Air and Spaceborne Radar Systems: An Introduction

by Philippe Lacomme, Jean-Claude Marchais, Jean-Philippe Hardange, Eric Normant

Overview

A practical tool on radar systems that will be of major help to technicians, student engineers and engineers working in industry and in radar research and development. The many users of radar as well as systems engineers and designers will also find it highly useful. Also of interest to pilots and flight engineers and military command personnel and military contractors. ""This introduction to the field of radar is intended for actual users of radar. It focuses on the history, main principles, functions, modes, properties and specific nature of modern airborne radar. The book examines radar's role within the system when carrying out is assigned missions, showing the possibilities of radar as well as its limitations. Finally, given the changing operational requirements and the potential opened up by modern technological developments, a concluding section describes how radar may evolve in the future. The authors review the current state of the main types of airborne and spaceborne radar systems, designed for specific missions as well as for the global environment of their host aircraft or satellites. They include numerous examples of the parameters of these radars. The emphasis in the book is not only on a particular radar technique, but equally on the main radar functions and missions. Even if a wide range of techniques are described in this book, the focus is on those which are connected to practical applications.

Product Details

ISBN-13:	9781891121135
Publisher:	Elsevier Science
Publication date:	12/03/2007
Series:	Press Monographs , #108
Edition description:	New Edition
Pages:	524
Product dimensions:	6.00(w) x 9.00(h) x (d)

About the Author

Philippe Lacomme is a Senior Radar Designer with Thomson-CSF Detexis Company. He is the Technical Director of the Radar Unit, which is in charge of developing and producing airborne radar systems for Rafale aircraft, the Mirage 2000, and others. Professor Lacomme has taught radar theory at Thomson-CSF and in many universities and schools, and has lectured at numerous international conferences.

Jean-Claude Marchais was Technical Director of Thomson-CSF Radars & Contre-Mesures until his retirement. During his long career, he was involved in the development of radar systems for the Mirage aircraft family, a lecturer on radar at the ESME-Sudria engineering school, and the author of three books, including a highly successful one on operational amplifiers.

Jean-Philippe Hardange joined Thomson-CSF in 1982 and has worked there as a radar engineer on all types of airborne radar. In 1996 he was head of the Airborne Radar Engineering Department. Later he launched the SOSTAR project of ground surveillance for NATO. He is now leading the Airborne Systems Engineering Department at Thomson-CSF.

Eric Normant works as a research scientist at at Thomson-CSF Detexis and is head of the airborne reconnaissance radar team. He has worked on SAR processing and system engineering. He holds a dozen patents in the field of SAR and teaches general radar theory and SAR.

Read an Excerpt

1: The History and Basic Principles of Radar

1.1 History

In 1887 the German physicist Heinrich Hertz discovered electromagnetic waves and demonstrated that they share the same properties as light waves. These electromagnetic waves are often known as "Hertzian waves."

In the very early 1900s, Telsa in the US and Hülsmeyer in Germany proposed detection of targets by the use of radio waves.

The principle behind RADAR (Radio Detection And Ranging), based on the propagation of electromagnetic waves or, more precisely, that of radiofrequency (RF) waves, was described by the American Hugo Gernsback in 1911. In 1934 the French scientist Pierre David successfully used radar for the first time to detect aircraft. In 1935 Maurice Ponte and Henri Gutton, during trials carried out onboard the Orégon, part of the Compagnie Generale Transatlantique fleet, detected icebergs using waves with a 16 cm wavelength (lamda). In 1936 Professor Kunhold (Germany) detected aircraft.

Radar came into its own during the Second World War as the ideal technique for detecting the enemy, both day and night. As early as 1940 the British RAF, led by Watson Watt, developed a dense network of groundbased radars. This clinched their victory in the Battle of Britain, as it provided sufficient warning to deploy fighter planes under optimum conditions. The German army also set up its own ground-based radar network, which, from 1942 onward, they used to transmit the position of detected targets to the fighter control center. In order to intercept and shoot down the waves of allied bombers deployed at night, German fighter pilots used either daytime fighters to attack allied planes tracked by light from ground projectors, or night fighters equipped with radar.

The first ever operational warplane equipped with an airborne radar was the Messerschmitt Me 110 G-4 in 1941. Its Telefunken radar, the FUG 212, used a bulky antenna comprising a number of dipoles located outside the aircraft, on the nose. By June 1944 the German fighter unit possessed over 400 aircraft of this type with a radar range of approximately 5 km, this range being limited by the altitude at which the carrier was flying. By 1944 the American Naval Air Service was equipped with a Corsair with a radar pod on the right wing, while the American Air Force had a Northrop P-61A Black Widow fitted with a Western Electric radar system.

During the night of July 24-25, 1943, 800 RAF bombers carried out a raid on Hamburg. During this raid the bombers carried out the first ever operational chaff launch (metal strips whose dimensions vary depending on the wavelength of the radar they attempt to confuse). This operation rendered German ground-based and airborne radars totally nonoperational, blinded by an excess of objects to detect. It marked the beginning of electronic warfare.

Radar operators noted that the British Mosquito fighter planes and the Japanese Zero fighter planes, both wooden constructions, were particularly difficult to detect; they were the original stealth aircraft.

In 1943 Allied surface ships fitted with radar were used to detect German submarine snorkels, causing the German navy to suffer heavy losses.

Later the main steps in radar technological evolutions were

• pulse compression (in the early `60s)
• pulse Doppler radar (late `60s)
• digital radars (`70s)
• medium PRF radar (late `70s, early `80s)
• multimode programmable radar (mid-`80s)
• airborne electronically scanned antenna radar (`90s)

The first radar images of the Earth were obtained in 1978 using Synthetic Aperture Radar (SAR), operating in the L-band (X = 30 cm) and mounted on the American satellite Seasat. Resolution of the images obtained, both day and night, was close to 25 m.

1.2 Basic Principles

Radar is a system that transmits an electromagnetic wave in a given direction and then detects this same wave reflected back by an obstacle in its path.

1.2.1 Basic Configuration

Figure 1.1 illustrates the first basic radar design. The various components of radar include: for transmission, a transmitter sending a continuous sinusoidal wave to a transmitting antenna and, for reception, an antenna plus a high-gain receiver and a detector whose output signal is displayed using a radar display such as a CRT.

The role of the transmitting antenna is to concentrate the energy transmitted in a chosen direction in space (beam center). The transmitting antenna gain, G_t, is maximum along the axis and varies depending on the direction (see Chapter 3).

The receiving antenna collects the transmitted energy backscattered by the target in the same chosen direction. This receiving antenna has a gain G_r. Supposing the two antennas are identical, G_t = G_r.

The wave transmitted (in this case continuously) is propagated to and from the target at the speed of light, c. In a non-magnetic medium, the following is true:

c = 299.7925.10⁶/ (K_e)^1/2 m/s

In a vacuum, the dielectric constant K_e is equal to one. In air, its value varies slightly depending on temperature, composition, and pressure. At sea level it equals 1.000 536. In practice, the speed of light for radars is taken to be 300 000 km/s....

...To ensure that the receiving channel only detects the signal backscattered by the obstacle or target, it must be decoupled from the transmision channel. An antenna, whatever technology it uses, has a radiation pattern composed of a main lobe and sind and far lobes (see Figure 1.2)....

...For the radar shown in Figure 1.1, despite the fact that both antennas are operating in the same direction, they have a leakage, in this case due to the far lobes. For example, if the far lobes of both antennas are 40 decibels below the maximum level of the main lobe (along the beam center), the isolation of the two channels is equal to 80 dB. Under such conditions, if the signal backscattered by the obstacle and received by the receiving channel is stronger than that caused by spurious coupling, the obstacle will be detected. In practice, numerous other factors come into play. These will be dealt with in turn, and in particular in Chapter 3.

The radar shown in Figure 1.1 is a bistatic system. Although transmission and reception are adjacent, they do not physically overlap. This frequently used concept (e.g., for launching semi-active missiles) will be examined in a later section.

1.2.1.1 Range Measurement

If the radar transmission is a pure continuous wave with frequency fo, the backscattered wave will have the same frequency (if the relative velocity between radar and target is equal to zero), whatever the range. However, the greater the target range, and the lower the Radar Cross Section (RCS) of the target, the weaker the received signal. The RCS characterizes the backscattering coefficient of the target.

The target range can be obtained using one of several methods:

• by calculating the time between the detected target echo and the transmitted wave
• by calculating the difference in frequency between the received echo and the transmitted wave in the case of linear frequency modulation
• by calculating the differential phase of the double detection of an echo obtained using two transmissions of different frequencies (Chapter 8.6)

The following sections give a rapid overview of the first two methods....

Table of Contents

Part I — General Principles
The History and Basic Principles of Radar
Initial Statements of Operational
Requirements
The RADAR Equation
Propagation
Noise and Spurious Signals
Detection of Point Targets
Part II — Target Detection and Tracking
Clutter Cancellation Air-to-Air Detection
Air Target Tracking
Ground Target Detection and Tracking
Maritime Target Detection and Tracking
Electromagnetic Pollution
Part III — Ground Mapping and Imagery
Ground Mapping
Radar Imagery
Synthetic Aperture Radar
Synthetic Aperture Radar Specific Aspects
Inverse Synthetic Aperture Radar (ISAR)Other Observation Radars
Part IV — Principal Applications
Radar Applications and Roles
Design Overview
Multifunction Radar
Technological Aspects
Part V — Radars of the Future
The Changing Target
Operational Aspects
Principal Limitations of Present-day Radars
Electronically Steered Antennas
Airborne and Spaceborne Radar Enhancement
Conclusions
List of Acronyms
List of Symbols
Bibliography
About the Authors
Index

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From the Publisher

A practical tool on radar systems that will be of major help to technicians, student engineers and engineers working in industry and in radar research and development.