Broadband Self-Compensating Phase Shifter Combining Delay Line and Equal-Length Unequal-Width Phaser

Abstract

In this paper, a broadband self-compensating phase shifter is presented and developed on the basis of substrate integrated waveguide (SIW) technology. Since the SIW is a dispersive guided-wave structure, the effective bandwidth of SIW phase shifter is usually narrow. Phase shifts generated by two different structures, namely delay line and equal-length unequal-width phase shifter, are discovered in this work to present interesting opposite tendencies versus frequency. Therefore, an appropriate combination of them will make the phase shift almost constant over a very wide band. Design equations and process are given following a mathematical analysis. To demonstrate the interesting and useful features of the proposed technique, a 90° and a 45° self-compensating phase shifters are designed as showcases with standard printed circuit board process. For the 90° version, the measured amplitude and phase imbalance between the two paths are within 0.2 dB and 2.5° , respectively, within the frequency band from 25.11 to 39.75 GHz, or around 49% bandwidth. The return loss is found to be better than 12 dB within the frequency band of interest. The 45° one has the similar excellent performance. The measurements demonstrate that this type of SIW phase shifter is superior to all of its counterparts.