According to the classic theory of electromagnetic (EM) fields, we develop a propellantless microwave thruster system that can convert microwave power directly into thrust without the need of propellant. It is expected to be useful for spacecraft. Different from conventional space plasma propulsion, the system can obviate a large propellant storage tank and the issues related to plasma plume interference with the spacecraft surface. Different from huge solar sails and microwave-propelled sails, the system uses a cylindrical tapered resonance cavity as a thruster and uses an integrated microwave source to generate continuous EM wave so that the EM wave is radiated into and then reflected from the thruster to form a pure standing wave with amplified wave amplitude. The pure standing wave produces a non-uniform EM pressure distribution on the inner surface of the thruster. Consequently, a non-zero net EM thrust exerting on the symmetric axis and directing to the minor end plate of the thruster appears. In experiments a magnetron is used as a microwave source with an output microwave power of 2.45 GHz frequency. The generated net EM thrust is measured using a force-feedback test stand. The developed thruster system is experimentally demonstrated to produce thrust from 70 to 720 mN when the microwave output power is from 80 to 2500 W.