Improvement of the Phase Shifter in 90 $^{\circ}$ Power Splitter for UWB Applications

This letter presents an improvement of the T-type high-pass network inside the phase shifter of a broadband 90 $^{\circ}$ or quadrature power splitter (QPS). This broadband QPS consists of a broadband Wilkinson power divider and a broadband 90 $^{\circ}$ phase shifter. By the proposed design, the bottom layers of MIM capacitors are utilized as a coupled line to improve the bandwidth of phase error and return loss. The measured results of this QPS show the phase error of less than $\pm 5^{\circ}$ and the imbalance at output ports of smaller than 0.3 dB from 3.1 to 11.1 GHz. Return losses of this QPS are better than 11.7 dB, and the isolation between two output ports is better than 15 dB within the same frequency range.