Design of Ultraflat Phase Shifters Using Multiple Quarter-Wavelength Short-Ended Stubs

This letter presents a kind of ultraflat phase shifters using multiple quarter-wavelength (λ/4) short-ended stubs. The proposed topology consists of a uniform line with multi-λ/4 short-ended stubs and a reference line. Inspired by the high-pass filter design, the phase difference can be analytically determined by the impedance and the number of the short-ended stubs. In order to obtain a wider phase bandwidth with ultraflat phase difference around the center operating frequency, a generalized design equation is newly derived over a wide achievable range from 15° to 360°. As a validation, the third-order proposed phase shifter with 135° phase difference is designed and implemented at 3 GHz. The measured results show a good agreement with those obtained from simulation. The measured 10-dB impedance bandwidth achieves 102%, and the bandwidth of 135° ±5° phase difference is about 78%.