Antennas Propagat Research Articles

Chromium plasmonic polarizer for high intensity light

In this work, we investigate a thin-film polarizer for a high intensity of the electromagnetic (EM) beam based on Cr nano wire arrays. Commonly used thin-film polarizing components are very sensitive for high power of EM waves and can be easily damaged by focused beams. The solution to this problem could be the thin-film polarizer based on metallic subwavelengths structures. This type of optical element has huge resistance comparing to typical thin-film polarizers. However, designing such an optical element for proper wavelength of EM wave and transmissions is not easy task. In this paper we present numerical as well as experimental results for specially designed chromium thin-film polarizer for wavelength 532nm Full Text: PDF ReferencesW. Zhou, K. Li, C. Song, P. Hao, M. Chi, M. Yu and Y. Wu, "Polarization-independent and omnidirectional nearly perfect absorber with ultra-thin 2D subwavelength metal grating in the visible region", Opt. Express 23, 11 (2015). CrossRef W. L. Barnes, A . Dereux, and T. W. Ebbesen, "Surface plasmon subwavelength optics", Nature 424, 824-830 (2003). CrossRef C. Lee, E. Sim, D. Kim, "Blazed wire-grid polarizer for plasmon-enhanced polarization extinction: design and analysis", Opt. Express 25, 7 (2017). CrossRef A. Lehmuskero, Metallic thin film structures and polarization shaping gratings (University of Eastern Finland 2010).Y. Leroux, J. C. Lacroix, C. Fave, V. Stockhausen, N. Felidj, J. Grandm, A. Hohenau, J. R. Krenn, "Active plasmonic devices with anisotropic optical response: a step toward active polarizer", Nano Lett. 5, 9 (2009). CrossRef R. T. Perkins, D. P. Hansen, E. W. Gardner, J. M. Thorne, A. A. Robbins, Broadband wire grid polarizer for the visible spectrum, US 6122103 (2000). DirectLink D. M. Sullivan, Electromagnetic simulation using the FDTD method, New York: IEEE Press Series (2000). CrossRef J. P. Berenger, Perfectly Matched Layer (PML) for Computational Electromagnetics, Morgan & Claypool Publishers (2007). CrossRef Yu, W., and R. Mittra, "A conformal FDTD software package modeling antennas and microstrip circuit components", IEEE Antennas Propagat. Magazine 42, 28 (2000) . CrossRef L. W. Bos, D. W. Lynch, "Optical Properties of Antiferromagnetic Chromium and Dilute Cr-Mn and Cr-Re Alloys", Phys. Rev. Sect. B, 2, 4267 (1970). CrossRef

Reply to "Comments on 'Loss Mechanisms in the Electrically Small Loop Antenna'\" [Antenna Designer's Notebook

Presents a reply to comments on “Loss mechanisms in the electrically small loop antennas,” (Austin, B.A., et al, IEEE Antennas Propagat. Mag., vol. 56, no. 4, pp. 142–147, Aug. 2014.

Comments on \"Loss Mechanisms in the Electrically Small Loop Antenna\" [Antenna Designer's Notebook

Presents comments on “Loss mechanisms in the electrically small loop antennas,” (Austin, B.A., et al, IEEE Antennas Propagat. Mag., vol. 56, no. 4, pp. 142–147, Aug. 2014.

Lanczos-type variants of the COCR method for complex nonsymmetric linear systems

Motivated by the celebrated extending applications of the well-established complex Biconjugate Gradient (CBiCG) method to deal with large three-dimensional electromagnetic scattering problems by Pocock and Walker [M.D. Pocock, S.P. Walker, The complex Bi-conjugate Gradient solver applied to large electromagnetic scattering problems, computational costs, and cost scalings, IEEE Trans. Antennas Propagat. 45 (1997) 140–146], three Lanczos-type variants of the recent Conjugate A-Orthogonal Conjugate Residual (COCR) method of Sogabe and Zhang [T. Sogabe, S.-L. Zhang, A COCR method for solving complex symmetric linear systems, J. Comput. Appl. Math. 199 (2007) 297–303] are explored for the solution of complex nonsymmetric linear systems. The first two can be respectively considered as mathematically equivalent but numerically improved popularizing versions of the BiCR and CRS methods for complex systems presented in Sogabe’s Ph.D. Dissertation. And the last one is somewhat new and is a stabilized and more smoothly converging variant of the first two in some circumstances. The presented algorithms are with the hope of obtaining smoother and, hopefully, faster convergence behavior in comparison with the CBiCG method as well as its two corresponding variants. This motivation is demonstrated by numerical experiments performed on some selective matrices borrowed from The University of Florida Sparse Matrix Collection by Davis.

Computationally efficient 2D direction finding and polarization estimation with arbitrarily spaced electromagnetic vector sensors at unknown locations using the propagator method

This paper proposes a computationally efficient method for estimating angle of arrival and polarization parameters of multiple farfield narrowband diversely polarized electromagnetic sources, using arbitrarily spaced electromagnetic vector sensors at unknown locations. The electromagnetic vector sensor is six-component in composition, consisting of three orthogonal electric dipoles plus three orthogonal magnetic loops, collocating in space. The presented method is based on an estimation method named propagator, which requires only linear operations but no eigenvalue decomposition or singular value decomposition into the signal and noise subspaces, to estimate the scaled electromagnetic vector sensors' steering vectors and then to estimate the azimuth arrival angle, the elevation arrival angle, and the polarization parameters. Comparing with its ESPRIT counterpart [K.T. Wong, M.D. Zoltowski, Closed-form direction finding and polarization estimation with arbitrarily spaced electromagnetic vector-sensors at unknown locations, IEEE Trans. Antennas Propagat. 48 (5) (2000) 671-681], the propagator method has its computational complexity reduced by this ratio: the number of sources to sextuple the number of vector sensors. Simulation results show that at high and medium signal-to-noise ratio, the proposed propagator method's estimation accuracy is similar to its ESPRIT counterpart.

2-D unitary matrix pencil method for efficient direction of arrival estimation

In this study, we extended the one-dimensional (1-D) unitary matrix pencil method (UMP) [N. Yilmazer, J. Koh, T.K. Sarkar, Utilization of a unitary transform for efficient computation in the matrix pencil method to find the direction of arrival, IEEE Trans. Antennas Propagat. 54 (1) (2006) 175-181] to two-dimensional case, where 2-D matrix pencil (MP) method are used to find the 2-D poles corresponding to the direction of arrival (DOA), azimuth and elevation angles, of the far field sources impinging on antenna arrays. This technique uses MP method to compute the DOA of the signals using a very efficient computational procedure in which the complexity of the computation can be reduced significantly by using a unitary matrix transformation. This method applies the technique directly to the data without forming a covariance matrix. Using real computations through the unitary transformation for the 2-D matrix pencil method leads to a very efficient computational methodology for real time implementation on a DSP chip. The numerical simulation results are provided to see the performance of the method.

Are cantor arrays effective for designing thinned arrays?

Cantor distributions of identical radiating apertures allow the design of low side-lobe arrays (see Puente-Baliarda and Pous, Antennas Propagat 44 (1996) 730–739). However we show here that Cantor arrays that achieve both a desired beamwidth in the broadside direction and a given peak side-lobe level for any main beam direction (scanning application) present a minimum number of radiating elements that is generally higher than that of thinned arrays designed by means of a genetic algorithm. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 2041–2043, 2006; Published online in Wiley Inter-Science (www.interscience.wiley.com). DOI 10.1002/mop.21855

Sommerfeld and Zenneck wave propagation for a finitely conducting one-dimensional rough surface

Starting with Zenneck and Sommerfeld wave propagation over a flat finitely conducting surface has been extensively studied by Wait (see IEEE Antennas Propagat. Mag., vol.40, p.7-24, 1998) and many other authors. We examine propagation over a finitely conducting rough surface, also studied by many people including Feinberg (1944), Bass and Fuks (1979), and Barrick (see Radio Sci., vol.6, p.517-26, and vol.6., p.527-33). This paper extends the multiple scattering theories based on Dyson and Bethe-Salpeter equations and their smoothing approximations. The theory developed here applies to rough surfaces with small root-mean-square (RMS) heights (/spl sigma/<0.1/spl lambda/). We limit ourselves to the one-dimensional (1-D) rough surface with finite conductivity excited by a magnetic line source, which is equivalent to the Sommerfeld dipole problem in two dimensions (x-z plane). With the presence of finite roughness, the total field decomposes into the coherent field and the incoherent field. The coherent (average) field is obtained by using Dyson's equation, a fundamental integral equation based on the modified perturbation method. Once the coherent field has been obtained, we determine the Sommerfeld pole, the effective surface impedance, and the Zenneck wave for rough surfaces of small RMS heights. The coherent field is written in terms of the Fourier transform, which is equivalent to the Sommerfeld integral. Numerical examples of the attenuation function are compared to Monte Carlo simulations and are shown to contrast the flat and rough surface cases. Next, we obtain the general expression for the incoherent mutual coherence functions and scattering cross section for rough conducting surfaces.

Laboratory models used in the investigation of radio wave propagation in irregular structures

A laboratory model first conceived by Wait (see IEEE Antennas Propagat. Mag., vol.40, p.7-24, 1998) to investigate radio wave propagation in the perturbed environment of the Earth-ionosphere waveguide is described. The construction of the laboratory model involves the exploitation of the following fundamental invariant properties of Maxwell's equations and the ability to physically simulate the appropriate boundary conditions including the Earth's curvature: (1) invariance of Maxwell's equations to size-wavelength transformations permits the scaling down in size of the Earth-ionosphere waveguide; (2) duality relationships between the electric and magnetic fields permits the representation of the azimuthally independent TM/sub n,0/ modes excited by vertical dipoles in the Earth ionosphere waveguide by the TE/sub n,0/ modes in rectangular waveguides; (3) a perfectly conducting magnetic wall (where the tangential component of the magnetic field vanishes) is simulated through the use of imaging techniques; (4) to account for dissipation in the ionosphere, an equivalent surface impedance boundary is simulated using a wall loading material with a specific thickness and complex permittivity; and (5) to simulate the Earth's curvature in the rectangular waveguide, an especially fabricated dielectric material with a prescribed permittivity height profile is used as the medium of propagation in the interior of the waveguide. All five of the above artifices have been employed in order to construct a scaled model of the Earth-ionosphere waveguide. However, one or a combination of them can be employed by researchers today to construct laboratory models from which controlled experimental data can be obtained to validate analytical and numerical solutions as well as to provide insights for novel approaches to solve difficult propagation problems.

Fixed point technique in computing power losses in a ferromagnetic bifilar lead

Abstract The electromagnetic field is investigated in a ferromagnetic bifilar lead consisting of circular conductors carrying opposite alternating current. By nature, the field in the lead is of an open boundary type. It is analysed by a hybrid approach first time applied for electromagnetic field scattering in (K.K. Mei, IEEE Trans. Antennas Propagat. AP-22 (1974) 760 and S.K. Chang and K.K. Mei, IEEE Trans. Antennas Propagat. AP-24 (1976) 35) and consisting of the Galerkin finite element method coupled with a separation of variables. The resultant system of nonlinear equations is solved applying a fixed point technique based on Brouwer’s theorem. The results are presented graphically in the form of field plots and the characteristics of relative power losses versus the current frequency.

Scattering from rough fluid–fluid interfaces using the finite-difference time-domain method

The finite-difference time-domain (FDTD) method is a numerical technique that can be used to solve a wide variety of problems via time-domain simulations. Results have been presented for scattering from pressure-release surfaces [F. Hastings et al., IEEE Trans. Antennas Propagat. 43, 1183–1191 (1995)] based on the FDTD method. This paper describes the use of the FDTD technique to study scattering from rough fluid–fluid interfaces. Precise results are obtained by employing several enhancements to the FDTD algorithm. Most importantly, a grid conforming to the rough interface is used to achieve accurate results at a reasonable computational cost. This is in contrast to a traditional stair-stepped model of the interface which gives spurious overprediction of the backscattered field. Numerical results are presented for the scattering strength obtained using a Monte Carlo technique and are compared with results obtained using a Monte Carlo integral equation approach. For both methods, the incident field is a tapered plane wave, and 50 surface realizations are used to obtain the average scattering strength. One advantage of the FDTD method is that it allows the addition of heterogeneities at little extra computational cost. [Work supported by ONR.]

A Monte Carlo finite-difference time-domain technique for scattering from rough elastic bottoms

Scattering from elastic ocean bottoms has been modeled using approximate analytical methods such as perturbation theory and the Kirchhoff and small slope approximations. An alternative approach is to use a numerical technique. This paper describes one such technique, the finite-difference time-domain (FDTD) method, which has been used successively to model scattering from pressure release surfaces [Hastings et al., IEEE Trans. Antennas Propagat.43 , 1183–1191 (1995)]. Monte Carlo scattering strengths are obtained for a tapered incident beam insonifying rough granite and basalt surfaces with either a Gaussian spectrum or a modified power law spectrum. These results are compared with those of formally averaged scattering strengths obtained for several different approximate models. One benefit of using the FDTD approach is that it allows the addition of heterogeneities at little extra computational cost. However, the initial computational cost is great, and the presence of surface and subsurface waves may result in strong scattering at grazing angles despite the use of the tapered incident field. Additionally, grazing incident angles may require surface lengths that are too computationally expensive. These issues and how they affect the applicability of the FDTD method to elastic problems are discussed. [Work supported by ONR.]

Photoconductively switched antennas for measuring target resonances

Coplanar-strip horn antennas are switched photoconductively to generate picosecond bursts of freely propagating electromagnetic energy with bandwidth covering 15–75 GHz. The antennas are fabricated on GaAs grown by molecular beam epitaxy at low substrate temperatures. These antennas are used to perform transient scattering measurements from slit-coupled circular and coaxial cavities; Prony’s method [IEEE Trans. Antennas Propagat. 23, 777 (1975)] is used to extract cavity resonances from the measured late-time scattered signal.

Using multiple microphones and LMS adaptive beamforming to reduce interference in hearing aids from competing talkers in reverberant rooms

To reduce interference in monoaural hearing aids from spatially separated sound sources, the information from multiple microphones might be useful in enhancing the signal from a desired source for monaural presentation. The technique of Griffiths and Jim [IEEE Trans. Antennas Propagat. AP‐30, 27–34 (1982)] was used to filter and combine microphone signals ins way that preserves signals arriving from straight ahead of the microphone array while minimizing output power from off‐axis signals. The filters adapt to the interference environment using a variation of the LMS (Widrow) algorithm. Although it adapts slowly (1 s), LMS approaches optimum performance in stationary, anechoic environments, providing a bound on performance in nonstationary, reverberant environments. In three simulated rooms, anechoic, living room, and conference room, with interferring babble 45° off‐axis and on‐axis target at − 12 dB/S/B, a two‐microphone system with 100‐point filters reduced the interference by 20, 12, and 4 dB, respectively. Informal listening indicated minimal degradation of the desired signal and substantial intelligibility improvement in anechoic and living room environments. [Work supported by NIH.]