Abstract
This paper evaluates the performance of three-dimensionally (3D) printed spiral phase plates (SPPs) for enabling an orbital angular momentum (OAM) multiplexed radio system. The design and realization of the SPPs by means of additive manufacturing exploiting a high-permittivity material is described. Modes 1 and 2 SPPs are then evaluated at 15 GHz in terms of 3D complex radiation pattern, mode purity and beam collimation by means of a 3D printed dielectric lens. The results with the lens yield a crosstalk of −8 dB for between modes 1 and −1, and −11.4 dB for between modes 2 and −2. We suggest a mode multiplexer architecture that is expected to further reduce the crosstalk for each mode. An additional loss of 4.2 dB is incurred with the SPPs inserted into the communication link, which is undesirable for obtaining reliable LTE-based communications. Thus, we suggest: using lower loss materials, seeking ways to reduce material interface reflections or alternative ways of OAM multiplexing to realize a viable OAM multiplexed radio system.
Highlights
This paper evaluates the performance of three-dimensionally (3D) printed spiral phase plates (SPPs) for enabling an orbital angular momentum (OAM) multiplexed radio system
Each OAM mode is independent of the others, but in practice a level of inter-modal crosstalk occurs between each mode because of: coupling of RF signal paths; generator imperfections resulting in transmission of non-ideal modes; detector imperfections resulting in reduced discrimination between received modes; and multipath interference caused by poor link positioning or nearby objects causing field perturbations
These have been used for further analysis of directivity and OAM mode purity, which enables the level of crosstalk between modes to be determined
Summary
This paper evaluates the performance of three-dimensionally (3D) printed spiral phase plates (SPPs) for enabling an orbital angular momentum (OAM) multiplexed radio system. OAM radio continues to attract much research attention as several unanswered questions remain about maximum practical performance limits in the radio domain Improvements in aspects such as link distance, crosstalk and optimum network architecture are sought by the research community [4]. The divergence of the modes means that it is important to consider the power efficiency, or link budget and size of the receiving aperture. This is dominated by the solid angle subtended by the boresight null of each OAM mode in the multiplex.
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