For a dipole antenna

Question

For a dipole antenna

1. A. the current distribution along its length is uniform irrespective of its length
2. B. the effective length equals thrice of its physical length
3. C. the radiation intensity is maximum along the normal to the dipole axis (Correct answer)
4. D. the input impedance is independent of the location of the feed point

Correct Answer

Option C — the radiation intensity is maximum along the normal to the dipole axis

Detailed Solution & Explanation

The correct answer is the radiation intensity is maximum along the normal to the dipole axis.

Key Points

• A dipole antenna radiates most strongly in the direction perpendicular (normal) to its own axis, producing the familiar doughnut-shaped pattern.
• Radiation along the axis itself is zero, which is why a dipole is never pointed at the station it is trying to reach.
• The other options are false: current distribution along a dipole is sinusoidal, not uniform; effective length is less than physical length, not three times it; and input impedance depends strongly on where the feed point is placed.

Additional Information

• A half-wave dipole has a radiation resistance of about 73 Ω, which is why 75 Ω feeder cable matches it well.
• Its directivity is 2.15 dBi, and antenna gains are often quoted in dBd — decibels relative to this dipole — precisely because it is the standard reference.