Total broadband transmission of microwaves through a subwavelength aperture by localized E-field coupling of split-ring resonators

Resonance coupling of two resonators with the same resonant frequency is a highly efficient energy transfer approach in physics. Here we report total broadband transmission of microwaves through a metallic subwavelength aperture using the coupled resonances of the strongly localized electric fields at the gaps of two split-ring resonators (SRRs) placed on either side of the aperture. At the center frequency of the broad band, the phase difference between the two localized time-varying electric fields is 90°, which is consistent with the critical coupling state that is a sufficient condition for the two-resonator system to realize total transmission if the resonators are assumed to be lossless.