Study of wideband microstrip 90° 3-dB two-branch coupler with minimum amplitude and phase imbalance

The properties, especially the phase properties, of a wideband microstrip coupler with very flat coupling are simulated, measured and analyzed. Then a modified wideband microstrip 90deg 3-dB two-branch coupler with flat amplitude response, low insertion loss, small amplitude imbalance and phase imbalance is proposed. This wideband coupler can be used to design wideband correlators. By tuning and optimizing the matching network at each output of a normal two-branch coupler according to both magnitude and phase properties, the relative bandwidth of this modified coupler with the minimum amplitude and phase imbalance can reach 50%, with frequency range of 3-5 GHz.