The definition of “active sonar” is applied to systems with a wide range of operating parameters. Sonar power amplifiers operate in environments ranging from large shipborne equipments housed in electronics cabinets to small, self contained expendable sonobuoys. Duty cycles of operation can range from high-resolution sonars, which deliver short, high frequency pulses with low duty cycle up to systems which are required to operate continuously, often over a very wide bandwidth. Additionally, control sophistication ranges from simple single-frequency generators to modules that deliver complex signals to closely defined tolerances in amplitude over a range of frequency. This chapter presents an overview of the application areas and their specific requirements. A more detailed examination of active surveillance-sonar parameter leads to a number of options for power amplifier design. Finally, the principles developed are demonstrated in design examples for power amplifiers.

In sonar, we are concerned with the detection of targets against a background of unwanted signals. These unwanted signals may be noise in several forms, or reverberation. The task of the receiving system designer is to ensure an optimal system response to the wanted signal and minimal response to the unwanted signal. The receive array can play an important part in this process. Sonar suffers from noise problems due to its use of sound waves whose influence on the receiving sensor may be indistinguishable from that due to other mechanical sources. Discrimination against vibration for example may be best achieved in the sound sensor itself rather than in the signal processing. This chapter is concerned with the very early stages in the sonar detection process.

This chapter discusses the radiowaves that arrive in communication receivers. In all except very simple transmission conditions, radio communication links are subjected to conditions in which energy can travel from the transmitter to the receiver via more than one path. This "multipath" situation arises in different ways depending upon the application, for example in MF and HF skywave transmissions it arises because of reflections from two or more ionospheric layers, or from two-hop propagation. In mobile radio, it arises because of reflection and scattering from buildings, trees and other obstacles along the path.

This chapter is concerned primarily with the use of integrated optical techniques in acousto-optic receivers. More specifically, we consider devices in which a light beam is confined in a waveguide deposited on the surface of a suitable planar substrate (typically a piece of single-crystal lithium niobate) and interacts with a surface acoustic wave (SAW) launched by a specially designed interdigital electrode structure.

A complete breadboard four-channel assembly of programmable beam-steering and signal processing has been tested at sea. Preliminary experiments have confirmed successful operation of computer-controlled beam-steering, signal amplitude conditioning, and active and passive processing under conditions representing a fully integrated system. Having demonstrated the viability of such an assembly, work is now progressing on a second version, adequately engineered, to stand the rigours of a comprehensive sea trials programme and operate reliably for long periods of time. As far as the future role of the c.c.d. in compact sonars is concerned, this is open to speculation. The c.c.d. development work summarised in this paper is the result of a six year programme of design, evaluation and improvement aimed at the sonar application. Present designs are considered to be close to the limits of what can be achieved in charge-coupled technology, and it remains to be seen whether equivalent digital devices, with improved stability and dynamic range, will eventually appear as a result of future programmes of work in VHSIC/VLSI technology. In the meantime it is felt that the existing c.c.d.-based system referred to above will continue to provide a very useful research tool in investigating the application of programmable spatial and signal processing to improve the performance of the small-array compact sonar.

This chapter addresses the principles, architectures and performance of acousto-optic correlator systems. Two specific applications which might benefit from these devices are considered, namely spread-spectrum signal processing and lidar ambiguity-function processing.

This chapter provides an overview of the various design methods available for the realisation of digital logic circuits used in signal processing with particular emphasis on silicon structures. The traditional methods of designing logic systems by deriving an optimum interconnection of basic logic modules (such as the SN74 series) using a mix of intuitive and theoretical techniques are no longer applicable to today's technol ogy. The major reason for this lies in the complexity of the systems which we are now capable of designing and the need to realise these designs in terms of integrated circuit technology designing in silicon.

The Very High Speed Integrated Circuits (VHSIC) Program of the United States Department of Defense will have very significant impact on present and future digital signal processing capabilities. Just as English forces used the longbow at the battle of Crecy in 1346 to multiply their effectiveness, so must modern Western military forces multiply their effectivness through the use of advanced technology, particularly electronics technology. The VHSIC Program will preserve and extend the Western lead in deployed electronics technology, providing improvements in signal processing capability for surveillance, com munications, target classification and several other appliction areas where technology can overcome numerical advantages of potential adversaries.

This chapter discusses those display types which are, or which potentially could be, used for graphics display applications within the fields of radar and sonar, and as text displays in these and other fields. In addition to the pre-eminent c.r.t., various flat panel technologies will be discussed flat panel displays having a particular attraction in confined spaces and for mounting in desk positions.

Ergonomics concerns the design of equipment for human use at work. With simple equipment it may be feasible to correct design deficiencies on the basis of operational experience, but in complex systems this approach is too costly, cumbersome, time-consuming, disruptive and ineffectual and it becomes essen tial to apply ergonomic principles during the specification and design of the system rather than to attempt to remedy ergonomic deficiencies after the system is in being. Modern systems with extensive software may seem to encourage once again system modification in response to operational experience, especially if the facility to modify in this way is claimed beguilingly to permit flexibility or adaptability, but such changes may lead to unwelcome human error unless the associated skills and learning can be transferred intact.

The performance of the next generation of operational sonars must be improved to counter the effects of target noise reduction and anechoic coatings. Improved performance dictates the use of large-area sensor arrays, with many more processing channels and "smarter" processing algorithms such as adaptive or high-resolution processing at the front end of the system and image processing methods at the display end. In addition, operational systems require fault tolerance, comprehensive online monitoring and maintenance facilities, reconfigurability and improved development aids. An increase in processing throughput of two or three orders of magnitude over current systems is necessary to provide these functions. Advances in semiconductor and integrated-circuit technology promise significant improvements in device performance over the next decade, but it is unlikely that these alone will provide the necessary increase in systems performance. Comparable improvements are required in the areas of algorithm development and system architecture if the capabilities of the advanced technologies currently being developed in various national VHPIC and VHSIC programmes are to be fully exploited. This chapter briefly reviews some aspects of recent developments in these fields and their impact on digital signal processing systems in future sonar applications.

The continuing high demand for global, regional and domestic communications is being satisfied by a variety of satellite systems of ever increasing capability and complexity. It was not until 1963 that rockets sufficiently powerful to launch satellites into geostationary orbit were available, and SYNCOM II was the first to lie on the geostationary arc 35,800 km above the equator. INTELSAT (the international telecommunications satellite consortium) commenced operations in the mid 60's. INTELSAT provides multichannel trunking facilities for international carriers as well as leasing transponders to individual nations for regional or domestic systems. WESTAR, RCA, SATCOM, Satellite Business Systems (SBS) and EUTELSAT are examples of domestic/regional systems. INMARSAT provides ship/shore communications in the Atlantic, Pacific and Indian Ocean regions, and a specialized search and rescue system exists in the form of SARSAT. High-quality signals are trans mitted over satellites to cable network link-ends, and more recently, directly to consumers in their homes. Direct-broadcasting should arrive in the U.K. after the launch of UNISAT, and should that system not materialize, it will be one of the services available from OLYMPUS.

This chapter discusses the future signal processing technology required for radar systems. Although signal processing can be considered to begin on the radio frequencies right at the antenna array, we confine our attention to post-r.f. processing, commencing with digital processing and beamforming for the antenna array and following the data stream to the fully-processed plot or track outputs. We use the phrase “very high performance integrated circuits” (VHPIC) without reference to any particular technology programme. Similarly, we do not refer to particular applications of radar, because we consider that all radars, whether on the battlefield, airborne, or for long-range ground-based air defence, will tend towards multi-mode operation, requiring flexible, coherent processing, adaptive antenna processing and false-alarm control.

Ada is a new programming language developed under contract for the US Department of Defense. It was procured and designed as, initially an alterna tive, and eventually a replacement, for the excessively large number of languages and dialects in use in the US defence industry. Its intended field of application is “embedded computer systems” by which is understood systems where the computer is a component rather than a tool in its own right. Such systems include radars, communications equipment, missile-guidance systems, fire con trol and navigation aids. From 1st January 1984, all new USDoD projects of this kind are required to use Ada as the programming language.

RSRE are sponsoring the development of a fast and powerful signal processor based on the architecture of the ICL Distributed Array Processor (DAP). A number of application areas exist where a suitable signal processor is critical to continued success. Possible examples may be found in the fields of image processing, antenna array processing and multi-mode pulse Doppler radars. This latter application is being used as a 'pace setter' to establish the design and performance criteria which must be met. It is believed that the variety of tasks, the data rates, the computational load and programmability required for this application will demand an array processor solution which will be suitable for the many other applications. This chapter describes the evolution of the ICL DAP from its original implementation in MSI technology, when it was incorporated into the architecture of a large mainframe computer, to the ruggedised 'MIL' DAP currently under development in LSI technology. This will function as a compact stand-alone signal processor suitable for the multi-mode radar. It should perhaps be mentioned however that the DAP is not the only solution and in the UK individual radar manufacturers are pursuing their own architectures, which also show great potential.

Some day, machines that recognise speech will be commonplace. People will talk to computers, typewriters, toys, TV sets, household appliances, cars, door locks and wrist-watches. Before looking at the signal processing and pattern processing that will be the basis of the next generation of automatic speech-recognition systems, we consider the nature of the signal that these devices will have to deal with.