.

$$\left ( \begin{array}{cccc} \alpha&\beta & 0 & 0\\ \beta &\a... ... \alpha & \beta \\ 0 & 0 & \beta & \alpha \end{array}\right )$$ (16)

and, at $\omega = \pi/2$ we have

$$\left ( \begin{array}{cccc} \alpha&0 & 0 & -\beta^h\\ 0 &\al... ... & \alpha & 0\\ -\beta^K & 0 & 0 & \alpha \end{array}\right )$$