Broadband Compact 180 $^{\circ}$ Hybrid Derived From the Wilkinson Divider

A novel 180?? hybrid is proposed. This hybrid is derived from the Wilkinson divider, where the resistor is simply replaced by a fourth port of equal characteristic impedance, which acts as the ?? port of the hybrid, while the input port of the original Wilkinson divider acts as the ?? port. Due to this structure, including only two quarter-wavelength transmission lines, this hybrid has a greatly reduced size compared with the conventional hybrid rat-race and miniaturized variants of it. Furthermore, it exhibits a significantly improved bandwidth. The measured 0.5-dB insertion loss bandwidth is over 200% for ?? power division and 66% for ?? power division (with 50-?? load). Due to its perfectly symmetric configuration, the proposed hybrid features frequency-independent power-dividing balance performance. The 0.5-dB amplitude imbalance for both the ?? and ?? port divisions has essentially unlimited bandwidth, and the measured phase imbalance is within 3^?? over all frequencies. The proposed hybrid also shows excellent ?? - ?? port isolation with a measured result exceeding 30 dB over all frequencies.