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Design of helix slow-wave structure for a high efficiency space TWT

Research output: Contribution to Journal/MagazineJournal articlepeer-review

<mark>Journal publication date</mark>1/12/1998
Issue number150
Number of pages3
Pages (from-to)349-351
Publication StatusPublished
<mark>Original language</mark>English


An approach of designing helix SWS for achieving high beam (interaction) efficiency of the TWT, is presented. The SWS parameters are determined for a C-band 60 W TWT at beam voltage 3.0kV and beam current 75mA. The rf phase velocity of the SWS is optimised with positive taper followed by negative taper. It is shown that the positive taper in the circuit not only enhances the beam efficiency but also improves linearity (reduced AM/PM factor and IM level) and reduces second harmonic power and provides less spreading in spent beam for high collector efficiency. The complete SWS is designed in two sections with sever in between for gain more than 50dB at saturation. Beam efficiency at saturation is computed more than 36% including the effect of circuit loss, second harmonic, 20% voltage reflection at the input and at output and the backward wave. AM/PM factor is found less than 3.0 degrees/dB; second harmonic power more than 12dB down; and 3rd order I/M level more than 10 dB down. The performance was checked over the full band from 3.60GHz to 4.20GHz.