How does a yagi aerial work

Chris - Why is it called a Yagi aerial? Skip to main content. Earth Science. How does a Yagi aerial work? Play Download. Question How does a Yagi aerial work? Chris - Dave, why are they that shape?

Next What's the natural way of severing the umbilical cord? Your name. Leave this field blank. That answer helps illustrate the difference between the micro and the macro. Nearly all radio wave theory is macro; almost none is micro. There is a huge missing piece in EM theory. The reflector is not providing cancellation. The reflector is not connected to the transmission line, however the driven element is.

The reflector must be the appropriate length to resonate at the frequency being used. The driven element lobe in the unwanted direction induces EMF in the reflector that is degrees out of phase with that of the driven element — this is because we know that induced EMF opposes the inducing effect. The reflector then re-radiates, now inducing EMF in the driven element and another degree phase shift occurs.

Since there have been two degree phase shifts, we are back in phase again and this action reinforces the radiated field of the driven element.

This enables us to maximise gain via focus in the opposite direction. Obviously the opposite is true for the directors which experience induction also, but resonate in phase with the driven element. They then re-radiate also. This has the effect of narrowing the beam width which explains the directivity of the yagi, resulting in more EM energy in a smaller area think of a polar coordinate graph which obviously means greater power density and therefore gain.

Remembering that the reflector length and spacing from the driven element is critical to ensure the appropriate phase shift and resonance at the desired frequency, it is worth noting that these characteristics are just as important for the other parasitic elements directors.

It is an accepted fact that trial and error plays a significant role in obtaining optimal radiation patterns. This explains why it is common to use a folded dipole with parasitic arrays, because the folded dipole reduces frequency sensitivity increases bandwidth and also compensates for the impedance changes caused by the parasitic elements. To shorten the cable length, you need to make a loop instead to flat the end and zip them. That way the cable will not have any kinky end. You have a kinky cable with your zip ties.

You are commenting using your WordPress. You are commenting using your Google account. You are commenting using your Twitter account. Does antenna height matter more than gain? Though it may seem to be paradoxical at first sight, the fact is that very often the antenna height above ground might matter more than its published gain when….

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Read our Privacy Policy. One of the major keys to understanding Yagi theory is a knowledge of the phases of the currents flowing in the different elements of the antenna. The parasitic elements of the Yagi antenna operate by re-radiating their signals in a slightly different phase to that of the driven element. In this way the signal is reinforced in some directions and cancelled out in others. As the additional antenna elements in the Yagi are not directly driven but pick up power from the driven element, these additional elements are referred to as parasitic elements.

One limitation of the design of Yagi anennas is that the power in these additional elements is not directly driven. Accordingly the amplitude and phase of the induced current cannot be completely controlled. It is dependent upon their length and the spacing between them and the dipole or driven element. This means that it is not possible to obtain complete cancellation in one direction.