Abstract: Air-dielectric sandwich structures for electrically tunable microwave devices provide two types of layered structures; one type comprising a first dielectric material, a second dielectric material, an air gap between the first and second dielectric materials and an electromechanical actuator for adjusting the width of the air gap by moving the first or second dielectric materials, and the other type comprising a dielectric material, a metal wall, an air gap between the dielectric material and the metal wall and an actuator for adjusting the width of the air gap by moving the dielectric material or the metal wall. The tunable microwave devices including the air-dielectric sandwich structure are elaborated such as a tunable dielectric resonator, a band stop and a band pass filter, a phase shifter and a phase array antenna.