P.D. Smith

Calculation of the characteristic impedance of TEM horn antennas using the conformal mapping approach

A new conformal mapping technique for determining the characteristic impedance of TEM horn antennas is presented. The original work by Carrel [1958], on noncoplanar fin antennas of this type, predicts incorrect impedance values which do not agree with experimental results. The present paper discusses fully the source of the error in Carrel and details the successive mappings involved in the new approach. Verification of the method is provided by experimental results and by comparison with an alternative numerical technique. >

A determination of transient antenna impedance via a numerical solution of the electric-field integral equation

A numerical method for determining the broadband characteristic impedance of an antenna is described. The method is based on a solution of the electric field integral equation for the antenna surface subject to a strongly localized incident field, representative of a desired transient source voltage. A method is outlined for calculating, from the numerically simulated feed current, the frequency-dependent impedance spectrum of a finite antenna, subject to a sharp pulse. It is shown that this may be used to determine reliably the characteristic impedance of TEM antennas. Particular attention is paid to the problem of effectively modeling the feed region of the transient antenna. A general approach which ensures the stability and accuracy (to within a few percent) of solutions is described. It uses surface patches to model the antenna and obviates potential difficulties associated with thin wire models of the feed region.

Designing input signals to disrupt commercial systems in band - a nonlinear dynamics approach

Describes a method for disrupting a standard, commercially available, nonlinear electronic system. In particular, we show how, with relatively little knowledge of the commercial system design, an in-band signal can be determined which will disrupt the operation of the circuit. Our approach is based on a nonlinear analysis of the most susceptible subsystem in the circuit. Analytical, numerical, and experimental results are reported to demonstrate the efficacy of our approach.

Stable boundaries of a third-order sigma-delta modulator

This paper studies the stable boundary of a type of third-order one-bit sigma-delta modulator (/spl Sigma//spl Delta/M) using an extended describing function method in which both the amplitude and phase shift of a sampled quantiser are modelled. By determination of the maximum DC input for the feedback coefficients of the sigma-delta modulator, the performance of the system can be optimised for stable modulator operation. This approach is potentially useful in the design and stability analysis of higher-order /spl Sigma//spl Delta/Ms.

Stability analysis of a sigma delta modulator

This paper illustrates how an adaptive iterative method may be used to verify large signal input stability of a third-order sigma delta modulator across a range of DC inputs, once the initial design parameters the system have been determined using small signal nonlinear stability analysis. This approach is potentially useful to design and optimise stored sigma delta sequences to the modulus controller for a fractional-N synthesiser.

THE EFFECT OF THE FORCING FUNCTION ON DISRUPTION OF A PHASE-LOCKED LOOP (PLL)

In this paper we compare the disruption of a second-order type II phase-locked loop (PLL) by two different waveforms: a sinusoid and a sawtooth. The choice of these two waveforms results from a novel approach to the problem of determining an appropriate forcing function for studying the disruption of such systems. It is shown that the sawtooth is the better disruptor for low frequencies of modulation, i.e. in the regime of physical interest. Analytical, numerical and experimental results are reported which support this conclusion. The paper presents the first results of a sawtooth modulated PLL, which viewed as a nonsmooth dynamical system with a nonsmooth forcing function is a problem of considerable theoretical interest. This paper demonstrates that forcing functions can be designed for nonlinear dynamical systems which are well suited to the study of certain aspects of the system dynamics, and significantly better than the conventional choice of a simple sinusoid.

Optimal Input Signals for Driving Nonlinear Electronic Systems into Chaos

In this paper we have described a novel approach to the problem of disrupting nonlinear electronic circuits; this approach is applicable to a wide range of nonlinear electronic systems. It allows us to calculate input signals of smallest amplitude and power which will induce homoclinic chaos and, hence, disruption in the circuit. Further-more, as is clearly demonstrated by the results described above, this approach allows us to develop in-band signals with which to disrupt such circuits.

A Numerical Determination of Transient Antenna Impedance Via Near-Field Integration

In this paper we describe a numerical method for determining the wideband impedance of a transient antenna, based on a method of moments solution of the time-domain electric field integral equation. The impedance is estimated from the antennas response to a short-pulse transient excitation ; the current is determined directly from the solution of the electric field integral equation and the potential difference between the antenna arms is determined from an integration of the electric near-field. Particular attention is paid to the form of the singular near-field integrals and an alternative representation is given for these in terms of non-singular boundary integrals. The approach described in this paper has several advantages over the previous numerical approach of [1] and is validated against a variety of canonical antennas, including directive and omnidirectional transient radiators. The present numerical method is shown to provide an accurate estimate of the characteristic impedance of such canonica...

Optimise the dynamic range of a sigma-delta modulator

This paper introduces analytic and numerical methods to optimise the dynamic range of a third-order sigma-delta analogue-to-digital converter (ADC). Quantisation noise in a specified bandwidth is predicted and expressed relative to the maximum sinusoidal output from the ADC, for a range of design parameters, in order to establish the optimum design to achieve maximum dynamic range.

IN-BAND CHAOS IN COMMERCIAL ELECTRONIC SYSTEMS

In this paper we have presented an approach to the problem of disrupting effectively a commercial nonlinear electronic system. Our approach is based on a minimal understanding of the circuit concerned, the basic design and operational specifications, rather than a detailed knowledge of the design implementation itself.