Wideband 3 dB Branch Line Coupler Based on $\lambda/4$ Open Circuited Coupled Lines

This letter introduces a new 3 dB branch line coupler for wideband applications. The wideband matching property of the coupler with four λ/4 open circuited coupled lines is briefly derived. The coupler with a suspended microstrip and microstrip line structures has been simulated with HFSS and fabricated. Measurement results show insertion loss better than 3.6 dB with a power imbalance of 0.5 dB; return loss and isolation characteristics both better than 20 dB over 49% fractional bandwidth.