摘要:

The paper describes certain general transformations for digital filters in the frequency domain. The term digital filter is used to denote a processing unit operating on a sampled waveform, so that the input, output and intermediate signals are only defined at discrete intervals of time; the signals may be either p.a.m. or p.c.m. The transformations discussed operate on a lowpass-digital-filter prototype to give either another lowpass or a highpass, bandpass or band-elimination characteristic. The transformations are carried out by mapping the lowpass complex variableZ−1[whereZ−1= exp ( −jωT) andTis the time interval between samples] by functions of the formejθπni=1z−1−αi/1−α*iz−1known as unit functions.

DOI:10.1049/piee.1970.0281

出版商:IEE    

年代:1970

数据来源: IET

摘要:

The multiterminal-gyrator concept is introduced as an extension of the well known 2-port device. In general, it is treated as havingninput andmoutput terminals plus a reference or earthed terminal, common to both input and output. The (n+m+ 1)-terminal device is therefore mathematically described using an (n+m)th-order admittance matrix. Both the mathematical characterisation and impedance-inverting properties of the multigyrator are shown to be directly analogous to those of its 2-port counterpart. An active realisation of the generalised multigyrator is proposed which uses unity-gain voltage and ± unity-gain current amplifiers. The method is quite general and usesn+mterminals. The actual gyrator transconductances are defined by an interconnecting network of resistors. The use of multigyrator capacitor networks to simulate inductor networks is shown to be possible and synthesis examples are given. Finally, the results of two experimental multigyrator filters are given.

DOI:10.1049/piee.1970.0282

出版商:IEE    

年代:1970

数据来源: IET

摘要:

A simplified derivation of the state-space equations is presented for linear circuits consisting of capacitors embedded in a conductive (i.e. nonreactive) structure (GCcircuits). Inductors which do not form cutsets containing only inductors and/or current sources can be included by gyrator simulation. A compact organisation of the derivation is made possible by this sacrifice in generality. Thus the only type of submatrix operation required is transport from one full matrix to another. The full-matrix operations required are one inversion, seven multiplications and one transposition. The method is thereby made programmable for small computer systems.

DOI:10.1049/piee.1970.0283

出版商:IEE    

年代:1970

数据来源: IET

摘要:

Apparatus to measure the correlation between two wideband (10–100MHz) noise signals has been developed for the stellar intensity interferometer at the Narrabri observatory. This instrument is used to measure the angular diameters of stars in the range 0.01–0.0001″ of arc, with an accuracy within about 5%. To achieve this precision with the low signal/noise ratio of an intensity interferometer, it is necessary to integrate and average the data for periods up to 100h, which may involve observations spread over several weeks. The paper describes the novel techniques which have been used to obtain the necessary efficiency and stability in the electronic correlator.

DOI:10.1049/piee.1970.0284

出版商:IEE    

年代:1970

数据来源: IET

摘要:

The techniques of switching-function analysis are used to extend previous work on the intermodultion and crossmodulation-distortion properties of the ring modulator to include the single-balanced series and shunt configurations. The influence of the local-oscillator source impedance is considered, and excellent agreement is demonstrated between the predicted 3rd-order intermodulation performance of two single-balanced circuits and results obtained for experimental modulators using Schottky-barrier diodes.

DOI:10.1049/piee.1970.0285

出版商:IEE    

年代:1970

数据来源: IET

摘要:

Effectiveness of mode filtering in multimode waveguides designed for long-distance communication is examined. Based on a general solution to weakly coupled transmission lines having different attenuation coefficients, an expression is derived for the fractional reduction of the average reconverted power by mode filters. It is shown that this improvement depends on the differential attenuation of the parasitic modes along the section of the line between adjacent filters and the attenuation of the parasitic modes in filters. If the latter is increased above about 10dB, it does not result in any improvement in the performance of the system. Further improvement can only be achieved by reducing the filter spacing. The effect of filtering on the delay distribution of the reconverted power is also considered. It is shown that mode filters attenuate echoes with long delay more strongly than those with short delays.

DOI:10.1049/piee.1970.0286

出版商:IEE    

年代:1970

数据来源: IET

摘要:

The shadows and blockage occurring in large antennas are approximated to by well-defined regions constructed from radii and arcs of circles, which are concentric with the aperture, projected onto the aperture plane. The radiation patterns of the obstructed aperture are obtained for both uniform and tapered illumination from the scalar integral. It is shown that apertures obstructed by four symmetrically placed shadows suffer comparatively little degradation, but that three symmetrically placed shadows give a considerable increase in the beamwidth in any plane that contains a shadow region.

DOI:10.1049/piee.1970.0287

出版商:IEE    

年代:1970

数据来源: IET

摘要:

The presence of crossproduct terms in multiplicative receiving systems, in particular 2-aerial synthetic-aperture receivers, is illustrated. Methods for suppression of these terms are discussed, as well as the residual level that may be acceptable. It is shown that crossproduct terms are adequately suppressed if there are many cycles of relative-phase variation between sources during the synthesis period, and, from the theory presented, the minimum synthesis time can be computed for any particular source behaviour.

DOI:10.1049/piee.1970.0288

出版商:IEE    

年代:1970

数据来源: IET

摘要:

The application of an aperture-synthesis technique to a particular type of radar, designed to observe ionospherically propagated ground backscatter, is proposed, since the bearing resolution of existing equipment has been limited by practical aerial dimensions. The incoherence of ionospherically propagated signals demands a multiaerial synthetic-aperture technique, and a 2-serial system is suggested. The technique requires data to be stored during the synthesis period, and a photographic method suitable for the radar has been evolved. A practical implementation of this is proposed, together with the accompanying data processor in the form of a 1-dimensional optical spectrum analyser. The theoretical predictions of the performance of such a system have been verified with an experimental ultrasonic model.

DOI:10.1049/piee.1970.0289

出版商:IEE    

年代:1970

数据来源: IET

摘要:

A new exact method is developed for investigating the scattering of plane electromagnetic waves from perfectly conducting bodies. The multipole scattering problem is solved exactly and the method is applicable to more than one body localised in a region. Expansion of Green's dyadic in concentric spherical regions, one of them containing the scatterers, leads to the corresponding multipole expansions for the fields in these regions; then a set of algebraic equations is obtained for the associated multipole coefficients by using the appropriate boundary conditions. Both theoretical and experimental results are presented for spheres, prolate spheroids and some other arbitrary bodies, and excellent agreement is obtained between theory and experiment.

DOI:10.1049/piee.1970.0290

出版商:IEE    

年代:1970

数据来源: IET