摘要:

In algebra, the values of a polynomial over a wide span of time can be inferred from its value and that of its derivatives, measured over a very short span of time. Somewhat analogously, closely-spaced measurements, defining the fine structure of the phase and amplitude distribution over a narrow antenna aperture, can provide the information conventionally obtained from a similar number of elements spaced at half-wavelength intervals over a wider aperture.Superdirective beam patterns, exploiting this principle, are conveniently synthesized by defining the directions in which zero (or minimum) response is required. The correlation between closely-spaced measurements will then cause some reduction of gain, even at the wanted peak of the directional response pattern, but the directivity, i.e. the gain in the wanted direction relative to that in other directions, can be significantly enhanced.Each direction of arrival produces a corresponding pattern of relative propagation delays to the different elements of an array. By suitably equalizing these with non-dispersive delay circuits and then subtracting for null-forming (in place of the usual phase changers), such superdirective arrays can be designed for bandwidths of up to several octaves. Thus superdirectivity can be of considerable value, in certain circumstances, for h.f. radio, sonar or radar.

DOI:10.1049/ree.1975.0091

出版商:IERE    

年代:1975

数据来源: IET

摘要:

The sensitivities to amplifier gain-bandwidth product of two active filters based on the Wien bridge are compared. It is shown that the performance of one of the filters can be optimized to give significantly smaller shifts in resonance frequency andQ-factor than the other filter which is generally recognized as the ‘standard’ circuit.

DOI:10.1049/ree.1975.0092

出版商:IERE    

年代:1975

数据来源: IET

摘要:

A traditional method of designing the ‘fine control’ mode of tracking systems is via the Bode plot relating system output to system error. This approach has a major disadvantage in failing to yield estimates of the system dynamic performance other than on an empirical basis which is somewhat unreliable. The paper shows how coefficient plane models may be used to solve this problem. Radar tracker and aircraft landing systems are used to illustrate the integrated coefficient plane-Bode plot approach.

DOI:10.1049/ree.1975.0093

出版商:IERE    

年代:1975

数据来源: IET

摘要:

The potential equation in a Hall plate is solved by an expansion method. The first-order expansion can be replaced by a variational principle which enables the finite element method to be used. This technique can be applied to arbitrary geometries and numerical results are presented for a rectangular Hall plate.

DOI:10.1049/ree.1975.0094

出版商:IERE    

年代:1975

数据来源: IET

摘要:

The paper deals with the design and construction of a dynamic data storage cell using stripline techniques, the data bit rate being 1 GHz. Taking into account both ohmic and dielectric loss factors, stripline losses have been computed and calculations indicate that, within the structure described, data bit rates up to 2 GHz are feasible.

DOI:10.1049/ree.1975.0095

出版商:IERE    

年代:1975

数据来源: IET

摘要:

This paper discusses the use of geometrical moments as possible information-extracting features for recognizing characters. The development of decision criteria is traced from the normal multivariate probability function to the Hamming distance, and the relative efficiencies compared. Decision boundaries are investigated by a stepwise transformation from character to character. Computer simulation of one-step recognition processes using these discriminants yields recognition rates which vary from low values using the simplest criterion, up to 100% in some cases using the most complicated criterion. Combinations of these methods into two-step processes are compared, and an attempt is made to find an optimum strategy for the case of poor quality hand-drawn capital letters.

DOI:10.1049/ree.1975.0096

出版商:IERE    

年代:1975

数据来源: IET