Collimating Cylindrical Surface Leaky Waves for Highly Improved Radiation Characteristics of Holograms

Abstract

High resolution microwave leaky wave holograms excited by center-fed cylindrical surface wave launcher show a null at object wave direction which is an undesired effect for electromagnetic beamforming. Also, planar leaky wave metasurfaces generating a tilted beam extremely suffer from the destructive effect of non-forward surface leaky waves at frequencies other than the design frequency and they are almost operable at a single frequency. Here we propose a 2-D modified hologram configuration using parabolic surface reflector to collimate the non-forward leaky modes into the forward leaky modes. The modified hologram presents null-free radiation pattern and highly improved operating frequency bandwidth. The consequent frequency bandwidth provides the scannabality property by frequency variation. The forward mode-dominant surface wave excitation of hologram lets the metasurface to generate the object beam more precisely; therefore, high directivity all over the operating bandwidth is obtained. The parabolic reflector lets the radiative surface of the metasurface to get shrunken in less than half of the conventional holograms. The concept is verified by fabrication and experimentally tested confirming the beam maintenance over a reasonable frequency range and scannability property.

Wide-scanning Circularly Polarized Reflector-based Modulated Metasurface Antenna Enabled by a Broadband Polarizer

“…One suitable method for eliminating the adverse effects of backward modes and improving the bandwidth of the antenna is through implementing surface wave reflectors. In [20], [21], surface wave reflectors are used to increase the bandwidth and to realize the scannability in isotropic holographic antennas.…”

“…The top and bottom surfaces of this substrate is covered by copper. The diameter of vias and the distances among them are chosen so that the row of vias acts as a metallic wall [20] and prevents the wave leakage. A monopole antenna is located at a distance of 5 mm from the corner of wedge-shaped reflector.…”

“…Although MoMetAs have the mentioned merits, but they suffer from narrow bandwidths and narrow frequency scanning range. In [20] and [21], surface wave reflectors are utilized to incorporate scannability to the isotropic holograms. Surface wave reflectors can eliminate the destructive effects of backward modes.…”

Reconfigurable honeycomb metamaterial absorber having incident angular stability

“…Artificial metamaterials composed of subwavelength engineered scatterers have attracted massive attention owing to their abilities to modify the permittivity and permeability values to reach beyond those of composite materials found in nature, which may be structured for complex manipulation of electromagnetic (EM) waves 1 – 4 . The metamaterial absorbers (MMA), as an interesting application of metamaterials, have become a research hotspot in the past decade and have also been of great interest for solving electromagnetic interference problems, such as the stealth technologies, solar cells and sensor applications 5 – 8 .…”

Spatial Wave Control Using a Self-biased Nonlinear Metasurface at Microwave Frequencies

“…Meanwhile, theoretical developments like the emergence of Generalized Snells law of reflection and refraction, paved this way. The result of the rapid growth of metasurfaces to wave control has witnessed and found a special place in achieving negative refraction [1,2], engineered antennas [3][4][5], beam scanning [6,7], invisibility cloak [8,9], absorbers [10], polarizers [11], dispersion engineering [12,13], and advanced analog computing [14][15][16][17][18]. Demands for any type of flexible structures made scientists of this field use the materials like graphene [19][20][21], vanadium dioxide [22][23][24] and semiconductors [25,26] as the phase change materials.…”