Erik Lier

A dielectric hybrid mode antenna feed: A simple alternative to the corrugated horn

A hybrid-mode horn antenna has been analyzed theoretically and experimentally. It consists of a conical metal horn with a dielectric core inside, separated from the metal wall by another dielectric layer with lower permittivity than for the core material. It is characterized by a very simple design and excellent electrical performance. The horn can support the balanced hybrid HE 11 -mode, and exhibits low cross polarization and low sidelobes over a wide frequency range. Compared to corrugated horns, the new horn has a simpler design, is easier to analyze, and has the potential of similar cross-polar bandwidth as for corrugated horns with ring-loaded corrugations. Drawbacks are the effects of dielectric losses. Thus the new horn represents an attractive alternative to the corrugated horn antenna.

Soft and hard horn antennas

Horn antennas with soft and hard boundaries are analyzed. A soft boundary which exists in classical hybrid-mode horns gives zero field intensity at the wall. A hard boundary corresponds to a uniform field distribution over the horn aperture. Soft and hard horn antennas are compared with respect to directivity, sidelobes, and beamwidth. The dependency between the edge taper directivity, and sidelobes is also calculated based on the solution to the spherical hybrid modes in a conical horn with arbitrary wall impedances. This makes it possible to study how to compromise between directivity and sidelobes. Also discussed is how the different wall impedances may be realized, and some preliminary experimental work on hard horns is presented. >

Rectangular microstrip patch antennas with infinite and finite ground plane dimensions

The rectangular microstrip patch antenna has been extensively analyzed with regard to its input impedance and resonant frequency, both for infinite and finite ground plane dimensions. For infinite ground planes existing formulas have been compared and improved parameters presented. The influence from the side current radiation has been discussed as well. For finite ground plane dimensions the contribution from the ground plane edge diffraction has been accounted for in an equivalent radiation conductance and an equivalent diffraction susceptance. Formulas for these parameters have been developed on the basis of different theories. They are valid under the condition that only one of the ground plane dimensions are finite at the same time. Experimental investigations are carried out to test the accuracy of the developed formulas, showing good accuracy under the given conditions.

An octave-bandwidth negligible-loss radiofrequency metamaterial

Metamaterials provide an unprecedented ability to manipulate electromagnetic waves and are an enabling technology for new devices ranging from flat lenses that focus light beyond the diffraction limit to coatings capable of cloaking an object. Nevertheless, narrow bandwidths and high intrinsic losses arising from the resonant properties of metamaterials have raised doubts about their usefulness. New design approaches seek to turn the perceived disadvantages of dispersion into assets that enhance a devices performance. Here we employ dispersion engineering of metamaterial properties to enable specific device performance over usable bandwidths. In particular, we design metamaterials that considerably improve conventional horn antennas over greater than an octave bandwidth with negligible loss and advance the state of the art in the process. Fabrication and measurement of a metahorn confirm its broadband, low-loss performance. This example illustrates the power of clever implementation combined with dispersion engineering to bring metamaterials into their full potential for revolutionizing practical devices.

A new class of dielectric-loaded hybrid-mode horn antennas with selective gain: design and analysis by single mode model and method of moments

A mechanically simple dielectric loaded hybrid mode horn is presented. It can be designed to satisfy either hard or soft boundary conditions, or any boundary between hard and soft under balanced hybrid condition (low cross-polarization) for any aperture size. Design curves are developed based on a plane wave model. Radiation performance is computed based on a single mode circular cylindrical wave model (CCWM) as well as by method of moments (MoM). Based on CCWM aperture efficiency of about 94% has been computed at the design frequency for a 3.38/spl lambda/ aperture with hard boundary condition and a dielectric constant of 4.0. The same horn with a dielectric constant of 2.5 can provide higher than 89% aperture efficiency and under -30 dB cross-polarization over a 15% frequency range. Predicted peak sidelobes ranging from -19 to -26.5 dB and corresponding aperture efficiency between 92% and 78% at the design frequency under balanced hybrid condition have been obtained for various horn designs. Computations based on MoM show that cross-polarization patterns agree well with what was predicted based on an ideal single hybrid-mode model, while computed aperture efficiency is even higher than predicted by CCWM. Results also indicate that implementing dielectric-to-air matching at the horn aperture is crucial to achieve good cross-polarization performance and input match for hard horns in general. The horn can also be designed to radiate a flat-top pattern. The horn could be useful as an element in cluster feeds or limited-scan arrays, as a feed for quasioptical amplifier arrays or in millimeter wave applications.

The strip-loaded hybrid-mode feed horn

A novel typed of hybrid-mode feed horn is presented. It comprises a hollow conical dielectric waveguide whose outer surface is metallized, and whose inner surface is coated with circumferentially oriented conducting strips. It may be designed to have mimimal cross polarization at two arbitrarily separated frequencies, as for a dual depth corrugated horn. Compared to the corrugated horn, it has the potential of lower weight and lower price. Small horns will have some cross polarization due to undesired radiation from the fields transmitted within the dielectric.

Review of Soft and Hard Horn Antennas, Including Metamaterial-Based Hybrid-Mode Horns

This paper is divided into three parts. Part one gives an overview of the early history of the design and implementation of hard horn antennas, and of the concept formulation of soft and hard electromagnetic surfaces. Part two presents a review of all known classes of soft and hard hybrid-mode horns. Part three presents a new class of hybrid-mode horns, based on the use of a low-index metamaterial liner on the wall. Moment-Method analysis of both soft and hard metamaterial horns indicates that it may be feasible to realize these horns with very large bandwidth. This is because the desired (analyzed) metamaterial dispersion is similar to the Drude dispersion curve (monotonically increasing permittivity as a function of frequency), which represents typical electromagnetic dispersion in dense media. A successful implementation of these horns depends on whether low-index metamaterials can be implemented with polarization-independent boundary impedance, favorable dispersion characteristics, and reasonable loss, mass, and production cost.

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.

Design Synthesis of Metasurfaces for Broadband Hybrid-Mode Horn Antennas With Enhanced Radiation Pattern and Polarization Characteristics

Metamaterial surfaces (metasurfaces) with a low effective index of refraction have been recently proposed for application in the design of hybrid-mode horn antennas, such as soft and hard horns. Here we explore designs of several metasurfaces and their use as liners for coating the interior walls of horn antennas. The design process combines the genetic algorithm optimization technique with a full-wave electromagnetic solver to create dispersion-engineered metamaterials that possess customized surface impedance properties. A metamaterial parameter extraction technique is developed and employed in the optimization process, which is based on the surface impedance expressions for a homogeneous slab backed by a perfectly conducting ground plane illuminated at near grazing incidence. The optimized metasurface is found to be equivalent to a low index metamaterial with a dispersion that can improve the performance of conventional horn antennas over the entire Ku -band while introducing negligible losses. We conclude with a numerical study of a conical horn antenna whose interior is lined with a low index metasurface. The far-field radiation patterns and aperture field distributions confirm hybrid-mode operation over a wide bandwidth, validating the proposed metasurface design methodology.

Phased array calibration and characterization based on orthogonal coding: Theory and experimental validation

This paper presents the Control Circuit Encoding (CCE) technique used for calibrating digitally controlled phased arrays. The CCE method employs sets of orthogonal codes that are sequentially applied to all attenuators and phase-shifters in the beamformer, allowing elements to be measured in-situ simultaneously with a calibration probe in the far or near field of the array. In addition to calibrating commanded gain & phase settings the technique enables the assessment of antenna array RMS gain & phase error, as well as fast and accurate measurement of in-situ element patterns and amplifier characteristics. The paper describes the theory and presents measured results performed on various active phased array antennas.