• Vivaldi slot

Besides the A, B and C clusters being similar to the slot line edge response, along the Vivaldi edge, the first-order scattering components affect significantly to the propagation process. Particularly, scattering of the A and B clusters at the transition positions forms a series of clusters, such as the F and G clusters illustrated in **Figure 16**. Additionally, the C cluster is also scattered at these transition positions when traveling in the �*l* direction. This disperses the EM energy and leads to a reduction in C and E clusters' intensities when compared with the A cluster. The scattering at the transition points and Vivaldi curve deflection in the þ*y=* � *y* directions also affect the A cluster. The cluster width increases and its peaks tend to earlier zones of ToA with increasing of *l*.

**Figure 16.**

*The vector magnitude signals of the EM fields on the edge of the Vivaldi slot versus time and versus distance from source l in the analysis band of 0–60 GHz.*

The H cluster in **Figure 16** reveals a noticeable feature in the Vivaldi slot propagation process. The accumulation and combination of second- and higherorder scattering components arriving from continuous spatial sections form the H cluster. Examples of the spatial sections creating second- and/or third-order scattering components are illustrated in **Figure 17**. Assume that point *M*<sup>1</sup> is the starting point for high-order scattering paths from the A cluster, and *M*2, having the same position as *M*1, is the end point for these high-order scattering paths and for H cluster examination. A major proportion of the H cluster is contributed from second-order scattering components, such as components propagating over the *M*1*PM*2, *M*1*NQM*<sup>2</sup> and *M*1*ORM*<sup>2</sup> paths, in which *M*<sup>1</sup> (in *M*1*PM*<sup>2</sup> path), *N* and *O* are the first-order scattering points of the A cluster; and *P*, *Q* and *R* are the secondorder scattering points. Third-order scattering components also contribute to intensity of the H cluster, such as *M*1*QNM*<sup>2</sup> and *M*1*ROM*<sup>2</sup> paths, in which *M*<sup>1</sup> is the first-order scattering point, *Q* and *R* are the second-order scattering points, and

*N* and *O* are the third-order scattering points. *M*1*OSOM*<sup>2</sup> is another third-order path, in which *O* is the first- and third-order scattering point and *S* is the secondorder scattering point.
