3D Printed 260 GHz Drawer-Like Bandpass Filter Using Groove Gap Waveguide Concept

This paper presents a 3D printed <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$2^{\text {nd }}$</tex> order bandpass filter operating at 260 GHz. This component is made of two parts that are fabricated using a high precision photopolymer-based polymer printer with high spatial resolution <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(2 \mu ~\mathrm{m})$</tex>. The central part is a waveguide section containing rows of pillars that are dimensioned using the groove gap waveguide approach (GGW) and that define two coupled waveguide resonators through an inductive iris. The printed polymer pillars are metallized using proprietary copper plating, leading to an effective conductivity of around <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$22 \text{MS} / \mathrm{m}$</tex> at this frequency. This part that looks like a drawer is then inserted into a custom printed and copper metallized WR3.4 flange (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$220-325 \text{GHz}$</tex>) for the measurement of the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$S$</tex> parameters. The bed of pillars helps here to maintain a virtual electrical continuity between the drawer and the flange even if there are no physical contact between the top of the pillars and the metal roof above them. The measured central frequency is 258.91 GHz and is very close to the simulated value of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{2 5 7. 5 5 ~ G H z}$</tex> (only <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{0. 5 3 \%}$</tex> deviation). The obtained bandwidth is 2.96 GHz (about 1.1 % of the operating frequency) with an insertion loss of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{1. 3 ~ d B}$</tex>, confirming an unloaded quality factor of about 845 at this frequency.