Why a guard ring with width of guidewave-length/2 suppress the surface wave of microstrip antennas?

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KatoAn

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Hi, I got a problem about the guard ring of microstrip antennas.
In this figure, there is a guard ring around the dipole. It is designed to suppress the surface wave.
In the paper, the author expresses as: it helps to suppress the surface wave because the guard ring of width wr=lamda_g/2 functions as an open circuit to the surface wave. However, I don't understand why the guard ring function as an open circuit and thus the surface wave is suppressed.

Thanks all.
 

I don't have the dimensions of the antenna from the picture you posted, but keeping the proportions the results which I got should be fine.
With the guard ring in place the return loss S11 is better with more than 10dB (from -9dB to -20dB) compared with no-ring situation.
But the radiation pattern looks much different when using the guard ring. Has more parasitic lobes, which means less radiated power from the main lobes.
 

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