This paper presents a frequency reconfigurable parasitically coupled rectangular loop antenna that can be tuned to three different frequencies in the sub-6 GHz band. The antenna structure consists of two rectangular loops, one rectangular loop fed with a 50 ohm transmission line and the other loop is parasitically coupled with the first one. The frequency tuning is achieved by using four pin diodes which are placed at appropriate positions on the parasitic rectangular loop. By switching the diodes (ON/OFF) three bands from 2.7 – 3.1 GHz, 3 – 3.5 GHz and 3.5 – 4.5 GHz are obtained. The simulation is carried out in CST Microwave studio and analysis of the antenna is done using parametric study and surface current distribution. The antenna exhibits omnidirectional radiation pattern in all three frequency bands with good stopband characteristics and is suitable for 5G and cognitive radio applications.