摘要:

The receiving and transmitting properties of a grid paraboloidal reflector of aperture diameter 2.73λ andf/Dratio 0.395, operating at 410 MHz, are analysed using the moment method. For the receiving situation, with a normally-incident plane wave illuminating the reflector, the distributions of current, obtained in the inner grids only, show a close resemblance to those predicted by the physical optics approximation. It is shown that neither maximum scattered nor maximum total electric field on axis is received at the geometrical focus, but at a point between this focus and the vertex. This result is in agreement with that calculated by the physical optics method for small solid paraboloids of the samef/Dratio. Contours of scattered off-axis fields are also presented in the geometric and true focal planes of the paraboloid as well as in longitudinal planes of such a reflector. In the transmitting situation, the grid paraboloid is excited by a centrally driven couplet feed, positioned at different points along the axis. It is shown that the feed position affects considerably the distributions of current in the feed elements but not in the reflector grids, and confirms that defocusing the couplet feed results in an increased forward power gain.

DOI:10.1049/piee.1979.0209

出版商:IEE    

年代:1979

数据来源: IET

摘要:

The input impedance and the electromagnetic fields of a circular-disc printed-circuit antenna are found. The antenna is driven at an arbritrary point. The present analysis takes into account the radiation through the side wall and the fringe field at the edge of the printed-circuit antenna.

DOI:10.1049/piee.1979.0210

出版商:IEE    

年代:1979

数据来源: IET

摘要:

A technique of analysing the principal-plane near-field patterns of pyramidal horns excited in the dominant mode based on the uniform geometrical theory of diffraction (u.g.t.d.)1, 2is presented in this paper. The geometrical-optics field is derived by approximating the horn as a quasipyramidal horn waveguide.9Numerical computations of the near-field amplitude patterns of a typical pyramidal horn based on the g.t.d. technique detailed here well correlate with the measured patterns, justifying the validity of the analysis presented. Further, the analysis presented is valid for any arbitrary field point (located in the principal planes) so that pattern computation is possible in the near field or in the Fresnel zone or in the far field.

DOI:10.1049/piee.1979.0211

出版商:IEE    

年代:1979

数据来源: IET

摘要:

The problem of surface-wave propagation over the modified Goubau line, which consists of a Goubau line with an airgap between the conductor and dielectric, is formulated by the boundary-value method. The various modes which exist on the line as well as their cutoff conditions and the specific effects of the airgap are obtained from a solution of the characteristic equation. The mode spectrum for the symmetric and hybrid modes as well as the transverse field distributions for theE00andH01modes are also presented. The axial power flow and the attenuation constant are calculated for the dominant mode and the salient low-loss feature may be explained perhaps in terms of total internal reflection or duct propagation phenomena.

DOI:10.1049/piee.1979.0212

出版商:IEE    

年代:1979

数据来源: IET

摘要:

The problem of optimum design of an m.t.i. system for clutter rejection is considered in this paper. The procedure involves minimisation of the output clutter power subject to the constraint that the average output-signal power over the expected target Doppler range is to be kept constant. Another constraint in the minimisation problem is incorporated, according to which the transfer function of the system has a null at the dominant clutter Doppler frequencyfm, which may often be zero. In this way, the distributed component of clutter is minimised at the filter output while the clutter component at a fixed mean relative velocity is completedly suppressed. With the two constraints specified above, the problem is mathematically formulated as a modified eigenvalue problem. Comprehensive results for the performance of the resulting filters are presented.

DOI:10.1049/piee.1979.0213

出版商:IEE    

年代:1979

数据来源: IET

摘要:

Five years of slant-path-attenuation and point-rain-rate measurements in Sweden have been used to estimate the prediction accuracy of a simple equivalent-distance model. Radiometer attenuation data at 11.4 and 14.0 GHz, obtained at 21° elevation and rain-rate data from a tipping-bucket-type rain gauge have been used. The long-term predication error is estimated to be within a few tenths of a dB, giving strong support to the usefulness of the method. The equivalent distance is found to be frequency independent over the range 11–14 GHz at least, and consequently frequency scaling of attenuation data, using the theoretical specific attenuation, is proposed.

DOI:10.1049/piee.1979.0214

出版商:IEE    

年代:1979

数据来源: IET

摘要:

The problem of applying a set of constraints to antenna arrays is discussed. It is shown that when the noise between different elements is uncorrelated, the optimum radiation pattern can be expressed as a sum of the quiescent beam and the constraint-vector beams. To determine the excitations of the array, only the weighting coefficients of the constraint-vector beams need to be calculated. The method can be used to set pattern nulls as well as sidelobes at some specified positions.

DOI:10.1049/piee.1979.0215

出版商:IEE    

年代:1979

数据来源: IET

摘要:

A variable-speed generating system is described which uses a 3-phase squirrel-cage induction machine with self-excitation capacitors. The variable-frequency/variable-voltage generated is then fed through a 3-phase controlled rectifier to provide a d.c. supply at constant voltage. The proposed scheme is suitable for wind power sources as it allows wide changes in wind turbine speed and, at all speeds, optimum generating power can be set up by rectifier delay angle control.

DOI:10.1049/piee.1979.0216

出版商:IEE    

年代:1979

数据来源: IET

摘要:

The starting and pull-in behaviour of typical, single-phase reluctance machines, with and without capacitive excitation, is explored experimentally and by computation. A comprehensive study of the effects of impedance variations on the pull-in performace is presented. This study enables new designs to be produced which are shown to exhibit greatly improved pull-in behaviour. The experimental machines are of segmented type but the general results are applicable regardless of construction.

DOI:10.1049/piee.1979.0217

出版商:IEE    

年代:1979

数据来源: IET

摘要:

The paper presents results of digital computer calculations of the sheath overvoltages and the energies absorbed by sheath-protecting surge arresters in a crossbonded cable system. Especially, the energy loading of the arresters during energisation and discharge of an underground cable-overhead line configuration is considered. An analysis of the natural wave propagation characteristics of the cable system is given. Based upon this analysis a frequency-independent wave propagation of all modes has been adopted as a basis of the calculation method. The requirements concerning the choice of the arrester are discussed.

DOI:10.1049/piee.1979.0218

出版商:IEE    

年代:1979

数据来源: IET