Low-loss millimeter-wave propagation of the Ex11 mode in a synthesized insulated image guide

An insulated image guide operating in Ex¹¹ mode (where the electric field is primarily parallel to the ground-plane) is investigated experimentally and by simulations in the frequency range of 80 GHz to 100 GHz. The proposed waveguide is characterized by a thick low-permittivity gap layer sandwiched between the ground-plane and the main high permittivity dielectric slab. This waveguide features low propagation loss and low coupling to unwanted modes at discontinuities. A resonator method is applied for accurate measurements. A waveguide based on alumina ceramic as a dielectric (tanδ = 0.002) and brass as ground metal, has an attenuation constant of 0.07 dB/mm at 90 GHz. A 60° bend adds 0.33 dB loss at 90 GHz.