An antenna system is provided. In one example implementation, the antenna system may include a modal antenna that is operable in a plurality of different modes, and each mode may be associated with a different radiation pattern. The antenna system may include a tuning circuit configured to operate the modal antenna in the plurality of different modes. A transmission line may couple a radio frequency circuit to the modal antenna. The radio frequency circuit may be configured to modulate a control signal onto an RF signal using amplitude-shift keying modulation to generate a transmit signal for communication over the transmission line to the tuning circuit. The tuning circuit may be configured to demodulate the control signal such that the radio frequency circuit can adjust a mode of the modal antenna via the control signal. In some embodiments, the amplitude-shift keying modulation may include on-off keying modulation.