摘要:

A null-steering technique is described that is applicable to mechanically scanned antennas that can be synthesised as a number of identical subarrays. The process generates a substantially stationary polar pattern in space in which the nulls are locked to the directions of the interfering sources. The system is particularly suited to frequency-agile radars. The average system loss is 3 dB per source suppressed.

DOI:10.1049/piee.1978.0150

出版商:IEE    

年代:1978

数据来源: IET

摘要:

The possibility of rendering a gradient-type adaptive equaliser able to acquire automatically the optimal adjusting step has been proved in the paper by proposing a new type of equaliser. The mentioned possibility enables the equaliser to be independent of the channel characteristic and very slightly dependent on the noise.

DOI:10.1049/piee.1978.0151

出版商:IEE    

年代:1978

数据来源: IET

摘要:

The method of an earlier paper is applied to calculate the disturbances due to a number of discontinuities encountered in typical antenna feed and network structures, such as impedance changes, power dividers, T-junctions, open and short circuits etc., and these are compared for relative radiation. Error estimates due to some secondary effects are calculated and shown to be generally negligible. The process of radiation from an open circuit is studied in detail and it is shown that, although most of the radiation comes from the tip, a substantial amount is radiated and also absorbed to. about a free-space wavelength behind the discontinuity. A method analogous to the induced e.m.f. method is formulated and shown to confirm existing results for radiated power. A distinction is made between the phase centre for radiation, which is usually located at a discontinuity, and the source region for radiation. The two are not coincident and the latter may be quite extensive for microstrip radiations. The results are applied to show how the disturbances can affect the performance of a comb antenna and how they can also be utilised to enhance the efficiency of a strip-end radiator on a thin substrate.

DOI:10.1049/piee.1978.0152

出版商:IEE    

年代:1978

数据来源: IET

摘要:

An important mode of operation of a general power amplifier using power transistors is described, whose output is a variable-frequency 3-phase current. The convertor operates from a fixed 3-phase source without a d.c. link, utilises only 18 power transistors and provides a regenerative output.

DOI:10.1049/piee.1978.0153

出版商:IEE    

年代:1978

数据来源: IET

摘要:

Problems of the power engineer can be provided with better solutions using microelectronics. Some of the significant power-engineering problems are examined together with microelectronic components available for solutions. A number of examples are given of solutions to selected power problems and these include the use of microcomputers for protection control and data collection for metering, remote load control, static distance protection, ‘hi-fi’ capacitor voltage transformers, phase-comparison protection, pilot-wire protection, transformer-differential protection, overcurrent protection of low-voltage networks, instrument transducers, power-factor correction and control of unwanted interference. The aim of this paper is to provide an insight into the functioning of engineers in this environment, an understanding of the problems that exist and an awareness of the advances that are being made in the solutions that are provided.

DOI:10.1049/piee.1978.0154

出版商:IEE    

年代:1978

数据来源: IET

摘要:

New theories for linear induction motors (l.i.m.s) with completely filled and half-filled primary endslots are presented. End effects due both to the discrete nature of the windings and the finite iron length are taken into account by formulating the boundary-value problem on the basis of the m.m.f. distribution and representing the m.m.f. wave packets of the stator windings by Fourier integrals. The paper reveals that the stationary pulsating m.m.f. wave, which appears in the air gap of an l.i.m. with completely filled slots owing to the finite length of the stator iron core, has a very adverse influence on the motor performance, a phenomenon which has not been previously discussed. A new theory of compensation is proposed to improve the performance of this type of motor. The paper also shows that idealised theories of the l.i.m. are very special cases of those given here. A simplified formulation of the boundary-value problem of the l.i.m., taking into account the end effects due both to the discrete nature of the windings and the finite stator iron length, is also given. The results are compared with published experimental data, and with those obtained from an idealised l.i.m. excited by a sinusoidally distributed current sheet of the same magnitude.

DOI:10.1049/piee.1978.0155

出版商:IEE    

年代:1978

数据来源: IET

摘要:

A general theory of induction machines with unlaminated secondary and constant-current excitation is presented, based on a previous treatment of such machines with constant-voltage supply. The results are presented in the form of generalised curves of nondimensional coefficients, which, in conjunction with simple scaling factors, enable the torque/speed characteristic of a given machine to be evaluated. A computational method is described for taking into account saturation in the magnetic circuit and the validity of the treatment is demonstrated by correlation with tests up to high levels of saturation. The results are particularly relevant to modern eddy-current machines such as dynamometers, brakes and couplings.

DOI:10.1049/piee.1978.0156

出版商:IEE    

年代:1978

数据来源: IET

摘要:

The method of the busbar impedance matrix is applied to the solution of asymmetrical faults through the use of sequence impedances and Kron's constraint matrix. An algorithm is proposed to facilitate the routine solution of complex configurations including simultaneous and cross-country faults.

DOI:10.1049/piee.1978.0157

出版商:IEE    

年代:1978

数据来源: IET

摘要:

The use of active control technology (a.c.t.) to alleviate the effects on both the dynamic and structural responses of an aircraft flying through atmospheric turbulence, while maintaining an acceptable degree of flight-handling qualities, is discussed.Two control schemes, derived from optimal-control theory and the algebraic theory of model following, are presented, and their value as practical methods of achieving satisfactory ride comfort in a gusty environment is discussed. A possible weakness in current methods of mathematical modelling of flexible, or deformable, aircraft is indicated.

DOI:10.1049/piee.1978.0159

出版商:IEE    

年代:1978

数据来源: IET

摘要:

Application of the principle of maximum likelihood to the problem of image registration is shown to yield an optimum process which is analogous to that of conventional cross correlation but in which the product function is replaced by a new function that has been called the ‘likelihood correlation’ function. This function is defined by the separate and joint probability distributions of the contents of the two pictures to be registered. The form of the likelihood correlation function is particularly simple in two special cases of practical interest and a suitable embodiment is described. It is shown that a number of algorithms described in the literature are special cases of the likelihood correlation function. Possible embodiments of this function in the general case are outlined. It is suggested that the likelihood correlation function has wider applicability than just for image registration.

DOI:10.1049/piee.1978.0160

出版商:IEE    

年代:1978

数据来源: IET