YAGI-UDA ANTENNA

PHYSICAL DESCRIPTION

The Yagi-Uda array has been widely used as a home TV antenna. IT is practically

used in the HF (330 MHz), VHF (30300 MHz), and UHF (3003,000 MHz) ranges.

It is simple to construct low in cost and has high gain, greater than 10 dB.

There are three types of elements within a yagi-uda antenna

DRIVEN ELAMENT

The driven element is the antenna element to which power is applied

.Mostly it is a folded dipole or a half dipole

REFLECTOR

The yagi antenna generally have one reflector .This is behind the main

driven element i.e

sideways from direction of maximum sensitivity.

DIRECTOR

There may be none ,one or more directors in yagi antenna. The

directors are placed in front of driven elements .Each director will add 1 dB of

gain in forward direction. This level reduces with increase in number of directors

ANALYSIS

A full analysis of yagi antenna requires computing the mutual impedances

between the dipole elements .Just considering two elements we can write the

voltage at each feed point as:

1 = 111 + 122

2 = 211 + 222

Z11 and Z22 are ordinary driving points impedances of dipole .Let the driven

element be designated 1 so that V and I supplied to the transmitter

2 = 211 + 222

And so

2 = 2122

1

This is the current impedance induced in parasitic element due to current I1 in the

driven element.