OAM Mode Order Conversion and Clutter Rejection with OAM-Coded RFID Tags

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 ${m}_{n}\\\in \\\{\ldots-2-1012\ldots \}$ 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 $\{-11\}$ and $\{-20\}$ 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.