Question

If the diameter of a \(\frac{\lambda }{2}\) the dipole antenna is increased from \(\frac{\lambda }{{100}}\) to \(\frac{\lambda }{{50}},\) then its
1. Bandwidth increases
2. Bandwidth decreases
3. Gain increases
4. Gain decreases

Answer 1

Correct Answer - Option 3 : Gain increases

Explanation:

The gain of the antenna is directly proportional to efficiency, which is defined as:

\({\eta _r} = \frac{{{P_{rad}}}}{{{P_{in}}}} = \frac{{{R_{rad}}}}{{{R_{rad}} + {R_l}}}\) 

R_l: Loss  resistance

R_ard: Radiation resistance

Diameter is changing from \(\frac{\lambda }{{100}}\) to \(\frac{\lambda }{{50}}\). i.e., the diameter is increased 2 times.

As the diameter of the dipole antenna increases (area of wire increases).

\({R_l} = \frac{{\rho l}}{{Area}}\) 

Loss resistance decreases as the area increases.

Thus efficiency increases.

Hence gain increases.