摘要:

It is shown that a null in the radiation pattern of a linear antenna array can be broadened into a null sector by the use of suitable forms of amplitude taper. For a uniformly spaced array, binomial taper coefficients with alternate positive and negative signs produce a maximally-flat null broadening. Null slewing by means of phase taper and null broadening by means of amplitude taper can be regarded as two independent operations.

DOI:10.1049/piee.1974.0029

出版商:IEE    

年代:1974

数据来源: IET

摘要:

A new technique is described in which f.e.t. sample-and-hold delay circuits are used to shape a square-wave digital pulse into a pulse whose spectrum approximates to a raised-cosine spectrum with 100% roll off. The technique, which is entirely digital, is examined both theoretically and experimentally, and it is found that the raised-cosine spectrum can be synthetised simply, and to a high degree of accuracy. The technique is easier to implement than methods based on conventional network synthesis.

DOI:10.1049/piee.1974.0030

出版商:IEE    

年代:1974

数据来源: IET

摘要:

A computer-based method for analysing the performance of d.c. chopper circuits is proposed. In the paper, a piecewise-linear description is established by considering sequential circuit modes, defined by the switching action of thyristors and diodes. The method is quite general, and could be applied to any particular chopper circuit to provide both transient and steady-state performance data. As an illustration, the method is used to describe the performance of a d.c. series motor controlled by a chopper circuit that provides both armature and field control. Control characteristics of this circuit are established, and these are compared with practical results obtained by measurement on a 220 V, 8 A series motor.

DOI:10.1049/piee.1974.0031

出版商:IEE    

年代:1974

数据来源: IET

摘要:

The existing analysis of the convertor-controlled d.c. drive is suitable only for the operation of the system under certain conditions; it does not take into account some modes of operation that appear to have been overlooked in the past. This paper redefines modes of operation of the drive, and presents a modified analysis and a suitable method for solving the system equations. Although the analysis is confined to single-phase systems, a similar analysis would apply to more complex configurations.

DOI:10.1049/piee.1974.0032

出版商:IEE    

年代:1974

数据来源: IET

摘要:

A new circuit is proposed for high-power synthetic tests of circuit-breaker performance. The new circuit is based on the current-injection principle, and is especially suited to economical tests with low-frequency transient recovery voltage (t.r.v.). Tests are possible with virtually any combination of t.r.v. and injection conditions, including those in which the t.r.v. frequency is lower than the injection frequency. The usual interaction which takes place between the t.r.v. and injection circuits is fully compensated, and, if necessary, components can be used in the t.r.v. network which are identical with those that would be used in a direct test under the same conditions. However, the usual restriction applies that there be no direct-current path to earth, if the recovery voltages is to be maintained. Examples are given of test circuits meeting the IEC requirements for the most difficult case of duty at 100% rated current.

DOI:10.1049/piee.1974.0033

出版商:IEE    

年代:1974

数据来源: IET

摘要:

As part of a programme of research on ultrahigh voltage (u.h.v.) lines, the impulse performance of a rig simulating the critical portion of a 1300 kV system transmission tower with 9.3 m clearance has been determined. Outcomes include the following: The minimum strength corresponds to a mean field of 230 kV m−1, and occurs with positive polarity on the conductor and with a front time of about 350 μs. The minimum withstand level corresponds to 1.8 p.u. The time lags before breakdowns are given over the range of crest times 50–750 μs. The effects of small changes in the dimensions of the rig were determined, and the performance was found to be relatively insensitive to these. A ratio of rig conductor length to gap spacing of 2.5:1 is shown to be adequate. Tests of the switching-impulse performance of the window were made over a period of one year, in a considerable variety of weather conditions, and negligible variations were found.

DOI:10.1049/piee.1974.0034

出版商:IEE    

年代:1974

数据来源: IET

摘要:

The internal design of unlaminated-rotor induction machines is investigated, with particular reference to hollow shell rotors either with or without a central steel web. The performance of these designs is explained in terms of flux-penetration, eddy-current and endeffect factors, and the theory is substantiated by measurements of machine performance and flux distribution. The examples given show that the webbed rotors can be designed to give either high torque or low inertia.

DOI:10.1049/piee.1974.0035

出版商:IEE    

年代:1974

数据来源: IET

DOI:10.1049/piee.1974.0036

出版商:IEE    

年代:1974

数据来源: IET

摘要:

The paper establishes the restrictions on the attainable closed-loop poles in single-input systems when constant feedback is employed from an output vector of smaller dimension than the state vector. These restrictions are linear equations in the coefficients of the closed-loop characteristic polynomial, and are obtained from the matrices describing the system in the state-space form. The closed-loop pole specifications are then expressed as linear equations in the coefficients of the characteristic polynomial, and these are solved simultaneously with the constraint equation to obtain the output-feedback vector required for pole assignment. The results developed for single-input systems are then extended to multivariable systems where the output-feedback matrices used are restricted to have unity rank. Further, arbitrary pole assignment in multivariable systems using unity-rank output feedback is studied. A number of illustrative examples are given.

DOI:10.1049/piee.1974.0037

出版商:IEE    

年代:1974

数据来源: IET

摘要:

An active probe is described that is suitable for measurement of current density J and electric-field strength E over an electrode boundary. It is capable of high mechanical resolution, since spatial accuracy of 0.5 mm is readily obtainable. Calibration of the probe is in terms of its mechanical dimensions, so that J may be determined to within ±1%, and E to within ±5%. The measurement of E is dependent on those situations where the motion of carriers is due to electrical drift; so that, in gases, the mean free path of ions should be less than a probe diameter. No such restriction applies to J. The probe has an interesting characteristic that is shown to have considerable generality in ionised air at s.t.p. It may prove to possess much wider generality. The method is presented and verified for static fields. Gaseous discharges and electrolytes may be usefully examined, and their conductivity measured directly.

DOI:10.1049/piee.1974.0038

出版商:IEE    

年代:1974

数据来源: IET