摘要:

A theory on intermodulation noise distortion owing to multipath reception in f.m./f.d.m. microwave links is developed for the case when the received signal is Nakagami-Rice distributed, i.e. depends on the addition of a constant signal and a Rayleigh-distributed random signal. The distortion formula derived by Medhurst concerning ‘the small constant echo of short delay’, is verified as a special case of the presented solution. It is shown that the median value of the distortion noise power produced when the echo is a non-coherent random signal may be computed as if the echo were constant with a power equal to the total echo power and with a relative delay time equal to the 2nd-order moment (radius of inertia) of the echo-power function with respect to the constant (direct) signal. The probability distribution of the distortion is derived when the received signal is Nakagami-Rice distributed.

DOI:10.1049/piee.1971.0311

出版商:IEE    

年代:1971

数据来源: IET

摘要:

The techniques used to remeasure the profile of the 25 m paraboloidal reflector on the UK Science Research Council steerable aerial at Chilbolton, Hants, England, are described, and the difficulties in obtaining such measurements are pointed out. Two methods are discussed: first, a specially constructed optical range finder for determining the co-ordinates of points on the reflector with respect to the vertex of the best-fit paraboloid, and secondly a laser system for determining the changes in reflector shape brought about by tilting the aerial through 90°. The procedures for calibrating these instruments which led to final r.m.s. errors of 0.36 and 0.4 mm, respectively, are outlined. The errors in profile of the reflector were found to be of a systematic rather than a random nature, and are discussed in relation to the radiation pattern measured at a wavelength of 3.1 cm. The change in reflector shape brought about by tilting through 90° is shown to be 1.3 mm r.m.s., which implies that, if the profile were readjusted to be perfect at the zenith, the gain at 0° elevation should be optimum (nearly 72 dB) at a wavelength of 9 mm.

DOI:10.1049/piee.1971.0312

出版商:IEE    

年代:1971

数据来源: IET

摘要:

A theoretical study of the input impedance of active loop-dipole aerials which possess height-reduction properties at resonance is made. This is compared with measurements on an aerial containing a BFY 90 transistor at 200 MHz for which the transistor parameters are available. Reasonable agreement is obtained. The existence of separate power gains and radiation patterns for transmitting and receiving is also established, and a comparison of the theoretical and experimental radiation patterns in the two cases is made. Numerical values of radiation resistance for these aerials are also calculated.

DOI:10.1049/piee.1971.0313

出版商:IEE    

年代:1971

数据来源: IET

摘要:

The structure of a conventional nonrecursive equaliser is modified so as to provide the equaliser with an automatic means of maintaining a frame of reference at all times. The output of the new equaliser is effectively the same as that of the conventional equaliser; the two equalisers merely differ in the procedure adopted for computing the forward tap weights. Another principal result is the formulation of a linear recursive adaptive equaliser which may be operated with or without a stability constraint. The paper concludes by presenting computer simulation studies of the performance of both nonrecursive and recursive adaptive equalisers.

DOI:10.1049/piee.1971.0314

出版商:IEE    

年代:1971

数据来源: IET

摘要:

The orthogonal network is introduced as a fundamental impedance-transforming element and a generalisation of the well known convertor and invertor. The transforming properties are related directly to the geometrical concepts of rotation and reflection and are exploited to give new forms of oscillator and filter.

DOI:10.1049/piee.1971.0316

出版商:IEE    

年代:1971

数据来源: IET

摘要:

The capacitor-fed parallel ‘chopper’ is shown to make a phase-sensitive demodulator with good zero stability, good linearity and a wide dynamic range for carrier frequencies of up to about 100kHz. Design problems are discussed in detail. A balanced version gives very low zero offsets, and allows fast response with relatively simple filters.

DOI:10.1049/piee.1971.0317

出版商:IEE    

年代:1971

数据来源: IET

摘要:

Improvements to ground secondary-radar interrogators, as described, will increase the accuracy of bearing measurements and, at the same time, permit the reduction of the interference with other stations. The system uses monopulse techniques to allow direction finding with errors of 5 minutes of arc r.m.s. at a range of 60 n.m. The proposals made represent a step towards selective interrogation.

DOI:10.1049/piee.1971.0318

出版商:IEE    

年代:1971

数据来源: IET

摘要:

The paper treats the backscattered field produced by a plane electromagnetic wave at oblique incidence on a perfectly conducting circular disc. The geometric theory of diffraction is used to obtain the first two terms of the asymptotic expansion at high frequencies. The first term is attributable to direct scatter from the edge of the disc and the second term arises from rays that cross the disc once. It has been found that the ray geometry is fixed for one polarisation but is aspect-dependent for the other. Owing to the axial caustic, functions must be introduced to match the wide-angle formulas to the known results for axial incidence. Bessel functions are used for the 1st-order terms and Fresnel integrals for the 2nd-order terms and evidence is presented to support this choice of function. The resulting 1st-order expression is in reasonable agreement with experimental data, and may be adequate for many purposes. However, the expressions incorporating the 2nd-order terms reveal the polarisation dependence of the scattering, and are in excellent agreement with measured data over a widt range of aspect angles.

DOI:10.1049/piee.1971.0319

出版商:IEE    

年代:1971

数据来源: IET

摘要:

A new method, based on the finite-element method of discretisation and compatible with existing finite-element techniques, is described for the solution of field problems in which the region of prime interest is embedded in an infinitely extending region where Laplace's equation holds. The essence of this method lies in representing the infinitely extending region by a single finite element, which may be included in an element assembly descriptive of the finite region of major interest. No iterative computation is necessary, and the computing effort required for solution is essentially the same as that required for solving the interiorfield problem alone.

DOI:10.1049/piee.1971.0320

出版商:IEE    

年代:1971

数据来源: IET

摘要:

The paper presents a new method for designing the auxiliary winding of a resistance-start split-phase type of small (f.h.p.) squirrel-cage motor. It is primarily aimed at helping a practical design engineer to choose an auxiliary winding which uses the minimum of copper while, at the same time, satisfying all specifications. The equations are developed in such a form as to facilitate the graphical display of information required during the design process. Also, it is demonstrated that a computer program can be developed using this method to give practical auxiliary-winding designs.

DOI:10.1049/piee.1971.0326

出版商:IEE    

年代:1971

数据来源: IET