Question

The far field of an antenna varies with distance r as

• A. \( r^2 \)
• B. \( 1/r^2 \)
• C. \( 1/r^3 \)
• D. \( 1/\sqrt{r} \)

Hint:

Understand the different fields near and far away from the antenna. The far field region is where radiation is dominant and the power density varies as the inverse square of the distance.

Answer 1

The Correct Option is A

In the far-field region of an antenna, the power density (and hence the electric and magnetic field) varies inversely with the distance (r) from the antenna. The power density varies as \( 1/r^2 \), however the field intensity (related to power) varies as \( 1/r \). This is a fundamental property of electromagnetic wave propagation in the far-field zone.