摘要:

The basic principle of time-domain imaging (i.e. the synthesis of the scattered electromagnetic field distribution over an object plane) is outlined. We have shown that from a set of responses obtained from different viewing directions, the two-dimensional field distribution can be synthesised using a technique similar to the computerised tomographic reconstruction. The limitations of the theory together with the practical difficulties in experimental realisation, are discussed. We have reconstructed the images of two flat metallic plates: one elliptical, one bow-tie shaped. Close resemblance between the objects the reconstructed images is observed for target sizes comparable to the source pulse width, this has given us confidence in the theory for imaging larger targets. The use of time-domain imaging as a broadband scattering measurement technique is also demonstrated. Results are given for a ‘one-dimensional’ metallic strip, 36 cm in width. The simple experimental arrangements the remarkable accuracy of the magnitude phase responses obtained over a broadband of frequencies warrants a further investigation in this area.

DOI:10.1049/ip-h-2.1985.0063

出版商:IEE    

年代:1985

数据来源: IET

摘要:

Previous work in the development of dual finite-element methods applied to the solution of quasistatic problems has concentrated attention on transmission lines whose cross-section has well-defined dual symmetries. Many real problems of interest have either a single symmetry axis or no symmetry axis at all. It is the purpose of the paper to deal with these special cases with the stated aim of widening the scope of application of dual methods to include any coaxial simply connected Cartesian geometry. The provision of upper and lower bounds already makes the dual-potential approach extremely powerful and flexible. Examples of practical interest are chosen including coupled rectangular metallic bars in square coaxial line.

DOI:10.1049/ip-h-2.1985.0064

出版商:IEE    

年代:1985

数据来源: IET

摘要:

A three-dimensional finite-difference scheme is used to solve Maxwell's equations in closed microwave systems. The calculation of the sinusoidal steady-state amplitude and phase of the EM-field, and the derivation of the power density are discussed. The method is tested on some canonical examples which can be solved analytically. Finally, some nontrivial three-dimensional examples are given.

DOI:10.1049/ip-h-2.1985.0065

出版商:IEE    

年代:1985

数据来源: IET

摘要:

Integral equations for both interior and exterior fields of microstrip antennas are formulated in terms of the tangential electric and magnetic field distributions over the conducting patch and dielectric substrate surfaces. Boundary conditions are applied, and a set of integral equations for the above surface distributions are obtained. Using a moment method, these integral equations are then reduced to a matrix equation, the solution of which gives the required field distributions. The method is then applied to both square and rectangular path geometries and their near- and far-field distributions are determined. The far-field results are compared with the experimental data and with the results of approximate analytic methods. The usefulness of the method for solving, numerically, the problem of microstrip radiators is then discussed.

DOI:10.1049/ip-h-2.1985.0066

出版商:IEE    

年代:1985

数据来源: IET

摘要:

The problem considered is that of determining the current induced on, and the field scattered by, a two-dimensional, flat, perfectly electrically conducting strip which is edge loaded by a dielectric cylinder of circular cross-section. The strip is oriented radially with respect to the centre of the cylinder and can be located outside, inside, or partially inside and partially outside the cylinder. The structure is excited by a plane wave polarised transverse electric to the cylinder axis. A system of two coupled integro-differential equations is derived for the current density on the strip in the presence of the cylinder, and is solved numerically by the method of moments. A series acceleration technique is employed to improve the convergence of the series incorporated in the kernels of the integral equations. Sample results are presented which illustrate how the current induced on the strip, the far field and the radar cross-section are affected by the presence of the dielectric cylinder.

DOI:10.1049/ip-h-2.1985.0067

出版商:IEE    

年代:1985

数据来源: IET

摘要:

The input impedance of a circular microstrip ring antenna excited by a coaxial probe is studied using cavity Green's-function technique. The model of an annular cavity with the boundary admittances at the edges is considered in the analysis. The boundary admittance is obtained by considering the radiated and reactive power flows through the apertures at the edges. Input impedance is formulated from the conservation of energy principle, taking into account the losses in feed pin, conducting patch and dielectric substrate. The expression for input impedance includes the feed location, the feed diameter, the ring dimensions, thickness and dielectric constant of the substrate. TM120mode is considered for antenna applications. Experimental results of input reflection coefficients show good agreement with the theory.

DOI:10.1049/ip-h-2.1985.0068

出版商:IEE    

年代:1985

数据来源: IET

摘要:

Some problems concerning phase measurements of antennas are described. Phase-measurement errors, due to the fact that the phase centre and the centre of rotation of the antenna under test do not coincide, are analysed. The results are used for application to phase-pattern correction and phase-centre evaluation.

DOI:10.1049/ip-h-2.1985.0069

出版商:IEE    

年代:1985

数据来源: IET

摘要:

The equivalent-circuit-modelling technique is useful for designing printed frequency-selective surfaces. A correction term is derived which enables transmission responses to be modelled at oblique angles of incidence. Models derived for arrays of gridded-square and double-square elements are compared with experimental results for plane waves at normal incidence and at oblique angles for TE- and TM-incidence. Good agreement is obtained for angles of incidence up to 45° in the principle planes. The importance of using the immittance correction terms in the models is also discussed.

DOI:10.1049/ip-h-2.1985.0070

出版商:IEE    

年代:1985

数据来源: IET

摘要:

One of the basic problems of realising an optimum contoured beam, together with sidelobe suppression, is the determination of the excitation coefficients for the individual horns of a reflector and horn-array geometry. The Fletcher-Powell and the Minimax methods of optimising an arbitrary coverage with sidelobe suppression have been studied. The paper presents the formulations applicable to the Fletcher-Powell and the Minimax methods. The Brasilsat antenna is used as the test case. Results obtained using the two methods, and also by manual optimisation, are presented and compared.

DOI:10.1049/ip-h-2.1985.0071

出版商:IEE    

年代:1985

数据来源: IET

摘要:

An iteration scheme, which converges to the unique solution of the integral equation for the current on a straight tubular antenna, is presented.

DOI:10.1049/ip-h-2.1985.0072

出版商:IEE    

年代:1985

数据来源: IET