摘要:

The celebrated discoveries of Maxwell, Hertz and many others heralded a century rich in the exploitation of ideas to create electronic systems beneficial to mankind. This address focuses on the recent exploitation of electromagnetics concerning the sensing of images, generation of force and dispensing of heat thus highlighting important trends in the kindred RF and microwave industries. A recapitulation of the milestones in the advances over the century emphasises the interdependence of theory, material development and system innovation. Today's CAD/CAM and chip-integration philosophies have taken the batch-oriented microwave component industry to the threshold of mass production. Improving both the accuracy of electromagnetic design equations and the manufacturing technology are critical issues, and the revolutionary antenna phased array technology well illustrates these challenges. The diverse advances in passive and active image sensing systems rely heavily on signal processing, and examples include the radiometric sensing of temperature and microwave diffraction tomography in medical diagnostics, and the synthetic aperture radar scanning of the earth. A complementary topic concerns the disguise of radar target signatures, mainly in defence, and the use of ingenious electromagnetic wave scattering behaviour. Equally daunting is the invention of microwave sources with astronomical power levels that make defensive electromagnetic beam weapons a possibility, and fascinating experiments on electromagnetic rocket launchers and guns for space scenarios have been reported. Finally commonplace microwave domestic cooking is seen to be but one of a multitude of applications including pest control, seed germination and cancer therapy. Skill shortages, achieving the potential of CAD in mass production, and exploiting the emerging technologies, are some of the stimulating challenges ahead.

DOI:10.1049/ip-h-2.1989.0001

出版商:IEE    

年代:1989

数据来源: IET

摘要:

Radio pulse transmission is studied along mixed paths in a stratified forest using a stochastic radiowave propagation model. The model considers the forest as a planar stratified, anisotropic and discrete random medium which is bounded above by air and below by the ground. It consists of randomly positioned and oriented canonical scatterers which represent the principal forest constituents. Analytical results are found for sample canonical geometries in which the fields can be described in terms of ray trajectories for different propagation paths. These are then used for the numerical application of the model.

DOI:10.1049/ip-h-2.1989.0002

出版商:IEE    

年代:1989

数据来源: IET

摘要:

The problem of plane wave diffraction from a plane discontinuity formed by impedance and resistive (or dielectric) half-planes is considered. As is known, diffraction by a two-part surface is an important topic in diffraction theory and is relevant for many applications. This two-part mixed boundary value problem is formulated by Fourier transform technique, and leads to a vector Wiener-Hopf equation which is reduced to scalar form and solved by standard techniques. Then asymptotic expressions for the diffraction coefficients are obtained by evaluating the field integrals asymptotically. These expressions reduce to the known results related to an impedance half-plane when the resistivity (ζ → ∞, which corresponds to the situation where no resistive half-plane exists.

DOI:10.1049/ip-h-2.1989.0003

出版商:IEE    

年代:1989

数据来源: IET

摘要:

A theory is presented for calculating the macroscopic effective permittivity of mixtures that are composed of a background medium and inhomogeneous scatterers. The scatterers are two-component spheres, where both the spherical core and the spherical shell that forms the surface of the scatterer are homogeneous with a constant permittivity. The effective permittivity is calculated as the function of the constituent permittivities and their volume fractions. The analysis is quasistatic and therefore the results only apply to mixtures where the sizes of the scatterers are considerably smaller than the wavelength of the operating RF field. The results are applied to calculating the microwave attenuation of melting hail, at a frequency of 1 GHz and where the hydrometeors are assumed to be in the form of a spherical ice core with a spherical water coating shell. There is a peak in the attenuation of hail as it falls through a warm layer. The attenuation is greater with a thin water coating (the fraction of water from the hail particle is 0.09) than it is when the hail particle has completely melted. This resembles the same phenomenon of increased extinction which is observed in the radar backscattering from melting hail.

DOI:10.1049/ip-h-2.1989.0004

出版商:IEE    

年代:1989

数据来源: IET

摘要:

We propose a wide slot antenna to expand the frequency bandwidth of a cavity-backed slot antenna. In the antenna the slot width is significant in comparison with the slot length. We present the analysis of the antenna including the feed line. The result obtained is a 35% frequency bandwidth (VSWR < = 2), which is also verified by experiment.

DOI:10.1049/ip-h-2.1989.0005

出版商:IEE    

年代:1989

数据来源: IET

摘要:

A computationally efficient technique for evaluating the approximate fields scattered by conducting bodies is presented, which involves neither iteration nor matrix inversion. The method is therefore faster than conventional scattering algorithms and requires less computer storage. The accuracy of the technique is demonstrated by comparisons between the predicted scattered fields of several objects and well established control solutions.

DOI:10.1049/ip-h-2.1989.0006

出版商:IEE    

年代:1989

数据来源: IET

摘要:

A computer aided design/synthesis procedure for array antennas of the slotted waveguide type is described. It differs from earlier contributions to this topic in that it uses theoretically evaluated self-admittances, rather than measured self-admittances, for the individual broadwall slots in the array. By adopting the moment method to generate the slot self-admittances, it is shown that accuracies which are comparable with those obtained from a measurement based procedure can be achieved.

DOI:10.1049/ip-h-2.1989.0007

出版商:IEE    

年代:1989

数据来源: IET

摘要:

The self-phased array, which achieves beam pointing automatically by the use of a pilot carrier, has a particularly unusual behaviour in the presence of multipath signals. The object of the paper is to investigate the underlying array behaviour in a two signal multipath condition, which can be used to determine the performance of a practical array system. Theoretical and experimental results are presented to show the beam forming properties of the array in such a situation for the two cases of operation with or without pilot channel limiting.

DOI:10.1049/ip-h-2.1989.0008

出版商:IEE    

年代:1989

数据来源: IET

摘要:

Microstrip Rotman lenses are multiple beam forming devices for antenna arrays. The research described here has investigated factors limiting the performance of microstrip lenses compared to parallel plate lenses. New techniques for sidewall absorption and lens port pointing have been identified and demonstrated.

DOI:10.1049/ip-h-2.1989.0009

出版商:IEE    

年代:1989

数据来源: IET

摘要:

A coaxial line flush mounted on an infinite perfectly conducting ground plane and covered by a dielectric hemisphere is investigated. Green's functions for the region above the ground plane are derived with separated homogeneous and particular solution parts so as to be compatible with numerical analysis techniques. A magnetic field integral equation is obtained in terms of the unknown annular aperture tangential electric field and is solved by the method of moments. A comparison between the present case and that of a flush-mounted coaxial line with an infinite homogeneous region above the ground plane is presented in terms of the tangential aperture electric field, the coaxial line apparent input impedance and the far radiated field.

DOI:10.1049/ip-h-2.1989.0010

出版商:IEE    

年代:1989

数据来源: IET