A Wideband Microfabricated Ka-Band Planar Helix Slow-Wave Structure

Abstract

A Ka-band planar helix slow-wave structure (SWS) which is suitable for microfabrication is proposed and its design is described in this paper. A wideband design is achieved by using dispersion control techniques. The design shows an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S_{11}$ </tex-math></inline-formula> better than −20 dB over a 42.8% cold-test bandwidth with discrete input and output ports. Cold-test results for coplanar waveguide ports are also presented. The hot-test parameters of the SWS with discrete ports are investigated using CST Particle Studio. For an elliptical cross-sectional electron beam with the beam voltage of 3.72 kV and the current of 50 mA, a 3-dB small-signal gain bandwidth of 48.5% and a maximum gain of 42 dB are achieved. Saturated power of 26.5 W is achieved by using pitch tapering. Hot-test performance of the proposed SWS including a sever for high gain applications is also presented. Thermal simulations using CST have been carried out showing that the proposed SWS can have very good thermal dissipation properties. RF electric field values at some critical locations in the SWS have also been examined from the point of view of dielectric breakdown.