Increasing the amplitude of ultrashort microwave pulses in a passive mode-locked oscillator by the method of double nonlinear filtering

We show the possibility of increasing the amplitude of ultrashort microwave pulses in a passive mode-locked oscillator in a circuit containing a chain of traveling wave tubes (TWTs) one of which operates in the amplification regime and the other two in the nonlinear Kompfner suppression regime. An increase in the number of nonlinear filtering stages makes it possible to enhance the filtering threshold level, below which low background noise is suppressed, while an almost complete transparency is maintained for peak amplitudes of the pulse signal. As a result, with an increase in the length of the amplifier, a linear growth in the peak amplitude of microwave pulses takes place because of the commutative extraction of energy from different electron fractions, along which the pulse is shifted due to the difference in its group velocity from the translational velocity of the particles. With an optimal selection of the parameters of the absorbers, the peak amplitude of the generated periodic sequence of ultrashort pulses can exceed the amplitude of stationary generation by more than an order of magnitude for given parameters of the TWT like current, voltage, and coupling impedance.