The Vertically Asymmetric X-Structure

The asymmetric factor of the X-structure can provide another factor for tuning the nonlinearity created by the X-structure. It is also noted that asymmetric X-structures could be more flexible in practical applications due to space restrictions in some application scenarios. Therefore, asymmetric X-structures are further investigated, as the asymmetry can be in the horizontal way as that in Chap. 3 , and also be in the vertical way or in an arbitrary manner. For the vertical way, it can also be divided into several cases due to modelling complexity, and it would be more challenging to consider an arbitrary asymmetric X-structure although a single-layer asymmetric X-structure is feasible.