5G mmWave broadcasting is considered to be the main method of future broadcasting. However, the mmWave transmission has a large space loss, especially in tunnels. In order to compensate for the attenuation of the broadcast signal, a directional horn antenna is designed in this paper. Substrate integrated waveguide (SIW) technology, dual-element arrays and extension structures are used to improve the antenna structure and achieve good directional characteristics. The multi-objective genetic algorithm (MOGA) is used to optimize the antenna parameters and improve optimization efficiency. Ultimately, the whole antenna was 28.2 mm in length and 28.6 mm in width, and the FR4 material, with a relative permittivity of 4.4, was used as a dielectric plate. The maximum gain of the antenna is 8.06 dB, and the bandwidth with gain greater than 6.5 dB is nearly 2 GHz. Antenna performance simulation and test results show that the extended semicircular structure is beneficial in enhancing the directional radiation of the antenna. This provides a reference method for directional antennas applied to 5G millimeter wave bands to increase gain and narrow beams.

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Today’s power systems are developing from traditional multi-sensor systems to ubiquitous power Internet of Things systems. The environmental backscatter technology makes communication equipment get rid of the dependence on power supply, is more energy-efficient, and effectively extends the communication distance, which is very suitable for power Internet of Things scenarios. Tag antenna is an important part of environmental backscattering, but it has problems such as low reliability and insufficient reading distance in the traditional power Internet of Things. In view of the above problems, this paper designs a double-antenna structure tag antenna, which adopts omnidirectional receiving and directional transmitting methods to achieve the purpose of comprehensive signal coverage for the power Internet of Things application scenarios. It has the characteristics of obvious gain, small side lobe, and strong anti-interference.

An increase in the quantity and density of antenna elements increases the mismatched failure rate and measurement difficulty of the multiple-input multiple-output. To simplify the measurement method of the S11 parameter utilizing the traditional vector network analyzer, this article proposes a multiple-input multiple-output measurement method based on microwave imaging. The multiple-input multiple-output element was designed, and then the existence of mismatched scattering of the mismatched state through microwave one-dimensional and two-dimensional imaging simulations was verified. A wideband Vivaldi antenna was designed for measurement imaging verification. The research results show that the proposed method is capable of detecting the mismatched scattering of mismatched elements as well as accurately locating the mismatched elements and mismatched position of circuits behind the element, which improves the measurement efficiency.

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