Ohta, I   XP Li   T Kawai   Y Kokubo   
1997 ASIA-PACIFIC MICROWAVE CONFERENCE PROCEEDINGS, VOLS I-III 1141-1144 1997年
In this paper, we first describe a general design procedure of a twofold symmetric directional coupler. Next, we design four types of lumped-element quadrature 3 dB hybrids and try to improve the bandwidth of the performance in accordance with the...