Broadband Antireflective Properties of Inverse Motheye Surfaces

Abstract

A new method for synthesizing broadband antireflective (AR) surfaces at microwave and millimeter wave frequencies is demonstrated. The AR surface, we call an inverse motheye, was formed by machining a multi-layer grating of subwavelength circular holes into a non-absorptive dielectric. This created low reflected energies ( 30 dB) over reasonably large bandwidths and incidence angles. An optimization algorithm, based on a direct pattern search, integrated with a rigorous electromagnetic model was used to design the grating geometries. Experimental results are provided at Ka-band demonstrating the validity of the method.

A Mini Review: Antireflective Coatings Processing Techniques, Applications and Future Perspective

“…Moth eye resembling bionic nanostructures resolves the issues of omnidirectional AR and replaces previous coatings in different optic equipment for enhancing transmittance due to ease of fabrication and low cost in comparison with multilayer coating stack. These moth eye and inverse moth eye nanostructures are fabricated in anechoic chambers to reduce microwave reflections in millimetres [164][165][166] . Similarly, moth eye nanostructures deposit on organic solar cell improves cell performance.…”

Analysis of Doubly Periodic Inhomogeneous Dielectric Structures by a Hybrid Projective Method

“…Assuming that the harmonic time dependence is chosen in the form , we represent the transverse components of the electric and magnetic fields in free space above the elements as expansions over a complete system of vector Floquet modes [33] (1) (2) where is the free space wave resistance, are specified amplitudes of the incident TE and TM modes, are unknown amplitudes of reflected TE and TM modes with propagation constants , ,…”

“…Note that relation (26) first provides the necessary condition for the magnetic field with components (7) and (9) and second reduces the number of the unknown coefficients standing in expressions (6) and (7) compared to the incomplete Galerkin method [20], [34] and the method of couple waves [2], [22]- [24].…”

“…Such applications include matching layers of artificial dielectric on surfaces of lens antennas [1], [2] and radio-absorbing covers of walls in anechoic chambers [3], [4]. Structures in the form of dielectric elements protruding from the metal waveguides are used in phased array antennas for shaping sector element patterns [5].…”

“…A list of such methods includes: -the method of surface integral equations [10], [11] -the method of auxiliary sources [12]; this method for twodimensional problems is easier than the method of surface integral equations, but it can be applied to the scatterers with smooth surfaces; -the method of integral equations for polarization currents [13], [14]; it is more universal than the previous two methods, since it allows analysis of inhomogeneous dielectric scatterers; -the finite-difference frequency-domain (FDFD) method [15], also allowing analysis of inhomogeneous scatterers; -the method of pattern equations [16], applicable only to homogeneous scatterers; its effectiveness is questionable, since [16] contains neither numerical results for comparisons with other methods; -the finite element method (FEM) [17] and its hybrid versions, for example [18], which are also universal; -the boundary element method [19]; and -a group of universal methods reducing the problem to systems of ordinary differential equations, including incomplete Galerkin method [20], unimoment method [21], method of coupled waves [22]- [24], used in [2], a modification of the coupled mode method combined with one-dimensional finite element method [25] and method of cross sections used in [26]. A hybrid projective method, relative to [25], was recently developed in [27] and [28] for analysis of one-dimensional periodic structures with wedge elements for application to matching layers and absorbing covers.…”