Abstract
We demonstrate an air-core single-mode hollow hybrid waveguide that uses Bragg reflector structures in place of the vertical metal walls of the standard rectangular waveguide or via holes of the so-called substrate integrated waveguide. The high-order modes in the waveguide are substantially suppressed by a modal-filtering effect, making the waveguide operate in the fundamental mode over more than one octave. Numerical simulations show that the propagation loss of the proposed waveguide can be lower than that of classic hollow metallic rectangular waveguides at terahertz frequencies, benefiting from a significant reduction in Ohmic loss. To facilitate fabrication and characterization, a proof-of-concept 20 to 45 GHz waveguide is demonstrated, which verifies the properties and advantages of the proposed waveguide. A zero group-velocity dispersion point is observed at near the middle of the operating band, which is ideal for reducing signal distortion. This work offers a step towards a hybrid transmission-line medium that can be used in a variety of functional components for multilayer integration and broadband applications.
Highlights
The millimeter-wave and terahertz (THz) frequency bands have attracted much attention owing to their unique applications, such as ultra-broadband spectroscopic sensing [1], high-data-rate wireless communication [2], imaging and non-destructive testing [3], security screening [4] and radio astronomy [5]
Planar transmission lines are widely used in functional components and multichip modules for realizing passive components and interconnects, but they generally suffer from high substrate and radiation losses at 1 THz and above, as well as mode competition with the substrate modes [6]
Substrate-integrated waveguide (SIW) has been reported to be broadband and operate to 0.5 THz with loss less than 3.5 dB/cm by selecting different operating modes at different bands, but it is difficult to metalize the vias in SIW - especially when the vias become very small at short wavelengths [18]
Summary
The millimeter-wave (mmW) and terahertz (THz) frequency bands have attracted much attention owing to their unique applications, such as ultra-broadband spectroscopic sensing [1], high-data-rate wireless communication [2], imaging and non-destructive testing [3], security screening [4] and radio astronomy [5]. By avoiding the vertical walls, the waveguide can be fabricated as a photonic crystal structure on a single planar substrate sandwiched between two parallel ground planes, with no metalized via holes It is, in essence, a flat form of the well-known Bragg fiber [25] that can be realized on a single substrate and so we call it a Substrate Integrated Bragg Waveguide (SIBW). A proof-of-concept millimeter-wave SIBW was designed and tested in order to verify the transmission properties of the proposed structure It has a relatively low operating frequency, it verifies the physical mechanisms for octave bandwidth single-mode operation and so demonstrates that this is an important candidate for an octave-bandwidth single-mode transmission line for mmW and THz functional components, such as filters, power dividers, and H-plane horn antennas
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