why does self-complementary antenna have constant input impedance

[ermai]

Dear All:

I would like to know the principle of why complementary antenna has a constant input impedance.Could someone tell me or show me the documents?I would appreciate very much

 

[PlanarMetamaterials]

Hi ermai,

Search Babinet's principle (for antennas). It will tell you that the input impedance is related to the electrical size of metal vs its compliment (no metal). Since this ratio is always the same for complimentary antennas, so will the input impedance be constant.