Grating-coupled oscillators: theory and the results of recent experiments

Summary form only given. In principle, grating-coupled oscillators can provide useful levels of radiation over a range extending from centimeter to micrometer wavelengths. In order to assess the difficulties associated with operating over this very large range, a general theory has been developed. It is structured in a manner which clearly displays the scaling of all essential performance criteria (tuning, gain, saturation, efficiency, and beam quality related constraints) with the electron beam and grating parameter choices. Experiments with grating-coupled devices at lower-millimeter and submillimeter wavelengths have been performed. These experiments were performed with pulse transformer thermionic-cathode-produced electron beams. Beam voltages ranged from 5 to 150 kV and beam currents from tens of milliamperes to several amperes. Output power levels between tens of watts and tens of kilowatts were obtained, and efficiencies varied from a fraction of a percent to a maximum near 10%. Both segmented and continuous gratings were tested, and a range of grating parameter ratios was examined. The highest frequencies observed were just above 300 GHz, and nearly 2:1 voltage tuning was found in the lower middle millimeter range (58-118 GHz from a single resonator)