Differential microstrip line to waveguide transitions for D-band based on irises

D-band waveguide transitions that combine a resonant patch on the printed circuit board with multiple waveguide irises are presented and shown to achieve a relative bandwidth of up to 35%. The irises implement an impedance-matching network that is described by a lumped-element circuit model. Parametric sweeps and Monte Carlo simulations quantify the influence of iris dimensions and manufacturing tolerances. The transitions’ group delay is characterized, and its influence on time-domain signals is demonstrated. As an application example, a transition design with six irises is integrated into a multichannel radar frontend with 40\,GHz bandwidth, and measured range profiles are presented. The derived design guidelines enable straightforward customization of iris-based transitions for various applications and frequency bands.