Effect of the metallisation thickness and mounting grooves on the propagation characteristics and bandwidth of finlines

The influence of finite metallisation thickness and mounting grooves on the millimetre-wave characteristics of unilateral and bilateral finlines has been studied in detail. A fully hybrid mode analysis has shown that the influence of the metallisation thickness depends on the frequency, the dielectric material and the gap width. Differences between the dominant mode dispersion in unilateral and bilateral finlines become evident. The influence of the mounting grooves on the dominant finline mode is negligible as long as the grooves are not deeper than half the waveguide height and the operating frequency remains in the lower two-thirds of the waveguide band. However, the higher-order modes are strongly affected even by very shallow grooves, which leads to a significant reduction of the single mode bandwidth.