Transitioning to RF Filtering

High-speed/high-data-rate signal transmission is a fundamental operational requirement for emerging beyond-5G/6G wireless communication applications, such as immersive augmented reality and virtual reality <xref ref-type="bibr" rid="ref1" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[1]</xref>. For the constituent monolithic microwave integrated circuits aimed at the RF transceiver front ends corresponding to these appealing technologies, microstrip-to-microstrip transitions are widely recognized as essential RF components <xref ref-type="bibr" rid="ref2" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[2]</xref>. They perform the role of transmission media necessary to maintain the RF power signal transmission/interconnection among two or more microstrip lines of the circuit modules corresponding to different layers in compact multistack RF systems. They should exhibit wideband/broadband transmission frequency responses with low power insertion loss levels within their operational ranges. To make them compatible with multilayer microwave integrated circuits, microstrip transitions are currently developed in two distinct basic types, namely, via hole transitions and vialess aperture-/slot-line-coupled transitions. Due to their simpler configuration of two microstrip lines that are directly connected through the circuit board layers by means of a via hole, via hole transitions have become popular, and today they are exploited in most RF/microwave multilayer components <xref ref-type="bibr" rid="ref3" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[3]</xref>. However, although they can attain broadband transmission bandwidths (BWs) above dc, their frequency selectivity can be restricted by low-pass-type responses and poor filtering performance <xref ref-type="bibr" rid="ref4" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[4]</xref>.