A leaky-wave groove antenna at optical frequency

In the framework of nanoantennas functioning at optical frequencies, we present here a new kind of leaky-wave antenna realized as a groove in an aluminum superstrate, supported by a silver substrate. The antenna works in the optical frequency range where the silver acts as a dielectric with equivalent refractive index between zero and one. Under these conditions, the dominant mode launched in the structure exhibits a phase velocity larger than the speed of light in free-space, thus producing a leaky-wave radiation in free-space. We propose a simplified analytical form of the dispersioncharacteristic of the fundamental mode supported by the structure, which allows for identification of the radiative leaky-wave condition. We also propose approximate formulas for calculating the antenna gain and loss efficiency. The results obtained through these formulas are successfully compared with full-wave simulations. The final parametric study shows how the radiationcharacteristic is affected by the variation of geometric features.