This disclosure describes antenna structures for use with implantable medical devices (IMDs). The IMD may include a housing that hermetically encloses electronic components of the IMD and a fixation mechanism that attaches the IMD to a target location within a patient, such as a wall of a vessel. The fixation mechanism may function as a radiating element of an antenna of the IMD. The fixation mechanism may be attached to a housing of the IMD with two different members. One member may be an anchoring structure that mechanically anchors the fixation mechanism to the housing. The second member may be a connector that electrically connects the fixation mechanism to the housing such that the fixation mechanism is configured to transmit and/or receive communication signals with other implantable or external devices.
