Simple ladder-like single-layer balanced wideband phase shifter with wide phase shift range and appropriate common-mode suppression

In this study, a single-layer balanced wideband phase shifter with a wide phase shift range of 45 degrees-315 degrees and acceptable common-mode (CM) suppression is proposed. The main branch has a simple ladder-like structure and the reference branch utilises a coupling structure. The main branch electrical length is constant for any desired differential-mode (DM) phase shift. Assuming a specific return loss (e.g. 16, 20, and 25 dB), the phase shifter is carefully analysed and a design procedure is given leading to an ultra-low phase error design. Then by making a trade-off between the CM and DM bandwidths at the cost of higher phase error, more design solutions for the phase shifter are given. To validate both the proposed structure as well as its design procedure, a balanced wideband phase shifter with the DM phase shift of 180 degrees +/- 4.2 degrees (1.851-4.017 GHz) and the CM suppression of better than 15 dB (1.81-4 GHz) is fabricated, resulting in 73.82 and 75.25% fractional bandwidth, respectively. The fabricated balanced phase shifter has a return loss of vertical bar S-11(dd)vertical bar < - 14.87 dB and insertion loss of vertical bar S-21(dd)vertical bar > - 0.95 dB. The synthesised, simulated, and measured results are in good agreement with each other.