Abstract: A microwave device comprises a cathode producing stream of electrons into the space defined by the cathode and electrodynamic or anode system cells connected in parallel with individual band-reject filters via coupling elements. The rejection band of the filters covers the operating frequency or operating frequency range of the micorwave device. The filters are electrically associated with broad-band microwave loads made as shorted transmission line sections with a variable characteristic impedance, whose surface has a microwave absorbing coating. This ensures suppression of the undesired modes on either side of the operating frequency or operating frequency range of the microwave device.