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.