FCC Exam Question: 6A460

The relationship between the antenna current and radiated power of an antenna:

A. P=I2 X R
B. P=I2 X radiated resistance
C. No relationship exists
D. P=E x I
Correct Answer: B

Explanation: Antennas convert electrical energy into electromagnetic waves, radiating power into space. The radiated power can be calculated using a form of Ohm's Law for power. Option B, P = I² x radiated resistance, correctly describes this relationship. "Radiated resistance" is a theoretical equivalent resistance that represents the power an antenna radiates as electromagnetic waves. It's not a physical resistor, but a concept used to quantify how efficiently an antenna transfers electrical power from its input current (I) into the propagating electromagnetic field. Just like power dissipated in a resistor is I²R, the power *radiated* by an antenna is the square of the antenna current multiplied by its radiated resistance. Option A, P = I² x R, is too general. "R" could refer to various resistances (ohmic, input impedance), but for *radiated* power, it must specifically be the radiated resistance. Option C is incorrect as a direct relationship exists. Option D, P = E x I, is a valid power formula, but P = I² x radiated resistance is more specifically applicable to calculating the *radiated* power from an antenna's current.

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Includes Elements 1, 3, 6, 7R, 8, and 9.