The power gain of an antenna is the ratio of its radiated power to?

The power gain of an antenna is defined as the ratio of the power radiated by the antenna in a given direction to the power radiated by a reference antenna, typically a dipole. This reference dipole serves as a standard for comparison, allowing for a clear understanding of how effectively the antenna converts input power into radiated power.

When measuring the gain, it is important to have a standard reference, and the dipole is commonly used because it has well-defined and predictable radiation characteristics. The gain is often expressed in decibels (dB), providing a logarithmic measure of the ratio which is helpful for comparing different antennas and their performance efficiency.

Other options pertain to different aspects of antenna operation or components. Reflector power relates to antennas that use a reflector to enhance gain or directivity, input power refers to the power supplied to the antenna, and feedhorn is a component typically associated with parabolic antennas to direct the radio waves. However, these do not serve as a basis for defining the power gain in relation to a standard measurement. Thus, the reference dipole is the appropriate choice for understanding power gain.