Course Sampler From ATI Professional Development Short Course                         Antenna and Antenna Array Fundamenta...
www.ATIcourses.comBoost Your Skills                                             349 Berkshire Drive                       ...
What you will learn from this course• Basic antenna concepts and definitions• The appropriate antenna for your  applicatio...
3Copyright 2012 © by Steven Weiss – all rights reserved
Example of a “Real World” Radar Antenna Array The MU (Middle and Upper atmosphere) radar constructed by the Radio Atmosphe...
Examples of AntennasThe VLA is an array of telescopes that can be linked                 CSIRO Parkes radio telescope is t...
Radio TelescopeArecibo, Puerto Rico 305m in Diameter                                                                      ...
Missile Defense   Eglin FPS-85 radar located near Ft. Walton                       Working inside a 10-story Pave Phased A...
European Remote Sensing satellite (ERS)                              Inmarsat     Provides information about the          ...
9Copyright 2012 © by Steven Weiss – all rights reserved
10Copyright 2012 © by Steven Weiss – all rights reserved
Types of Antennas•   Electrically small antennas•   Resonant antennas•   Broadband antennas•   Aperture antennas          ...
Electrically Small AntennasThe extent of the antenna structure is much less than the wavelength• Very low directivity• Low...
Resonant Antennas  The antenna operates well at a single or selected narrow frequency band  • Low to moderate gain  • Real...
Broadband AntennasThe pattern, gain, and impedance remain acceptable and are nearly constantover a wide frequency range. T...
Aperture AntennasHave a physical aperture through which the waves flow.• High Gain• Gain increases with frequency• Moderat...
Basic Concepts•   Directivity•   Gain•   Antenna Patterns•   Beamwidth•   Polarization•   Bandwidth•   Radiation Resistanc...
What is the directivity of antenna? Ratio of radiation intensity in a given direction      to the radiation intensity that...
Simple Illustration (light bulb)        Radiating with equal intensity in all           directions (isotropic radiation)  ...
Directivity and Gain•   The directivity can be thought of as the ratio of the maximum radiation    intensity emanating fro...
Formulas for Directivity and Gain              U  ,                                         U   ,   max D  ,  ...
A Directed Beam is Described by its         Antenna Pattern                                                               ...
More Details about Radiation         Patterns                                        Beamwidth (between 3 dB points)      ...
PatternsOmni-directional pattern          Hemispherical pattern                                  Equal power everywhere   ...
Polarization• Electric fields must be aligned for maximum  power transfer between two antennas.• The alignment is describe...
An Introduction to Polarization• When speaking of “polarization,” we are describingthe behavior of electric field of the a...
An Introduction to PolarizationHere is an interesting antenna that has two input ports. We willdesignate these as port 1 a...
An Introduction to Polarization                                                           Port 2            Port 1        ...
An Introduction to PolarizationExciting port 1 causes an electric field to exist between the two horizontal fins  and the ...
An Introduction to PolarizationExciting port 2 causes an electric field to exist between the two vertical fins and the fie...
An Introduction to PolarizationWe already know that we can represent time-varying fields as phasors.If we excited both por...
An Introduction to Polarizationt            (a x  a y ) Cos (  t )               ˆ     ˆ                               ...
An Introduction to PolarizationNow we make one "small" change to our phasor representation of                             ...
An Introduction to Polarizationt       a x Cos (  t )  a y Sin (  t )         ˆ                 ˆ 0                   ...
An Introduction to PolarizationIs it right-hand or left-hand polarization?1) Place your thumb towards the direction of pro...
An Introduction to PolarizationSo, is left-hand polarization counterclockwise and right-hand clockwise?Answer: Not enough ...
An Introduction to Polarization                                                                       Port 2              ...
An Introduction to Polarization                                                                       Port 2              ...
An Introduction to PolarizationWe could achieve circular polarization with and RF source, a power splitter, and a 90 Degre...
Polarization (elliptical) y , x   Assume any valueEx , E y       Not necessarily equal                     OAAR  Axial ...
CP MeasurementsAxial Ratio                Copyright 2012 © by Steven Weiss – all rights reserved
Polarization Loss Factor                                                   2                         EInc  ETrans        ...
Polarization Polarization is a critical issue when considering antennas    Proper alignment – Maximum power transferred fr...
Bandwidth• There are 3 equivalent ways do describe the  bandwidth of an antenna  – Return loss (-10 dB convention)  – VSWR...
Definition of the Reflection CoefficientCharacteristic impedance of the transmission line                                T...
Reflected Power                               r  j i   r  j i                                       2  ...
Bandwidth – A Logarithmic PlotA return loss of -10 dB is conventionally defines as the bandwidth of the antenna           ...
Bandwidth – VSWR Plot                                                               1             21.75                ...
Bandwidth – Polar Plot                                                                        I  Bandwidth  f H  f L   ...
Bandwidth – Polar Plot/Smith Chart From transmission line theory                                                 I       ...
Realized (or actual) GainGrealized  ( 1   ) Go  ( 1   )  Do                           2                            ...
Bandwidth – Equivalent Quantities           Return Loss                       VSWR                      1              ...
Antenna Impedance                                    (Transmit)                             The input impedance is the    ...
Input Impedance of Antennas (Transmit)          Vg                               Vg                                       ...
Input Impedance of Antennas (transmit)              2         Vg      Rr                    Radiated power assuming conjug...
Antenna Impedance                                (receive)                        Again, the input impedance is           ...
Input Impedance of Antennas (receive) Assuming conjugate matched conditions delivering the maximum power to the antenna.  ...
Reciprocity for Antennas                                          V2 ( ,  )                                             ...
Aperture Size• Antenna engineers frequently discuss antennas in  terms of Aperture Size.• A common term is the “effective ...
Effective Aperture Size• The effective aperture size is a relationship between the  incident electromagnetic field and the...
Effective Aperture Size• The effective aperture size is related to the directivity of the antenna• Anything that diminishe...
Physical Aperture Size and            Aperture Efficiency   Area  Length x Width                                Area   ...
Friis Transmission Formula                                                              62     Copyright 2012 © by Steven ...
Friis Transmission FormulaTime average power density transmitted by satellite                                        Satel...
Communication Link    Gt ( t , t )                                                            Gr ( r , r )            ...
Communication Links in dBm                                 Power Milliwatts             Pr (dBm)  10 Log10            ...
The Friis Transmission Formula                                                              Our work with the Friis transm...
Much more!!!                                                         67Copyright 2012 © by Steven Weiss – all rights reser...
To learn more please attend ATI course        Hyperspectral and Multispectral Imaging    Please post your comments and que...
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Antenna & Array Fundamentals Technical Training Courses Sampler

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This three-day course teaches the basics of antenna and antenna array theory. Fundamental concepts such as beam patterns, radiation resistance, polarization, gain/directivity, aperture size, reciprocity, and matching techniques are presented. Different types of antennas such as dipole, loop, patch, horn, dish, and helical antennas are discussed and compared and contrasted from a performance - applications standpoint. The locations of the reactive near-field, radiating near-field (Fresnel region), and far-field (Fraunhofer region) are described and the Friis transmission formula is presented with worked examples. Propagation effects are presented. Antenna arrays are discussed, and array factors for different types of distributions (e.g., uniform, binomial, and Tschebyscheff arrays) are analyzed giving insight to sidelobe levels, null locations, and beam broadening (as the array scans from broadside.) The end-fire condition is discussed. Beam steering is described using phase shifters and true-time delay devices. Problems such as grating lobes, beam squint, quantization errors, and scan blindness are presented. Antenna systems (transmit/receive) with active amplifiers are introduced. Finally, measurement techniques commonly used in anechoic chambers are outlined. The textbook, Antenna Theory, Analysis & Design, is included as well as a comprehensive set of course notes.

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Antenna & Array Fundamentals Technical Training Courses Sampler

  1. 1. Course Sampler From ATI Professional Development Short Course Antenna and Antenna Array Fundamentals Instructor: Dr. Steven WeissATI Course Schedule: http://www.ATIcourses.com/schedule.htmATIs Antenna & Array: http://www.aticourses.com/antenna_and_antenna_array_fundamentals.htm
  2. 2. www.ATIcourses.comBoost Your Skills 349 Berkshire Drive Riva, Maryland 21140with On-Site Courses Telephone 1-888-501-2100 / (410) 965-8805Tailored to Your Needs Fax (410) 956-5785 Email: ATI@ATIcourses.comThe Applied Technology Institute specializes in training programs for technical professionals. Our courses keep youcurrent in the state-of-the-art technology that is essential to keep your company on the cutting edge in today’s highlycompetitive marketplace. Since 1984, ATI has earned the trust of training departments nationwide, and has presentedon-site training at the major Navy, Air Force and NASA centers, and for a large number of contractors. Our trainingincreases effectiveness and productivity. Learn from the proven best.For a Free On-Site Quote Visit Us At: http://www.ATIcourses.com/free_onsite_quote.aspFor Our Current Public Course Schedule Go To: http://www.ATIcourses.com/schedule.htm
  3. 3. What you will learn from this course• Basic antenna concepts and definitions• The appropriate antenna for your application• Factors that affect antenna array designs and antenna systems• Measurement techniques commonly used in anechoic chambers Copyright 2012 © by Steven Weiss – all rights reserved
  4. 4. 3Copyright 2012 © by Steven Weiss – all rights reserved
  5. 5. Example of a “Real World” Radar Antenna Array The MU (Middle and Upper atmosphere) radar constructed by the Radio Atmospheric Science Center of Kyoto University at Shigaraki, Shiga prefecture, Japan• Investigates atmospheric and plasma dynamics in the wide region from the troposphere to the ionosphere.• The radar is a powerful monostatic pulse Doppler radar operating at 46.5MHz• It uses active phased array antenna, which consists of 475 crossed Yagi antennas and identical number of solid-state transmit/receive modules.• The antenna beam direction can be switched to any direction within the steering range of 30deg from zenith from pulse to pulse.• The antenna aperture is 8,330m^2 (103m in diameter), and the peak and average output power is 1MW and 50kW, respectively.• The antenna beam has a conical shape with the round-trip (two-way) half-power beamwidth of 2.6deg. 4 Copyright 2012 © by Steven Weiss – all rights reserved
  6. 6. Examples of AntennasThe VLA is an array of telescopes that can be linked CSIRO Parkes radio telescope is the largest and oldesttogether to synthesize the resolving power of a telescope of the eight antennas comprising the Australianupto 36 km (22 miles) across, or grouped together to Telescope National Facility. The Compact Array of sixsynthesize one only a km (0.6 mile) across: the varying 22-metre dishes near Narrabri and another nearresolutions are the equivalent of an astronomical zoom Coonabarabran link up with the 64 meter Parkes tolens. This array is located near Socorro, NM synthesize a telescope some 300 kilometers across. 5 Copyright 2012 © by Steven Weiss – all rights reserved
  7. 7. Radio TelescopeArecibo, Puerto Rico 305m in Diameter 6 Copyright 2012 © by Steven Weiss – all rights reserved
  8. 8. Missile Defense Eglin FPS-85 radar located near Ft. Walton Working inside a 10-story Pave Phased Array Warning System, or Pave PAWS, the men and women of the 7th Space WarningBeach, FL. This phased array radar is a dedicated Squadron continuously scan the horizon for missiles, satellites and sensor to the U.S. satellite catalog. other man-made objects in space. 7 Copyright 2012 © by Steven Weiss – all rights reserved
  9. 9. European Remote Sensing satellite (ERS) Inmarsat Provides information about the Used for Global Communications Earth’s land, oceans and polar caps 8 Copyright 2012 © by Steven Weiss – all rights reserved
  10. 10. 9Copyright 2012 © by Steven Weiss – all rights reserved
  11. 11. 10Copyright 2012 © by Steven Weiss – all rights reserved
  12. 12. Types of Antennas• Electrically small antennas• Resonant antennas• Broadband antennas• Aperture antennas 11 Copyright 2012 © by Steven Weiss – all rights reserved
  13. 13. Electrically Small AntennasThe extent of the antenna structure is much less than the wavelength• Very low directivity• Low input resistance• High input reactance• Low radiation efficiency   Short Dipole   Small Loop 12 Copyright 2012 © by Steven Weiss – all rights reserved
  14. 14. Resonant Antennas The antenna operates well at a single or selected narrow frequency band • Low to moderate gain • Real input impedance • Narrow bandwidth   ~ ~ 2 2Half-wave Dipole  ~ 2 Yagi Microstrip Patch 13 Copyright 2012 © by Steven Weiss – all rights reserved
  15. 15. Broadband AntennasThe pattern, gain, and impedance remain acceptable and are nearly constantover a wide frequency range. They are characterized by an active region witha circumference of one wavelength or an extent of a half-wavelength whichrelocates on the antenna as the frequency changes• Low to moderate gain• Constant gain• Real input impedance• Wide Bandwidth Spiral Log-periodic dipole array 14 Copyright 2012 © by Steven Weiss – all rights reserved
  16. 16. Aperture AntennasHave a physical aperture through which the waves flow.• High Gain• Gain increases with frequency• Moderate bandwidth Aperture Aperture 15 Copyright 2012 © by Steven Weiss – all rights reserved
  17. 17. Basic Concepts• Directivity• Gain• Antenna Patterns• Beamwidth• Polarization• Bandwidth• Radiation Resistance/Input impedance• Reciprocity• Effective Aperture 16 Copyright 2012 © by Steven Weiss – all rights reserved
  18. 18. What is the directivity of antenna? Ratio of radiation intensity in a given direction to the radiation intensity that would be obtained if the total power radiated by the antenna were to be radiated isotropically What is the gain of antenna?Ratio of radiation intensity in a given direction to the radiation intensity that would be obtained if the total power accepted by the antenna were to be radiated isotropically 17 Copyright 2012 © by Steven Weiss – all rights reserved
  19. 19. Simple Illustration (light bulb) Radiating with equal intensity in all directions (isotropic radiation) Power meter reading radiated power (isotropic) P (isotropic) Radiation is focused in a particular direction due to the reflector Power meter reading of radiated power (in a given direction) P (direction) 18 Note that polarization must –be considered with RF antennas Copyright 2012 © by Steven Weiss all rights reserved
  20. 20. Directivity and Gain• The directivity can be thought of as the ratio of the maximum radiation intensity emanating from an antenna to the total power leaving the antenna radiated isotropically per solid angle of a sphere.• The radiation intensity of an isotropic source is: (Prad ) / (solid angle of a sphere). U isotropic  Pradiated / 4 • The gain of an antenna can be thought of as the ratio of the maximum radiation intensity emanating from an antenna to the total power introduced into the antenna: (Pin ) / (solid angle of a sphere).• Losses prevent the power input into the antenna from equaling the radiated power. Prad   Pin • The gain of an antenna is always less than the directivity of a antenna. 19 Copyright 2012 © by Steven Weiss – all rights reserved
  21. 21. Formulas for Directivity and Gain U  ,   U   ,   max D  ,    Do  Prad Prad 4 4 U  ,    U  ,   G  ,       D  ,   Pin Prad 4 4 U   ,   max  U   ,   max Go     Do Pin Prad 4 4 Gain is usually expressed in log form : G dBi  10 Log (  Do )  10 Log ( Do )  10 Log (  ) 20 Copyright 2012 © by Steven Weiss – all rights reserved
  22. 22. A Directed Beam is Described by its Antenna Pattern Main lobeSide lobes Back lobes 21 Copyright 2012 © by Steven Weiss – all rights reserved
  23. 23. More Details about Radiation Patterns Beamwidth (between 3 dB points) 22 Copyright 2012 © by Steven Weiss – all rights reserved
  24. 24. PatternsOmni-directional pattern Hemispherical pattern Equal power everywhere Isotropic patternEqual power in one plane. in upper half-plane. Equal power everywhere. 23 Copyright 2012 © by Steven Weiss – all rights reserved
  25. 25. Polarization• Electric fields must be aligned for maximum power transfer between two antennas.• The alignment is described by a polarization loss factor (PLF).• Analytically, the polarization loss factor is the electric field of the incoming wave dotted with the electric field that would be transmitted by the receiving antenna. 24 Copyright 2012 © by Steven Weiss – all rights reserved
  26. 26. An Introduction to Polarization• When speaking of “polarization,” we are describingthe behavior of electric field of the antenna.• The field may remain oriented in one direction as theelectric field propagates (linear polarization)• The field may spin as the electric field propagates(circular or elliptical polarization)• Polarization will be considered in detail later in thiscourse, but you already have enough material tounderstand how our math can describe such electricfields! 25 Copyright 2012 © by Steven Weiss – all rights reserved
  27. 27. An Introduction to PolarizationHere is an interesting antenna that has two input ports. We willdesignate these as port 1 and port 2 Port 2 Port 1 26 Copyright 2012 © by Steven Weiss – all rights reserved
  28. 28. An Introduction to Polarization Port 2 Port 1 Y Add somegeometry ! X 27 Copyright 2012 © by Steven Weiss – all rights reserved
  29. 29. An Introduction to PolarizationExciting port 1 causes an electric field to exist between the two horizontal fins and the field at the “aperture” of the antenna is oriented in the x-direction E  a x Eo ˆ Port 1 Y X 28 Copyright 2012 © by Steven Weiss – all rights reserved
  30. 30. An Introduction to PolarizationExciting port 2 causes an electric field to exist between the two vertical fins and the field at the “aperture” of the antenna is oriented in the y-direction E  a y Eo ˆ Port 2 Y X 29 Copyright 2012 © by Steven Weiss – all rights reserved
  31. 31. An Introduction to PolarizationWe already know that we can represent time-varying fields as phasors.If we excited both ports at once (with equal strength) , we expect thephasor representation of the electric field at the aperture to be of theform: E  a x Eo  a y Eo ˆ ˆThe time-dependent behavoir at the aperture becomes: j t (t )  Re[ (a x E o  a y E o ) e ˆ ˆ ]  (a x E o  a y E o ) Cos (  t ) ˆ ˆIt is illustrative to plot this electric field using certain "snapshots" of time.Holding "" as a constant, there is an instant when the product  t equalszero. Similarly, there are different instances when  t equals  /2 and and 3 /2 and so forth. Letting E o  1 V / m, we can make a table andparametrically plot the time-dependent electric field at the aperture. 30 Copyright 2012 © by Steven Weiss – all rights reserved
  32. 32. An Introduction to Polarizationt (a x  a y ) Cos (  t ) ˆ ˆ t   0 (a x  a y ) ˆ ˆ /2 0 X   (a x  a y ) ˆ ˆ t   /2 3 / 2 0 t  0 YThe y-axis is pointed downward so that the z-axis would be into the page.We observe the behavior of the electric field at z  0 (at the aperture.)The electric field is linearly polarized oriented at a 45 Degree angle with they-axis (the tilt angle " .") It is also at a 45 Degree angle with the x-axis,but we define the tilt angle with respect to the y-axis. 31 Copyright 2012 © by Steven Weiss – all rights reserved
  33. 33. An Introduction to PolarizationNow we make one "small" change to our phasor representation of ˆthe electric field at the aperture placing a "j" in front of the a y term:So, E  a x Eo  j a y Eo ˆ ˆThis term has a significant impact on the time-dependent behavoir ofthe elctric field: j t (t )  Re[ (a x E o  j a y E o ) e ˆ ˆ ]  Re[ (a x E o  j a y E o ) (Cos (  t )  j Sin (  t )) ] ˆ ˆ  a x E o Cos (  t )  a y E o Sin (  t ) ˆ ˆAgain, we hold "" as a constant and parametrically plot the time-dependent electric field at the aperture. Again, let E o  1 V / m. 32 Copyright 2012 © by Steven Weiss – all rights reserved
  34. 34. An Introduction to Polarizationt a x Cos (  t )  a y Sin (  t ) ˆ ˆ 0 ˆ ax /2 ay ˆ t   /2   ax ˆ3 / 2 ˆ ay X t   t  0  t  3 / 2 Y The electric field is spinning in a counter-clockwise direction! 33 Copyright 2012 © by Steven Weiss – all rights reserved
  35. 35. An Introduction to PolarizationIs it right-hand or left-hand polarization?1) Place your thumb towards the direction of propagation. This would beinto the page.2) If your fingers align with the "spin" you have answered the question!Try it with each hand and you will find that this example is left-handcircularly polarized (LHCP.) t   /2 X t   t  0  t  3 / 2 34 Copyright 2012 © by Steven Weiss – all rights reserved Y
  36. 36. An Introduction to PolarizationSo, is left-hand polarization counterclockwise and right-hand clockwise?Answer: Not enough information!You must state whether the field is "leaving" or "arriving."A thumb pointed away from you indicates a leaving wave.A thumb pointed toward you indicates an arriving wave. le ft-h a n d is le ft-h a n d is r ig h t-h a n d is r ig h t-h a n d isc o u n te rc lo c k w is e c lo c k w is e c lo c k w is e c o u n te r c lo c k w is e le a v in g a rr iv in g le a v in g a r r iv in g 35 Copyright 2012 © by Steven Weiss – all rights reserved
  37. 37. An Introduction to Polarization Port 2 Port 1 Y XThis antenna is capable of exciting orthogonal electric fields (i.e., in the x- and y-directions.) If the fields are excited in phase, the field leaving the antenna will be linearly polarized leaving the antenna at a 45 Degree angle – if the signal strength is the same at both feeds. For example: Port 1 = V o Cos (  t ) and Port 2 = V o Cos (  t ) 36 Copyright 2012 © by Steven Weiss – all rights reserved
  38. 38. An Introduction to Polarization Port 2 Port 1 Y X Again, the antenna is capable of exciting orthogonal electric fields (i.e., in the x- and y-directions.) If the fields are excited in phase quadrature, the field leaving the antenna will be circularly polarized – if the signal strength is the same at both feeds.For example: Port 1 = V o Cos (  t ) and Port 2 =  V o Sin (  t ) 37 Copyright 2012 © by Steven Weiss – all rights reserved
  39. 39. An Introduction to PolarizationWe could achieve circular polarization with and RF source, a power splitter, and a 90 Degree phase shifter. Power Splitter 90  RF Source 38 Copyright 2012 © by Steven Weiss – all rights reserved
  40. 40. Polarization (elliptical) y , x Assume any valueEx , E y Not necessarily equal OAAR  Axial Ratio   OB 1  AR   + for RH polarization - for LH polarization Tilt angle    1 1  2 E x E y    tan  cos    Ex 2  E y  2 2 2        39 x y Copyright 2012 © by Steven Weiss – all rights reserved
  41. 41. CP MeasurementsAxial Ratio Copyright 2012 © by Steven Weiss – all rights reserved
  42. 42. Polarization Loss Factor 2 EInc  ETrans PLF  2 2 EInc ETrans EInc ETrans w  ˆ a  ˆ EInc Etrans 2 PLF   w   a ˆ ˆThe electric fields are in phasor form and may be complex quantities Copyright 2012 © by Steven Weiss – all rights reserved 41
  43. 43. Polarization Polarization is a critical issue when considering antennas Proper alignment – Maximum power transferred from antenna A to antenna B.A B Antenna “A” transmits a Antenna “B” is oriented vertically polarized signal to receive a vertically polarized signalImproper alignment – Minimum power transferred from antenna A to antenna B.A B Antenna “A” transmits a Antenna “B” is oriented vertically polarized signal to receive a horizontally polarized signalCircular to linear – 1 / 2 the power transferred from antenna A to antenna B.A B Antenna “A” transmits a Antenna “B” is oriented to receive circularly polarized signal linear polarization in any direction 42 Copyright 2012 © by Steven Weiss – all rights reserved
  44. 44. Bandwidth• There are 3 equivalent ways do describe the bandwidth of an antenna – Return loss (-10 dB convention) – VSWR (2:1 convention) – Polar Plot (Smith chart)   0.316228 43 Copyright 2012 © by Steven Weiss – all rights reserved
  45. 45. Definition of the Reflection CoefficientCharacteristic impedance of the transmission line Transmitted Voltage V Zo V Reflected Voltage  Reflection Coefficient – a complex ratio of the V reflected voltage divided by the transmitted voltage   V measured at a defined reference place (e.g., the input port of the antenna. 44 Copyright 2012 © by Steven Weiss – all rights reserved
  46. 46. Reflected Power       r  j i   r  j i     2 * 2 2 r i  2  1   2  2   Percentage of power reflected from the antenna 1   2   Percentage of power entering the antennaNote that the power entering the antenna is not equal to the power radiatedby the antenna. Some power is consumed in conductor and other losses 45 Copyright 2012 © by Steven Weiss – all rights reserved
  47. 47. Bandwidth – A Logarithmic PlotA return loss of -10 dB is conventionally defines as the bandwidth of the antenna Bandwidth  f H  f L 0 fHfL -5 - 10 dB - 15 - 20 - 25 2 4 6 8 10 Frequency fo 46 Copyright 2012 © by Steven Weiss – all rights reserved
  48. 48. Bandwidth – VSWR Plot 1   21.75  1.51.25 The impedance mismatch between the 1 Antenna’s input impedance and the0.75 characteristic impedance of the 0.5 transmission line causes a standing wave to exist along the length of the0.25 transmission line. 0.2 0.4 0.6 0.8 1 Distance back from the reference plane Frequency1    6 5Bandwidth  f H  f L 4 V SWR 3 VSWR  1    2 fH 1    fL 1 fo 2 4 6 8 47 10 Copyright 2012 © by Steven Weiss – all rights reserved Frequency
  49. 49. Bandwidth – Polar Plot I Bandwidth  f H  f L   1Discrete Data pointsmeasured on a fLNetwork Analyzer R fH fo   0.316228 48 Copyright 2012 © by Steven Weiss – all rights reserved
  50. 50. Bandwidth – Polar Plot/Smith Chart From transmission line theory I ZL  Zo  R  j I  ZL  ZoWhen the real and fLimaginary parts of the loadimpedance aredetermined as a functionof the real and imaginary Rparts of the reflectioncoefficient, the resulting fH fHcircles and arcs define theSmith Chart.   0.316228 49 Copyright 2012 © by Steven Weiss – all rights reserved
  51. 51. Realized (or actual) GainGrealized  ( 1   ) Go  ( 1   )  Do 2 2 50 Copyright 2012 © by Steven Weiss – all rights reserved
  52. 52. Bandwidth – Equivalent Quantities  Return Loss VSWR 1  2 0.316228 -10 dB 1.9245 0.9 0.100000 -20 dB 1.2222 0.99 0.031622 -30 dB 1.0653 0.999 51 Copyright 2012 © by Steven Weiss – all rights reserved
  53. 53. Antenna Impedance (Transmit) The input impedance is the impedance presented by an antenna at its terminals generator a radiated waves Zg b Z A  RA  jX A radiation resistance RA  RR  RL 52Copyright 2012 © by Steven Weiss – all rights reserved
  54. 54. Input Impedance of Antennas (Transmit) Vg Vg From circuit theory Ig   ZA  Zg ( RR  RL  Rg )  j ( X A  X g ) 2 1 2 Vg  Rr Pr  I g RR    Power delivered to the 2 2  ( RR  RL  Rg ) 2  ( X A  X g ) 2    antenna for radiation Power dissipated as 2 1 2 Vg  RL PL  I g RL    heat on the antenna 2 2  ( RR  RL  Rg ) 2  ( X A  X g ) 2    2 Power dissipated as heat 1 2 Vg  Rg  on the internal resistance Pg  I g Rg    2 2  ( RR  RL  Rg ) 2  ( X A  X g ) 2  of the generator   ZA  Zg * Conjugate matched conditions deliver the the maximum power to the antenna. RR  RL  Rg X A  X g 53 Copyright 2012 © by Steven Weiss – all rights reserved
  55. 55. Input Impedance of Antennas (transmit) 2 Vg Rr Radiated power assuming conjugate matching Pr  8 ( RR  RL ) 2 2 Vg RL Dissipated power in the antenna assuming conjugate matching PL  8 ( RR  RL ) 2 2 2 Vg Rg Vg Dissipated power in the generator’s internal impedance Pg   8 ( RR  RL ) 2 8 RgThe total power is: Pg  PR  PL 2 Power supplied by the 1 Vg 1 generator : Pg  Vg I g  * 2 4 RR  RLTherefore, under conjugate match conditions, half the power that issupplied by the generator is dissipated as heat in its internal resistanceand the other half is delivered to the antenna. 54 Copyright 2012 © by Steven Weiss – all rights reserved
  56. 56. Antenna Impedance (receive) Again, the input impedance is the impedance presented by an antenna at its terminals 55Copyright 2012 © by Steven Weiss – all rights reserved
  57. 57. Input Impedance of Antennas (receive) Assuming conjugate matched conditions delivering the maximum power to the antenna. 2 VT Power delivered to the antenna’s terminating impedance PT  8 RT VT 2 RR  Power across the radiation resistance of the antennaPr    8  ( R R  R L )2     VT 2 RL PL   2  Power dissipated as heat due to the losses in the antenna 8  (R R RL )    56 Copyright 2012 © by Steven Weiss – all rights reserved
  58. 58. Reciprocity for Antennas V2 ( ,  ) I2 1 2 I1 V1 ( ,  ) Transmitting pattern of antenna “1” Receiving pattern of antenna “2” V2 ( ,  ) V2 ( ,  ) Z12 ( ,  )  Z 21 ( ,  )  I1 I1 Z12 ( ,  )  Z 21 ( ,  )Important Point!!! The transmit and receive patterns of an antenna are the same for a reciprocal antenna. 57 Copyright 2012 © by Steven Weiss – all rights reserved
  59. 59. Aperture Size• Antenna engineers frequently discuss antennas in terms of Aperture Size.• A common term is the “effective aperture” size.• Another term is the “physical aperture” size.• Aperture size is related to the beamwidth and accordingly the directivity and gain. ZL 58 Copyright 2012 © by Steven Weiss – all rights reserved
  60. 60. Effective Aperture Size• The effective aperture size is a relationship between the incident electromagnetic field and the power delivered to the terminating impedance on the antenna’s input port. PT Aeffective  (m 2 ) Wincident PT  The power developed across the terminating impedance (w)Wincident  The strength of the incident electromagnetic field at the aperture of the antenna (w/m 2 ) PT Wincident ZL 59 Copyright 2012 © by Steven Weiss – all rights reserved
  61. 61. Effective Aperture Size• The effective aperture size is related to the directivity of the antenna• Anything that diminishes the power across the terminating impedance decreases the effective aperture size• If no power develops across the terminating impedance, the effective aperture size is zero - even if there is an incident electromagnetic field. 2 Ae m  DO (m 2 ) 4 PT 2 2 Ae    cd  (1   ) DO w  a 2 ˆ ˆ (m 2 ) W inc 4 PT Wincident ZL 60 Copyright 2012 © by Steven Weiss – all rights reserved
  62. 62. Physical Aperture Size and Aperture Efficiency Area  Length x Width Area   r 2 Ae m Maximium Effective Aperture ap   Ap Physical Area 61 Copyright 2012 © by Steven Weiss – all rights reserved
  63. 63. Friis Transmission Formula 62 Copyright 2012 © by Steven Weiss – all rights reserved
  64. 64. Friis Transmission FormulaTime average power density transmitted by satellite Satellite Antenna Pr  W Aer effective aperture of Pt , Gt receiving antenna R total transmitted power Gr dish antenna Pt W Gt gain of transmitting antenna 4 R 2 4 2 Gr  2 Aer so Aer  Gr  4  2 Friis transmission formula Pr  Pt Gt Gr (4 R) 2 63 Copyright 2012 © by Steven Weiss – all rights reserved
  65. 65. Communication Link Gt ( t , t ) Gr ( r , r ) R ZLPr  2  (1  t ) (1   r ) ( ) Gt ( t ,  t ) Gr ( r ,  r )  w  a 2 2 2 ˆ ˆPt 4 R 64 Copyright 2012 © by Steven Weiss – all rights reserved
  66. 66. Communication Links in dBm  Power Milliwatts  Pr (dBm)  10 Log10    1 Milliwatt  2Friis transmission formula Pr  Pt Gt Gr (4 R) 2 G (dB)  10 log GDivide each side by 1 mw and take the logPr (dBm)  Pt (dBm)  Gt (dB)  Gr (dB )  20 log R (km)  20 log f ( MHz )  32.44 c C = Speed of light Note:   f F = frequency 65 Copyright 2012 © by Steven Weiss – all rights reserved
  67. 67. The Friis Transmission Formula Our work with the Friis transmission formula presumed a rather pristine environment where one did not have to worry about the attenuation through the atmosphere. Of course, these effects cannot be ignored. Shown to the left is a plot of attenuation effects due to oxygen and water vapor. Accordingly, any link budget would need to be adjusted to take these (and other) propagation effects into account. At this point we begin to leave the study of antenna theory and enter the realm of propagation theory.R. E. Collin, Antennas and Radiowave Propagation, New York, McGraw Hill, 1985, pp 409. 66 Copyright 2012 © by Steven Weiss – all rights reserved
  68. 68. Much more!!! 67Copyright 2012 © by Steven Weiss – all rights reserved
  69. 69. To learn more please attend ATI course Hyperspectral and Multispectral Imaging Please post your comments and questions to our blog: http://www.aticourses.com/blog/ Sign-up for ATIs monthly Course Schedule Updates :http://www.aticourses.com/email_signup_page.html

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