Finite element analysis of transmission loss across a coplanar waveguide-integrated printed circuit board for quantum information science applications

Quantum information science (QIS) relies heavily on low-loss transmission lines for exciting and measuring myriad quantum devices in the RF bandwidth. However, factors such as impedance mismatches and parasitic mode coupling lead to loss and spurious reflection across a printed circuit board (PCB) array, especially when signal wavelength is comparable to feature size. This talk outlines the various considerations needed when designing a PCB sample box and which optimizations contribute to the achieved performance improvements. We use the ANSYS electronics workbench, HFSS, to investigate the effects of coupler configuration, PCB thickness, dielectric constant, and PCB via pattern on transmission spectra across a transmission line printed on a silicon substrate. We report on common sources of PCB loss, then proceed to detail optimal parameters for < 0.25 dB return loss in the crucial 4-8 GHz bandwidth. These steps lead to favorable simulated PCB performance and can serve as a guide for those designing sample boxes for QIS applications.