A design of wideband 3-dB coupler with N-section microstrip tandem structure

New design equations and a 3-dB microstrip coupler example for N-section tandem connected structure with wide bandwidth are presented. The proposed four-port S-parameters and equations are obtained from a port reduction method. The designed microstrip 3-dB coupler not only does not need high impedance lines, but also uses tight coupling gaps differently from conventional couplers such as Lange couplers, parallel coupled line couplers, etc. The measured data agrees well with the expected data, which show a wide bandwidth of 42%, an amplitude imbalance of ±0.5 dB, a phase unbalance of 1.0°, and isolation characteristics of 15 dB at the band of 3.6 to 5.5 GHz.