Design of a slot-coupled Ultra-Wideband 180° hybrid coupler

In this paper a wideband microstrip 180° hybrid coupler is proposed. The coupler is designed using a double sided single layer substrate for Ultra-Wideband (UWB) applications. The device is constructed from Wilkinson Power Divider (WPD) employing microstrip line to slot transition for the construction of a delta (Δ) port. The input port (Σ port) of the WPD acts as the in phase power divider. The Σ and Δ ports are located opposite to each other, making the overall size compact and easy for measurements. The proposed method of design results in a 180° hybrid coupler with good UWB performance. The return loss of the sum port and delta port is less than 10 dB. The power imbalance and the phase imbalance between the output ports is less than 0.5 dB and 0.8°, respectively, for complete UWB frequency range. The isolation between sum and delta ports is more than 40 dB.