconfiguration capability is proposed. By integrating the transmissive metasurface with a planar array antenna, a 4.64λ ₀ × 4.64λ ₀ antenna operating over 5.77-5.83 GHz is realized with a thickness of 0.54λ ₀ . The planar feeding design reduces the total antenna height by approximately 99% compared to the conventional programmable metasurface. Experimental results have demonstrated that the presented antenna can achieve ±60° beam steering. In addition, a simple antenna-based wireless communication platform is established, allowing for direct nonlinear harmonic modulation and information transmission without mixing devices. The proposed programmable metasurface antenna opens a new avenue to advance compact and efficient applications across diverse fields, including satellite communications, IoT devices, and smart city infrastructure.