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

Abstract

SummaryUtilization 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.

Near-field formation of the UCA-based OAM EM fields and short-range EM power flux profiles

“…The local OAM wave's P z maxima positioned most far away from the source plane are denoted in figure 7(a) by ℓ = 1, ℓ = 2, ℓ = 3, and ℓ = 4. In [26], we have analytically estimated the optimal link range based on the spreading cone of EM field maxima, given here as equation (9). The analytically estimated optimal receiving distance, z L,opt , for each mode, matches very well with the P z maxima positioned most far away from the source plane.…”

“…Such investigations will be conducted as a part of our future work. To facilitate comparison with other similar investigations, the longitudinal distances, z, were reported as the multiples of Rayleigh distance, z R , which for the OAM UCA was approximated as [26]…”

“…We have previously defined [26] the optimal link range for the short-range point-to-point and point-to-multipoint wireless communications using the OAM waves, as the distance enabling the reception in the regions of the EM field maxima. Based on the known expressions for the vortex angle θ v [30], and assuming equal transmitting and receiving OAM array radius, R a , the optimal link range equals…”

“…Therefore, the receiving distance should preferably be set at z L,opt or somewhat larger distance where the EM fields have not yet decreased too much. In practice, as discussed in [26], a design approach where the desired link range is set first seems promising, as the sizes of the receiving OAM UCA arrays could then be estimated to enable near-optimal EM wave reception at the same link range distance for multiple OAM modes. It should be noted that (9) corresponds to the case of an equally sized transmitting and receiving array, R rec = R a , while in the most general case, we would have to consider separately for each OAM mode [26], that…”

“…The turbulence-induced crosstalk between the modes has been studied analytically in [20]. Many of the previous investigations [21][22][23][24][25][26], have already pointed toward the most probable utility of OAM UCA in short-range communications. However, there is still a lack of in-depth investigations into the properties of such short-range OAM wave transmission.…”