First of all we inform the audiences that this article is a Review Paper (RP) for the PIERS17 Proceedings Paper (Zheng et al. ). The reason why we publish this RP is that: although the paper  reported important ideas and simulation facts, details of the contents were insufficient, and the audiences of the report were not satisfied. This was because the page number was limited, and we saved the number of pages. However, because the contents of~ are important, we decided to publish an RP, which would provide additional explanations or give considerations supporting main issues. Now, we start the abstract from Section~1. Here, we mention historical topics and RP-related things. In Section~2, we explain the problem of diffraction by a conically-mounted metal grating. To save the page number, we skip the method of solution. In Section~3, we explain our method in noise free case. We show the high precision of the quadratic (or parabola) approximation. We define the workspace (WS: relation between index range of a sample and a proper azimuth angle) and one-to-one correspondence between sample index and resonance angle. In Section~4, we try our method in a noisy environments. A curve-fitting procedure and three types of noise filters work to find satisfactory solutions. That is, in both 3. and 4., the resolution of the index is 7-digit usually, which is our target from the beginning. We think that the introduction of AI or statistical processing would increase the stability of the result. In Section~5, we mention some of future works. In APPENDIX A, we explain the method: How to find the azimuth angle, which we need in solving the diffraction problems by conically-mounted grating.
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