Question
What is an isotropic radiator?
Answer Options
- A) A calibrated, unidirectional antenna used to make precise antenna gain measurements
- B) An omnidirectional, horizontally polarized, precisely calibrated antenna used to make field measurements of antenna gain
- C) A hypothetical, lossless antenna having equal radiation intensity in all directions used as a reference for antenna gain
- D) A spacecraft antenna used to direct signals toward Earth
Correct Answer: C
Explanation
In antenna theory, a benchmark is needed to compare the performance and gain of real-world antennas. The concept of an isotropic radiator fulfills this need by providing a theoretical reference point that is independent of direction or polarization. This allows for standardized measurement of directivity and gain.
An isotropic radiator is a hypothetical, lossless antenna having equal radiation intensity in all directions (in all three dimensions). It is used as a reference for antenna gain. Gain measurements relative to an isotropic radiator are designated in units of dBi (decibels relative to isotropic). Because no real antenna can radiate equally in all directions, the isotropic radiator only exists as a theoretical concept for mathematical calculation and reference.
(An alternative reference antenna is the dipole, which has a maximum 2.15dB of gain relative to the theoretical isotropic radiator, which is seen in the horizontal plane for a horizontal dipole. Gain relative to a dipole is expressed in units of dBd; decibels relative to dipole. Therefore, dBi = dBd + 2.15dB)
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