Millimeter wave image guide band reject filter and mixer circuit using the same

A magnetically tunable band reject filter, comprising:

• a semi-insulating dielectric transmission medium including a length of a semiconductor material and a conductive ground plane supporting said semiconductor material;
• a body of a high anisotropy ferromagnetic material embedded in said semiconductor material and having a ferromagnetic resonance characteristic in response to a biasing magnetic field which is operative with signals within a predetermined band of millimeter wave frequencies propagating along the semiconductor material, said signals driving said ferromagnetic material body into a coupling mode causing signal energy at said band of frequencies to be absorbed while other signal frequency energy passes substantially unattenuated;
• and
• selectively variable magnetic field means for providing said biasing magnetic field and thereby varying the resonance frequency characteristic thereof, said magnetic field means including a pair of magnets positioned on opposite sides of said semiconductor material at the location of said ferromagnetic material, a tuning coil wound around said magnets, and a source of variable direct voltage applied across said coil for varying the current in said coil and strength of said magnetic field.