An antenna assembly includes: an antenna including: a metal signal layer having a radiating surface; and a feed port; and a waveguide surrounding the antenna and configured to guide electromagnetic energy transmitted from the radiating surface in a direction away from the antenna; and a controller module connected to the feed port and configured to drive the antenna to transmit electromagnetic energy from the radiating surface; wherein the antenna, waveguide, and controller module are configured such that, when the controller module drives the antenna, the transmitted electromagnetic energy matches a reception characteristic of an implantable device and is sufficient for the implantable device to create one or more electrical pulses of sufficient amplitude to stimulate neural tissue of a patient, solely using electromagnetic energy received from the antenna, when the implantable device is located at least 10 centimeters away from the antenna.