摘要:

The microwave axicon considered is the analogue of the simple optical axicon. It consists of a dielectric cone of large semivertex angle placed in the aperture of a focused antenna. The effect shown both theoretically and experimentally is to reduce the beamwidth of the far-field radiation pattern to about two-thirds of the original value with an increase in the sidelobe level. In certain conditions this can give rise to a narrower pattern than that from a uniformly illuminated aperture of the same diameter.

DOI:10.1049/piee.1970.0173

出版商:IEE    

年代:1970

数据来源: IET

摘要:

Current distributions and admittances of an isolated symmetrical cylindrical dipole, and of two nonstaggered parallel dipoles, are analysed using a polynomial approximation for current along the dipoles. For antennas of lengths less than or not greatly exceeding the free-space wavelength, a polynomial of only second order approximates the current distribution quite closely, and results in self and mutual admittances which are, on average, as accurate as those according to the Chang—King 5-term theory. For longer antennas, of lengths up to approximately 1.5λ, a polynomial of only third order is an excellent approximation.

DOI:10.1049/piee.1970.0174

出版商:IEE    

年代:1970

数据来源: IET

摘要:

500 MHz propagation measurements have been carried out on a 189 km path over the Baltic Sea over a period of three years. The field strengths were compared for different refractivity and meteorological conditions. For the monthly median field strength, a dependence on surface refractivity of 0.32dB perNunit has been found. The correlation was somewhat better when using the gradient in the lower troposphere instead of surface refractivity. Comparisons were made with some other v.h.f. paths and a 500 MHz mixed land-sea path. The diurnal field-strength variation on the sea path was rather low. The mean diurnal amplitude ofF50was not more than 1.5dB. When the field strength exceeded 10% of the time the mean diurnal amplitude increased to 7dB, with a maximum in the late hours of the afternoon.

DOI:10.1049/piee.1970.0175

出版商:IEE    

年代:1970

数据来源: IET

摘要:

The obstacle gains are numerically illustrated as functions of the distance between the obstacle and the path terminal for the typical examples of a ridge, a bluff on a homogeneous earth and a cliff at a coastline. As the distance increases, these obstacle gains tend to become constants (i.e. the ridge gain, the bluff gain and the cliff gain that have been previously obtained), while, at short distances, they are directly affected by a diffraction loss, interference between the direct and reflected waves and other effects which are not optical in character. A convenient formula for the obstacle gain is introduced for the poor convergence of the relevant residue series. The obstacle gain defined here can be understood to be the gain caused by the earth's inhomogeneity and also the gain caused by the antenna height, or it can be the ‘terminal gain’, in the sense that the inhomogeneity in the vicinity of the path terminal is particularly emphasised by the effect of the antenna height. It can be used in the same way as the ordinary antenna-height gain over a homogeneous earth.

DOI:10.1049/piee.1970.0176

出版商:IEE    

年代:1970

数据来源: IET

摘要:

The results of an experimental estimation of the statical characteristics of the number of atmospherics per unit time which exceed a fixed threshold of field strength are given for the case when reception is at very low frequencies, in a frequency bandwidth greater than the effective bandwidth of the atmospherics spectrum.

DOI:10.1049/piee.1970.0177

出版商:IEE    

年代:1970

数据来源: IET

摘要:

For a parallel-plate or coaxial transmission line, a dielectric layer of sufficiently high permittivity placed in the space between the conductors, but adjacent to neither, can result in an attenuation coefficient which is significantly lower than that of the air-filled line. The dominant mode in these lines is shown to be a TM mode with no lower cutoff frequency. The expressions for the attenuation coefficient, derived by a perturbational technique, are applicable for any range of line dimensions and dielectric-layer permittivity and thickness.

DOI:10.1049/piee.1970.0178

出版商:IEE    

年代:1970

数据来源: IET

摘要:

The paper presents a state-space synthesis of multiport passive reciprocal networks using a minimum number of resistors. The method relies on a Gauss-factorisation procedure similar to Bayard's classical synthesis procedure. After a brief review of state-space formulation of the synthesis problem, a construction of a state-space realisation for a prescribed symmetric impedance is developed with the aid of a Gauss factorisation. The realisation constructed is nonminimal in general, but it is passive and used a minimal number of resistors. The constraint on the Gauss factorisation imposed by symmetry is then examined and interpreted in state-space terms to give a reciprocal synthesis.

DOI:10.1049/piee.1970.0179

出版商:IEE    

年代:1970

数据来源: IET

摘要:

The paper deals with the use of a digitally controlled voltage source (d.c.v.s.) as a general-purpose interface element. This concept has been successfully applied to bidirectional analogue-digital (a.d.) and radix conversions. The element may also be controlled from a digital computer to synthetise ‘analogue’ functions. A further application involves the use of a series of d.c.v.s. elements to generate a power series of terms from which sine, exponential, logarithmic and other functions may be constructed using a binary counter to provide the digital input. Methods of generating repetitive or nonrepetitive functions are outlined which can be given precisely controlled frequencies and/or amplitude. The D.C.V.S. element may be given to independent digital inputs as well as an analogue input, and this allows the generation of very complex waveforms. Relatively unsophisticated linear- and logic-circuit packages will achieve accuracies within 0.1% in the applications described.

DOI:10.1049/piee.1970.0180

出版商:IEE    

年代:1970

数据来源: IET

摘要:

Three methods of binary division are described and contrasted for accuracy and speed of operation. These use cellular arrays of logical gates and are particularly appropriate for consideration with large scale integrated silicon slices.

DOI:10.1049/piee.1970.0181

出版商:IEE    

年代:1970

数据来源: IET

摘要:

A method is described for locating the interface boundary between the space-charge-neutral regions in semiconductor devices. This is based on a two-dimensional S.O.R. solution of Poisson's equation for complete depletion within the space-charge region and Laplace's equation within the neutral region. Applications of this 2-dimensional analytical technique are considered, and particular reference is made to the junction field-effect transistor and the metal-oxide-silicon transistor.

DOI:10.1049/piee.1970.0182

出版商:IEE    

年代:1970

数据来源: IET