BROAD-BAND OPERATION OF A KA-BAND TAPERED GYRO-TRAVELING WAVE AMPLIFIER

A wideband low-voltage millimeter-wave gyro-traveling wave tube (gyro- TWT) amplifier operating in the TE(10) rectangular waveguide mode at t he fundamental cyclotron frequency is under investigation. The device incorporates precise axial tapering of both the magnetic field and the interaction circuit for broadband operation. Experimental results of a wide (33%) instantaneous bandwidth with a small signal gain in exces s of 20 dB and saturated efficiency of similar to 10% were achieved an d shown to be in good agreement with the theory. Reflective instabilit y due to multi-pass effects by mismatches was observed and characteriz ed. Gain and efficiency have been limited by this reflective instabili ty rather than by absolute instabilities which limit the performance o f gyro-TWT's with uniform cross-section. The start-oscillation current in terms of the relevant experimental parameters such as the beam vel ocity ratio (alpha), magnetic field detuning and reflection coefficien t has been measured and compared with theory. Measurements of the phas e variation in terms of the rf frequency have shown that the phase var ies +/-30 degrees from fitted linear phase line.