Transmission enhancement of a half-wave wall under extreme angles by synergy of double lorentz resonances

Abstract

The a half-wave wall is usually adopted as the transparent window for electromagnetic (EM) waves ranging from microwave to optical regimes. Due to the interference nature, the bandwidth of the half-wave wall is usually quite narrow, especially under extreme angles for TE-polarized waves. It is usually contradictory to expand the bandwidth and to keep high transmission. To overcome this contradiction, we propose to extend the transmission bandwidth of half-wave walls under extreme angles by introducing Lorentz-type resonances using metasurfaces. The impedance of the half-wave wall is firstly analyzed. To improve the impedance matching, the impedance below and above the half-wave frequency should be increased. To this end, metallic wires and I-shaped structures are incorporated into the half-wave wall as the mid-layer. Due to the Lorentz-type resonance of the metallic wire, effective permittivity below the half-wave frequency can be reduced while that above the half-wave frequency can be increased due to Lorentz-type resonance of the I-shaped structures, both under large incident angles. In this way, the impedance matching, and thus the transmission, can be improved within an extended band. A proof-of-principle prototype was designed, fabricated, and measured to verify this strategy. Both simulated and measured results show that the prototype can operate in 14.0-19.0GHZ under incident angle [70°, 85°] with significant transmission enhancement for TE-polarized waves. This work provides an effective method of enhancing the transmission of EM waves and may find applications in radomes, IR windows, and others.