Branch-Line Coupler Design Operating in Four Arbitrary Frequencies

This letter presents a successful design approach for a branch-line coupler operating in four arbitrary frequencies. An optimized compensation technique is adopted to fulfill satisfactory matching, transmission and isolation properties within each operating band. Based on the simple planar microstrip technology, the proposed quad-band coupler has been realized and tested. A return loss better than 16 dB, together with an amplitude imbalance limited to 0.3 dB and an isolation higher than 17.5 dB, have been experimentally measured on each operating band, validating the proposed design methodology.