Courseware Sample F0

Transcription

1 Telecommunications Radar Courseware Sample F0

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4 TELECOMMUNICATIONS RADAR COURSEWARE SAMPLE by the Staff of Lab-Volt (Quebec) Ltd Copyright 2001 Lab-Volt Ltd All rights reserved. No part of this publication may be reproduced, in any form or by any means, without the prior written permission of Lab-Volt Quebec Ltd. Printed in Canada April 2004

5 Table of contents Introduction... V Courseware Outline Principles of Radar Systems... Analog MTI Processing... Digital MTD Processing... VII X XII Tracking Radar...XIV Radar in an Active Target Environment...XVI The Phased Array Antenna...XIX Sample Exercise from Principles of Radar Systems Ex. 2-3 The PPI Display... 3 The generation and use of the PPI display. Markers. Measuring the range and angular resolution using the PPI display. Sample Exercise from Analog MTI Processing Ex. 1-3 Staggered PRF Blind speeds. Second-trace echoes and range ambiguities. The effect of staggered PRF on blind speeds and second-trace echoes. The frequency response of a single delay-line canceller in staggered PRF mode. Sample Exercise from Digital MTD Processing Ex. 3-2 Surveillance (Track-While-Scan) Processing Processing steps used in surveillance processing. Track scoring. Sample Exercise from Tracking Radar Ex. 3 Angle Tracking Techniques Lobe switching technique. Crossover loss. Conical scan technique. Monopulse technique. Advantages of the monopulse technique over the lobe switching and conical scan techniques. Lobe switching implementation in the Lab-Volt tracking radar. III

6 Table of Contents (cont'd) Sample Exercise from Radar in an Active Target Environment Ex. 3-1 Deceptive Jamming Using Amplitude-Modulated Signals The principles of inverse gain jamming as used against conical scan and sequential lobing angular tracking systems. Distinction between asynchronous/synchronous inverse gain jamming and AM noise. The importance of lobing/scanning rate agility as a radar EP against amplitude-modulation angle deception techniques. Sample Exercise from The Phased Array Antenna Ex. 1-1 Basic Principles, Operation and Adjustment Setting up and operating the PAA with the Digital Radar System. Other samples extracted from Principles of Radar Systems Unit Test Instructor s Guide Sample Extract from Principles of Radar Systems Unit 2 A Pulsed Radar System Bibliography IV

7 Introduction The Lab-Volt Radar Training System, Model 8095, is a modular table-top radar system especially designed for teaching radar in a laboratory classroom. It is a real radar system, not a simulator, that uses innovative technology to detect passive targets at very short ranges. The low-power of its transmitter allows safe operation in a variety of training environments. The Radar Training System can operate as a pulsed, continuous wave (CW), or frequency-modulated continuous wave (FM-CW) radar. When operated as a pulsed radar, the A-scope and plan position indicator (PPI) displays are available. Only a few connections and adjustments are required to rapidly pass from the hands-on study of a pulsed radar to that of a CW or FM-CW radar. The design of the Radar Training System emphasizes functionality, with block diagrams silk-screened on the module front panels. Major inputs and outputs are readily accessible through various connectors on the front panels. For certain instructional modules, test points are brought out to the front panel, whereas for others, they are located on the printed circuit board. In this case, they are accessed through a hinged door located on top of the module. All test points and outputs are short-circuit protected. Faults can be inserted by the instructor in the instructional modules, for teaching troubleshooting, using the fault switches located on the printed circuit boards of these modules. These switches are accessed through the hinged door located on top of each instructional module. Another hinged panel inside each of these modules prevents students from accessing the fault switches. The student courseware for the Radar Training System consists of four volumes and a set of additional exercises. The courseware covers the following subject matter: The first volume, titled Principles of Radar Systems, deals with the principles and operation of pulsed, CW, and FM-CW radars. A second volume, titled Analog MTI Processing, covers the principles of analog signal processing and MTI radar. The next volume in the series, titles Digital MTD Processing, presents modern digital processing techniques related to those used in air-traffic-control radars. The last volume in the series, titled Tracking Radar, explains the principles of operation of tracking radars (with emphasis on the lobe-switching tracking radar) and discusses the factors which may affect the range and angle tracking performance. The additional exercises make use of the capability of the Radar Training System to perform various radar measurements of fundamental parameters, particularly radar cross sections. An instructor s guide is also available. This guide provides outlines of the theory presented in the courseware, and describes many demonstrations that, in most cases, have not been included in the student manuals. These demonstrations are a useful complement to radar teaching. The instructor s guide also provides aids to the presentation of the various topics covered in the courseware. V

8 Introduction (cont d) The Unit-Exercise structure of the radar courseware is similar to that used in the courseware for the Analog and Digital Communications Training Systems. Each unit of instruction consists of several exercises designed to present material in convenient instructional segments. Principles and concepts are presented first, and hands-on procedures complete the learning process to involve and better acquaint the student with each module, and with complete radar systems. At the end of each exercise, there is a five-questions review section requiring brief written answers. Suggested answers for these questions, as well as for those found in the exercise procedures, are included in the appendices of the student manuals. Each unit terminates with a ten-question multiple-choice test to verify the knowledge gained in the unit. The answers for these questions are given in the radar instructor s guide only. VI

9 Courseware Outline PRINCIPLES OF RADAR SYSTEMS Unit 1 Fundamentals of Pulsed Radar The fundamentals of pulsed radar, including the range-delay relationship, radar antennas, and the radar equation, as well as safety measures applicable to all radar systems. Ex. 1-1 Basic Principles of Pulsed Radar Basic principles of pulsed radar. Introduction to the Radar Training System and the A-scope display. Safety measures applicable to all radar systems. Ex. 1-2 The Range-Delay Relationship The relationship between target range and the delay between pulse transmission and echo reception. The concept of range resolution. Measuring target range and range resolution using the A-scope display. Ex. 1-3 Radar Antennas The role of the antenna in a radar system. Radar antenna characteristics. Plotting the radiation pattern and measuring angular resolution of the radar antenna. Ex. 1-4 The Radar Equation The various parameters in the radar equation and their interaction in a radar system. Unit 2 A Pulsed Radar System The transmitter, the receiver, the antenna driving system, the PPI display, and the PPI scan converter in a pulsed radar system. Ex. 2-1 Radar Transmitter and Receiver The operating principles of a pulsed radar transmitter and receiver. The Radar Transmitter and Radar Receiver of the Radar Training System. Ex. 2-2 Antenna Driving System The mechanical aspects and control of a rotating or scanning radar antenna. VII

10 Courseware Outline PRINCIPLES OF RADAR SYSTEMS Ex. 2-3 The PPI Display The generation and use of the PPI display. Markers. Measuring the range and angular resolution using the PPI display. Ex. 2-4 The PPI Scan Converter The operation of a digital PPI scan converter. Unit 3 CW Radars Continuous-wave and frequency-modulated continuous-wave radars. Ex. 3-1 CW Radar and the Doppler Effect The principles of CW radar and the Doppler effect. Observation and quantification of the frequency components associated with the Doppler effect. Ex. 3-2 Frequency-Modulated CW Radar FM ranging using frequency-modulated continuous-wave radar. The relationship between range and beat frequency. Unit 4 Troubleshooting Radar Systems A methodical approach to troubleshooting CW, FM-CW and pulsed radar systems. Ex. 4-1 Troubleshooting a CW Radar A methodical approach to troubleshooting. Troubleshooting techniques applicable to radar equipment. Locating and diagnosing instructor-inserted faults in a CW radar. Ex. 4-2 Troubleshooting an FM-CW Radar Locating and diagnosing instructor-inserted faults in an FM-CW radar. Ex. 4-3 Troubleshooting a Pulsed Radar: The RF Section Locating and diagnosing instructor-inserted faults in the RF section of a pulsed radar. VIII

11 Courseware Outline PRINCIPLES OF RADAR SYSTEMS Ex. 4-4 Troubleshooting a Pulsed Radar: The PPI Scan Converter Locating and diagnosing instructor-inserted faults in the display section of a pulsed radar. Appendices A Setting Up the Radar Training System B Calibration of the Radar Displays C Targets and Radar Cross Section D Operation of the Dual-Channel Sampler E Common Symbols F Module Front Panels G Test Points and Diagrams H Answers to Procedure Step Questions I Answers to Review Questions J Index of New Terms K Equipment Utilization Chart Bibliography Reader s Comment Form IX

12 Courseware Outline ANALOG MTI PROCESSING Unit 1 Analog MTI Radar The operation and use of analog MTI processing for enhancing the detection of moving targets. Ex. 1-1 Phase-Processing MTI The principle of phase detection in a coherent pulsed radar. The use of phase processing to detect moving targets. The frequency response of a single delay-line canceller. Ex. 1-2 Vector-Processing MTI Blind phases. Elimination of blind phases using vector-processing MTI. Ex. 1-3 Staggered PRF Blind speeds. Second-trace echoes and range ambiguities. The effect of staggered PRF on blind speeds and second-trace echoes. The frequency response of a single delay-line canceller in staggered PRF mode. Ex. 1-4 MTI Limitations Factors limiting MTI performance. Parameters used in measuring MTI performance. Unit 2 Target Detection in Noise and Clutter The characteristics of noise and clutter and their effects on target detection. Ex. 2-1 Threshold Detection Threshold detection of targets. The relationship between probability of false alarm, probability of detection and signal-to-noise ratio. Ex. 2-2 Pulse Integration The role of pulse integration in radar detection. The operation of the feedback integrator. Ex. 2-3 Sensitivity Time Control The role and operation of sensitivity time control in pulsed radar. X

13 Courseware Outline ANALOG MTI PROCESSING Ex. 2-4 Instantaneous Automatic Gain Control The instantaneous automatic gain control technique used in linear receivers. Ex. 2-5 The Log-FTC Receiver The principle of the log-ftc receiver. The effect of the log-ftc receiver on target detection in the presence of rain clutter. Ex. 2-6 Constant False-Alarm Rate The adaptive threshold technique used to obtain a constant false-alarm rate. Unit 3 Troubleshooting A methodical approach to troubleshooting MTI radar systems. Ex. 3-1 Troubleshooting the Analog MTI Processor Troubleshooting techniques. Locating and diagnosing instructor-inserted faults in an analog MTI signal processor. Ex. 3-2 Troubleshooting an MTI Radar System Locating and diagnosing instructor-inserted faults in a complete analog MTI radar system. Appendices A Setting Up the Radar Training System B Calibration and Adjustment of the Radar Training System C Radar Training System Targets D Common Symbols E Module Front Panels F Test Points and Diagrams G Answers to Procedure Step Questions H Answers to Review Questions I Index of New Terms J Equipment Utilization Chart Bibliography Reader s Comment Form XI

14 Courseware Outline DIGITAL MTD PROCESSING Unit 1 Digital Radar Systems Advantages of digital signal processing. The Digital MTD/PPI Processor. Ex. 1-1 Familiarization with the Digital Radar System The importance of coherence and synchronization of the PRF with the antenna rotation. Sensitivity time control (STC). Description of the Digital Radar System. Operation in the PPI mode. Ex. 1-2 The PPI and Raster-Scan Displays Types of radar displays. The digital PPI display. Generating the raster-scan display in the Digital MTD/PPI Processor. Unit 2 MTD Processing Techniques involved in first-stage MTD processing. Ex. 2-1 Cell Mapping Range-azimuth cells. Coherent processing intervals. Doppler cells. Clutter maps. Ex. 2-2 Fast Fourier Transform (FFT) Processing Forming digital filters. Velocity sorting. Doppler ambiguities. Blind (dim) speeds. Ex. 2-3 Constant False-Alarm Rate (CFAR) Adaptive thresholding. Time-average and cell-average CFAR. Target detection in a noisy environment. Unit 3 Alarm Processing Techniques involved in second- and third-stage MTD processing. Ex. 3-1 Correlation and Interpolation (C&I) Processing Clustering and correlation of primitive target reports. Centroiding. Interpolation. XII

15 Courseware Outline DIGITAL MTD PROCESSING Ex. 3-2 Surveillance (Track-While-Scan) Processing Processing steps used in surveillance processing. Track scoring. Unit 4 Troubleshooting A methodical approach to troubleshooting. Ex. 4-1 Troubleshooting the Digital MTD/PPI Processor Locating and diagnosing instructor-inserted faults in the Digital MTD/PPI Processor. Appendices A Setting Up the Radar Training System B Setting Up and Connecting the Modules C Calibrating the Digital Radar Training System D Functions E Radar Training System Targets F Common Symbols G Module Front Panel H Test Points and Diagrams I Answers to Procedure Step Questions Bibliography Reader's Comment Form XIII

16 Courseware Outline TRACKING RADAR Exercise 1 Manual Tracking of a Target What is a tracking radar? Track-while-scan (TWS) radar versus continuous tracking radar. Manual tracking of a target. Range gate, range gate marker, and O-scope display. Manual control of the antenna and range gate positions in the Lab-Volt tracking radar. Exercise 2 Automatic Range Tracking Principle of automatic range tracking. Applications of range trackers. Target search and acquisition. Split range-gate tracking. Leading-edge range tracking and trailing-edge range tracking. Range tracking rate limitation. Operation of the range tracker in the Lab-Volt tracking radar. Exercise 3 Angle Tracking Techniques Lobe switching technique. Crossover loss. Conical scan technique. Monopulse technique. Advantages of the monopulse technique over the lobe switching and conical scan techniques. Lobe switching implementation in the Lab-Volt tracking radar. Exercise 4 Automatic Angle Tracking Principle of automatic angle tracking. Operation of the angle tracker in the Lab-Volt tracking radar. Exercise 5 Range and Angle Tracking Performance (Radar-Dependent Errors) Resolution, precision, and accuracy of tracking radars. Radardependent errors. Effect of the receiver thermal noise and antenna servosystem noise and limitations on the tracking error. Use of an AGC circuit to reduce the variation of the echo amplitude due to fluctuations of the target radar cross section. XIV

17 Courseware Outline TRACKING RADAR Exercise 6 Range and Angle Tracking Performance (Target-Caused Errors) Amplitude scintillation. Effect of the amplitude scintillation on the angular tracking error in lobe switching and conical scan tracking radars. Angular scintillation (glint). Effect of the angular scintillation on the angular tracking error. Principle of frequency agility. Use of frequency agility to reduce the angular tracking error. Exercise 7 Troubleshooting an Analog Target Tracker Use of a methodical approach to locate and diagnose instructorinserted faults in the Radar Target Tracker. Appendices A Setting Up the Radar Training System B Calibration and Adjustment of the Tracking Radar Training System C Answers to Procedure Step Questions D Answers to Review Questions Bibliography Reader's Comment Form XV

18 Courseware Outline RADAR IN AN ACTIVE TARGET ENVIRONMENT Unit 1 Noise Jamming The context of electronic warfare in modern conflicts. Introduction to electronic warfare and its subdivisions (EA, EP, ES). The relationship between the subdivisions. Ex. 1-1 Familiarization with the Radar Jamming Pod Familiarization with the various controls, input/output connectors, and accessories on the Radar Jamming Pod. Radar Jamming Pod properties and jamming signal capabilities. Ex. 1-2 Spot Noise Jamming and Burn-Through Range Description of spot noise jamming. Difference between the selfscreening, mutual-support, escort, and stand-off EA missions. The concept of burn-through range. Introduction of the radar range equation modified for spot noise jamming. Ex. 1-3 Frequency Agility and Barrage Noise Jamming Discussion relating to the radar receiver passband. Introduction to frequency agility as an electronic protection against spot noise jamming. Description of barrage noise jamming. Justification of the use of barrage noise jamming against frequency-agile radars. Swept spot jamming as used with the Radar Jamming Pod. Ex. 1-4 Video Integration and Track-On-Jamming The importance of signal discrimination (signal processing techniques) used as radar EPs against noise jamming. A case example, the effects of video integration when used by a radar confronted with noise jamming. Discussion of the jammer strobe. The angle track-on jamming capability of certain radars. Ex. 1-5 Antennas in EW: Sidelobe Jamming and Space Discrimination Presentation of the difference between mainlobe and sidelobe jamming. Outline of the effects of effective sidelobe noise jamming. Presentation of certain antenna space discrimination techniques used as radar EP against stand-off noise jammers. XVI

19 Courseware Outline RADAR IN AN ACTIVE TARGET ENVIRONMENT Unit 2 Range Deception Jamming The fundamental differences between noise jamming and deception jamming. Presentation of the different categories of deceptive jamming. Comparison between range deception and angle deception jamming techniques. Ex. 2-1 Deception Jamming using the Radar Jamming Pod Generating false targets with the Radar Jamming Pod. Familiarization with the RGPO and the on-off modulation capabilities of the Jamming Pod. Ex. 2-2 Range Gate Pull-Off The implementation of range DECM against radars that use split range-gate tracking. Introduction to range gate pull-off (RGPO), and the phases of an RGPO jamming cycle. Use of a range-rate tracking limiter as an EP against unrealistic RGPO. Use of leading-edge range tracking as an EP against RGPO. Ex. 2-3 Stealth Technology: The Quest for Reduced RCS Introduction to the basic material and design principles behind radar stealth technology. The role of hard-body shaping and radar absorbent materials (RAM) in the implementation of these principles. Implications of stealth technology to electronic warfare. Unit 3 Angle Deception Jamming Reasons that angle and range DECM are implemented together against tracking radars. Differentiation between those angle deception techniques used against conical scanning and sequential lobing radars, and those used against monopulse radars. Introduction to silent lobing as an EP. Ex. 3-1 Deceptive Jamming Using Amplitude-Modulated Signals The principles of inverse gain jamming as used against conical scan and sequential lobing angular tracking systems. Distinction between asynchronous/synchronous inverse gain jamming and AM noise. The importance of lobing/scanning rate agility as a radar EP against amplitude-modulation angle deception techniques. XVII

20 Courseware Outline RADAR IN AN ACTIVE TARGET ENVIRONMENT Ex. 3-2 Cross-Polarization Jamming The main reason for the existence of the cross-polarized (Condon lobes) antenna radiation pattern. Comparison between typical parabolic antenna cross- and co-polarized antenna patterns. Introduction to cross-polarization jamming. Ex. 3-3 Multiple-Source Jamming Techniques The mutual support EA mission and its relation to cooperative jamming techniques. How multiple-source jamming techniques induce artificial glint onto the jamming signal. Distinction between coherent and incoherent multiple-source jamming. The difference between formation and blinking jamming, and how victim radars use angle-rate limiters as electronic protection. Unit 4 Chaff Fundamentals of chaff physics, and reasons why the Lab-Volt variabledensity chaff cloud (VDCC) reproduces the effects of chaff. Dispensing and uses of chaff. Chaff placed within its historical context. Ex. 4-1 Chaff Clouds Corridor dispensing of chaff. Discrimination of chaff echoes using radar MTI processing. Setting-up the Lab-Volt variable-density chaff cloud (VDCC). Ex. 4-2 Chaff Clouds used as Decoys Burst dispensing of chaff to create false targets. Introduction to jammer-illuminated chaff (JAFF). Defeating the processing ability of MTI radars via the noisy Doppler frequency imparted to chaff clouds via JAFF. Appendices A Setting Up the Radar Training System B Calibration and Adjustment of the Tracking Radar Training System C Answers to Procedure Step Questions D Answers to Review Questions E Glossary Bibliography We Value Your Opinion! XVIII

21 Courseware Outline THE PHASED ARRAY ANTENNA Unit 1 Basic Operation Ex. 1-1 Basic Principles, Operation and Adjustments Setting up and operating the PAA with the Digital Radar System. Ex. 1-2 The True-Time Delay Rotman Lens Principles of the Rotman lens. Ex. 1-3 The Switching Matrix Operation of the RF switching matrix. Unit 2 Measurement of Useful Phased Array Antenna Characteristics Ex. 2-1 Beamwidth Measurement Measuring the 3 db beamwidth of the PAA. Ex. 2-2 Radiation Pattern Measurement Measuring the PAA radiation pattern and plotting the radiation pattern from your results. Ex. 2-3 Angular Separation Measurement Measuring the angular separation between two consecutive PAA beams. Ex. 2-4 Phased Array Antenna Gain Measurement Measuring the PAA gain for various beams (center and far end). PAA gain versus scan angle. Ex. 2-5 Maximum Scan Angle Measurement Measuring the maximum scan angle of the PAA. Ex. 2-6 Target Bearing Estimation Target position relative to a selected beam. XIX

22 Courseware Outline THE PHASED ARRAY ANTENNA Ex. 2-7 Target Speed Estimation Calculating the speed of a target moving perpendicularly to the radar line of sight, using the angular displacement and the scan speed to estimate the target speed. Appendices A Set-up and adjustment of the PAA with the Analog Radar B Set-up and adjustment of the PAA with the Digital Radar C Answers to Procedure Step Questions D Answers to Review Questions E Glossary F Equipment Utilization Chart Bibliography We Value Your Opinion! XX

23 Sample Exercise from Principles of Radar Systems

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25 Exercise 2-3 The PPI Display EXERCISE OBJECTIVE When you have completed this exercise, you will be familiar with the generation and use of the PPI display and with the various markers available on the display. You will also be able to measure the range and angular resolution of a radar system using the PPI display. Note: This exercise can be performed using either the Analog Radar Training System or the Complete Radar Training System. Both of these systems include the PPI Scan Converter. DISCUSSION Indicators and displays are used in radar systems to present information about the targets in a suitable form. When only the target range and echo signal strength are important, the A-scope display is usually used. This is often the case when the antenna is fixed in one particular direction. Most radar systems, however, are used to observe targets in more than one direction at once. Air surveillance radar systems, for example, must search in all directions, and indicate the range and bearing, that is the horizontal direction expressed as an angle in the horizontal plane from a reference direction, of each target. 0 BLIP ORIGIN BEARING Þ RANGE R Figure PPI Display. 3

26 The PPI Display The most common type of display used in radar systems is the plan position indicator (PPI), illustrated in Figure On this type of display, the targets appear as luminous spots (blips) on a screen in a two-dimensional map-like presentation. The centre, or origin, of the display represents the location of the radar. The distance of any blip from the origin represents the range R of the target, and the angle from a reference angle on the screen represents the target bearing. This type of display provides equal coverage in all directions. In some radar applications, the antenna does not rotate a full 360(, but scans over a limited sector. In this case, the PPI display is called a sector PPI, as shown in Figure R Þ ORIGIN Figure Sector PPI. Generating the PPI display The PPI display is generated using a cathode ray tube (CRT) and circuits for producing the signals required to control the position and intensity of the electron beam. Many different techniques exist for generating the PPI display on a CRT. The conventional method is to produce a radial scan which rotates at the same speed as the antenna. Although more sophisticated methods are usually used today, this technique illustrates the basic principles common to all PPI displays. Each radial scan is triggered by a synchronization signal in the radar system so that it begins at the same moment that a radar pulse is transmitted. The scan begins at the origin of the display and travels at a uniform rate along a straight line towards the edge, as shown in Figure Once the scan is completed, the beam is rapidly returned to the origin. During this retrace, the beam is blanked, or turned off completely. An azimuth signal from the antenna driving system provides azimuth information to the PPI display. This information is used to make the direction of the scan correspond to the antenna azimuth at that moment. The next scan also begins at the origin, but if the antenna azimuth has changed slightly, the direction of the scan will also have changed. Therefore, the angle of each successive scan changes as the antenna rotates. 4

27 The PPI Display The blips on the screen, indicating target positions, are created by making the intensity of the electron beam proportional to the strength of the target echo signal. In some cases, the electron beam is turned on, during each scan, only when the target echo signal exceeds a certain detection threshold. END OF SCAN BEGINNING OF SCAN BEAM IS BLANKED DURING RETRACE Figure Radial scans in a conventional PPI display. At any time during the scan, distance of the beam from the origin is proportional to the time that has elapsed since the transmission of the radar pulse. Since the round-trip transit time for near targets is relatively short, these targets are displayed close to the origin of the display. The greater the target range, the further the corresponding blip is from the origin. This process can be understood by comparing each radial scan to a scan on an A-scope display, produced using a rotating antenna. Figure 2-32 (a) shows a radar antenna rotating clockwise as radar pulses are transmitted. In this example, the antenna rotation between pulses is greatly exaggerated. At azimuth 1, a radar pulse is transmitted. This pulse strikes two nearby targets, at slightly different ranges, each of which produces an echo. A second pulse is transmitted at azimuth 2, but no targets are in its path. At azimuth 3, a third pulse is transmitted. This pulse strikes one distant target, which produces one echo. Figure 2-32 (b) shows three scans on an A-scope display, one for each transmitted pulse. The receiver used in this example produces a unipolar video signal. 5

28 The PPI Display Þ 1 Þ 2 Þ 3 a) Rotating Antenna AMPLITUDE DETECTION THRESHOLD ORIGIN Þ 1 ORIGIN AZIMUTH = Þ 1 RANGE Þ 3 Þ 2 RANGE AMPLITUDE DETECTION THRESHOLD c) PPI display ORIGIN AZIMUTH = Þ 2 RANGE AMPLITUDE DETECTION THRESHOLD ORIGIN AZIMUTH = Þ 3 b) A-scope scans RANGE Figure Generation of a conventional (radial-scan) PPI display. 6

29 The PPI Display Two echoes are received at azimuth 1, one for each target. Since the echoes are received at slightly different times, they produce two distinct blips on the display as the electron beam scans from left (the origin) to right. Both of these echoes exceed the detection threshold. At azimuth 2, some noise is present, but the noise does not exceed the detection threshold. At azimuth 3, one echo exceeds the detection threshold. Since this echo corresponds to a distant target, the blip appears to the right of the display. Figure 2-32 (c) shows how these three scans would appear on a PPI display. The scan at angle 1 begins at the origin and moves towards the edge. The electron beam, however, is off. When the first echo exceeds the detection threshold, the beam turns on producing a blip on the PPI display. The beam stays on as long as the echo pulse amplitude is greater than the detection threshold, then it turns off. As this scan continues towards the edge of the screen, it is again turned on by the second echo, producing a second blip. Since no echo is received while the antenna azimuth is equal to 2, the beam is not turned on during the second scan. During the third scan, at angle 3, the beam is turned on once. This example shows that each radial scan on a PPI display, from the origin to the edge, is comparable to a scan on an A-scope display. The blips on the PPI screen are created by turning the electron beam on whenever the target echo signal exceeds the detection threshold. In both displays, the distance of the blip from the origin represents the target range. In a practical radar system, the antenna may rotate only a fraction of a degree between transmitted pulses. As a result, each target is illuminated by many pulses, rather than by just one, as in the example. Many modern radars convert the radial-scan display into a raster-scan format similar to television. This allows the display to be produced on a TV-type monitor. The overall appearance of the PPI display, however, is not changed. Markers Besides the blips corresponding to the targets detected, many PPI displays can display various types of markers which help the operator to determine the ranges and bearings of the targets. Controls on the display usually allow the markers to be turned on or off. One of the simplest types of markers is range rings. These are fixed, concentric rings placed at regular ranges on the display. Figure 2-33 shows a PPI display with range rings spaced at 10 km intervals. In this figure, there are two targets within 10 km of the radar, one at approximately 20 km, four between 20 and 30 km, and one beyond 30 km. 7

30 The PPI Display Besides the fixed range rings, two types of variable markers may be available. The variable range marker (VRM) is a ring whose radius can be varied using controls on the display. A digital display indicates the range corresponding to the VRM radius. The electronic bearing line (EBL) is a straight line, starting at the origin of the screen, whose azimuth on the screen can be varied using controls on the display. A second digital display indicates the bearing corresponding to the EBL. 10 km 20 km 30 km Figure PPI display with range rings. To determine the range and bearing of a target using the VRM and the EBL, these markers are positioned so that their intersection coincides with the target blip on the display, as in Figure The range and bearing indicated on the digital displays then indicate the position of the target in polar coordinates. 8

31 The PPI Display VRM VRM [km] TARGET BLIP EBL EBL [DEGREES] PPI DISPLAY Figure Use of the variable range marker (VRM) and the electronic bearing line (EBL) on a PPI display. Range and angular resolution The effects of the pulse width on the range resolution of a radar system can be readily observed on the PPI display. As shown in Figure 2-32, the electron beam of the PPI display is turned on whenever the amplitude of the echo signal exceeds the detection threshold, producing a blip on the screen. As the pulse width of the radar pulses is increased, the length of the blips on the display also increases. The blips of two closely spaced targets may merge together to form a single blip, as in Figure 2-35 (a), at which point the two targets are no longer resolved. 9

32 The PPI Display AMPLITUDE DETECTION THRESHOLD A-SCOPE DISPLAY PPI DISPLAY a) Pulse width increased, targets unresolved. AMPLITUDE DETECTION THRESHOLD A-SCOPE DISPLAY PPI DISPLAY b) Gain reduced, targets resolved. Figure Effect of pulse width and signal amplitude on range resolution. The two targets in Figure 2-35 (a) are unresolved on the PPI display, even though they are separately visible on the A-scope display. This is because the dip in amplitude between the echo blips does not drop down below the detection threshold. By reducing the gain of the video amplifier in the receiver section of the radar, the amplitude of the video signal is reduced. In some cases, as in Figure 2-35 (b), this will allow the two targets to be resolved. The same result would be achieved by keeping the amplitude constant and increasing the detection 10

33 The PPI Display threshold. Most radar systems have a gain control which can be adjusted for optimum resolution. As was discussed in Unit 1, the theoretical range resolution of a pulsed radar is equal to one half the pulse length: Theoretical range resolution L p 2 - c 2 where L p is the pulse length - is the pulse width c is the speed of light. The angular resolution of a radar system can also be observed using the PPI display. Two targets at the same range but at different bearings will appear as two distinct blips if they are resolved. The angular resolution depends mostly on the antenna beamwidth. As in the case of range resolution, optimum angular resolution depends on correct adjustment of the gain and the detection threshold. As stated in Unit 1, the angular resolution is usually between 1 and 1.5 times the antenna 3-dB beamwidth. Procedure Summary In the first part of this exercise, you will set up a pulsed radar including a PPI display. The block diagram of the system you will use is shown in Figure The connection of the oscilloscope is not shown in this figure since it is required during adjustment of the pulsed radar. In the second part of this exercise, you will carry out the adjustment of the dc offset voltages at the SAMPLED OUTPUTS of the Dual-Channel Sampler. This adjustment will prevent undesired dc offset voltages from saturating the PPI display. In the third part of this exercise, you will calibrate the origin of the PPI display. This will allow you to learn the operation and use of a VRM, since you will use the VRM of the PPI Scan Converter to calibrate the PPI display. In the fourth part of this exercise, you will learn the operation and use of other markers by using the RANGE RINGS and EBL of the PPI Scan Converter. You will use the VRM and the EBL to determine the polar coordinates of various blips on the PPI display, and then try to find which objects in the laboratory classroom correspond to these blips. You will observe the effect that the range of observation has on the position of blips on the PPI display, by selecting two different ranges of observation. In the fifth part of this exercise, you will measure the angular resolution of the pulsed radar using the PPI display, and compare this to the angular resolution expected. 11

34 The PPI Display In the sixth part of this exercise, you will observe the effect of the pulse width on the aspect of the blips on the PPI display. You will measure the range resolution of the pulsed radar using the PPI display, and compare this to the theoretical range resolution. PROCEDURE Setting up a pulsed radar * 1. The main elements of the Radar Training System, that is the antenna and its pedestal, the target table and the training modules, must be set up properly before beginning this exercise. Refer to Appendix A of this manual for setting up the Radar Training System, if this is not done yet. Set up the modules on the Power Supply / Antenna Motor Driver as shown in Figure On the Radar Transmitter, make sure that the RF POWER switch is in the STANDBY position. On the Antenna Controller, make sure that the MANual ANTENNA ROTATION MODE push button is depressed and that the SPEED control is in the 0 position. Set the POWER switch of the Power Supply to the I (on) position, and then those of the other modules. RADAR TRANSMITTER DUAL-CHANNEL SAMPLER RADAR RECEIVER ANALOG MTI PROCESSOR RADAR SYNCHRONIZER/ ANTENNA CONTROLLER PPI SCAN CONVERTER OSCILLOSCOPE POWER SUPPLY ANTENNA MOTOR DRIVER Figure Module Arrangement. * 2. Figure 2-37 shows the block diagram of the pulsed radar, including the PPI display, that can be obtained using the Radar Training System. 12

35 The PPI Display Install a BNC T-connector on OUTPUT B of the Radar Synchronizer, then connect the modules according to this block diagram. The connection of the oscilloscope is not shown in Figure 2-37 since it is required during adjust-ment of the pulsed radar. Note: The SYNC. TRIGGER INPUT of the Dual-Channel Sampler and the PULSE GENERATOR TRIGGER INPUT of the Radar Transmitter must be connected directly to OUTPUT B of the Radar Synchronizer without passing through BNC T-connectors. * 3. Make the following adjustments: On the Radar Transmitter RF OSCILLATOR FREQUENCY...CAL. PULSE GENERATOR PULSE WIDTH.. 1 ns On the Radar Synchronizer PRF MODE... SINGLE PRF Hz On the Dual-Channel Sampler ORIGIN... Max. clockwise * 4. On the Antenna Controller, use the SPEED control so that the Radar Antenna rotates at least one turn, then stop it. Depress the POSITION MODE push button, then use the SPEED control to set the position (azimuth) of the Radar Antenna to approximately 0(. 13

36 14 RF INPUT ROTATING- ANTENNA PEDESTAL RF OUTPUT OSCILLOSCOPE The PPI Display MOTOR FEEDBACK OUTPUT MOTOR POWER INTPUT RF OSCILLATOR Figure Block diagram of the pulsed radar. OUTPUT RF OSCILLATOR RADAR TRANSMITTER CW/FM-CW RF OUTPUT PULSE GENERATOR TRIGGER INPUT CW RF INPUT MODULATOR OUTPUT PULSE INPUT MOTOR FEEDBACK INPUT PULSED RF OUTPUT ANTENNA CONTROLLER AZIMUTH OUTPUT OUTPUT INPUT RF INPUT LOCAL OSCILLATOR INPUT ANTENNA MOTOR DRIVER RADAR RECEIVER POWER OUTPUT I CHANNEL PULSED OUTPUT Q CHANNEL PULSED OUTPUT I CHANNEL PULSE INPUTS Q CHANNEL SYNC. I CHANNEL DUAL- SAMPLED CHANNEL OUTPUTS SAMPLER Q CHANNEL TRIGGER PRF INPUTS VIDEO I CHANNEL OUTPUT ANALOG INPUTS MTI PROCESSOR Q CHANNEL SYNC. INPUTS PRF OUTPUTS VIDEO TO SCOPE INPUT PPI X AZIMUTH SCAN Y INPUT CONVERTER Z TRIGGER SYNC. PRF INPUTS OUTPUT B OUTPUT A RADAR SYNCHRONIZER

37 The PPI Display Connect the cable of the target table to the multi-pin connector located on the rear panel of the Target Controller. Make sure that the surface of the target table is free of any objects and then set the POWER switch of the Target Positioning System to the I (on) position. Position the target table and the Rotating-Antenna Pedestal so that the grid of the target table is located approximately 2.0 m from the horn of the Radar Antenna, as shown in Figure Make sure that the Radar Antenna beam axis is correctly aligned with the metal rail of the target table, but do not alter the position of the Radar Antenna using the Antenna Controller. Y X 2.0 m Figure Position of the Rotating-Antenna Pedestal and target table. Place a small metal plate target on the mast of the target table. Make sure that the target is oriented perpendicular to the metal rail of the target table, and then tighten the screw to secure the target to the mast. Adjustment of the dc offset voltages at the SAMPLED OUTPUTS of the Dual- Channel Sampler * 5. On the Dual-Channel Sampler, make sure that the GAIN controls are in the CALibrated position. Using probes, connect TP1 and TP2 of the Analog MTI Processor to channels 1 and 2 of the oscilloscope, respectively. The signals on these test points come from the I- and Q-CHANNEL SAMPLED OUTPUTS of the Dual-Channel Sampler, respectively. Connect the A-SCOPE TIME BASE OUTPUT of the Dual-Channel Sampler to the external triggering input of the oscilloscope. 15

38 The PPI Display Adjust the oscilloscope as follows: Channel V/DIV (set to GND) Channel V/DIV (set to GND) Vertical Mode... ALT Time Base... 1 ms/div Trigger...EXT Set the vertical position controls so that the traces of channels 1 and 2 are centred in the upper and lower halves of the oscilloscope screen, respectively. Set the input coupling switches of both channels to the DC position. On the Dual-Channel Sampler, set the I- and Q-CHANNEL DC OFFSET controls so that there is no noticeable offset voltage at TP1 and TP2 of the Analog MTI Processor. * 6. Disconnect the probes going to channels 1 and 2 of the oscilloscope from TP1 and TP2 of the Analog MTI Processor, then connect them to TP5 and TP6 of the same module, respectively. The signals on these test points are related to channels I and Q, respectively. On the Analog MTI Processor, place the STC switch in the I (on) position and depress the 7.2-m RANGE push button. The operation of the controls of the Analog MTI Processor is covered in Volume 2 of the Radar Training System. On the oscilloscope, set the sensitivity of the two channels to an appropriate level. Figure 2-39 (a) shows an example of what you might observed on the oscilloscope screen. On the Dual-Channel Sampler, set the I- and Q-CHANNEL DC OFFSET controls so that the signals at TP5 and TP6 of the Analog MTI Processor resembles those shown in Figure 2-39 (b). This completes the adjustment of the dc offset voltages at the SAMPLED OUTPUTS of the Dual-Channel Sampler. A generalized procedure is found in Appendix B of this manual. 16

39 The PPI Display TP5 TP6 Channel 1... : 0.5 V/DIV. (DC coupled) Channel 2... : 0.5 V/DIV. (DC coupled) Time Base... : 1 ms/div. a) Before the adjustment of the DC OFFSET controls. TP5 TP6 Channel 1... : 0.5 V/DIV. (DC coupled) Channel 2... : 0.5 V/DIV. (DC coupled) Time Base... : 1 ms/div. b) After the adjustment of the DC OFFSET controls. Figure Signals at TP5 and TP6 of the Analog MTI Processor. 17

40 The PPI Display Calibration of the PPI display * 7. Remove the cable and probes connected to the oscilloscope. Connect the X, Y, and Z OUTPUTS TO SCOPE of the PPI Scan Converter to channels X, Y, and Z of the oscilloscope, respectively. Make the following adjustments: On the Analog MTI Processor RANGE m STC...O MTI...O IAGC...O MODE... LIN. VIDEO INTEGRATOR...O GAIN... MIN. On the PPI Scan Converter RANGE m RANGE RINGS...O VRM...O EBL...O On the Dual-Channel Sampler RANGE SPAN m On the oscilloscope Channel V/DIV (DC coupled) Channel V/DIV (DC coupled) Time Base... X-Y A circle should appear on the oscilloscope screen. Set the X- and Y-axis position controls of the oscilloscope so that the circle is centred on the screen. This circle delimits the area of the PPI display. * 8. On the Target Controller, make sure that the X- and Y-axis SPEED controls are in the MINimum position and then make the following settings: MODE... SPEED DISPLAY MODE... SPEED Set the Y-axis SPEED control so that the target speed is equal to approximately 15 cm/s. On the Antenna Controller, depress the SPEED MODE push button, select the SCANning/TRACKing ANTENNA ROTATION MODE, then set the SPEED control so that the rotation speed of the Radar Antenna is 18

41 The PPI Display approximately 10 r/min. The Radar Antenna should start to scan back and forth in the direction of the moving target. On the Analog MTI Processor, set the GAIN control to one quarter of MAXimum. This control varies the level of the video signal sent to the VIDEO INPUT of the PPI Scan Converter. * 9. On the Radar Transmitter, depress the RF POWER push button. The RF POWER ON LED should start to flash on and off. This indicates that RF power is being radiated by the Radar Antenna. On the Dual-Channel Sampler, slowly rotate the ORIGIN control counter clockwise until some blips appear on the PPI display, as shown in Figure These blips correspond to reflecting objects in the laboratory classroom and to the moving target. The arrows in Figure 2-40 show the displacement of the moving-target blip on the PPI display. Note: If there are too many blips on the PPI display, it may be difficult to recognize the blip produced by the moving target. In this case, slightly decrease the GAIN of the Analog MTI Processor to decrease the level of the video signal. This will eliminate some undesired blips from the PPI display. If, on the other hand the blips on the PPI display appear to be very small, slightly increase the GAIN of the Analog MTI Processor to increase the level of the video signal. This will magnify the blips on the PPI display. MOVING TARGET BLIP Range...: 3.6 m Figure Non-calibrated origin sector PPI display. 19

42 The PPI Display On the Dual-Channel Sampler, continue to rotate the ORIGIN control counterclockwise in order to bring the origin of the PPI display nearer to the horn of the Radar Antenna, until the PPI display resembles that shown in Figure Range...: 3.6 m Figure A sector PPI display whose origin is too close to the Radar Antenna. What causes these large blips on the PPI display? (Hint: see Figure 1-9 of this manual.) * 10. On the Dual-Channel Sampler, set the ORIGIN control so that the movingtarget blip appears on the PPI display. On the Target Controller, set the Y-axis SPEED to 0, then make the following settings: MODE...POSITION DISPLAY MODE...POSITION Use the Y-axis position control to place the target at the far end of the target table. The target range is now approximately 2.9 m since the grid of the target table is approximately 2.0 m from the horn of the Radar Antenna. 20

43 The PPI Display On the PPI Scan Converter, place the VRM switch in the I (on) position to enable the VRM. The range related to the VRM is indicated on the VRM display. Successively depress the + and push buttons located below the VRM display while observing the PPI display. Describe the VRM. What is the main purpose of the VRM? * 11. On the PPI Scan Converter, use the VRM controls to set the VRM to approximately 2.9 m. This corresponds to the range of the target installed on the target table. On the Dual-Channel Sampler, set the ORIGIN control so that the blip corresponding to the target installed on the target table is centred on the VRM. On the Antenna Controller, set the SPEED control to 0, then select the PRF LOCKed ANTENNA ROTATION MODE. The Radar Antenna should now rotate clockwise. Figure 2-42 shows an example of what you might observe on the PPI display. 21

44 The PPI Display TARGET BLIP Range...: 3.6 m Figure Calibrated PPI display. This completes the origin calibration of the PPI display. A generalized procedure is found in Appendix B of this manual. Operation and use of markers * 12. On the PPI Scan Converter, place the VRM switch in the O (off) position to disable the VRM, then place the RANGE RINGS switch in the I (on) position to enable the range rings. Observe the PPI display, then describe the range rings. What is the main purpose of the range rings? 22

45 The PPI Display Count the number of target blips located between 2 and 3 m on the PPI display, and note the result below. * 13. On the Dual-Channel Sampler, select the 7.2-m RANGE SPAN. On the Analog MTI Processor and PPI Scan Converter, select the 7.2-m RANGE. Describe what has happened on the PPI display. Explain. * 14. On the Dual-Channel Sampler, select the 3.6-m RANGE SPAN. On the Analog MTI Processor and PPI Scan Converter, select the 3.6-m RANGE. On the PPI Scan Converter, place the RANGE RINGS switch in the O (off) position to disable the range rings, then place the EBL switch in the I (on) position to enable the EBL. The azimuth related to the EBL is indicated on the EBL display. Successively depress the + and push buttons located below the EBL display while observing the PPI display. Describe the EBL. What is the main purpose of the EBL? * 15. Use the VRM and the EBL to determine the polar coordinates of some of the blips on the PPI display. Try to find which objects in the laboratory classroom correspond to these blips. 23

46 The PPI Display Angular resolution of the pulsed radar * 16. On the Target Controller, use the X- and Y-axis POSITION controls to place the target at the following coordinates: X = 75 cm and Y = 90 cm. Set the orientation of the target so that it faces the Radar Antenna. Place the fixed mast provided with the target table at the following coordinates: X = 15 cm and Y = 90 cm. Install the other small metal plate target on the fixed mast and set the orientation of the target so that it faces the Radar Antenna. Note: In the rest of this exercise, you are often asked to vary the position of the target table or to change or orient the target while the RF power is on. This requires standing near or in front of the antenna. This practice could be very dangerous with a full-scale radar and should normally be avoided. However, the low radiation levels of the Radar Training System allow these manipulations to be carried out safely. For the rest of this section, the target installed on the mast mounted on the movable carriage of the target table will be called the movable target, whereas the target installed on the fixed mast will be called the fixed target. * 17. Slightly vary the orientation of each target so that the two target blips on the PPI display are of the same size. On the Analog MTI Processor, set the GAIN control so that the two target blips on the PPI display are as small as possible. Figure 2-43 shows an example of what you might observed on the PPI display. On the Target Controller, use the X-axis POSITION control to approach the movable target towards the fixed target, a few centimeters at a time, until the two target blips on the PPI display are as close as possible without merging into one blip. Each time you move the movable target, readjust its orientation so that its blip on the PPI display remains approximately the same size. Figure 2-44 shows an example of what you might observe on the PPI display. * 18. On the PPI Scan Converter, use the EBL controls to determine the bearings of the fixed and movable targets. Note the results, then calculate the difference between the bearings of the two targets. The result is the angle, with respect to the Radar Antenna, which separates the two targets. 24