Substrate integrated waveguide (SIW) broadband compensating phase shifter

In this paper, a broadband compensating phase shifter is presented based on the substrate integrated waveguide (SIW) technology. The SIW is a dispersive guided-wave structure, but the phase shifts generated by two different structures (the delay line and the equal-length unequal-width phase shifter) have just reverse varying tendencies versus frequency. Thus, the complementing combination of them will make phase shift almost constant over a wide band. Detailed design equations are given following a mathematical analysis. The limitation of variation of SIW width and the tolerance issue are investigated as well. As an example, a 90deg compensating phase shifter is designed on a single-layer substrate with normal PCB process at the center frequency of 30 GHz. The amplitude imbalance between the two paths is within 0.2 dB while the phase error is less than 2.5deg over the frequency band from 25.1125 to 39.75 GHz, or around 49% relative bandwidth. The return loss is found to be better than 12 dB over the whole frequency band. Measured and simulated results of the proposed structure are in a good agreement. This type of SIW phase shifter is superior to all of its counterparts and increases the relative bandwidth of early designs about five times.