Variable element length, but fixed element distance?
One of the most frequently asked questions is “Shouldn’t the distance of the elements also change when changing element lengths?”. To answer this question it is important to understand that Yagis can be designed to maximise different values. That can be max. gain, best Front/Back ratio, good bandwidth etc. But – these goals cannot be achieved all at once with the same design. Either you optimize a yagi for best gain, useful bandwidth and not so good F/B ratio. Or excellent F/B ratio at narrow bandwidth and mediocre gain etc. etc. With a 3-element beam the optimum gain would be reached at a boom length of 0.4 λ. The best F/B ratio is achieved with a boom length of approx. 0.25 λ, but only at limited bandwidth. This results in 0.3 λ as a good compromise, with this it can be shown that a variable element length results in much greater effect than variable distance. Bandwidth is of no importance with a SteppIR antenna because the antenna can be adjusted to any operating frequency (within s
