Broadband Phase Shifter with Constant Phase Based on Negative Group Delay Circuit

A broadband phase shifter (PS) with a constant phase based on a negative group delay (NGD) microwave circuit is proposed. The presented broadband PS is composed of distributed microstrip lines and two resistors, which is based on the positive group delay compensation principle. By tuning the electrical length of the phase shift transmission line, the constant phase can be obtained in the range of -360 degrees similar to 0 degrees. For verification, three broadband PSs with the phase shift of -90 degrees, -180 degrees, and -270 degrees (90 degrees) are designed, fabricated, and measured at the center frequency of 1.0 GHz. The measurements show that the -90 degrees PS can achieve a constant phase of -90 degrees +/- 3.0 degrees with a fractional bandwidth (FBW) of 73.1%; the -180 degrees PS can achieve a constant phase of -180 degrees +/- 5.0 degrees with an FBW of 51.1%; and the -270 degrees PS can achieve a constant phase of -270 degrees +/- 4.0 degrees with an FBW of 40.4%. Besides, the return loss is greater than 13.6 dB in the flat-phase bands.