1,212
edits
Changes
→Yagi
=== Yagi ===
[[File:Yagi2.gif|frame|thumb|Yagi Antenna. Image reproduced from [https://commons.wikimedia.org/wiki/File:Yagi.gif here]]]
* While monopole and dipole are omnidirectional antennas, yagi is a directional antenna. It's made up of only wires and has only one feed (where you apply signal). It has three elements - feed(folded dipole in the diagram), directors and reflector. All the three elements are attached to a single long rod which is called “boom”. The feed, directors and reflector are perpendicular to the boom and in the same plane. Their order is - reflector then feed then directors. Feed is the element where signal to be transmitted is applied. The feed is typically a dipole or a folded dipole. The feed is made resonant in the presence of other elements. This length is different from the resonant length of isolated antenna. It is mostly calculated using simulations.
* The other two elements are also called parasitic elements as they are not excited by any signal. The directors are used to increase the directivity of the antenna. Increasing the number of directors increases directivity of the antenna. Their length is slightly less than the feed element and progressively decreases when we move further away from feed. The number of directors can be as large as 20-30. The reflector, as the name suggests, seem to reflect radiation thus decreasing its radiation in unwanted direction. Usually only one reflector is used but antennas having more than one reflectors have been designed. They are physically longer than feed element. Its theory of operation is quite interesting, so do give it a [https://en.wikipedia.org/wiki/Yagi%E2%80%93Uda_antenna#Theory_of_operation read].
* About its characteristics, it is a highly directive antenna whose gain is usually more than 10 dBcan go upto 20dBi. <ref>https://en.wikipedia.org/wiki/Yagi%E2%80%93Uda_antenna</ref> Its bandwidth is typically small. The input impedance is that of the feed which can be simulated.
* To design this antenna, quite a lot of variables are needed to be decided. These include length of all elements and their spacing. All these variable belong to a small range of lengths and are tweaked using simulations before actually making the antenna.
* Most of you may have seen these kind on antennas on your roof. They were widely used as television antennas and even today are very popular amongst ham enthusiasts. They are quite easy to make and its directivity can be increased by just increasing the number of directors. They are regarded as IEEE Milestone. Their importance just can’t be overstated.
