Antenna system being tunable over multiple frequency bands. One planar surface of the antenna structure has metallic radiating elements of various geometries with selectable electrical interconnections between the radiating elements. An opposite side of the antenna structure has a signal transmission network with signal feedthroughs to selected metallic radiating elements. The signal transmission network also has phase shift inducing means. Depending on the frequency band of operation, metallic radiating elements are appropriately combined through the electrical interconnections to form composite radiating elements with resonant frequencies within the frequency band of operation. Induced phase shifts in the signal paths feeding selected metallic radiating elements cause a net resultant free-space directivity gain.