摘要:

A simple moment solution is summarised for the problem of electromagnetic scattering from a perfectly conducting cylinder of arbitrary cross-section which is covered by multiple dielectric layers of arbitrary cross section. The system is excited by a plane wave polarised transverse electric to the axis of the cylinder. The equivalence principle is used to replace the cylinders by equivalent electric and magnetic surface currents radiating into an unbounded medium. A set of coupled integral equations involving the surface currents is obtained by enforcing the boundary conditions on the tangential component of the total magnetic field. The method of moments is used to solve the integral equations. Pulse expansion and point matching are used. Some of the limitations of the method are briefly discussed. Results for the surface currents and the scattering cross-sections are presented. Computed results are in very good agreement with the exact or other available published data.

DOI:10.1049/ip-h-2.1989.0078

出版商:IEE    

年代:1989

数据来源: IET

摘要:

A method of moments solution is presented for the problem of electromagnetic scattering from homogeneous cylinders with edges. Transverse magnetic (TM) and transverse electric (TE) cases for metallic and penetrable cylinders are also treated. The moment solution uses a recently suggested multifilament current model to simulate the fields, special attention being paid to the accommodation of edges when using this model. An alternative hybrid method that uses a combination of a few on-surface pulse functions to negotiate the field behavior near the edges together with a filamentary current model whose field can represent the smooth field constituent on the boundary very well is also presented. Results of both methods are given and compared with available known solutions based on a standard moment method solution that employs surface pulse functions.

DOI:10.1049/ip-h-2.1989.0079

出版商:IEE    

年代:1989

数据来源: IET

摘要:

It should be the ultimate goal of the adaptive antenna that not only the magnitude of the variable weights but also their number should be adaptively determined. It is shown that the beamspace adaptive antenna system is most appropriate to realise it. Next, the beam weight control based on the eigen/analysis technique is described, together with a simple and accurate method to discriminate the signal subspace from the noise subspace. When the constraint for the desired signal direction contains some pointing error, the conventional system tends to suppress the desired signal, taking it for an unwanted interference, but the authors' algorithm proves to be a robust system which guarantees the protection of the desired signal.

DOI:10.1049/ip-h-2.1989.0080

出版商:IEE    

年代:1989

数据来源: IET

摘要:

In shaped offset dual-reflector antennas, special care must be taken to prevent crosspolarisation for linear polarisation and beam squint for circular polarisation. This problem is addressed by deriving the laws that determine the mapping of the feed pattern onto the aperture of the reflector. There is a presentation of the conditions that must be satisfied for a GO mapping to be ideal without crosspolarisation and beam squint. The paper even present equations which allow the crosspolarisation and phase errors in the reflector aperture to be calculated directly from the mapping function. As an example, this theory is used to specify and characterise offset dual-reflector antennas with both circular and elliptical apertures. The equation for the crosspolarisation is generally valid only for dual-reflector antennas, but can in many cases also be applied to multireflector systems to obtain useful approximate results. This is shown by the application to a trireflector system; the proposed dual-reflector feed of the spherical reflector of the Arecibo Observatory.

DOI:10.1049/ip-h-2.1989.0081

出版商:IEE    

年代:1989

数据来源: IET

摘要:

A wideband, semiconductor-compatible dipole, derived from the conventional metallic half-wavelength dipole is described. This dipole is resistively loaded along its length, producing a travelling wave current distribution that is insensitive to frequency variations. The resistive loading, however, produces a reduction in efficiency but an increase in bandwidth. Graphs are presented which relate the resistive loading, with efficiency and bandwidth for a given length to diameter ratio of the dipole. These graphs could be useful as design curves in the tradeoff between bandwidth and efficiency. The current distributions along the length of the dipole under various resistive loading conditions are also plotted, as well as the radiation patterns due to these current distributions. The resistive loading for a conventional dipole can be achieved by varying the thickness of the resistive material coating along the length of the dipole. For a semiconductor, however, the resistivity can be varied by changing the doping concentration (ND) of the impurities. Hence, a wideband resistively loaded dipole can now be realised on a semiconductor substrate.

DOI:10.1049/ip-h-2.1989.0082

出版商:IEE    

年代:1989

数据来源: IET

摘要:

Vertical monopoles over an infinite ground plane that are embedded in a dielectric slab are studied using a mixed potential integral equation formulation. The method of moments is used to solve for the induced currents from which impedance parameters are calculated. The vector and scalar potentials are written in terms of Sommerfeld integrals that are evaluated using efficient techniques developed for the analysis of microstrip antennas. A magnetic current frill is used to model the coaxial aperture in the ground plane that excites the monopole. Measured and calculated input impedance and mutual coupling data are compared and a study of the effect of the dielectric inhomogeneity is performed.

DOI:10.1049/ip-h-2.1989.0083

出版商:IEE    

年代:1989

数据来源: IET

摘要:

Waveguiding structures consisting of dielectric-loaded rectangular waveguides are important both in their own right and as a model for other configurations of much interest in the millimetre-wave area. Discontinuities and obstacles in such guiding structures provide the circuit elements used in microwave device design. Accurate prediction of device behaviour requires evaluation of the fields in the system. An increasingly used mathematical formulation is that of the integral equations approach, for which the Green's function of the structure is required. The development of the complete electric dyadic Green's function for an inhomogeneously loaded waveguide, which has not yet appeared in the literature is presented. The components of the dyadic are found in the form of eigenfunction expansions.

DOI:10.1049/ip-h-2.1989.0084

出版商:IEE    

年代:1989

数据来源: IET

摘要:

The paper presents a method of estimation of coupling of a slot coupled H-plane T-junction, in which the primary waveguide is a rectangular one and the T-arm is a circular waveguide. An equivalent network of the junction is determined from a precise formulation for the effect of wall thickness. Appropriate dyadic Green's functions in the two waveguides are used for the determination of equivalent circuit parameters by the variational method. A comparison between the theoretical and experimental results on the variation of coupling with frequency is presented.

DOI:10.1049/ip-h-2.1989.0085

出版商:IEE    

年代:1989

数据来源: IET

摘要:

In a serpentine cylindrical waveguide the radius is constant and the centre varies harmonically in the axial direction about a straight line in a plane. The propagation of the guided modes in a weakly corrugated serpentine cylindrical waveguide with imperfectly conducting walls is investigated using the expansion of the fields in terms of the ideal normal modes. The selective interaction between two transverse electric modes is treated. The theory is applied to the design of a mode convertor that selectively transforms the power in the TEpqmode to the TEp+1,rmode. The spectral response of the mode convertor is discussed.

DOI:10.1049/ip-h-2.1989.0086

出版商:IEE    

年代:1989

数据来源: IET

摘要:

A systematical analysis of nonuniform dielectric waveguides by the method of staircase approximation is presented. The transition problem of curved dielectric waveguides is investigated in terms of scattering of surface waves by the nonuniform waveguide as a whole. Extensive numerical data are obtained to develop guidelines for the design of transition dielectric waveguides for millimetre-wave application.

DOI:10.1049/ip-h-2.1989.0087

出版商:IEE    

年代:1989

数据来源: IET