**5.1 Self-compensating wideband shifter**

A phase shifter just using a delay line cannot be used to achieve the phase shift in a wide frequency range because it will cause a large phase deviation. To solve this problem, we can use the phenomenon that the delay line and the unequal-width structure to make an opposite dispersive phase shift and realize a wideband compensation phase shifter [42]. As shown in **Figure 31**, a broadband SIW selfcompensating phase shifter is proposed. The differential topology reduces the frequency sensitivity. The fabricated phase shifter achieves a 90° phase shift from 25.11 to 39.75 GHz, and the phase imbalance between the two paths is within 0.2 dB and 2.5 dB, respectively [43].

Another compensation method is slotting compensation [44]. By taking advantage of the effects of the slots on the value and slope of the phase shift, slotted SIW is proposed to produce the phase shift slopes which are opposite to the microstrip delay lines to achieve a wide bandwidth phase shifter. The concept of such a technique is verified by designing 90°, 45°, 45°, and 90° phase shifter prototypes, as shown in **Figure 32**.
