Bonnie Martin

Low Cost and Broadband Dual-Polarization Metamaterial Lens for Directivity Enhancement

Metamaterials have been used in many different configurations to enhance the radiation properties of antennas. However, the vast majority of these metamaterial applications only consider linearly polarized antennas. This paper discusses the theory, design, implementation, and measurements of a far-field collimating lens for use with a circularly-polarized crossed-dipole antenna constructed from a 3D-volumetric metamaterial slab. Zero-index materials (ZIM) and low-index materials (LIM) cause the magnitude and phase of the radiated field across the face of the lens to be distributed uniformly, increasing the broadside gain over the feed antenna alone. Full-wave simulations were used in design of the lens, and a prototype metamaterial lens (meta-lens) was constructed and measured to verify the theoretical predictions. The meta-lens was found to increase the measured directivity of a crossed-dipole feed antenna by more than 6 dB, in good agreement with numerical simulations.

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Metamaterials with properly engineered surface properties have been recently proposed for application in the design of broadband hybrid-mode horn antennas, such as soft and hard horns. In this paper, we present the design, fabrication, and measured results of a square dual-polarization horn antenna with thin metasurfaces lining the four walls, demonstrating broadband, negligible-loss hybrid-mode operation. By employing a powerful genetic-algorithm (GA) design optimization technique, we have dispersion-engineered low-index metaliners whose surface impedances satisfy the balanced hybrid condition across the Ku-band. The optimized metaliners were synthesized based on conventional printed-circuit board technology, leading to a lightweight and low-cost construction. To improve the cross-polarization response, a simple dielectric plug was placed in the throat of the horn to perform effective mode conversion. Measurements showed that the fabricated horn antenna prototype provided low sidelobes, low cross-polarization levels, and radiation patterns that are approximately independent of polarization. Excellent agreement was found between measured and simulated results across the entire band of operation. Both the far-field radiation patterns and the aperture field distributions confirm the hybrid-mode operation of the horn, validating the balanced metasurface design. This metamaterial-enabled antenna represents a low-cost alternative to other types of soft feed horns, such as corrugated horns.

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This paper reports on the detailed design and experimental demonstration of a metamaterial-enabled low-sidelobe horn antenna (metahorn) based on principles similar to those of earlier soft horn antennas. The target application is a linearly polarized feed horn in the super-extended C-band (3.4-6.725 GHz) for communication satellite reflector antennas. The paper describes the detailed design and manufacturing of the -plane metamaterial liner (metaliner) based on a freestanding wire grid without the need for a dielectric substrate material. The measured copolarized and cross-polarized antenna patterns from the feed horn demonstrate over an octave pattern bandwidth with negligible loss. The results show similar bandwidth with lower sidelobes and backlobes than those of the trifurcated horn that is currently used as the standard C-band feed for single linear polarization. This demonstration shows promise for lightweight metamaterial horns to replace heavy and expensive C-band corrugated horns.

-Band Dual Polarization Hybrid-Mode Horn Antenna Enabled by Printed-Circuit-Board Metasurfaces

A metamaterial design is presented that implements a far-field collimating lens for microwave antenna gain enhancement applications. Using a combination of dual-split ring resonators and end-loaded dipole meta-molecules, the bulk properties are shown to be a good approximation of a low-index uniaxial material with a z-oriented optical axis for both permittivity and permeability between 8 and 9 GHz. Full-wave simulations demonstrate that a large-area lens comprised of the designed unit cell and fed by a crossed-dipole successfully acts as a collimating lens with 6dB gain improvement over the same antenna without the meta-lens.

Demonstration of an Octave-Bandwidth Negligible-Loss Metamaterial Horn Antenna for Satellite Applications

Passive and active L Band phased array tiles based on RF on Flex interconnect have been successfully demonstrated. The tile is a modular building block for light weight, high performance phased arrays to be used in space based radar applications. Each tile contains 6 radiating elements with a maximum radiated power per element of ~ 2 W. Each tile includes two beamformers and two T/R modules per radiating element so that any transmit polarization may be formed and both V and H polarizations may be received. Each tile weighs 0.41 kg (3.9 kg/m²). In order to minimize production cost the tile is designed to be fabricated on an industry standard Printed Circuit Board assembly line and the T/R modules are packaged as Plastic Encapsulated Modules (PEMs). A thirty tile build has demonstrated high yield and a path to meeting the tile high volume production cost goal of

Anisotropic metamaterial realization of a flat gain-enhancing lens for antenna applications

50K/m².

RF on Flex tile for L Band phased arrays

Short Backfire Antennas (SBFAs), first published in 1965 (H. W. Ehrenspeck, “The Short Backfire Antenna,” Proc. IEEE, Vol. 53, No. 8, pp. 1138–1140, Aug. 1965), have seen wide use in terrestrial, maritime and space-based applications due to their relatively high directivity and low profile. Typical SBFA height is 1/8 that of comparable end-fire elements like the Yagi for the same nominal 15 dBi directivity, and typical SBFA aperture diameter is on the order of 2λ. Achievable SBFA aperture efficiency is 84% at a single frequency, and about 75% average for a dual-band application like that of the L1 (1.575 GHz) and L2 (1.227 GHz) GPS frequencies. In an array application, an additional 10% aperture efficiency loss will occur due to packaging of circular SBFA elements, bringing the overall GPS L-band array aperture efficiency down to 67%.

High efficiency hexagonal short backfire antenna with hard walls for GPS satellite antennas

A square dual-polarization horn antenna with a thin metamaterial lining the walls is shown to provide low sidelobes, low cross-polarized radiation, and radiation patterns that are approximately independent of polarization. This horn represents a low cost alternative to corrugated and other soft feed horns. By operating a distance away from the resonance in the metamaterial, the liner introduces a minimum of loss to the horn.

A square dual polarization metahorn design

A dual-band short backfire antenna with high aperture efficiency for satellite communications is presented. The high aperture efficiency is enabled by loading anisotropic impedance metasurfaces (AIMs) to the cavity walls of a hexagonal short backfire antenna fed by a slot-loaded suspended patch. By optimizing the surface impedance values of the AIM loadings, the achieved aperture efficiency averaged over the GPS L2 and L1 bands is 90.5% for a hexagonal SBFA. The corresponding efficiency for a circular SBFA with cavity walls is 99%. Cross-polarization is also greatly improved. The homogeneous AIM can be realized by a finite periodic array of low-loss electric resonators that are comprised of metallic patterns.

Anisotropic impedance metasurface enabled dual-band short backfire antennas with high aperture efficiency

As an extension to previous work on flat metamaterial lenses for antenna gain enhancement, we present a dual-metamaterial design for a far-field collimating lens using an artificial magnetic conducting (AMC) ground plane to reduce the antenna profile by 20%. Simulations show good radiation performance over a 10% bandwidth.