Ultra-wideband compact slot-coupled 180° hybrid based on ultra-wideband Wilkinson power divider

In this paper, a novel 180° coupler is proposed. The proposed hybrid uses the input port of an ultra wide band Wilkinson power divider as the summation port and replaces the resistor by an additional fourth port having the same characteristic impedance; this port will act as the difference port. The design of the proposed hybrid is developed using microstrip line and slot line, hence avoiding any complex structures. This configuration results in a broadband frequency performance where the return loss of the sum port and delta port is less than 10 dB for 80% bandwidth. Due to its symmetric configuration, the power imbalance and the phase imbalance between the output ports is less than 0.5 dB and 1°, respectively for over 200% bandwidth. The proposed hybrid also exhibits summation and difference port isolation with a measured result less than -40 dB over the complete range of frequency.