Dipole Antenna

The Dipole antenna Has many practical applications Can be considered as a sum (integration) of Hertzian dipoles elements Prime variables refer to distance to the source from the origin.

Dipole Using Cosine Law: Using the Taylor series: Then it is:

To ignore the terms of 1 / r in below impose a condition, which is that the phase error in the third term contributes in R is less than pi/ 8 (22.5 °). Evaluating the worst case, ie when sin(theta) = 1 and z '= z'max = l / 2, is obtained, where the minimum value of r (rff) is to reduce the error in the phase,

Substituting... In 'Far Field' can be approximated to: Which can be written as: where: Note I(  ) is Fourier transformation of I(z')

If know A z … can find H and E. I need to know the distribution of current in the dipole I (  )

What is measured is: Which can be approximated to:

To integrate: It is divided into two integrals:

E  y H ø are proportional to sin  I (  ); therefore the pattern of power (not standardized) random length dipole is; Now we will see special cases.

Dipole Half wavelength dipole ( l = /2) Full wavelength dipole ( l = ) 3/4 wavelength dipole ( l =3 /4)