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TCOM 707 Advanced Link Design

TCOM 707 Advanced Link Design. FALL 2004 Innovation Hall 135 Thursdays 4:30 – 7:10 p.m. Dr. Jeremy Allnutt jallnutt@gmu.edu. General Information - 1. Contact Information Room: Science & Technology II, Room 269 Telephone (703) 993-3969 Email: jallnutt@gmu.edu

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TCOM 707 Advanced Link Design

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  1. TCOM 707Advanced Link Design FALL 2004 Innovation Hall 135 Thursdays 4:30 – 7:10 p.m. Dr. Jeremy Allnutt jallnutt@gmu.edu TCOM 707

  2. General Information - 1 • Contact Information • Room: Science & Technology II, Room 269 • Telephone (703) 993-3969 • Email: jallnutt@gmu.edu • Office Manager: lfortney@gmu.edu • Office Hours • Mondays and Tuesdays 3:00 – 6:00 p.m.Please, by appointmentonly TCOM 707

  3. General Information - 2 • Course Outline • Go to http://ece.gmu.edu/coursepages.htmor http://telecom.gmu.edu and click on Course Schedule • Scroll down to TCOM 707 • Snow days: call (703) 993-1000 • You MUST have a Mathematical Calculator – please, simple ones only TCOM 707

  4. As a general rule, no more than 40% of any paper should be drawn directly from another source General Information - 3 • Homework Assignments • Feel free to work together on these, BUT • All submitted work must be your own work • Web and other sources of information • You may use any and all resources, BUT • You must acknowledge all sources • You must enclose in quotation marks all parts copied directly – and you must give the full source information TCOM 707

  5. General Information - 4 • Exam and Homework Answers • For problems set, most marks will be given for the solution procedure used, not the answer • So: please give as much information as you can when answering questions: partial credit cannot be given if there is nothing to go on • If something appears to be missing from the question set, make – and give – assumptions used to find the solution TCOM 707

  6. General Information - 7 • Class Grades • Emphasis on overall effort and results • Balance between HW, tests, and class project: • Homework - 10% • Tests - 30 + 30% • Project Presentation - 30% This is the final exam TCOM 707

  7. TCOM 707 Course Plan • Go to http://ece.gmu.edu/coursepages.htm or http://telecom.gmu.edu and click on Course Schedule; scroll down to TCOM 707 • In-Class Tests scheduled for - October 7th, 2004 – Radar systems - November 4th, 2004 – Satellite Systems • In-Class Final exam (Project presentation) - December 16th, 2004 TCOM 707

  8. TCOM 707 Lecture 1 Outline • Introduction to Radar Systems • Background • Time, frequency, and spectrum considerations • Range calculations • Pulse repetition frequency issues • Derivation of radar equation • Radar applications Check out “Introduction to Radar Systems”, 2nd ed., Merrill I. Skolnik, McGraw-Hill, 2001, ISBN 0-07-290980-3 And special thanks to Dr. Tim Pratt of VT, primary author of ECE 5635 TCOM 707

  9. TCOM 707 Lecture 1 Outline • Introduction to Radar Systems • Background • Time, frequency, and spectrum considerations • Range calculations • Pulse repetition frequency issues • Derivation of radar equation • Radar applications TCOM 707

  10. Background – 1 • RADAR = Radio Detection And Ranging • Detection of targets (primary – skin reflection) • Range (time delay) • Velocity (differential time delay or Doppler) • Angle (azimuth) • Target Characteristics (echo properties) • Ground mapping (under, above, space) TCOM 707

  11. Background – 2 • Radar principles: • Transmit a very short (~ 1s) burst of radio waves (usually at microwave frequencies) • Wait for reflected radiowaves (the “echo”) to come back to the radar • Process the returned signal (the echo) using radar parameters TCOM 707

  12. Background – 3 • Echo Strength • This is proportional to the Radar Cross Section (RCS) of the target, and it tells us about the SIZE of the target in radar terms • Delay Time • This is proportional to the range from the radar to the target (and back!) TCOM 707

  13. Background – 4 scatterer Short RF pulse (kW) t1 Received pulse (pW) Time delay = t2 – t1 = td t2 TCOM 707

  14. Necessitated by imminence of WW II Background – 5 • First radar was Chain Home • Primitive ‘COTS’ approach • HF (four spot frequencies, 20 to 55 MHz) • Tall transmit towers • Dipole detectors • A-Scan display We’ll take a brief look at CH For more details, please visit http://www.radarpages.co.uk/mob/ch/chainhome.htm TCOM 707

  15. Chain Home – 1 “Curtain Array” Receive crossed dipoles 360´ 240´ Transmit Receive TCOM 707

  16. Chain Home – 2 Transmit towers The radar did not track – it merely ‘floodlit’ the area to be investigated. Receive lobes were similar Backlobe Forwardlobe Plan view of transmit facility with a schematic of the antenna pattern TCOM 707

  17. Chain Home – 3 Here, five CH radars cover a large section of the coast TCOM 707

  18. Chain Home – 4 Possible targets Movement of radar trace Amplitude Possible targets Clutter ? Clutter Distance A-Scan display PPI display TCOM 707

  19. Background – 6 • CH and all subsequent surveillance radars are Primary Radars • Primary Radars use skin echo to detect targets • Most airports and controlled airspaces use both Primary and Secondary Radars • Secondary radars relies on a cooperative target to relay information from a transponder TCOM 707

  20. 1see http:/virtualskies.arc.nasa.gov/communication/youDecide/Transponder and http://www.trvacc.org/web/training/ref/squak.asp Background – 7 • Secondary radars transmit an encoded signal to the target’s transponder • The transponder replies with an encoded message with information about the airplane • A typical transponder can be set to any of 4096 identifying codes1 • Military transponders are called IFF (Identification, Friend or Foe) TCOM 707

  21. TCOM 707 Lecture 1 Outline • Introduction to Radar Systems • Background • Time, frequency, and spectrum considerations • Range calculations • Pulse repetition frequency issues • Derivation of radar equation • Radar applications TCOM 707

  22. Time, frequency, and spectrum considerations – 1 c = f , where c = velocity of light in vacuo = 3  108 m/s, f = frequency, in Hz and  = wavelength, in metersExample:What is the wavelength for a frequency of 3 GHz?Answer:Wavelength =  = c/f = (3  108)/(3  109) = 10-1 = 0.1m = 10 cm Important note on units TCOM 707

  23. Time, frequency, and spectrum considerations – 2 • Radar engineers use a wide mix of units: • Miles, yards, meters, nautical miles, knots, hours, etc. • Calculations are easier if a standard set of units are used • The international standards for electrical engineers is the MKS system • meters, kilograms, seconds Do NOT mix units! TCOM 707

  24. Time, frequency, and spectrum considerations – 3 Scaling in MKS units 1,000 or 103 kilo k  1,000,000 or 106 Mega M  1,000,000,000 or 109 Giga G  1,000,000,000,000 or 1012 Tera T  1,000 (or  10-3) milli m  1,000,000 (or  10-6) micro   1,000,000,000 (or  10-9) nano n  1,000,000,000,000 (or  10-12) pico p  1,000,000,000,000,000 (or  10-15) femto f TCOM 707

  25. Time, frequency, and spectrum considerations – 4A • All radio waves are polarized • The direction of the E field defines the polarization sense Direction of travel (z-axis) E = Electric fieldH = Magnetic field This is a linearly polarized wave E E, H, and z-axes are mutually orthogonal H TCOM 707

  26. Time, frequency, and spectrum considerations – 4B • The E vector may rotate – leading to another special case: Circular Polarization E = Electric field This is a right hand circularly polarized wave Direction of travel (z-axis) E TCOM 707

  27. Time, frequency, and spectrum considerations – 5 The E and H fields vary sinusoidally at the frequency of the wave and with distance from the source (and reflector) Direction of travel (z-axis) This is a linearly polarized wave E H TCOM 707

  28. Time, frequency, and spectrum considerations – 6 • Radio waves are reflected by smooth conducting surfaces; e.g. a metal sheet, water • Treat reflection using ray theory, as in optics. Normal to surface Incident ray Reflected ray   TCOM 707

  29. Time, frequency, and spectrum considerations – 7A • Non-conductive materials allow radio waves to pass through, but …. • If dielectric constant  1.0 (air), partial reflection will occur Medium 1 Medium 2 Incident ray Partially reflected ray Partially transmitted ray TCOM 707

  30. Time, frequency, and spectrum considerations – 7B • Can take the real part of the dielectric constant = refractive index = n • reflection coefficient, ,can be found from the two refractive indices of media 1 and 2  = 1 - (n1 - n2)2 (n1 + n2)2 TCOM 707

  31. Time, frequency, and spectrum considerations – 8 • How to measure the energy of a radio wave? • Difficult to measure volts and amps above about 100 MHz • Can measure power (watts) • All radar calculations are carried out in Watts • but more likely in W, nW, pW, etc.; • or in dBW, dBm, etc. Preferred units for link budget calculations TCOM 707

  32. Time, frequency, and spectrum considerations – 9 • All radio signals have a defined bandwidth • Many definitions of bandwidth • null-to-null, 3 dB, absolute, noise, etc. • In general, bandwidth =amount of frequency space occupied by the signal • Some examples are • FM radio (200 kHz) • Analog TV (video + sound = 6 MHz) Otherwise known as spectrum occupancy TCOM 707

  33. Time, frequency, and spectrum considerations – 10A • Bandwidth (spectrum) is related to the time waveform through the Fourier transform, V(f) • Rectangular pulse  {(sin x)/(x)} spectrum V(f) This is a “Two-sided” spectrum V(t) t (s) f (Hz) 0 T -2/T -1/T +1/T +2/T 0 TCOM 707

  34. Time, frequency, and spectrum considerations – 10B V(t) t (s) 0 T V(f) This is a “One-sided” spectrum Radar pulse at a carrier frequency of fc f (Hz) fc -2/T fc -1/T fc +1/T fc +2/T fc TCOM 707

  35. Time, frequency, and spectrum considerations – 11 • Radio receiver bandwidth is defined by filters (usually at IF) • Noise bandwidth = B Hz Baseband Passband Ideal V(f) V(f) Real f f 0 B fc - B/2 fc fc + B/2 TCOM 707

  36. TCOM 707 Lecture 1 Outline • Introduction to Radar Systems • Background • Time, frequency, and spectrum considerations • Range calculations • Pulse repetition frequency issues • Derivation of radar equation • Radar applications TCOM 707

  37. Range Calculation - 1 • Velocity, v, = distance/time • Can assume v = 3  108 m/s = 300 m/s • Round trip distance = 150 m/sExample: if the delay is 1,500 s, the range to the target is 225 km • Some useful numbersTime delay = 1 s per 150 m of target range Time delay for a target at 1 km = 6.67 s TCOM 707

  38. Range Calculation - 2 • Range, R = (c TR)/2 (eqn. 1.1 in Skolnik)where TR is the time taken for the round trip of the pulse from the radar to the target and back again, in seconds. The factor 2 appears in the denominator because of the two-way (round- trip) propagation.With the range in kilometers (km) or nautical miles (nmi), and TR in microseconds (s), eqn. (1.1) becomes • R(km) = 0.15TR(s) or R(nmi) = 0.081 TR (s) Example TCOM 707

  39. Range Calculation - 3 What is the range in kilometers and nautical miles to a target with a time delay of 27 s? R(km) = 0.15TR(s) or R(nmi) = 0.081 TR (s) = 0.15  27 or = 0.081  27 = 4.05 km or = 2.187 nmi This calculation is for a single pulse. Most radars send more than one pulse to provide for sample averaging and updates on target position in the required time interval for tracking resolution. Echo from a distant target can arrive after the second pulse in the pulse train, leading to range ambiguities TCOM 707

  40. Range Calculation – 4A Target #2, range 18 km Target #1, range 6 km Primary radar prf = 10 kHz Time, seconds TCOM 707

  41. Range Calculation – 4B Target #2, range 18 km A prf of 10 kHz gives one pulse every 0.0001 s = 0.1 ms Target #1, range 6 km Primary radar prf = 10 kHz Remembering Range in km = 0.15TR(s), let’s look at the A-scan Time, seconds TCOM 707

  42. Range Calculation – 5 A range of 6 km gives a delay time of 40 s and a range of 18 km gives a delay time of 120 sNote that target #2 is so far away that the echo does not reach the radar until after the next pulse, giving an incorrect range of 3 km Amplitude Transmit pulse Transmit pulse Target #1 Target #2 Target #1 Time, t, in ms 0 0.04 0.1 0.12 0.14 TCOM 707

  43. TCOM 707 Lecture 1 Outline • Introduction to Radar Systems • Background • Time, frequency, and spectrum considerations • Range calculations • Pulse repetition frequency issues • Derivation of radar equation • Radar applications TCOM 707

  44. Pulse Repetition Frequency Issues – 1 Equation 1.2 in Skolnik • Unambiguous range = Runamb=c/(2fp)where fp = the pulse repetition frequency (prf) • NOTE:Keep the units the same! If the velocity of light is in m/s, the range will be in meters • Example:fp = 1 kHz = 1,000 HzRunamb = c/(2fp) = (3  108)/(2  1,000) = 1.5  105 = 150 km TCOM 707

  45. Pulse Repetition Frequency Issues – 2 Example: We require an unambiguous range of at least 200 km. What is the maximum prf to meet this requirement?Round trip time = tp = (2  range)/c seconds = (2  2  105)/(3  108) seconds = 1.33  10-3 seconds = 1.33 msThus max. prf = fp = 1/tp = 1/(1.33  10-3) = 751.8797  750 Hz Alternatively, since Runamb= c/(2fp), fp = c/(2  200 103) = (3  108)/(2  200 103) = 750 Hz TCOM 707

  46. Pulse Repetition Frequency Issues – 3 • Typical prf values • 300 Hz long range radar – 500 km max. range(strategic defense and airport facilities) • 8,000 Hz very short range radar – 18.75 km max. range(local defense against missiles) • 300 – 1,700 Hz are widely used values of prf C- and S-band radars Ku- and Ka-band radars TCOM 707

  47. Radar Frequencies – 1 Specific radiolocationBand Nominal (radar) bands based on ITUdesignation frequency range assignments for Region 2HF 3 – 30 MHzVHF 30 – 300 MHz 138 – 144; 216 – 225 MHzUHF 300 – 1000 MHz 420 – 450; 890 – 942 MHzL 1000 – 2000 MHz 1215 – 1400 MHz S 2000 – 4000 MHz 2300 – 2500; 2700 – 3700 MHzC 4000 – 8000 MHz 5250 – 5925 MHzX 8000 – 12,000 MHz 8500 – 10680 MHzKu 12 – 18 GHz 13.4 – 14.0; 15.7 – 17.7 GHz K 18 – 27 GHz 24.05 – 24.25 GHzKa 27 – 40 GHz 33.4 – 36.0 GHzmm 40 – 300 GHz Table 1.1 in Skolnik TCOM 707

  48. Radar Frequencies – 2 • Low frequencies (<6 GHz) • Little rain attenuation, hence • Long(er) range, which requires • High(er) power and • Low prf • Large dead zone possible • Simpler T/R cell design • Best for large area defense TCOM 707

  49. Radar Frequencies – 3 • High frequencies (>8 GHz) • Rain attenuation becoming significant, hence • Short(er) range, which can use • Low(er) power and • High prf • Large dead zone NOT possible • More complicated T/R cell design • Best for local defense Eased by low power needs TCOM 707

  50. Radar Frequencies – 4 High frequencies and elevation angles, very directive Plane wavefront launched by radar As frequencies/ elevation angles reduce, energy forms strong ground wave and can also produce some scattered energy over the horizon (OTH) TCOM 707

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