Flexible Ultrathin Strip-on-Substrate Coaxial Gap Waveguide Technology for Millimeter-Wave

This paper presents Strip-on-Substrate Coaxial Gap Waveguide (SCGW) technology, a novel transmission line for millimeter-wave applications. Its key distinction is an open coaxial structure requiring no electrical contact for the outer conductor. To suppress wave leakage, an electromagnetic bandgap structure—formed by vertically stacked metal pin-bed sheets and a substrate sheet—serves as the outer conductor, encapsulating the strip -type inner conductor. Several fabricated prototypes show that in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\bf {76{-}81}$</tex-math></inline-formula> GHz range, reflection coefficients are better than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\bf {-10}$</tex-math></inline-formula> dB, with transmission losses of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\bf {0.25{-}0.32}$</tex-math></inline-formula> dB/cm for single-sided-strip SCGW and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\bf {0.18{-}0.26}$</tex-math></inline-formula> dB/cm for double-sided-strip SCGW, confirming the potential of the design for mmWave applications.