Lecture 49 : Radiation Characteristics of an Antenna
A typical radiation pattern for a general antenna is shown in Fig.
Direction of Maximum Radiation (Main Beam)
The direction along which the field strength is maximum is called the direction of maximum radiation. The angular zone around the direction of maximum radiation is called the main beam of the antenna.
For the Hertz dipole, the direction of maximum radiation is for all . The maximum radiation goes in a plane perpendicular to the dipole.
Direction of Nulls
The directions along which the field strength is zero, i.e. along which no power is radiated are called the directions of nulls.
For the Hertz dipole there are two nulls one along direction and other along direction.
Beam Width between First Nulls(BWFN)
At times the effective width of the main beam is given by the angular separation between the nulls around the direction of the maximum radiation is called the BWFN.
For any antenna the BWFNs are to be defined in E and H-planes.
For the Hertz dipole the BWFN in the E-plane is , and the BWFN for the H-plane is not defined since there is no null in the H-plane radiation pattern.
for all 
. The maximum radiation goes in a plane perpendicular to the dipole. 
direction and other along 
direction. 
, and the BWFN for the H-plane is not defined since there is no null in the H-plane radiation pattern. 
