Microwave devices with field emission cathodes

TO OBTAIN appreciable power from electron beams at millimeter or sub-millimeter wavelengths, it is necessary to employ devices that allow high power transfer per unit volume between the electrons and the circuit fields. This requirement results from the usual scaling laws that apply to the dimensions of devices as the wavelength is decreased. Unless very-high-energy electrons are used, the dimensions of the interaction region where the energy interchange takes place must be small in terms of the wavelength, and the power transferred per unit volume becomes of fundamental importance.