Optimized planar printed UCA configurations for OAM waves and the associated OAM mode content at the receiver

Utilization of planar printed uniform circular antenna arrays (UCA) to generate the orbital angular momentum (OAM) carrying waves in the millimeter-wave (mmWave) frequency band is advantageous from the viewpoints of easy signal modulation and mode reconfiguration, low cost, low profile, and straightforward integration with the existing broadband wireless infrastructure. The OAM mmWave UCA are highly promising as the enablers of very high transmission data rates required by hybrid 5G/6G optical and wireless communication systems by complementing and enhancing other technologies currently in use. Therefore, we here contribute a detailed electromagnetic analysis of important constraints of such antenna arrangements aimed at short-range multimode OAM wave transmission. We investigate (i) the required antenna array dimensions and optimized UCA arrangements for a particular link range and (ii) the corresponding mode structure of OAM waves in the plane of receiving arrays. Four relatively simple antenna configurations operating in the 60-GHz band are compared. Theoretical assumptions based on ideal OAM modes are critically assessed and, using state-of-the-art numerical electromagnetic analysis, compared to realistically generated OAM waves. The proposed "cyclic transmission setup" resulted in much lower unwanted field components in the region of receiving arrays. RMS magnitudes of unwanted modes are on average about 64% of the received mode, in comparison with 80% (up to 94%) for sequential transmission. The observed mode impurities and mode mixing effects at the receiver indicate the need to dedicate more attention to the system-level design, the development of efficient receiving arrays, the MIMO processing, and the stream separation. We present the system-level design and important design constraints of uniform circular antenna array (UCA) arrangements aimed at short-range multimode OAM wave transmission, in terms of (i) the required antenna array dimensions and optimized UCA arrangements for a particular link range and (ii) the corresponding mode structure of OAM waves in the plane of receiving arrays. State-of-the-art numerical electromagnetic analysis based on the method of moments is used for the assessment of various OAM antenna configurations operating in the 60-GHz band.image