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对于电子枪区用均匀磁场而在管子其余部分用周期场(周期永磁场)聚焦的低噪声行波管,它的噪声系数通常要比均匀永磁聚焦的管子高3～5分贝。本文描述了噪声较高的缺点是怎样通过磁性材料和周期永磁聚焦迴路设计的改进而在很大程度上得到克服的。为了改善通过率,用更均匀的磁铁(以降低横向磁场)及减小周期的方法来降低静电透镜效应。通过增加枪区均匀场的长度,使漂移区的磁透镜效应减至最小,以便在此长度上至少获有3分贝的增益。最终的管子表明,其电性能和适应环境的性能得到了改进。在6.4～10.2千兆赫频带内获得的最大噪声系数为7.9分贝,而在9.2～10.2千兆赫频带内得到的噪声系数为6.7～6.9分贝。总重量为5.3磅的低噪声放大器在大多数低噪声应用场合中使重量和体积都有显著的减小,并且它的特性符合MIL-E-5400 F第二类设备技术条件的要求。
For low-noise TWTs with a uniform magnetic field in the gun's area and focused in a periodic field (periodic PMF) in the rest of the tube, the noise figure is typically 3 to 5 dB higher than a uniform PM-focused tube. This paper describes how the disadvantage of higher noise is largely overcome by the improvements in the design of magnetic materials and periodic PM focusing circuits. In order to improve the throughput, the use of more uniform magnets (to reduce the lateral magnetic field) and reduce the cycle method to reduce the electrostatic lens effect. By increasing the length of the uniform field of the gun zone, the effect of the magnetic lens in the drift zone is minimized to achieve a gain of at least 3 dB over this length. The final tube shows that its electrical and environmental performance has been improved. The maximum noise figure obtained in the 6.4-10.2 GHz band is 7.9 dB while the noise figure obtained in the 9.2-10.2 GHz band is 6.7-6.9 dB. The 5.3-pound low-noise amplifier significantly reduces both weight and volume in most low-noise applications and its characteristics meet the requirements of MIL-E-5400 F Type-2 equipment.