E9A01

What is an isotropic radiator?

1. AA calibrated, unidirectional antenna used to make precise antenna gain measurements
2. BAn omnidirectional, horizontally polarized, precisely calibrated antenna used to make field measurements of antenna gain
3. CA hypothetical, lossless antenna having equal radiation intensity in all directions used as a reference for antenna gain
4. DA spacecraft antenna used to direct signals toward Earth

Pick an answer to check it.