The distribution of electrons on a carbon nanotube (CNT) under microwave excitation is analyzed here. Numerical results demonstrate that electrons on CNTs are oscillating under the microwave excitation, which means that the electrons can radiate microwaves with the same frequency. The length of CNTs required for microwave radiation is estimated. Both results reveal that it is possible to construct a microwave antenna with carbon nanotubes or nanotube arrays. (C) 2007 American Vacuum Society.