To suppress the deep fading of radio waves caused by the tunnel waveguide effect, this paper presents an optimized scheme for the spatial and polarization diversities of tunnel antennas. Through the correlation coefficient analysis of path loss curves obtained by antennas placed at different positions, the two antenna positions that generate path loss curves with the lowest correlation coefficient are found, and these two antennas are defined as a diversity antenna pair. Using this scheme, the spatial diversity properties of the transmitting antenna and receiving antenna, as well as the spatial-polarization combined diversity property of the transmitting antenna, are obtained. Furthermore, the impact of antenna polarization on the spatial diversity property is investigated. The performance of the proposed scheme for spatial and polarization diversities is evaluated in terms of the intensity and uniformity of the path loss. The simulation results illustrate that the proposed diversity optimization scheme can suppress the influence of the waveguide effect and achieve more uniform and flatter radio wave coverage in a tunnel environment.
In this paper, a smart antenna array based on the image-aware technique that can automatically switch its beam to track users is proposed. Mobilenet, a deep neural network (DNN), is utilized to find the users' position information from images; it is trained using the collected dataset, and the parameters are optimized. The modified DNN is then implanted into a miniaturized embedded system RK3399. To obtain beam switchable radiation, a 2×2 microstrip patch antenna array with a 4×4 Butler feeding matrix is designed in the 2.4 GHz ISM band. Then, the RK3399 is compactly integrated with the patch antenna array, and a microcamera is used as the eye of the antenna to capture the environment information. A series of measurements of the received power and error vector magnitude (EVM) are performed in a real indoor scenario to verify the design. The results agree well with the expected results and show that the design is capable of guaranteeing communication quality and improving energy efficiency, making this technique a good candidate for indoor wireless applications. INDEX TERMS Automatic beam switching, butler matrix, deep neural network, error vector magnitude, smart antenna.
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