Antenna systems have a substrate and antenna on the substrate, where the antenna has a plurality of leg elements. The plurality of leg elements comprises a conductive ink and forms a continuous path. At least one of the plurality of leg elements is individually selectable or de-selectable to change a resonant frequency of the antenna, and leg elements that are selected create an antenna path length corresponding to the resonant frequency. In some embodiments, the antennas are energy harvesters.