A novel waveguide called multilayer porous waveguide (MPW) is proposed as microwave low-loss transmission lines. MPW is a fully rectangular dielectric waveguide composed of several periodically rectangular air gaps in a bulk dielectric that can be easily formed by placing several dielectric substrates in interval with air gaps. The loss and propagating characteristics of both TE and TM modes in MPW are studied. The TE mode confined in the air gaps has a lower loss than the TM mode spread out in air gaps and dielectric; however, the loss of TM mode is still less than that of conventional microwave waveguides. Finally, MPW is an artificial material with desirable electrical permittivity and loss that can be used in structure of conventional waveguides.
