Answer to Question #90182 in Electricity and Magnetism for Shivam Nishad

Question

For a parabolic dish antenna, show that the
–3db beam width with D = 6m and Wavelength= 3 cm is 0.35°.

Answer 1

The beamwidth of the parabolic dish antenna can be estimated as

$$\Psi=\frac{70\lambda}{D}=\frac{70\cdot0.03}{6}=0.35^\circ.$$

At

$$10\text{log}\frac{1}{2}=-3\text{ db}$$

the power becomes twice as less.