Spurious suppression in a 3:1 bandwidth crossed-field amplifier

This paper describes the significant results obtained from a two-year development of an injected-beam, high-power crossed-field amplifier with the following general characteristics: Frequency Band: 350- 1100 Mc CW Output Power: 1 - 2 Kilowatts Low Level Gain: 25 db Saturated Gain: 14.5 ± 1.3 db Of particular interest is a detailed description of the following: 1. A rectangular helix slow-wave structure wound from hollow tubing which is directly cooled. 2. The addition of periodic perturbations to the helix to create a stop band about π phase shift with 35 db insertion loss to suppress backward wave and π-mode oscillations. 3. An inductively coupled, segmented sole structure designed as a strip-line low pass filter with an upper cut-off frequency of 150 Mc. Reduced fast mode coupling in conjunction with a severed helix results in greater than 60 db isolation between input and output couplers. 4. The effect of drive power, beam current and other parameters on the helix current and on the reduction of harmonic content which results from the nonlinear CFA gain characteristics. 5. The predicted gain variation over the 3:1 band-width is experimentally verified. Uniform gain is the result of balancing the greater number of wavelengths at the high end of the band with reduced beam impedance. 6. The present status of relased programs, with the objective of scaling the basic slow-wave structure for higher frequency, octave bandwidth operation with no sacrifice in output power.