This paper presents the design of a dual-port dual-band circular polarized annular slot antenna, suitable to use in the feed-back path of an oscillator resulting in an active antenna configuration. The proposed antenna is designed to radiate and transmit equal amounts of power. The return loss of the proposed antenna is higher than that desired for one-port antenna application at the desired dual-band frequencies. The antenna is fabricated on one side of a Neltec substrate (εr=3.2 and thickness = 0.762 mm) and the microstrip feeding line is fabricated on the opposite side of the board. The antenna was designed to operate at WLAN bands centered at 2.4 and 5.2 GHz. The simulated and measured results show fairly good agreement. The measured return losses were found 10 dB at 2.4 GHz and 14.5 dB at 5.2 GHz while simulated return losses were 8.57 dB at 2.4 GHz and 15.2 dB at 5.2 GHz. The radiation pattern is approximately omnidirectional at both frequencies in H-plane. © 2014 IEEE.