Artificial Magnetic Conductor Surface Research Articles

Wideband composite AMC surfaces for RCS reduction

AbstractA composite artificial magnetic conductor (AMC) surface is presented for wide band radar cross section (RCS) reduction. The composite surface consists of two kinds of AMC cells with different resonance frequencies. The phase difference between them can be tuned to be within a range close to ±π over a wide bandwidth. Therefore, the reflections from these two different AMC cells cancel each other. The basic principle was discussed and a sample was measured. The results show that a nearly 10 dB RCS reduction was achieved with a 32% bandwidth. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:712–715, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25835

Improved RCS and efficient waveguide slot antenna

A simple and successful design for a small radar cross-section (RCS) and highly efficient waveguide slot antenna is presented. An artificial magnetic conductor and perfect electric conductor surface are combined together for RCS reduction and radiation improvement based on the principle of passive cancellation. A ring structure is first used in the waveguide slot antenna design. The novel antenna is compared with the traditional antenna and the results are better.

On Bandwidth Limitation and Operating Frequency in Artificial Magnetic Conductors

A perfect magnetic conductor (PMC) surface reflects electromagnetic waves without any change in the electric field phase. However, there is no natural PMC material. Instead, artificial magnetic conductors (AMCs) have been developed, which mimic the behavior of PMCs at a particular frequency. There has been an extensive amount of research to increase the bandwidth in different AMC structures and to characterize its operating frequency. Here, the general reflection characteristics from an AMC surface is demonstrated. A theoretical upper limit for AMC bandwidth is derived in terms of AMC structural parameters and validated for different AMC structures. Finally the effects of AMC structural parameters on the operating frequency of an AMC are investigated.

Miniature platform tolerant antenna composed of microstrip line and AMC surface

A novel small antenna based on a microstrip line over a miniaturised artificial magnetic conductor (AMC) using lumped capacitors is presented. This antenna, measuring λ/12.5×λ/15.6×λ/47, has platform tolerant reflectivity against frequency characteristics whilst maintaining broad beam radiation performance. Operating at 1.2 GHz the miniaturised AMC antenna has a measured −10 dB bandwidth of 0.8% with radiation efficiency of 27%.

Experimental Evaluations of Printed Circuit Board and On-Chip Inductors Backed by AMC Surfaces

This letter investigates the role of artificial magnetic conductor (AMC) surfaces in increasing the inductance of printed inductors. Both printed circuit board (PCB) and on-chip loop inductor prototypes backed by spiral AMC surfaces are designed and fabricated for this purpose. Measurements of PCB prototypes demonstrate that the loop inductance increases by a factor of 2 or higher within the AMC operation bands. Furthermore, experimental evaluations of the developed test-chips prove successful miniaturization of a loop inductor when the AMC reflector is employed. The drawback of this technique is degradation of the quality factor near the AMC operation regions, which is shown to be caused by the generation of eddy currents in the spiral conductor paths of the AMC surface.

Concept of Virtual Electric/Magnetic Walls and its Realization With Artificial Magnetic Conductor Technique

In this letter, we present a novel concept of virtual electric/magnetic walls which are formed by combining perfect electric conducting parallel plates and perfect magnetic conducting parallel plates. In practice, the perfect magnetic wall can be replaced with an artificial magnetic conductor surface. Two types of complementary transverse electromagnetic waveguides are built with the virtual electric/magnetic walls. The field distribution in the waveguide was simulated and measured. The existence of virtual electric wall was verified.

Decorrelation of two closely spaced antennas with a metamaterial AMC surface

AbstractA metamaterial spacer to decorrelate two closely spaced antennas has been designed and tested. The metamaterial spacer exhibits an artificial magnetic conductor (AMC) behavior around 2.6 GHz. Its performance has been checked against a simple metal spacer (PEC), providing a quasi orthogonal radiation pattern and good results in terms of decoupling and decorrelating a two‐antenna system. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1414–1417, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23365

Characterization of artificial magnetic conductor strips for parallel plate planar antennas

AbstractMetamaterial structures have unique properties in controlling the propagation of electromagnetic waves. In this work, we analyze the effect of artificial magnetic conductor (AMC) surface strips on the bottom face of an oversized parallel plate waveguide to enhance the wave guidance within it. The results using these configurations in a linear slot array antenna fed by a rectangular parallel plate waveguide are presented as an example of application. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 498–504, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23092

GA/FDTD technique for the design and optimisation of periodic metamaterials

An efficient and powerful full-wave electromagnetic technique is presented to characterise and design periodic metamaterial structures. First, the spectral finite-difference time-domain (FDTD) method with periodic boundary conditions and uniaxial perfect matched layer is employed to predict the performance of a mushroom-like artificial magnetic conductor (AMC) surface and further extended to characterise a negative-refractive-index material consisting of lumped and distributed transmission-line elements. Then, a new computational technique is developed to design and optimise periodic metamaterial structures by integrating the spectral FDTD method with a genetic algorithm (GA), namely the micro-genetic algorithm. This computational technique is successfully applied to design and optimise single-band and dual-band AMC structures consisting of a frequency-selective surface and a ground plane. It is demonstrated that the GA/FDTD technique is a very effective approach for the design and optimisation of periodic metamaterial structures consisting of dielectrics and conductors of arbitrary configurations.

Miniaturisation schemes for metallodielectric electromagnetic bandgap structures

Two miniaturisation schemes for metallodielectric electromagnetic bandgap (MEBG) arrays are presented. Miniaturisation by virtue of the closely coupling technique as well as by employing complex element geometries is demonstrated by means of full-wave simulations and experimental results. A combination of the two techniques is shown to produce a further miniaturisation. An MEBG array with unit cell λ/35 is experimentally demonstrated. The concepts are expanded for the miniaturisation of artificial magnetic conductor (AMC) surfaces. It is demonstrated that there is a trade-off between AMC miniaturisation and bandwidth. The motivation behind the miniaturisation is demonstrated with a test mobile handset employing a miniaturised conformal MEBG surface. The handset's antenna efficiency and frequency detuning are improved in the presence of the user's hand.

Limitation on the bandwidth of artificial perfect magnetic conductor surfaces

A perfect magnetic conductor surface reflects electromagnetic waves without phase change of the electric field, in contrast to the 180° phase change from a perfect electric conductor. Existing structures achieve this condition only at a particular frequency. The phase variation away from this frequency is larger for thinner structures, leading to smaller bandwidth over which the desired condition is achieved to given tolerance. There is fundamental upper limit on the bandwidth of structures based on frequency-selective surfaces arising from the causality and passivity of the structure.

Theoretical Investigation of Artificial Magnetic Conductors Using Effective Medium Model and Finite-Difference Time-Domain Method

Metamaterials such as left-handed systems and artificial magnetic conductors (AMCs) are very attractive for producing a variety of new functional components. Two major structures for AMCs have been proposed to mimic the magnetic conductor in dual relation to an electric conductor. One has a two-dimensional microstrip patch array with a conducting via connecting the center of each patch to the ground plane, whereas the other has no vias. It is important to elucidate the operation mechanisms of these AMC structures from the viewpoint of not only fundamental physics but also device applications. In this study, we theoretically investigate the basic properties of AMC structures with and without vias. Finite-difference time-domain (FDTD) simulations clarify the mechanism of the plane wave reflection on the AMC surface. The difference between the dispersion characteristics of two AMC structures is investigated in detail.

Electromagnetic bandgap structures as artificial magnetic conductor surfaces sidewalls in parallel plate slot antennas

AbstractMetamaterial structures have unique properties in controlling the propagation of electromagnetic waves. In this work we analyze the effect of a metamaterial denominated EBG structures acting as if they had artificial magnetic conductor (AMC) properties to enhance the main radiation characteristics of parallel‐plate slot antennas. The results using these structures in comparison with conventional perfect electric conductor (PEC) sidewalls in a planar slot antenna are presented as an example of application. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1441–1446, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21633

COMPARATIVE STUDY ON VARIOUS ARTFICIAL MAGNETIC CONDUCTORS FOR LOW-PROFILE ANTENNA

Abstract—This paper investigated comparatively the characteristics of four types of artificial magnetic conductor (AMC) surface, including a mushroom-like (electromagnetic band gap) EBG, uniplanar compact EBG (UC-EBG), Peano curve, and Hilbert curve, as a ground plane for a low-profile antenna. The AMC surface structures are designed to have an in-phase reflection property for a plane wave of normal incidence in the vicinity of 2.45 GHz. The bandwidths of the in-phase reflection for the AMC surfaces and return losses, radiation patterns, and gains of the horizontal wire antennas on the AMC ground planes are all measured and compared with each other. The measured data show that all the AMC surfaces act as good ground planes for a lowprofile antenna, yet the bandwidth and gain of the mushroom-like EBG structure are broader and larger, respectively, than those of the other structures.

Artificial magnetic conductor surfaces and their application to low-profile high-gain planar antennas

Planar periodic metallic arrays behave as artificial magnetic conductor (AMC) surfaces when placed on a grounded dielectric substrate and they introduce a zero degrees reflection phase shift to incident waves. In this paper the AMC operation of single-layer arrays without vias is studied using a resonant cavity model and a new application to high-gain printed antennas is presented. A ray analysis is employed in order to give physical insight into the performance of AMCs and derive design guidelines. The bandwidth and center frequency of AMC surfaces are investigated using full-wave analysis and the qualitative predictions of the ray model are validated. Planar AMC surfaces are used for the first time as the ground plane in a high-gain microstrip patch antenna with a partially reflective surface as superstrate. A significant reduction of the antenna profile is achieved. A ray theory approach is employed in order to describe the functioning of the antenna and to predict the existence of quarter wavelength resonant cavities.