Wideband Single-Layer 90 $^{\circ}$ Phase Shifter Using Stepped Impedance Open Stub and Coupled-Line With Weak Coupling

This letter proposes a novel design approach of wideband 90
^°
phase shifter, which comprises a stepped impedance open stub (SIOS) and a coupled-line with weak coupling. The result of analyses demonstrates that the bandwidths of return loss (RL) and phase deviation (PD) can be expanded by increasing the impedance ratio of the SIOS and the coupling strength of the coupled-line. For RL > 10 dB, insertion loss (IL) 1.1 dB, and PD of ±5
^°
, the fabricated microstrip single-layer phase shifter exhibits bandwidth of 105% from 0.75 to 2.4 GHz.