摘要:

Stationary complex-valued functionals are discussed and seen to have unique stationary points if they are analytic, which corresponds to analyticity of functions in complex-valued function theory. As an application, the problem of wave propagation in a circular waveguide with an impedance boundary and the corresponding two-dimensional resonator are discussed. It is seen that the variational method for nonstandard eigenvalue problems, introduced a few years ago, can be generalised to complex-valued functionals if the functional is analytic. The method can be applied to result in simple analytic formulas for the waveguide with impedance boundaries.

DOI:10.1049/ip-h-2.1989.0053

出版商:IEE    

年代:1989

数据来源: IET

摘要:

A new computer analysis method is presented by which the noise contributions of the various noise sources within a MESFET mixer can be determined and its overall single sideband and double sideband noise figure and noise temperature calculated. The method extends Kerr's work on diode type mixers and utilises a frequency conversion matrix of a MESFET mixer which was described previously. The simulation program was run for a mixer circuit based on an NEC720 transistor, and the results for the noise sources and noise figure behaviour as functions of the LO power are presented and compared to measured values with good agreement. An optimal operating point from the standpoint of minimum noise figure can thus be determined for transistor biasing conditions and the LO input power.

DOI:10.1049/ip-h-2.1989.0054

出版商:IEE    

年代:1989

数据来源: IET

摘要:

A new microwave iterative technique for obtaining the inhomogeneous profile of semiconductor permittivity and conductivity is optimised. The optimum physical conditions for applying the gradient method in solving microwave inverse problems are studied and underlined. A new regularisation approach is applied to improve the profiles of oscillating solutions. Numerical experiments are used to prove the validity of this technique in solving ill-posed problems.

DOI:10.1049/ip-h-2.1989.0055

出版商:IEE    

年代:1989

数据来源: IET

摘要:

A simple set of integral equations with reduced unknowns and kernel singularity are derived for simulating arbitrarily-shaped two-dimensional inhomogeneous composite scatterers. By utilising a known equivalence between electric and magnetic currents, new equivalent currents are introduced with the resultant integral formulation exhibiting a volume integral in addition to a surface integral, each in terms of a single equivalent current component. A pulse basis-point matching moment method implementation of the reduced unknown integral equations is presented. Scattering patterns computed with the numerical code are compared with results obtained via alternative analytical techniques.

DOI:10.1049/ip-h-2.1989.0056

出版商:IEE    

年代:1989

数据来源: IET

摘要:

A numerical method based on the joint application of Kirchoff's integral formulation and the moment method is proposed for the study of a wide class of axially-symmetrical resonant devices. The tuning frequencies of a shielded dielectric resonator operating in TE01δmode are obtained using this numerical method. Comparison of the numerical results with experimental results, and with numerical results obtained by other authors, shows the accuracy of the method.

DOI:10.1049/ip-h-2.1989.0057

出版商:IEE    

年代:1989

数据来源: IET

摘要:

Although relatively new, the principle of measuring the radiation pattern of an antenna using the time domain rather than frequency domain is well known and relies on gating out unwanted reflections. Time domain measurements on horn and spiral antennas illustrate the need for error criteria and in this paper the nature of the gating error, and its relationship to the anti-interference enclosure size and the antenna frequency response, are investigated by both analytical and computer simulation methods. The results show that a lower frequency antenna can be expected to require a larger enclosure for a given gating error and that, for small enclosures, the time domain method has advantages over the conventional frequency domain method. The practical implementation of time domain measurement involves other factors such as the effects of aliasing, the need for a high quality reference channel for calibration, matching and noise levels. It is concluded that, in the time domain method, the amount of absorbent material in a chamber may be reduced but at the expense of a fast signal processing facility and, to some extent, a more critical equipment installation.

DOI:10.1049/ip-h-2.1989.0058

出版商:IEE    

年代:1989

数据来源: IET

摘要:

This paper describes a moment method program for computing electromagnetic scattering (for bothE- andH-polarisation) from multiple perfectly conducting and penetrable inhomogeneous cylinders. (The latter can be lossy and have both permittivity and permeability different from their free-space values.) The program is a numerical implementation of a recently derived volume-surface integral equation and uses the pulse expansion and point-matching technique. The main feature of this program is its simplicity in generating the model and transforming the integral equation into a linear system of equations. Using this program, we explore and demonstrate the usefulness as well as the limitations of the volume-surface integral equation formulation.

DOI:10.1049/ip-h-2.1989.0059

出版商:IEE    

年代:1989

数据来源: IET

摘要:

The problem of determining the diffraction loss between a transmitter and receiver in clear air conditions, when the intervening terrain is given, is treated for propagation at microwave frequencies. A model is developed which simulates the terrain by means of a cascaded arrangement of cylinders. This model, which remains valid at grazing angles, extends Vogler's result for cascaded half planes to treat cylinders. Experiments are conducted on two cylinders which share the same shadow boundary, for both vertical and horizontal polarisation. Measurements are performed on cylinders which present both zero and non zero surface impedance, and these are found to be in good agreement with predictions.

DOI:10.1049/ip-h-2.1989.0060

出版商:IEE    

年代:1989

数据来源: IET

摘要:

The impedance and radiation properties of a square microstrip antenna operated in the dominant mode is compared with those of an equivalent circular microstrip antenna. On the basis of this comparison, closed-form expressions for the impedance and far fields of circular microstrip antennas are derived.

DOI:10.1049/ip-h-2.1989.0061

出版商:IEE    

年代:1989

数据来源: IET

摘要:

The measurement of reflector antenna surface profiles using a phase-only metrology technique is presented. By measuring the near-field phase of a pencil beam antenna and the use of a suitable algorithm, deviations from the desired reflector aperture phase can be related to distortions on the reflector surface. By a suitable choice of measurement wavelength, quite high accuracies can be achieved. Experiments using a wavelength of 8.5 mm have shown that surface deviations as small as 0.1 mm can be detected. Two experimental techniques for obtaining this near-field phase data have been investigated. One uses a conventional plane-polar near-field measurement range employing electromagnetic waves at 35 GHz. The other uses a linear array of ultrasonic receivers operating at 40 kHz, again in a plane-polar measurement configuration. In this latter case the radial part of the plane-polar scan is performed electronically using the linear array, providing a very rapid scanning system. Both systems have been built and tested using a 1.2 m diameter parabolic reflector antenna whose surface profile has been accurately measured using a 3-axis computer controlled mechanical measurement machine. Very good agreement between this profile and those measured using the phase only metrology method are demonstrated.

DOI:10.1049/ip-h-2.1989.0062

出版商:IEE    

年代:1989

数据来源: IET