Transmission resonances and antiresonances in metallic arrays of compound subwavelength holes

Transmission characteristics in metallic arrays of compound subwavelength holes are theoretically investigated. The structure consists of multiple slender holes in a unit cell. In addition to the dual transmission resonances that usually occur in single-hole arrays, the compound-hole arrays exhibit an extra pair of transmission resonance and antiresonance located at nearby frequencies. This feature is identified as the Fano resonance with the transmission line shape characterized by a Fano formula. The transmission resonance and antiresonance are further illustrated with the electric or field magnetic patterns at the corresponding frequencies. The underlying mechanisms of dual transmission and Fano resonances in the compound-hole arrays are also discussed.