Design of Broadband Branch-Line Couplers Utilizing Coupled Transmission Lines at Ka-Band

This paper describes broadband branch-line couplers (BLCs)with arbitrary coupling factors at Ka-band. The coupler has open-/short-circuited coupled transmission lines as external matching networks and a pair of branch-lines. Electromagnetic simulations for designed broadband couplers with coupling factors from -3 dB to -30 dB based on the equivalent admittance approach are carried out to verify the band-broadening design method.