摘要:

An improved method for accurately analysing symmetrical primary-fed reflector antennas is presented. The method, which is referred to as the multiple-scattering approach, takes into account the blockage caused by the feed in a very accurate way by also including the mutual coupling between the feed and the reflector. The coupling is treated as a multiple-scattering process. It is expressed in terms of the scattering pattern of the feed, which is the scattered field when the feed is excited by a plane wave with unity amplitude. To validate the method, a reflector antenna with a self-supported dipole-disk feed is investigated. The gain, the copolar sidelobes and the cross-polar level are much more accurately predicted by the multiple-scattering approach than by existing methods, provided that the scattering pattern of the feed can be determined with sufficient accuracy.

DOI:10.1049/ip-h-2.1992.0011

出版商:IEE    

年代:1992

数据来源: IET

摘要:

A forest-propagation model has been developed which includes the effects of trunks, branches, leaves and the ground. This model represents the forest as a planar, stratified, anisotropic, discrete, random medium, bounded above by air and below by ground. The mean field of the propagating wave has been obtained by recognising that the ensemble of discrete scatterers can be replaced by an equivalent continuous medium characterised by a linear dyadic permittivity. Fourier-transform techniques have been employed to generalise the model so that it accommodates arbitrarily modulated waveforms. Comparison of the model predictions with experimental data are presented for typical forest parameters. The paper also discusses predicted values of transmission loss as they relate to distance, antenna height, frequency, polarisation and biophysical forest parameters.

DOI:10.1049/ip-h-2.1992.0012

出版商:IEE    

年代:1992

数据来源: IET

摘要:

A radial-line slot antenna (RLSA) is a high-efficiency planar array. A double-layered radial line and uniform slot length have been adopted in conventional RLSAs. A single-layered RLSA is much simpler in structure, but the slot length must be varied to synthesise uniform aperture illumination. The authors propose theoretical methods for the slot design. The paper presents excellent characteristics of single-layered RLSAs of small sizes (0.25–0.60 m diameter) and confirms the design. These are now commercialised for 12 GHz band DBS reception.

DOI:10.1049/ip-h-2.1992.0013

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The attenuation function is derived with respect to the free space field for waves propagating over a perfectly conducting cliff edge. The general case of having a raised transmitter and receiver is considered. Based on physical arguments and the Feynman path integral, the exact propagator describing propagation over a ground plane which is the elementary building block of a cliff edge is derived. The total propagator for the cliff-edge geometry is derived using Markov's property of the paraxial wave equation propagator. The result reduces to that obtained using the compensation theorem, when both the source and the observation points are set at ground level. The validity of the result is confirmed by laboratory experiments.

DOI:10.1049/ip-h-2.1992.0014

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The simulation and practical results of a short range microwave holographic technique for the measurement of reflector antenna surface profile are presented. The technique uses a linearly scanned transmit/receive CW probe located on-axis at approximately two focal lengths from the reflector vertex. A compact plane polar data set is obtained and used to reconstruct the surface profile error map. A comparison is made between the microwave measurement technique and a more traditional mechanical measurement of the reflector surface. It is shown that synthetic aperture holographic principles can be employed in a non-anechoic environment. The method is aimed primarily at reflectors up to 5 m in diameter, but with suitable scanning systems it can be applied equally well to larger antennas.

DOI:10.1049/ip-h-2.1992.0015

出版商:IEE    

年代:1992

数据来源: IET

摘要:

In the paper the theoretical and experimental resonant frequencies of isolated and shielded rectangular dielectric resonators are reported. The dielectric waveguide model has been used for the analysis. Lowest-order modes of the resonator have been identified. The effect of shielding on the resonant frequencies of different modes has been studied. Experimental schemes that have been tried to excite various modes of the resonator are reported. Results of theory are compared with those of experiment.

DOI:10.1049/ip-h-2.1992.0016

出版商:IEE    

年代:1992

数据来源: IET

摘要:

An integral equation from whose solution the electromagnetic scattering from a conducting wedge loaded by a slot can be determined is formulated and solved numerically. Efficient techniques for summing the Green's function series present in such equations are considered. The aperture field, given in terms of an equivalent magnetic surface current and the resulting farzone scattered fields are determined and presented. Results are given for a variety of configurations and are compared with data available in the literature.

DOI:10.1049/ip-h-2.1992.0017

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The eigenvalue description is the most complete description of any symmetrical network. The purpose of this short paper is to give the eigenvalue description of the classic quarter wave plate. This may be done by starting from either its matrix description or a knowledge of its eigenvalues or eigen-networks. It is done here by recognising that the eigen-networks of this device may be deduced by applying electric and magnetic walls in all combinations to the circuit.

DOI:10.1049/ip-h-2.1992.0018

出版商:IEE    

年代:1992

数据来源: IET

摘要:

Highly resolved microwave imaging reveals that, for a bistatic angle of about 130° horizontally polarised edge scattering gives rise to a localised intensity distribution (scattering centre) with a double peak structure. Theory traces its origin back to the interference of partial waves arising from the coherent currents induced on the two surfaces shaping the edge.

DOI:10.1049/ip-h-2.1992.0019

出版商:IEE    

年代:1992

数据来源: IET

摘要:

A boundary-element method is presented for the rigorous investigation of a generalised finline configuration. The method is accurate and covers the metallization thickness, mounting grooves and arbitrary cross-sections. Calculations can be performed using far fewer nodes than with the finite element method. Two examples are given to show the efficiency of this approach.

DOI:10.1049/ip-h-2.1992.0020

出版商:IEE    

年代:1992

数据来源: IET