A Low-Impedance Transmission Line Transformer Based on the Multicore Coaxial Transmission Line

Abstract

The design, construction, and operational characteristics of a low-impedance and low pulse drop transmission line transformer (TLT) are described in this paper. The multicore coaxial transmission line used for this transformer is different from traditional coaxial transmission line since its inner conductor consists of several high-voltage cables that are connected in parallel by using two metal disks placed at both ends of them. Simultaneously, the impedance of the coaxial transmission lines with ten cables designed in this paper is perfectly reduced from 60 to $13.5~\Omega $ . Moreover, the transmission lines can withstand a high voltage of several tens of kilovolts with 13.9 mm in diameter. The transmission lines were then used to construct TLTs. The transformers are wound inductively in separated cylinders made of polypropylene to enhance the isolation from the input to the output of the transformers. Consequently, the pulse drop is substantially reduced, minimizing pulse distortion in the transformer. A three-stage TLT, whose input and output impedances are 4.5 and $40.5~\Omega $ , respectively, was developed with the transmission lines. The experimental results show that the three-stage transformer based on the low-impedance and low pulse drop design transmission lines can achieve a voltage gain factor of almost 3.0.