How do the lengths of a three-element Yagi reflector and director compare to that of the driven element?

In a Yagi antenna, the parasitic elements must be sized specifically to create the desired directional radiation pattern. The reflector is placed behind the driven element and is made about 5% longer than the driven element, which makes it inductive and reflects the radio signal forward. Conversely, the director is placed in front of the driven element and is made about 5% shorter. This makes it capacitive, pulling the radio energy forward and focusing the beam. A helpful memory trick is to think of the elements tapering down in size toward the direction the signal travels.