Broadband Single-Mode Hollow Substrate Integrated Waveguide with Photonic Crystal Sidewalls for Multilayer System-in-Package Applications

We numerically and experimentally demonstrate a broadband single-mode hollow substrate integrated waveguide using one-dimensional photonic crystal as sidewalls in place of metallic via holes. By avoiding the vertical metallic walls, the waveguide can be easily fabricated as a photonic crystal structure on a single planar substrate sandwiched between two parallel metal plates. Such a hybrid flat waveguide can tightly confine the millimeter and terahertz waves in the low-loss air core. With the aid of the photonic crystal sidewalls, high-order competing modes in the waveguide are substantially suppressed based on the so-called modal-filtering effect, allowing the waveguide to be operated in a single-HE 01 -mode pattern over an octave bandwidth. Benefiting from the less use of metallic walls, the propagation loss of the proposed hybrid waveguide can be less than that of the classic hollow metallic rectangular waveguide at millimeter-wave and terahertz frequencies according to our numerical simulation. A proof-of-concept experimental demonstration operating between 20 to 45 GHz is presented verifying the properties and the advantages of the proposed waveguide. This works offers a promising candidate for an octave-bandwidth single-mode transmission line for millimeter-wave and THz multilayer system-in-package applications.