Abstract: In response to the new requirements of 5G development for indoor access antennas, a frequency reconfigurable antenna that can switch between the N78 (3.4-36 GHz) and N79 (4.8-5.0 GHz) frequency bands is designed. The antenna radiator is printed on a circuit board and contains a circular metal cavity at the bottom to serve as a reflector for the Yagi and short backfire antennas. The PIN diode bias circuit is optimized. By changing a pair of PIN diode switches on the active dipole arm of the antenna, two operating modes are generated and the frequency reconfigurable function is realized. The antenna model is simulated and analyzed by simulation software. According to the simulation results, a prototype of the antenna is manufactured and verified by experiment. The actual measurement shows that the antenna has superior matching and gain. When the PIN diode is connected, the antenna works in the N78 frequency band, the return loss is less than −19.58 dB, and the gain is greater than 7.44 dBi. When the PIN diode is disconnected, the antenna works in the N79 frequency band, the return loss is less than −18.58 dB, and the gain is greater than 9.48 dBi.