P.R. Shepherd

Hierarchical fault diagnosis of analog integrated circuits

This paper introduces a hierarchical-fault-diagnosis algorithm as an aid to testing analog and mixed signal circuits. The diagnosis approach is based on that introduced by Wey and others and makes use of the self-test algorithm, and the component-connection model. The main extension to these techniques is the use of a hierarchical approach whereby blocks of circuitry are grouped together leading to a reduction in matrix size, so making even large scale circuits diagnosable. Other improvements from this approach include a novel test-point selection procedure and the fact that hard faults can also be diagnosed, provided they lie completely within a hierarchical block. The overall algorithm is described and the results from example circuits show good functionality of the diagnosis algorithm. Fault masking and sensitivity to the simulation/measurement resolution of test point values are examined and are highlighted as future activities to further improve the approach.

A novel W-MUSIC algorithm for GPR target detection in noisy and distorted signals

When applied to ground penetrating radar (GPR), the multiple signal classification (MUSIC) algorithm is an important frequency estimation method as it can detect very closely spaced targets, particularly when one of the target responses is substantially less than another. The MUSIC algorithm however must be seeded with the number of targets to find and will indicate that number of targets regardless of the number of targets actually present. In addition, there is no reliable indication of the magnitude of the responses of the targets. In the presence of relatively low levels of noise the MUSIC algorithm is prone to reporting the position of false target positions in preference to weaker genuine target responses. In this paper a superimposed MUSIC technique is proposed to suppress false targets. A novel windowed FFT MUSIC (W-MUSIC) algorithm is examined using a linear sweep frequency in noise, and it is seen to give a clear indication of targets. In the presence of distortion, FFT is seen to be a more robust approach than the MUSIC algorithm, the latter method becoming very prone to inaccuracy in the presence of distortion.

TDOA/AOA Data Fusion for Enhancing Positioning in an Ultra Wideband System

This paper considers a new location scheme for ultra wideband (UWB) positioning system. The newly adopted scheme combines the time difference of arrival (TDOA) and the angle of arrival (AOA) positioning techniques in order to enhance the accuracy of the positioning system compared to the classical technique (TDOA). The new technique is simulated in a sports tracking application in a football field. Results are compared with results from a similar system using classical TDOA technique in order to establish a proof-of-concept. Simulation shows that the new technique is actually giving better performance with an acceptably longer processing time. This technique has the promise of boosting positioning accuracy with a relatively low level of complexity.

Outage probability comparison of distributed antenna diversity and single site antenna diversity

In highly built-up urban areas, where shadowing is a severe problem, distributed antenna diversity represents a more effective fade mitigation scheme than conventional single site antenna diversity. It integrates the advantage of both micro and macro antenna diversities. In this contribution, a hybrid model using Gaussian fast fading and ray tracing is used to obtain the unconditional outage probability and the performance of the distributed antenna and single site antenna structures are compared. For the distributed antenna a comparison between coherent combining diversity and selection diversity schemes has also been made.

Measurement and Modelling of MIC Components Using Conductive Lithographic Films

Conductive Lithographic Films (CLFs) have previously demonstrated useful properties in printed microwave circuits, combining low cost with high speed of manufacture. In this paper we examine the formation of various passive components via the CLF process, which enables further integration of printed microwave integrated circuits. The printed components include vias, resistors and overlay capacitors, and offer viable alternatives to traditional manufacturing processes for Microwave Integrated Circuits (MICs). Manufacturing data, measurements on test structures and equivalent circuit modelling for a range of CLF circuit structures are presented.

FMCW Radar Range Performance Improvement With Modified Adaptive Sampling Method

The nonlinear frequency sweep in frequency-modulated continuous-wave radar systems is analyzed. The main lobe broadens with the fast Fourier transform in the presence of distortion, which makes it difficult to resolve closely spaced targets. A novel modified-adaptive-sampling method is presented. To demonstrate the validity of the presented technique, a computer simulation was conducted, and the results show a marked improvement in the shape of the spectrum and the range resolution.

Improving ground penetrating radar signal analysis through FFT superimposition

The paper deals with the signal analysis problem encountered with ground penetrating radar (GPR) applications that use the fast Fourier transform (FFT). A technique for improved signal analysis based on superimposing multiple FFT analyses from the same data is presented. Results from applying the technique are seen to reduce the side lobes with minimal increase in main lobe width.

Co-phase transmission diversity for distributed antenna

Due to the single element nature of the antenna at the mobile station, the traditional downlink diversity schemes of distributed antennas, such as simulcast or multipath antenna diversity, cannot exploit the advantage of distributed antennas as much as the uplink. In this paper, through the analysis of an indoor measurement, we propose co-phase transmission diversity. A simulation using the measurement shows that this scheme can achieve better downlink quality.

Transition Characterisation for De-Embedding Purposes

A technique for characterising transitions between different transmission line media is examined. Applications include development of novel circuit media and use as a de-embedding measurement tool. The technique requires measurement of only two sets of back to back transitions, separated by different, known, electrical lengths, and is therefore simple to implement. Both theoretical and measured results are presented.

Indoor Ray Tracing evaluation of enhanced High Frequency communications using Directional Antennas at the Basestation and Space Diversity at the Terminal

This paper analyses field strength coverage predictions for high frequency indoor communications at 17 GHz using directional antennas at the basestation and 2 branch spaced antenna diversity at the terminal. Detailed propagation information is generated for a typical two-dimensional indoor environment using a ray-tracing propagation tool developed at the University of Bath. As a performance benchmark, initial field strength predictions are generated for omni-directional basestation and terminal antennas. Downlink performance is enhanced by the use of 2 branch spaced antenna diversity at the terminal. Factors such as antenna spacing and the choice of diversity combining algorithm are considered. At the basestation, a novel 3 branch phased array beam pattern diversity system is compared with an ideal six branch sectorised antenna. For each configuration, detailed propagation studies are performed to determine the relative (compared to omni-directional antennas) coverage improvement over the entire environment. Results indicate that the use of spaced diversity at the terminal can improve the expected coverage by as much as 10.7dB. Beam pattern and sector switching arrangements at the basestation result in a 7.2-10.4dB improvement. The most impressive gains were observed using directional antennas at the basestation and spaced antenna diversity at the terminal. Gains of 17.2dB and 19.4dB were observed for 3 (beam pattern) and 6 (sectorised) branch systems respectively at the basestation.