Abstract
In this article, a uniform helically arranged dielectric resonator array can generate Orbital Angular Momentum waves (OAM) causing a conversion of OAM mode orders $m$ from an incoming mode ${m}_{in}$ to an outgoing mode ${m}_{out}$ . The operating frequency is set as 10 GHz to facilitate the measuring process. This new approach provides additional OAM values per digit in the RFID technology according to the excited OAM modes ${m}_{n}\,\,\in \,\,\{\ldots,-2,-1,0,1,2,\ldots \}$ instead of the conventional binary values ${b}_{n}~\in ~\{0, 1\}$ . Thus, more information content is revealed. Through the OAM concept, a ${m}_{1} {m}_{2}~2$ -digits OAM coded tag is obtained upon the employment of two uniform helically arranged cylindrical dielectric resonator arrays operating at two different frequencies ${f}_{1} = 10\,\,\text {GHz}$ , and ${f}_{2} = 11\,\,\text {GHz}$ . Each array has 8 DRs but with different radius yielding a reduction of the mutual coupling between the varied circular arrays. The interaction between the phase delayed radiation of each DR element in the array generates different vortex waves with corresponding OAM mode orders. In order to achieve the correct phase delay, the elevation of each DR is specified by the desirable OAM mode order, the number of elements and the propagation wavelength. At first, the generation of OAM mode orders −1, 2, and −3 is carried out. Then, mode conversion from 0 to −1, +1 to −2, −1 to 0, +2 to −3, and −2 to +1 are depicted. After that, two simulated examples of 2-digits OAM coded tags with the code $\{-1,1\}$ and $\{-2,0\}$ are presented. A conversion of mode 0 to mode 1 has been simulated and also measured, where an additional metal sheet is used to evaluate the distortion in the OAM modes. As a result, this study demonstrates that the uniform helically arranged DR arrays can convert the incoming OAM mode order into another one, where the clutter from broadside direction is rejected due to the Butler matrix (BM), which interferes the clutter destructively.
Highlights
R ADIO Frequency Identification Technology (RFID) offers a solution to the issue of the difficult distinction and identification of many articles where it can detect, locate, identify and track these items using radio waves
Orbital Angular Momentum waves (OAM) MODE CONVERSION The cylindrical dielectric resonators (DRs) mentioned in the previous section is used to form a helically arranged cylindrical DR array in order to re-radiate vortex waves once illuminated by an antenna
The maximum number of values per digit D in one circular array is based on the number of the DRs N, which determines the number of possible mode orders [28]
Summary
R ADIO Frequency Identification Technology (RFID) offers a solution to the issue of the difficult distinction and identification of many articles where it can detect, locate, identify and track these items using radio waves. Concerning the generation of vortex waves, there are many available ways such as metasurfaces [11], spiral phase plates (SPP) [12], holographic plates (HP) [13], elliptical patch antennas which excite two at the same time orthogonally oriented resonant mode patterns [14], [15], reflectors [16] or uniform circular patch arrays (UCA) [17]. These approaches do not discuss the limitations compared to MIMO systems [18].
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