Enhanced super-radiant emission of FEM near waveguide-cutoff and near zero-slippage conditions

We report on super-radiance obtained from the TAU FEM just above waveguide cutoff and near grazing intersection. Grazing intersection (or ''Zero Slippage'') is defined as the point at which the two synchronous frequencies merge to one frequency. In this case, the radiated power frequency can be tuned over a very wide band by change of the pre-modulation frequency. Near the lower synchronous frequency, the super-radiance power is much greater and the spectral width is much narrower than those at the higher synchronous frequency. The super-radiance emission near cutoff (lower synchronous frequency) and near to the upper synchronous frequency was measured and compared to those predicted by an analytical model for a wide range of frequencies