A yagi uda antenna contains one dtiven element ,one reflector and one or more directors

1.The input is supplied to the driven element so it is known as active element.

2.For reflectors and directors we are not applying any input.So the reflectors and directors are called as parasitic elements.

3.Driven element and the parasatic elements are placed parallel to each other and close to each other.

4.The reflector is placed back side of the driven element which is longer than driven element and compare to all elements.

5.The element infront of the driven element is director which is smaller than all elements.

6.The length of all elements will be calculated by relation.

      lambda=c/f

7.If the driven element is halfwave dipole the length is

    L=150/f(MHZ)

Approximate values

8.The length of driven element is L=143/f(MHZ).

9.The length of reflector is L=152/f(MHZ).

10.The length of director is L=137/f(MHZ).

11.Spacing between reflector and driven element is 75/f(MHZ).

12.Spacing between driven element and director is 40/f(MHZ).

13.Spacing between director 1 & director 2 is 38/f(MHZ).

example of yagi uda antenna: