摘要:

Optical ray theory is used to design a phase-corrected microwave horn antenna of shortlength which produces a tapered aperture amplitude distribution in the E-plane. The basis of the design is the creation of a region where the effective refractive index varies with hyperbolic secant (HYSEC) form in a direction normal to the horn axis. In a practical realisation this effective refractive index distribution is achieved in both smooth and stepped form by varying the plate separation of the planar waveguide supporting a TE01mode. Good agreement is found between predicted and experimentally determined aperture and far-field distributions. Finally, the study is extended to the design of a novel antenna incorporating dielectric loading which, in theory, allows for operation at even shorter horn lengths.

DOI:10.1049/ip-h-2.1990.0016

出版商:IEE    

年代:1990

数据来源: IET

摘要:

A new model for use in predicting rain attenuation from rain rate statistics has been developed based on the concept of moving rain cells with limited extension. Relevant CCIR information has been used for the necessary parameters. Results measured from 53 satellite paths were used to evaluate the prediction accuracy. The median value of the prediction error found to be ⊕ 0.5 dB with a 1-sigma value of 1.0 dB for attenuation values in the range 0–10 dB. No significant variation in the prediction accuracy has been found for satellite paths in Europe, North America or East Asia, for frequencies in the range 10–20 GHz or elevation angles in the range 10–60 degrees.

DOI:10.1049/ip-h-2.1990.0017

出版商:IEE    

年代:1990

数据来源: IET

摘要:

Scan performance of infinite planar arrays can be approximated using Floquet excitations in a large but finite array. This method is evaluated for arrays of dipoles with and without a backscreen for comparison with exact unit cell results.

DOI:10.1049/ip-h-2.1990.0018

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The paper presents an analytical technique for the calculation of the electromagnetic fields and surface currents associated to conducting patches of arbitrary shape embedded in a stratified medium. Surface waves arising in such structures are discussed in detail and approximate analytical formulas for their propagation constants are calculated. Two integral equation formulations are presented and their respective merits discussed. It is shown that for multilayered structures both formulations can be combined into an optimised hybrid approach. Numerical results, obtained with a method of moments, are presented for a cross-shaped patch embedded in a multilayered substrate.

DOI:10.1049/ip-h-2.1990.0019

出版商:IEE    

年代:1990

数据来源: IET

摘要:

An extension of Taylor's circular aperture pattern synthesis technique permits the generation of a flat-topped beam that is rotationally symmetric, surrounded by ring side lobes of controllable height, with the ripple amplitude also controllable. The corresponding continuous aperture distribution can be made pure real by appropriate root-pairing, which makes the results applicable, via sampling, to resonantly-spaced waveguide slot arrays. A one-dimensional linear stretch extends the results to rectangular grid planar arrays possessing an elliptical boundary. In that case the pattern is a fiat-topped beam with an elliptical contour, surrounded by ring side lobes also of elliptical contour, but with amplitude and side lobe level still controlled. The principal application is to space vehicle communication systems required to place a footprint pattern on a selected portion of the earth's surface.

DOI:10.1049/ip-h-2.1990.0020

出版商:IEE    

年代:1990

数据来源: IET

摘要:

A simple extension to the Fresnel-Kirchhoff theory of double knife-edge diffraction leads to expressions for the attenuation due to an obstacle with vertical sides and a flat, but not necessarily level, top. The method is to find the sum of the double knife-edge field and the field due to a wave that is reflected by the top of the obstacle as well as diffracted by the sides. It is assumed that the diffraction angle is small and that the top is perfectly reflecting. The attenuation is found in terms of the Fresnel surface integral in much the same way as for double knife-edge diffraction. The results of some calculations are displayed.

DOI:10.1049/ip-h-2.1990.0021

出版商:IEE    

年代:1990

数据来源: IET

摘要:

A full-wave solution is presented for the problem of an infinite array of vertical monopoles embedded in a grounded dielectric sheet. Calculated results are compared with experimental data from waveguide simulators for εr= 1 (air) and εr= 2.5 (acrylic) cases. Scan blindness is observed for the dielectric loaded case, and a grating lobe diagram augmented with surface wave circles is used to explain this phenomenon.

DOI:10.1049/ip-h-2.1990.0022

出版商:IEE    

年代:1990

数据来源: IET

摘要:

Radiation from elliptical waveguides terminating in a ground plane is analysed using a Green's function approach. In the waveguides the field is expressed as a sum of the TEcmn, TMcmn,TEsmnandTMsmnelliptical waveguide modes, and expressions for the mutual admittances of modes excited at the apertures are obtained. From these expressions the mode reflection and conversion coefficients are determined. Of the techniques available for calculating the mutual admittances, the transform representation and direct integration approaches are used, with the latter preferred for detailed calculations. These show that for a single aperture the TEcmnmode couples only to the TEcm'n'andTMsm'n'. modes whenmandm' have the same parity. Similarly, the TEsm'n'mode couples only to TEsm'n'and TMcm'n'modes. Computed and measured results are given for reflection coefficient in a single waveguide due to the open end, and calculations of mutual coupling between two elliptical waveguides are presented for E- and H-plane dispositions. Results obtained for elliptical waveguides are compared with corresponding results for rectangular waveguides in a ground plane. Within limits, the less computationally intense rectangular waveguide solution can be a useful first approximation to the elliptical waveguide solution.

DOI:10.1049/ip-h-2.1990.0023

出版商:IEE    

年代:1990

数据来源: IET

摘要:

An effort to unify three major numerical methods in electromagnetics is presented. Harrington's direct method of moments, the iterative methods, and the reaction integral equation method are shown to be generally equivalent and are unified as the generalised method of moments. It is shown that the reaction integral equation method is in general a moment method, and that the moment method, when defined in a symmetric space, generally satisfies the reaction theorem, and therefore reciprocity. A broad, though limited, equivalence between the moment and the iterative methods is also demonstrated. A numerical example is discussed to illustrate these and other points.

DOI:10.1049/ip-h-2.1990.0024

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The AC resistance is an important factor in determining the insertion loss of miniature MMIC circuits over their passband. The metallisation of an MMIC is in the form of rectangular strips. The paper gives detailed formulation and analysis of the isolated rectangular strip conductor. Meixner's edge condition for the rectangular strip with loss is investigated. It is found that such a condition is obeyed. Based on this condition and the analysis, a simple and accurate curve fitted approximation of the AC resistance is presented.

DOI:10.1049/ip-h-2.1990.0025

出版商:IEE    

年代:1990

数据来源: IET