While this works well, the splitter and delay line take up valuable board space, introduce losses, tend to radiate and may degrade the radiation pattern.
A different approach is based on the fact that each patch mode (TM10, TM01) behaves like a parallel RLC resonant circuit. If we make the x and y dimensions of the patch slightly different, there will be two resonant frequencies, fa and fb and we will see two different RLC circuits. This creates a phase shift change versus frequency as shown in Figure 6: