The intention of this book is to give the reader an introduction to the area of modern radar techniques based on active array antennas, either for use in development and research or as a decision and planning aid for the authorities within the government or industry. In particular, many new possibilities are discussed which should find consideration for future radar systems. I have assumed the general basics of radar technology to be familiar to the reader; introductory literature is widely available.
I have tried to present the techniques, procedures and concepts, which can mostly be derived from signal-theoretical views and which are described with approaches and equations, from an engineering point of view, with a minimum of mathematical treatment. As far as is possible, a descriptive and functional explanation is given for each procedure.
Despite its long history, radar technology will continue to receive attention for many years to come. The importance of radar results from its ability to provide reconnaissance, especially target detection, location and imaging, in all weather conditions and from short to long ranges. This ability results from the relatively small propagation attenuation of the electromagnetic waves with wavelengths in the centimetre to metre range. These wavelengths also permit sufficient location accuracies and resolutions with reasonable antenna dimensions. Radar works actively, illuminating the scene to be observed with its own transmitter. From this results its ability to measure target range and its independence from daylight in contrast to visual optics.
One can thus expect future lively interest and importance for radar technology. This statement is among other aspects confirmed by a well-established regular series of international radar conferences organised by respected and famous professional institutions such as IET (UK), IEEE (USA), DGON/ITG (GE) and SEE (F).
The idea of writing this book was first developed by contributions and the scientific coordination of the training course ‘future radar systems’ of the ‘Carl Cranz’ society in Germany. Here in this book the material is presented in much more detail than possible in a short course. Beyond this, the book is essentially based on experiences, implementations and new concepts which my colleagues and I have developed and collected in the course of more than 30 years of scientific work in the radar field at the ‘Forschungsinstitut für Funk und Mathematik’ (FFM, which translates into ‘Research Institute for Radio Sensors and Mathematics’) of the ‘Forschungs-Gesellschaft für Angewandte Naturwissenschaften’ (FGAN, which translates into ‘Research Association for Applied Natural Sciences’).
In the introduction a general representation of the substantial future requirements for radar systems is given. Afterwards, the future importance of multifunction systems on the basis of electronically steered array antennas is discussed. In the Chapters 2, 3 and 4 there follows a short introduction into representation of signals, into the statistical signal theory and into the substantial characteristics, architectures and relationships of array antennas. These array antennas may be of linear, planar, cylindrical or a volume type. These chapters shall be used as a basis for the following chapters. In Chapter 5 the receiving beam forming is discussed. Chapter 6 deals with the time-discrete signal sampling and derivation of the orthogonal signal components. Chapter 7 is dedicated to pulse compression with the use of polyphase codes, with special compression procedures for sidelobe reduction and an improvement of the range resolution. In Chapter 8 we treat problems and possibilities for target detection from signal series, i.e. the incoherent and coherent integration, Doppler filtering, adaptive clutter suppression and the coherent processing of very long pulse series with a special test function. Chapter 9 presents sequential detection for radar application and its advantages, together with a solution for the problem of simultaneously testing multiple range bins.
Chapters 10–15 are dedicated to concepts, procedures and applications of array signal processing. In Chapters 10, 11 and 12 adaptive jammer suppression, correction of monopulse under jamming conditions and angular super-resolution are discussed. In Chapters 13 and 14 the additional possibilities and special problems of radar on flying platforms are presented, especially with respect to the detection of slowly moving targets, that is space-time adaptive processing (STAP) procedures and synthetic aperture radar (SAR) with moving target indication (MTI) and target imaging. In Chapter 15 the principles of inverse synthetic aperture radar (ISAR) are introduced as a way of generating radar images for detected moving targets. In Chapter 16 fluctuation and spectral target characteristics, especially by jet engine modulation, are described. Both of these last chapters demonstrate the contributions to the target classification which can be achieved with a multifunction radar.
In Chapter 17 a survey of the experimental phased-array radar system ELRA which has been developed at FFM is given. In Chapter 18 follows the description of a special system concept with omni-directional or floodlight transmission and a multi-beam receiving system for a radar operation with protection against antiradar missiles (ARMs). An additional application of this concept is the detection and classification of hovering helicopters. The corresponding experimental system OLPI following these concept ideas is described. Finally, in Chapter 19 some remarks are made on system parameter relations and their choice for a multifunction radar system which is based on a phased-array antenna.