Wideband Quadrature Coupler Implementation for a Balanced S Band Amplifier

An implementation of a wideband quadrature coupler for a balanced S band amplifier is proposed in this paper. By adopting a previously proposed design, a wideband branchline coupler is implemented on a 3.66 relative permittivity and 0.762 mm thick substrate to operate from 2.9 GHz up to 3.5 GHz. A meandering approach is taken to minimize the branchline coupler's relatively large structure, achieving roughly 75% area reduction in the process. The final design layout is then implemented on an amplifier-MMIC based S band balanced amplifier to characterize its performance in regards to the amplifier's return loss and gain. Measurement results show excellent return loss of the quadrature coupler despite open-circuit terminations of under -13 dB, although a 2 dB gain loss is observed when comparing the balanced amplifier's gain to the used amplifier MMIC's original gain.