Design of Microstrip Transversal Signal-Interference Circuit With Large Group Delay

This letter presents the group-delay (GD) analysis and design of a microwave stub-loaded structure. This circuit can be designed using transversal signal-interference (TSI) principles, which were previously applied to realize sharp-rejection microwave filters with transmission zeros (TZs) through constructive/destructive signal-interaction effects. The engineered circuit topology consists of a bi-path in-parallel transmission-line (TL) filtering stage loaded with an open-ended TL segment or stub at one of its electrical paths. This type of circuit exploits the spectral phase-slope variation of its transfer function, which is caused by modifying the frequency spacing between the two created notched bands or TZs below/above its main passband to generate a large GD within it. A microstrip prototype of the devised TSI-based GD circuit is built and tested for experimental-validation purposes. It exhibits among the highest GD of 10.3 ns at its operational frequency of 1 GHz compared to prior-art large-GD structures reviewed in the open literature.