Tunable RF cavity. The cavity (24) includes a magnetostrictive material (20) coupled to the cavity (24) and a magnetic coil (22) configured to impress a magnetic field on the magnetostrictive material (20). Control circuitry energizes the magnetic coil (22) to control the shape of the magnetostrictive material (20), thereby to control the length of the cavity (24) to tune its resonant frequency.
