Eigenvalue position determination method is unreliable near singular frequencies

[grwei]

Describe the bug

The relative position of the eigenvalues cannot be maintained near singular frequencies, which may introduce artificial phase discontinuities and reduce the reliability of subsequent steps (for example, #3 ).

To Reproduce

Steps to reproduce the behavior:

1. Includes all frequency points, then view Figure gammaLenEigWrap or Figure gammaEigUnwrap.
2. Remove singular frequency points, then view Figure gammaLenEigWrap or Figure gammaEigUnwrap.
3. Note that the order of Eigenvalue in the two cases is different. At the same time, Figure prodTable figure shows that intermediate values appear near the singular frequency points, which may be the direct cause of this error.

Expected behavior

• The curve in Figure gammaEigUnwrap increases smoothly with increasing frequency
• The curve in FiguregammaLenEigWrap is smooth in any single period
• The data points in Figure prodTable should either be close to 0, or close to 1.

Desktop (please complete the following information):

• Number of lines (excluding reference lines): 4
• Type of input network parameters: Scattering parameters
• Number of singular intervals: 1

Additional context

If removing the singular frequency interval does not affect the parameter extraction result of the non-singular interval, then the singular frequency points can be safely removed from the input data. Future works should be focused on (refer to #1 ):

• Criterion for singular frequency
• Sufficient condition that singular frequency interval does not affect non-singular interval
• Interpolation method for singular frequency intervals