Development of a planar helix slow-wave structure based on ball-grid array technology

Abstract

The fabrication process for a planar helix slow-wave structure (SWS) based on ball-grid array (BGA) technology is developed to be used in the traveling wave tube (TWT). The planar helix layers are structured on two printed circuit boards and the solder ball is used to connect each other upside down. The material properties of the used substrate and also the solder ball connection for being used by TWT are described. Additional to previous work, filled via paths are applied inner side of the RF-substrate as an enhancement of thermal management. A typical planar helix is modeled, and the parameters of the cold and hot tests are calculated in CST microwave studio. The simulation results show that the proposed structure has high interaction impedance and wide bandwidth. The fundamental space harmonic mode overlaps with a 5.5 kV electron beam in the dispersion diagram. The scattering parameters are reported for 100 periods of the proposed structure that 1−15 GHz frequency range has a minimum reflection. The maximum gain of 22 dB is achieved at 10 GHz frequency.