As noted, the three element Yagi is just an optimized and further developed version of the array with reflector and director described in Chapter 18. The configuration is shown in Fig 19-2. The spacing between the elements of a Yagi is a key design parameter, in general, wider spacings provide higher performance: while closer spacings result in a more compact physical configuration, but with less gain. You usually select a boom (the structural element supporting the elements) and then optimize the number of elements and their spacing on the available boom length to maximize performance. For my first example, I will start with a boom length of 0.3 X and use 0.15?. spacing between the driven element and both the reflector and director.