Wideband vertical microstrip-to-microstrip transition designed with cross-coupled microstrip/slotline resonators

In this paper, a wideband vertical microstrip-to-microstrip transition designed with cross-coupled microstrip and slotline resonators is proposed. By utilizing two identical microstrip lines on top and bottom layers perpendicularly coupled with a uniform slotline resonator on the ground plane, a wideband filtering performance with three transmission poles can be obtained. To confirm the predicted results, a prototype vertical transition centered at 6 GHz is fabricated with a two-layered substrate. The operating bandwidth from 3.60 to 8.16 GHz with maximum insertion loss around 1.0 dB and group delay less than 0.45 ns is measured. Furthermore, owing to the existing tolerance in the fabrication process, the discrepancies between the simulation and measurement results is analyzed and discussed.