2G051 Volume 2 URE Practice Exam

What is the typical impedance of a dipole antenna in free space?

75 ohms 73 ohms 50 ohms 100 ohms

Correct Answer:

73 ohms

Explanation:

A resonant center-fed half-wavelength dipole in free space presents an impedance that is essentially resistive and about 73 ohms at the feedpoint. The radiation resistance of a thin half-wave dipole is around 73 ohms, and the reactive part is minimal when the dipole is exactly at resonance, so the feedpoint looks like a real 73-ohm impedance. That’s why 73 ohms is the typical reference value for a dipole in free space. The other values are less representative of the dipole’s own impedance: 75 ohms is close but not as precise; 50 ohms and 100 ohms are common line or system impedances, not the dipole’s intrinsic feedpoint impedance, which is why they aren’t the best fit without matching.

Access more questions from this quiz

Continue to 2G051 Volume 2 URE Practice Exam for more practice questions and the full quiz experience.

Access More Questions