We discuss here under which conditions a periodic line with a twist-symmetric shape can\nbe replaced by an equivalent non-twist symmetric structure having the same dispersive behavior.\nTo this aim, we explain the effect of twist symmetry in terms of coupling among adjacent cells through\nhigher-order waveguide modes. We use several waveguide modes to accurately derive the dispersion\ndiagram of a line through a multimodal transmission matrix. With this method, we can calculate\nboth the phase and attenuation constants of Bloch modes, both in shielded and open structures.\nIn addition, we use the higher symmetry of these structures to further reduce the computational cost\nby restricting the analysis to a subunit cell of the structure instead of the entire unit cell. We confirm\nthe validity of our analysis by comparing our results with those of a commercial software.
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