摘要:

This paper summarizes the design and development of a 4-frequency selective surface (FSS) for the NASA Cassini high gain antenna (HGA). Specifically, two FSS/HGA design approaches were considered for multiplexing the four frequency bands (S-, X-, Ku-, and Ka-band) of the Cassini Project. In the first approach (with two transmit and two reflect bands), a double screen FSS with double ring patch elements was developed to transmit the S- and Ku-band signals and to reflect the X- and Ka-band signals. However, this FSS presents relatively high insertion loss at the S-band. Therefore, the second approach (with one transmit and three reflect bands) was developed, using a single screen FSS with double square loop slot elements to transmit the Ka-band and to reflect the S-, X-, and Ku-band waves. Significant improvement in the S-band loss performance is obtained with this second approach. However, it will require a dual reflector shaping study to optimize the subreflector size for minimizing the spill over and blockage losses.

ISSN:0920-5071    

DOI:10.1163/156939394X00399

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Exact, closed-form field expressions are derived for the canonical problem of electromagnetic radiation by a semi-infinite traveling-wave current filament in free space. In order to avoid time consuming numerical integration, the fields are represented in terms of complementary incomplete Lipschitz-Hankel integrals, whose series expansions allow for accurate and efficient computation of the field components everywhere in space. The field expressions are also shown to reduce to elementary functions in many special cases, e.g., in the far-zone, in the vicinity of the current filament, and when the propagation constant along the wire is that of free space. Representative plots for the electric field components are presented for values of the propagation constant corresponding to both fast and slow-wave propagation. Since a superposition of two semi-infinite current filaments yields a finite-length current filament, the method and the results obtained in this paper can be readily applied to a number of problems in electromagnetics.

ISSN:0920-5071    

DOI:10.1163/156939394X00407

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

In this paper we consider scattering from systems of densely distributed, non-tenuous spheres that exhibit surface adhesion. The Percus-Yevick sticky particle pair function is used to describe the clustering nature of the particles and to include this in low frequency solutions of the quasi-crystalline approximation (QCA) and the quasi-crystalline approximation with coherent potential (QCA-CP). Results from these calculations show an increase in scattering from the adhesive particles which is caused by their larger cluster size. The scattering behavior cannot be explained by distributions of non-sticky particles. Experimental data from optical attenuation by colloidal silica particles is shown to be in good agreement with QCA calculations of sticky particles.

ISSN:0920-5071    

DOI:10.1163/156939394X00416

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

This report studies the dielectric properties of mixtures with components that can have an arbitrary permittivity dyadic. The anisotropic inclusions are assumed to be spherical. In the analysis, a quasistatic approach is used, and it leads to the general Maxwell Garnett formula. This is represented in many forms, and depending on the orientation distribution of the inclusions, the effective permittivity can be dyadic or scalar. Special emphasis is on the case of random orientation of the inclusions. The macroscopic permittivity depends on seven parameters of the mixture, six coming from the symmetric and antisymmetric parts of the inclusion permittivity dyadic, and one from the volume fraction. Numerical illustrations focus on the gyrotropy effects that are shown to lead to sharp maxima and minima in the polarizabilities and macroscopic permittivities.

ISSN:0920-5071    

DOI:10.1163/156939394X00425

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

An analytic solution is obtained for a plane electromagnetic wave scattering by an infinitely imperfectly conducting cylinder clad by a composite anisotropic chiral sheath. The coating medium is assumed homogeneous. Closed form expressions are derived for the electromagnetic fields in composite anisotropic chiral media. Both TE and TM polarized wave incident normally on the circular cylinder are considered. Numerical results for various values of the parameters are presented and discussed.

ISSN:0920-5071    

DOI:10.1163/156939394X00434

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

We consider the 2D-problem of the reflection of a plane wave from non-identical layers of gratings made of fibers of arbitrary cross-section and presenting electric and magnetic contrasts with respect to the surrounding medium. The structure is of finite thickness and backed by a perfectly conducting plane. A domain integral equation is derived for the electric and magnetic currents in the fibers, from which the reflected field is computed. Comparisons with other approaches are made and examples are given to illustrate the absorbing properties of these structures.

ISSN:0920-5071    

DOI:10.1163/156939394X00443

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A numerical method for determining the broadband characteristic impedance of an antenna is described. The method is based on a solution of the electric field integral equation for the antenna surface subject to a strongly localized incident field, representative of a desired transient source voltage. A method is outlined for calculating, from the numerically simulated feed current, the frequency-dependent impedance spectrum of a finite antenna, subject to a sharp pulse. It is shown that this may be used to determine reliably the characteristic impedance of TEM antennas. Particular attention is paid to the problem of effectively modeling the feed region of the transient antenna. A general approach which ensures the stability and accuracy (to within a few percent) of solutions is described. It uses surface patches to model the antenna and obviates potential difficulties associated with thin wire models of the feed region.

ISSN:0920-5071    

DOI:10.1163/156939394X00452

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939394X00461

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939394X00470

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939394X00489

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor