Radar Technology Radar Technology Edited by Guy Kouemou I-Tech IV Published by In-Teh In-Teh Olajnica 19/2, 32000 Vukovar, Croatia Abstracting and non-profit use of the material is permitted with credit to the source. Statements and opinions expressed in the chapters are these of the individual contributors and not necessarily those of the editors or publisher. No responsibility is accepted for the accuracy of information contained in the published articles. Publisher assumes no responsibility liability for any damage or injury to persons or property arising out of the use of any materials, instructions, methods or ideas contained inside. After this work has been published by the In-Teh, authors have the right to republish it, in whole or part, in any publication of which they are an author or editor, and the make other personal use of the work. © 2009 In-teh www.in-teh.org Additional copies can be obtained from: publication@intechweb.org First published December 2009 Printed in India Technical Editor: Teodora Smiljanic Radar Technology, Edited by Dr. Guy Kouemou p. cm. ISBN 978-953-307-029-2 Preface One of the most important inventions for the development of radars was made by Christian Huelsmeyer in 1904. The German scientist demonstrated the possibility of detecting metallic objects at a distance of a few kilometres. While many basic principles of radar, namely using electromagnetic waves to measure the range, altitude, direction or speed of objects are remained up to now practically unchanged, the user requirements and technologies to realise modern radar systems are highly elaborated. Nowadays many modern types of radar (originally an acronym for Radio Detection and Ranging) are not designed only to be able to detect objects. They are also designed or required to track, classify and even identify different objects with very high resolution, accuracy and update rate. A modern radar system usually consists of an antenna, a transmitter, a receiver and a signal processing unit. A simple signal processing unit can be divided into parameter extractor and plot extractor. An extended signal processing unit consists additionally of a tracking module. The new category of signal processing units has also the possibility of automatically target classification, recognition, identification or typing. There are numerous classifications of radars. On the one hand they can be classified by their platform as ground based, air borne, space borne, or ship based radar. On the other hand they can be classified based on specific radar characteristics, such as the frequency band, antenna type, and waveforms utilized. Considering the mission or functionality one may find another categorization, such as weather, tracking, fire control, early warning, over the horizon and more. Other types are phased array radars, also called in some literatures as multifunction or multimode radars (not necessary the same). They use a phased array antenna, which is a composite antenna with at least two basic radiators, and emit narrow directive beams that are steered mechanically or electronically, for example by controlling the phase of the electric current. Mostly radars are classified by the type of waveforms they use or by their operating frequency. Considering the waveforms, radars can be Continuous Wave (CW) or Pulsed Radars (PR). CW radars continuously emit electromagnetic energy, and use separate transmit and receive antennas. Unmodulated CW radars determine target radial velocity and angular position accurately whereas target range information only can be gathered by using some form of modulation. Primarily unmodulated CW radars are used for target velocity search and track and in missile guidance. Pulsed radars use a train of pulsed waveforms, mainly with modulation. These systems can be divided based on the Pulse Repetition Frequency VI (PRF) into low PRF (mainly for ranging; velocity is not of interest), medium PRF, and high PRF (primarily for velocity measurement) radars. By using different modulation schemes, both CW and PR radars are able to determine target range as well as radial velocity. These radar bands from 3 MHz to 300 MHz have a long historically tradition since the World War II. These frequencies are well known as the passage from radar technology to the radio technology. Using electromagnetic waves reflection of the ionosphere, High Frequency (HF, 3MHz – 30MHz) radars such as the United States Over the Horizon Backscatter (U.S. OTH/B, 5 – 28 MHz), the U.S. Navy Relocatable Over the Horizon (ROTHR) and the Russian Woodpecker radar, can detect targets beyond the horizon. Today these frequencies are used for early warning radars and so called Over The Horizon (OTH) Radars. By using these very low frequencies, it is quite simple to obtain transmitters with sufficient needed power. The attenuation of the electromagnetic waves is therefore lower than using higher frequencies. On the other hand the accuracy is limited, because a lower frequency requires antennas with very large physical size which determines the needed angle resolution and accuracy. But since the most frequency-bands have been previously attributed to many operating communications and broadcasting systems, the bandwidth for new radar systems in these frequencies area is very limited. A comeback of new radar systems operating in these frequency bands could be observed the last year. Many radar experts explain this return with the fact that such HF radars are particularly robust against target with Stealth based technologies. Many Very High Frequency (VHF, 30MHz – 300MHz) and Ultra High Frequency (UHF, 300MHz – 1GHz) bands are used for very long range Early Warning Radars. A well known example in these categories of radar is for example, The Ballistic Missile Early Warning System (BMEWS). It is a search and track monopulse radar that operates at a frequency of about 245 MHz. The also well known Perimeter and Acquisition Radar (PAR), is a very long range multifunction phased array radar. The PAVE PAWS is also a multifunction phased array radar that operates at the UHF frequencies. The UHF operating radar frequency band (300 MHz to1 GHz), is a good frequency for detection, tracking and classification of satellites, re-entry vehicles or ballistic missiles over a long range. These radars operate for early warning and target acquisition like the surveillance radar for the Medium Extended Air Defence System (MEADS). Some weather radar-applications like the wind profilers also work with these frequencies because the electromagnetic waves are very robust against the volume clutter (rain, snow, graupel, clouds). Ultra wideband Radars (UWB-Radars) use all HF-, VHF-, and UHF- frequencies. They transmit very low pulses in all frequencies simultaneously. Nowadays, they are often used for technically material examination and as Ground Penetrating Radar (GPR) for different kind of geosciences applications. Radars in the L-band (1GHz – 2GHz) are primarily ground and ship based systems, used in long range military and air traffic control search operations. Their typical ranges are as high as about 350-500 Kilometres. They often transmit pulses with high power, broad bandwidth and an intrapulse modulation. Due to the curvature of the earth the achievable maximum range is limited for targets flying with low altitude. These objects disappear very fast behind the radar horizon. In Air Traffic Management (ATM) long-range surveillance radars like the Air Surveillance Radar the ASR-L or the ASR-23SS works in this frequency band. L-band radar can also be coupled with a Monopulse Secondary Surveillance Radar VII (MSSR).They so use a relatively large, but slower rotating antenna. One well known maritime example in this category is the SMART-L radar systems. S-band (2GHz – 4GHz), are often used as airport surveillance radar for civil but also for military applications. The terminology S-Band was originally introduced as counterpart to L-Band and means "smaller antenna" or "shorter range". The atmospheric and rain attenuation of S-band radar is higher than in L-Band. The radar sets need a considerably higher transmitting power than in lower frequency ranges to achieve a good maximum range. In this frequency range the influence of weather conditions is higher than in the L- band above. For this raison, many weather forecast and precipitation radars in the subtropics and tropic climatic zone (Africa, Asia, Latin America) operate in S-band. One advantage here is that these radars (usually Doppler-radar) are often able to see beyond typical severe storm or storm system (hurricane, typhoon, tropical storm, cyclonic storm). Special Airport Surveillance Radars (ASR) are used at airports to detect and display the position of aircraft in the terminal area with a medium range up to about 100 kilometres. An ASR detects aircraft position and weather conditions in the vicinity of civilian and military airfields. The most medium range radar systems operate in the S-band (2GHz – 4GHz), e.g. the ASR-E (Air Surveillance Radar) or the Airborne Warning And Control System (AWACS). The C-band radar systems (4GHz – 8GHz) are often understand in the radar community as a kind of compromising frequency-band that is often used for medium range search. The majority of precipitation radars used in the temperate climate zones (e.g. Europe, Nord America) operates in this frequency band. But C-band radars are also often used for fire control military applications. There exist many mobile battlefield radars with short and medium range. For these defence application for example, C-band antennas are used for weapon guidance. One of the reasons is that, additionally to there high precision, they are also small and light enough for usually transport systems (Truck, Small boat). The influence of weather phenomena is also very large and for this reason, the C-band antennas air surveillance purposes mostly operate with circular polarization. In the C-band radar series, the TRML-3D (Ground) and the TRS-3D (Naval) Surveillance Radar are well known operating systems. The X-band (8GHz – 12.5GHz) radar systems are often used for applications where the size of the antenna constitutes a physical. In this frequency band the ratio of the signal wavelength to the antenna size provide a comfortable value. It can be achieved with very small antennas, sufficient angle measurement accuracy, which favours military use for example as airborne radar (airborne radar).This band is often used for civilian and military maritime navigation radar equipment. Several small and fast-rotating X-band radar are also used for short-range ground surveillance with very good coverage precision. The antennas can be constructed as a simple slit lamp or patch antennas. For space borne activities, X- band Systems are often used as Synthetic Aperture Radars (SAR). This covers many activities like weather forecast, military reconnaissance, or geosciences related activities (climate change, global warming, and ozone layer). Special applications of the Inverse Synthetic Aperture Radar (ISAR) are in the maritime surveillance also to prevent environmental pollution. Some well known examples of X-band Radar are: the APAR Radar System (Active Phased Array, Ship borne multi-function Radar), The TRGS Radar Systems (Tactical Radar Ground Surveillance, active phased array system), The SOSTAR-X (Stand-Off Surveillance VIII and Target Acquisition Radar), TerraSAR-X (Earth observation satellite that uses an X-band SAR to provide high-quality topographic information for commercial and scientific applications). In the higher frequency bands (Ku (12.5GHz – 18GHz), K (18GHz – 26.5GHz), and Ka (26.5GHz – 40GHz)) weather and atmospheric attenuation are very strong which leads to a limitation to short range applications, such as police traffic radars. With expectant higher frequency, the atmosphrerical attenuation increases, but the possible range accuracy and resolution also augment. Long range cannot be achieved. Some well known Radar applications examples in this frequency range are: the airfield surveillance radar, also known as the Surface Movement Radar (SMR) or the Airport Surface Detection Equipment (ASDE). With extremely short transmission pulses of few nanoseconds, excellent range resolutions are achieved. On this mater contours of targets like aircraft or vehicles can briefly be recognised on the radar operator screen. In the Millimetre Wave frequency bands (MMW, above 34GHz), the most operating radars are limited to very short range Radio Frequency (RF) seekers and experimental radar systems. Due to molecular scattering of the atmosphere at these frequencies, (through the water as the humidity here) the electromagnetic waves here are very strong attenuated. Therefore the most Radar applications here are limited to a range of some few meters. For frequencies bigger than 75 GHz two phenomena of atmospheric attenuation can be observed. A maximum of attenuation at about 75 GHz and a relative minimum at about 96 GHz. Both frequencies are effectively used. At about 75 to 76 GHz, short-range radar equipment in the automotive industry as a parking aid, brake assist and automatic avoidance of accidents are common. Due to the very high attenuation from the molecular scattering effects (the oxygen molecule), mutual disturbances of this radar devices would occur. On the other side, the most MMW Radars from 96 to 98 GHz exist as a technical laboratory and give an idea of operational radar with much greater frequency. Nowadays, the nomenclature of the frequency bands used above originates from world war two and is very common in radar literature all over the world. They vary very often from country to country. The last year's efforts were made in the world radar community in order to unify the radar frequency nomenclature. In this matter the following nomenclature convention is supposed to be adapted in Europe in the future: A-band (< 250MHz), B-band (250MHz – 500MHz), C-band (500MHz – 1GHz), D-band (1GHz – 2GHz), E-band (2GHz- 3GHz), F-band (3GHz – 4GHz), G-band (4GHz – 6GHz), H-band (6GHz – 8GHz), I-band (8GHz – 10GHz), J-band (10GHz – 20GHz), K-band (20GHz – 40GHz), L-band (40GHz – 60GHz), M-band (> 60GHz). In this book “Radar Technology”, the chapters are divided into four main topic areas: Topic area 1: “Radar Systems” consists of chapters which treat whole radar systems, environment and target functional chain. Topic area 2: “Radar Applications” shows various applications of radar systems, including meteorological radars, ground penetrating radars and glaciology. Topic area 3: “Radar Functional Chain and Signal Processing” describes several aspects of the radar signal processing. From parameter extraction, target detection over tracking and classification technologies. IX Topic area 4: “Radar Subsystems and Components” consists of design technology of radar subsystem components like antenna design or waveform design. The editor would like to thank all authors for their contribution and all those people who directly or indirectly helped make this work possible, especially Vedran Kordic who was responsible for the coordination of this project. Editor Dr. Guy Kouemou EADS Deutschland GmbH, Germany [...]... performance measures for a given radar system In this chapter only the SDR and related parameters will be discussed Another important characteristic of a radar waveform is how the radar system behave if the radar target is moving relative to the radar This can be studied by calculating the ambiguity function for the radar system In a narrow band radar the velocity of the radar target gives a shift in... this technology, the UWB radar presents good precision in distance calculation Below, the principle of UWB radar and its benefits are introduced 21 Short Range Radar Based on UWB Technology 3 UWB radar UWB radar sends very short electromagnetic pulses This type of radar can employ traditional UWB waveforms such as Gaussian or monocycle pulses To calculate the distance between radar and obstacle, the... receiver The radar needs to transmit nb = 212 pulses to get one radar trace at 12-bit resolution This gives a reduction of 36.1 dB compared to the real time sampling, only 3.1 dB lower than the sequential sampling receiver Radar Performance of Ultra Wideband Waveforms 15 Table 3 General radar parameters used for all the radar systems under study Table 4 SDR for the different waveforms for the radar parameters... power of mB/B compared to impulse radar The SDR for a SF -radar is: (16) 3.3 Frequency modulated continuous wave (FMCW) Another widely used radar technique in UWB systems is the Frequency-Modulated Continuous-Wave (FMCW) radar This radar is also collecting the data in the frequency domain as with the SFR technique In stead of changing the frequency in steps, as with SFradars, the frequency is changed... by: Radar Performance of Ultra Wideband Waveforms 5 (5) Bringing all this into Equation 3 and splitting the radar equation in two separate parts where the first contains the radar system dependent parameters and the second the medium dependent parameters we have (6) The left side contains the radar system dependent parts and the right the propagation and reflection dependent parts The SDR of the radar. .. 80% a pulse and measuring the reflected signal This method is used in radar and is called a Step Frequency (SF) radar Radar Performance of Ultra Wideband Waveforms 7 All UWB radar waveforms have a way to reduce sampling speed in the receiver so that the full transmitted signal bandwidth does not need to be sampled directly In impulse radars only one sample per transmitted pulse can generally be taken... may blur the resulting radar image The average transmitted power for an impulse radar with peak power PT , pulse length T and pulse repetition interval TR is: (9) The SDR, given in equation 7, for an impulse radar that has a real time sampling of all the receiver range gates and is therefore matched is given as: Radar Performance of Ultra Wideband Waveforms 9 (10) If the impulse radar has a sequential... Penetration Radars (GPR) is given in Section 2 together with a definition on System Dynamic Range (SDR) In Section 3 a short presentation on the mostly used UWB -radar waveforms are given together with an expression for the SDR An example calculation for the different waveforms are done in Section 4 and a discussion on how radar performance can be measured in Section 5 2 Radar performance There are different radar. .. 17 Wideband Antennas for Modern Radar Systems 341 Yu-Jiun Ren and Chieh-Ping Lai 18 Reconfigurable Virtual Instrumentation Design for Radar using Object-Oriented Techniques and Open-Source Tools 367 Ryan Seal and Julio Urbina 19 Superconducting Receiver Front-End and Its Application In Meteorological Radar Yusheng He and Chunguang Li 385 TOPIC AREA 1: Radar Systems 1 Radar Performance of Ultra Wideband... granite, or even several kilometres into the ice Finally, UWB radar could be used for short range collision avoidance as mentioned in this paper This collision avoidance system, 24 GHz UWB Short Range Radar (SRR), was developed principally by European car manufacturers It is a combination of an UWB radar and a 20 Radar Technology conventional Doppler radar to measure vehicle speeds and to detect obstacles . V TOPIC AREA 1: Radar Systems 1. Radar Performance of Ultra Wideband Waveforms 0 01 Svein-Erik Hamran 2. Short Range Radar Based on UWB Technology 019 L. Sakkila, C Domains 12 7 Yukimasa Nakano and Akira Hirose 8. Application of Radar Technology to Deflection Measurement and Dynamic Testing of Bridges 14 1 Carmelo Gentile XII 9. Radar Systems. Urbina 19 . Superconducting Receiver Front-End and Its Application In Meteorological Radar 385 Yusheng He and Chunguang Li TOPIC AREA 1: Radar Systems 1 Radar Performance