By using complementary rhombus resonator (CRR), a small-size and low-profile microstrip patch antenna (MPA) with broad bandwidth has been proposed. Parametric studies were conducted to illustrate the working principle of the proposed antenna. An additional resonance is introduced by the CRR to broaden the bandwidth. Compared with the MPA without the CRR, the bandwidth of the proposed antenna is increased by 200%. The measured results are in good agreements with the simulated ones, which demonstrate that this design provides a way to obtain the broadband antenna.

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An indirect approach based on phase measurement is proposed to measure the rotational Doppler frequency shift, which takes full advantage of the phase structure of orbital angular momentum (OAM) beams in radio domain, using a vector network analyzer (VNA) as a phase discriminator. A proof-of-concept experiment is established by an optical-controlled system with the OAM state of 1. By analyzing the experiment's results, the rotational Doppler frequency shift is measured as 24.83 Hz (max error rate 0.67%) at 50π rad/s rotational velocity, deducing the rotational velocity as 50.18π (average error rate 0.36%).

A magnetically tunable metamaterial perfect absorber (MPA) based on ferromagnetic resonance is experimentally and numerically demonstrated. The ferrite-based MPA is composed of an array of ferrite rods and a metallic ground plane. Frequency dependent absorption of the ferrite-based MPA under a series of applied magnetic fields is discussed. An absorption peak induced by ferromagnetic resonance appears in the range of 8–12 GHz under a certain magnetic field. Both the simulated and experimental results demonstrate that the absorption frequency of the ferrite-based MPA can be tuned by the applied magnetic field. This work provides an effective way to fabricate the magnetically tunable metamaterial perfect absorber.

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Electromagnetic waves carrying an orbital angular momentum (OAM) are of great interest. However, most OAM antennas present disadvantages such as a complicated structure, low efficiency, and large divergence angle, which prevents their practical applications. So far, there are few papers and research focuses on the problem of the divergence angle. Herein, a metasurface antenna is proposed to obtain the OAM beams with a small divergence angle. The circular arrangement and phase gradient were used to simplify the structure of the metasurface and obtain the small divergence angle, respectively. The proposed metasurface antenna presents a high transmission coefficient and effectively decreases the divergence angle of the OAM beam. All the theoretical analyses and derivation calculations were validated by both simulations and experiments. This compact structure paves the way to generate OAM beams with a small divergence angle.

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Orbital angular momentum (OAM) beams can be generated at many microwave frequencies by using antenna array. However, the complexity of the system and inability to transmit over long distances limit the applications of OAM beams in the radio domain. Here, a significantly simplified global positioning system (GPS) ceramic antenna array is employed to generate OAM beams without the assistance of phase shifting devices. Simulation of the GPS ceramic antenna array verifies that the OAM beams with the mode of ±1 show small divergence angle and very standard spiral phase distribution. To test the transmission capability of the proposed antenna array, a measurement system that can detect the onedimension spatial distribution of electromagnetic characteristic for the OAM beams is set up. Even considering the enormous loss in cables and power divider, the receiving antenna still can receive the electromagnetic characteristic of the OAM beams at a place more than 2 m away from the antenna array. Experimental results presented in this paper demonstrate the excellent performance of the OAM beams when generated with the proposed ceramic antenna array configuration.