A novel compact and low profile microstrip antenna is proposed as a suitable radiating device for a software defined radio system. The antenna allows the frequency reconfigurability by activating a subset of the four groups of pin diodes connecting a central patch to four different peripheral elements. Each one of the four peripheral elements provides a resonance mode independent from the others that can be tailored by the designer. The radiating device guarantees an overall of 2(4)=16 different states with both single and multifrequency resonances within a wide bandwidth going from 0.8 GHz-3.0 GHz, without requiring any extra matching network. Measurements on a realized prototype assess the level of performance estimated in simulations and prove the usefulness of the proposed antenna in a device exploiting the cognitive radio paradigm.