The fundamental properties of carbon nanotube (CN) loop antennas have been determined using numerical modeling in both transmitting and receiving modes. The variation of the antenna impedance, reflection coefficient, radiation efficiency, Q-factor, and extinction cross section with varying loop radii was determined numerically using method-of-moment simulations incorporating the quantum mechanical conductivity of carbon nanotubes. Contrary to metallic loop antennas (well known for their inductive input impedance), the carbon nanotube loops with a large circumference show capacitive reactance over the entire frequency range. Therefore, one cannot make CN loop to act as an inductive radiator or even a simple inductor (when ka → 0) if the circumference is beyond ~56 μm. However, the carbon nanotube loops with circumference smaller than ~56 μm exhibit properties similar to ordinary loop antennas by going through antiresonance and then resonance regions. Despite the dispersive conductivity model, carbon nanotube loop antennas possess normalized dispersion relation, which is linearly related to the frequency.