A compact wideband parallelstrip 180° hybrid coupler

In this study, a wideband compact parallel-strip 180° hybrid coupler with the center frequency of 2 GHz is presented. By replacing the 270° section in the 180° hybrid coupler with a parallel-strip phase reversal swap, the total circuit size is reduced by half. In this structure, the phase gradients of the four arms of the coupler are equalized; therefore, the operation bandwidth is dramatically enhanced. S-parameters of the coupler are simulated and measured with good agreement. As predicted from the measured data, the bandwidth of the 90% combining efficiency is increased from 45 to 124%. The proposed design achieves more than -25 dB signal suppression within the whole measured frequency range (0-4 GHz) as opposed to 1.8 to 2.2 GHz of the conventional design. The proposed 180° hybrid coupler can serve as a wideband in-phase/differential power divider/combiner, which are essential for many RF and microwave subsystem designs. © 2008 Wiley Periodicals, Inc.