An Experimental Second-Harmonic Axis-Encircling Beam Gyro-TWT
Despite the bright potential as a broad band source for future radar and communication applications, the area of harmonic gyro-TWTs with axis-encircling beams has been relatively unexplored. A second-harmonic TE21 gyro-TWT has been constructed at UCD that is predicted to produce 50 kW in Ka-band with 20% efficiency, 30 dB saturated gain and 3% bandwidth and is ready for hot testing. The device is driven by an axis-encircling electron beam from a novel Northrop Grumman cusp gun.
Cusp gun TE/sub 21/ second-harmonic Ka-band gyro-TWT amplifier
A second-harmonic TE/sub 21/ gyrotron traveling-wave tube (gyro-TWT) amplifier with an axis-encircling electron beam is being constructed at the University of California-Davis that is predicted to double the efficiency of our previous 200-kW 12%-efficient magnetron injection gun (MIG) TE/sub 21//sup (2)/ gyro-TWT. Both devices employ a sliced mode-selective circuit to suppress the odd-order azimuthal modes. The new device will avoid the loss in efficiency that is due to off-axis electrons interacting with the resulting linearly polarized mode. The amplifier is predicted by our large signal code to produce 50 kW in Ka-band with 20% efficiency, 30 dB saturated gain, and 3% bandwidth. The 70-kV 3.5-A axis-encircling electron beam with /spl upsi//sub /spl perp////spl upsi//sub z/ = 1.2 and /spl Delta//spl upsi//sub z///spl upsi//sub z/ = 7% will be produced by a Cusp electron gun delivered by Northrop Grumman. The amplifier has been designed using linear theory to provide a 30% safety margin from absolute instability. Distributed loss is added to the first 30.5 cm of the circuit to ensure the device is stable to harmonic gyro-BWO. The last 11.5 cm of the circuit is standard copper to avoid attenuating the wave at high power levels.
An experimental gyro-TWT
Three experimental gyro traveling wave tubes (TWT'S) have been built and tested. All tubes used a fundamental cyclotron resonance interaction with the circularly polarized TE/sup 0/sub 11/ dominant waveguide mode. The tubes differed in the length of the single circuit section and in the amount of distributed loss used. The experiments were conducted at 5 GHz, with the object of producing a design that could be scaled to 94 GHz. Results on the third experiment include measurements of stable gain as high as 24 dB small signal and 18 dB saturated. A saturated power output of 120 kW at a total beam efficiency of 26 percent was measured with a 3-dB saturated power output bandwidth of 6 percent. The design features of the tubes and the experimental results are described fully.