A construction of coupled-line 3-dB couplers using quarter-wave connecting lines

This paper presents a construction of coupled-line 3 dB couplers in a fully-planar structure. By connecting two identical λ/4 coupled-lines in cascade by two λ/4 non-coupled lines, a realizable combination of the even- and odd-mode characteristic impedances for the coupled-lines is fulfilled. After the fundamental behavior of TEM-line couplers is described, microstrip couplers are designed actually. As a result, a 27 % bandwidth is obtained for 0.5 dB amplitude balance tolerance, and return loss and isolation better than 20 dB. In addition, em-simulations performed for three circuit configurations verify the design procedure and the flexibility of circuit layout. Finally, experimental results are shown.