Measurement and Analysis of Millimetre-Wave OAM Reflection Characteristics Under the Action of Indoor Building Materials

Orbital angular momentum (OAM) communication is considered as a potential key technology for the sixth generation (6G) mobile communication system. To fully understand and characterize the propagation properties of OAM waves, such as reflection and transmission, in the indoor multipath propagation and the interaction with building materials, OAM channel modeling and target detection can be achieved. However, the special spiral phase wavefront structure of OAM creates divergence, which makes the theoretical study of OAM wave propagation characteristics and channel modeling face great challenges. In this paper, a measurement campaign is carried out in the 38 GHz band to measure the reflection of OAM waves on various building materials, such as glass, wood panels, and PVC, and to analyze the results of the received power angular spectra and propagation coefficients. The reflection curves of OAM and plane waves are compared, and the mean square error (MAE) between the theoretical Fresnel propagation coefficients and the measured values are calculated. The results show that with the introduction of OAM wave modes, it is difficult for the classical propagation model to accurately describe the propagation characteristics of OAM waves. Based on this, a Bessel modified propagation model is proposed in this paper, which introduces the fluctuation component in the OAM primary reflection path, accurately expresses the fluctuation of OAM waves in real situations, and calculates the error between the modified OAM propagation model and the measured values, which is better than the classical model, and lays a foundation for the further modification of the OAM propagation model by utilizing the actual data of OAM propagation. The results show that it is better than the classical model.