Novel Air-Filled Waveguide Transmission Line Based on Multilayer Thin Metal Plates

This paper presents a novel way of constructing waveguiding structures by stacking several thin metal plates for millimeter-wave and terahertz applications. The metallic layers do not require any electrical contacts among them. An air-filled multi-layer waveguide (MLW) transmission line is successfully designed and manufactured at D-band. Five vertically stacked thin metal layers are used to form an air-filled rectangular waveguide line. The layers are simply assembled by allowing a small air gap among them, without the need of using advanced manufacturing methods such as adhesive bonding techniques. The possible field leakage due to the air gaps is prevented by using an electromagnetic bandgap structure, consisting of glide-symmetric holes. A straight MLW line and a line with double 90° bends are fabricated by using chemical metal etching, as a proof of concept. The measurement results of the straight line show that the reflection coefficient is better than -18 dB with an average insertion loss of 0.02 dB/mm over the frequency band 110-170 GHz. For the double 90° bend line, the reflection coefficient is better than -18 dB with a similar average insertion loss of 0.02 dB/mm over the frequency band 110-150 GHz. The proposed concept could be an excellent candidate for designing compact and thin passive waveguide components and active components packaging, with a great potential for low-cost, light weight, and mass producible at millimeter-wave frequencies.

I. Introduction

Transmission lines are the fundamental building blocks of any high-frequency systems to guide, manipulate, and transmit signals. They play an important role in passive and active component design and integration. Conventional guiding structures, such as metal-pipe hollow waveguides and planar transmission lines (e.g., microstrip, substrate integrated waveguide (SIW), and coplanar waveguide), are popular and widely used technologies. Hollow waveguides show superior performance in terms of loss, while planar technologies exhibit compact and flexible manufacturing advantages.