Dual-band rat-race coupler with arbitrary power divisions using microwave C-sections

Rat-race coupler is designed to have dual-band operation, a miniaturized area, and arbitrary power division using microwave C-sections. With a C-section and two transmission line sections attached to both of its ends, an elementary two-port is designed to play the role of a quarter-wave section in a conventional rat-race. It is designed to possess phase changes of 90° and 270° at the first and second frequencies, respectively. Transcendental equations are derived for calculating its structure parameters. Two circuits operating at 2.45/5.8 GHz with various output power ratios are fabricated and measured. Both couplers have only 31% area of conventional rat-race at the first band. It is believed that these circuits have the best size reduction for microstrip dual-band rat-race with arbitrary power division in open literature. Measured results agree well with their simulation counterparts.