摘要:

A coupled finite boundary element method (CFBM) solution is developed for the EM fields scattered by an arbitrary multiple-dielectric coated conducting cylinder. The field in the dielectric coating domain is formulated by the finite element method, while the radiation condition is included by adopting a boundary element method. Numerical results show that the CFBM does not suffer from non-uniqueness in the resonance frequency. An excellent agreement between CFBM solutions and exact solutions for coated circular cylinders is observed.

DOI:10.1049/ip-h-2.1990.0001

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The dyadic Green's functions in three dimensions are constructed for a general uniaxial medium. This is a structure whereby the presence of a distinguished axis introduces an anisotropy into the constitutive relations of the medium. All four dyadic Green's functions (which are of the electric, magnetic and mixed types) are given and some of their properties (for example, symmetries) are discussed. By specifying the source to an electric dipole it is shown how singularities of the Green's functions have to be treated. The presented results can be applied to magnetised plasmas, magnetised ferrites and other substrates for microwave and optical devices as well as for moving isotropic media.

DOI:10.1049/ip-h-2.1990.0002

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The prblem of a cylindrical feed radiating in the presence of an axisymmetric reflector is formulated in terms of a combined electric and magnetic field integral equation. This equation is simplified by means of an optical approximation and numerical solutions are obtained using the method of moments. The field radiated by the combination of feed and reflector is computed using a hybrid physical optics and moment method approach, where the effects of feed-reflector coupling are taken into account. Examples are given of the method applied to the analysis of a splash-plate feed and a dual-mode coaxial feed illuminating a paraboloidal reflector.

DOI:10.1049/ip-h-2.1990.0003

出版商:IEE    

年代:1990

数据来源: IET

摘要:

Input impedance, resonant frequency, bandwidth and radiation characteristics of microstrip circular patch antennas coaxially shorted by a cylindrical post are investigated. The analytical results for the dominant and higher modes are compared with experimental data. The radiation conductance, the fringing field and the effect of feed position, i.e. a coaxial probe, are included by the mode expansion and matching methods. The dielectric effect of the substrate is also taken into account for the computation of the radiation characteristics. The results show that the electrical performance parameters of a centrally shorted circular microstrip antenna are sufficiently adjustable by a modification of the radius of the shorted post. The characteristics indicate that the proposed radiation element is a useful antenna with higher gain, wider bandwidth and improved impedance behaviour.

DOI:10.1049/ip-h-2.1990.0004

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The wavefronts of high-frequency (HF) radio waves received after reflection from the ionosphere exhibit both spatial nonlinearities and temporal variations which may limit the performance of large aperture antenna arrays. An experimental investigation has been undertaken in which the phase and amplitude of ionospherically propagated signals have been measured at several widely spaced antennas and the measurements have been interpreted in terms of the reflection process. Signals were received over a 122 km path for which pulsed soundings were available and from several European broadcast transmitters. The received signals exhibited widely differing behaviour and this is interpreted in terms of their modal content. For predominantly single moded signals, the observations indicate that for midlatitude paths any random components normally contribute less than 10% of the received power.

DOI:10.1049/ip-h-2.1990.0005

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The possibility of synthesising dual offset reflector systems to produce a prescribed far-field power pattern with no depolarisation is examined under the principles of geometrical optics. A formulation is developed based upon a model in which both source and antenna far fields are represented by Huygen's fields. Numerical implementation in general appears difficult but a useful special case emerges in which the reference axes of the Huygen's fields are parallel. Results for a contoured beam application reveal that a shaped dual offset system with no optical depolarisation is possible, and further analysis using physical optics suggests that extremely good axial ratios can be obtained.

DOI:10.1049/ip-h-2.1990.0006

出版商:IEE    

年代:1990

数据来源: IET

摘要:

Attenuation and reflection of a melting layer are calculated using a meteorological model. The model employs a new scheme for the calculation of the dielectric properties of melting ice particles with densities ranging from those of loose snow to hail, and a new scheme for calculating the melting rate is employed. The input parameters are derived from high resolution Doppler radar data and provide a data set for statistical analysis. Statistical relations were derived for attenuation in the melting layer based on measurements made with a surface rain gauge, a radar (with and without a polarisation facility), and a lower frequency satellite link. It was found that the specific attenuation of melting snow surpasses the value of rain because of the larger size and particle number density during melting, the attenuation within the melting layer increasing with its reflection. In stratiform precipitation, the attenuation in the melting layer is found to increase only slightly with frequency. The reflection in the melting layer decreases with the frequency of the radio waves in such a way that a bright band is only observed for frequencies below 20 GHz.

DOI:10.1049/ip-h-2.1990.0007

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The crosspolarisation of antenna systems involving 4-arm-structures depends on two factors: the quality of the feeding network and the shape of the antenna arms. Using a mathematical description for the separate treatment of these factors, planar archimedean and logarithmic spirals are investigated to optimise the arm shape. It is shown that a proper choice of the antenna shape can improve the crosspolarisation discrimination of the antenna system by more than 15 dB. It is also demonstrated that an optimised antenna shape yields significantly improved polarisation performance for the entire main beam region, even in the case of a poor excitation network.

DOI:10.1049/ip-h-2.1990.0008

出版商:IEE    

年代:1990

数据来源: IET

摘要:

A three element frequency dependent equivalent circuit which characterises a symmetric step microstrip discontinuity is determined using the method of lines. This method was applied so as to exploit to the full the processing capabilities of the available Cyber 205 computer, and to obtain results with the highest possible accuracy at frequencies in the range 4–16 GHz. Numerical values of scattering parameters are given for three geometries.

DOI:10.1049/ip-h-2.1990.0009

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The aspect ratio of the gyromagnetic resonator and susceptance slope parameter of the junction are important parameters in the design of a junction circulator. The purpose of this paper is to provide some additional information on these two quantities in the case of the evanescentE-plane junction loaded byH-plane openHE11½gyromagnetic resonators. The primary physical variables are the radial wavenumber of each resonator and the spacing between them. The design of a quarter-wave coupled device is outlined separately.

DOI:10.1049/ip-h-2.1990.0010

出版商:IEE    

年代:1990

数据来源: IET