A 45 Gc bandwidth low noise TWT for the 3mm region

Abstract

A breakthrough has occurred which eliminates the traveling-wave tube amplifier void in the three millimeter region. Brute force extension of standard techniques combined with a multiplicity of new approaches has yielded an exceptionally wide-band low-noise traveling-wave amplifier for the 70 - 115 Gc band. With noise figure of only 12 db and gain of 25 db, this wide-band amplifier will provide important impetus to radiometric, radar, and communication system exploitation of the 3 mm band. The tubes' .005" diameter helix is copper-plated and then glazed to the .002" wide knife edge of a ceramic wedge. The circuits' dielectric loading factor is 0.87 and its loss is 0.3 decibels per guide wavelength. The electron gun is characterized by a low-potential accelerating anode pulling a space charge limited beam current of 4 amp/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The gun is a modification of standard 3-region low-noise guns in that lens cancellation is incorporated to achieve focusing at reasonable magnetic fields. Circuit-to-gun alignment better than .0004" is achieved, although gun parts are fabricated to standard shop tolerances. This is accomplished by aligning both the cathode and drift tube sections of the gun directly with the helix using a .005" diameter light beam as a mandrel. The focusing solenoid was fabricated so its transverse components would be less than .03 per cent of the longitudinal field. By these means it has been possible to achieve excellent focusing, 99 per cent transmission being typical. Life experience has been good. All tubes have been emission stable and the single life test vehicle showed improved emission throughout the 1500 hour test period.