An antenna structure for an implantable medical device (IMD) is provided that includes an antenna embedded within a structure derived from a plurality of discrete dielectric layers. An array of electrodes are connected to the antenna structure and arranged for applying a bias across selected segments of the dielectric layers for altering the performance characteristics of the antenna. The bias applied by the array of electrodes can be selected to provide desired impedance matching between the antenna and the surrounding environment of the implant location to mitigate energy reflection effects at the transition from the antenna structure to the surrounding environment, to provide beam steering functionality for the antenna, or to alter the gain of the signals received by the antenna. IMD is configured to monitor received signal characteristics (e.g., RSSI, EVM or bit error rate) and alter material properties of the dielectric material through biasing to control antenna performance.