This paper presents a frequency reconfigurable printed monopole antenna that can be reconfigured to two operating bands – UWB (3.1 – 10.2 GHz) and sub-6 GHz (3.1 – 6 GHz). To attain frequency reconfigurability, the partial ground plane of the printed monopole is loaded with a quarter wave stub resonator which can be either connected or disconnected with the ground plane with the aid of a p-i-n diode. The quarter wave stub resonator is designed in such a way that it provides a wide stopband in the UWB band of the antenna giving the sub-6 GHz band. The proposed resonator structure has minimal effects on the antenna’s radiation characteristics while providing good stopband performance. The antenna is suitable for UWB, sub-6 GHz 5G and Cognitive Radio applications.