Broadband 90$^{\circ}$ Differential Phase Shifter Constructed Using a Pair of Multisection Radial Line Stubs

The current paper proposes a broadband 90
^°
differential phase shifter using a pair of multisection radial transmission-line (TL) stubs. The scattering parameters of the differential phase shifter are calculated based on the radial TL theory to evaluate the differential phase shifter's performance. Global optimization is performed using the TL model followed by a local optimization based on a more accurate electromagnetic simulation. The measured operating bandwidth of the circuit is 101.5%, which is larger than many designs in the literature.