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Introduction   An antenna is an electrical conductor or    system of conductors       Transmission - radiates electromag...
Antenna Definition   An antenna is a circuit element that    provides a transition form a guided    wave on a transmissio...
Antenna Definition-cont’d   In transmit systems the RF signal is    generated, amplified, modulated and    applied to the...
Reciprocity   An antenna ability to transfer energy form    the atmosphere to its receiver with the same    efficiency wi...
Polarization   Polarization is the direction of the electric    field and is the same as the physical attitude    of the ...
Types of Antennas   Isotropic antenna (idealized)       Radiates power equally in all directions   Dipole antennas    ...
Directional Antenna                 beamwidthMax power            •   A   Radiated energy is                             f...
Beamwidth   Beamwidth is the angular    separation of the half-power points    of the radiated pattern
Half-wave Dipole (Hertz) Antenna   An antenna having a physical length    that is one-half wavelength of the    applied f...
Vertical (Marconi) Antenna   Vertical   Antennas    are used for    frequencies under 2 MHz. It uses a    conducting path...
Vertical (Marconi) Antenna – cont’d   Poor grounding conditions of the    earth/soil surrounding the antenna can    resul...
Counterpoise   Counterpoise    is a grounding grid    established where the earth grounding    cannot satisfy electrical ...
Counterpoise-cont’d                    radius = ¼          antenna           supports
Antenna Array   Antenna array is a group of antennas or antenna    elements arranged to provide the desired directional  ...
Yagi-Uda Antenna   The Yagi-Uda antenna is a simple    form of a directional antenna based    off of a reflector placed /...
Yagi-Uda Antenna-cont’dreflector                           /4                 dipole                 antenna
Radiated Directed Signalantenna    2 dipole radiated signal    2 dipole radiated signal   without reflector           with...
The Antenna Formula         c          186,000 mi sec                 frequency of the signal•c is the speed of light  is ...
The Antenna Formula - applied   If a half-wave dipole antenna needed to    be constructed for a 60 Hz signal, how    larg...
Radiation & Induction Fields   The mechanics launching radio    frequencies from an antenna are not    full understood. T...
Radiation & Induction Fields-cont’d   There are two induction fields or areas    where signals collapse and radiate from ...
Radiation & Induction Fields-cont’d                        2              R    2DWhere:   R = the distance from the antenn...
Radiation Resistance   Radiation Resistance is the portion of    the antenna’s impedance that results in    power radiate...
Effective Radiated Power (ERP)   ERP is the power input value and the    gain of the antenna multiplied together       d...
Radiation Pattern   Radiation pattern is an indication of    radiated field strength around the    antenna. Power radiate...
Radiation Patterns   Radiation pattern     Graphical representation of radiation properties      of an antenna     Depi...
Radiation Pattern for Vertical Antennas                         /4/2            antenna
Antenna Gain   Antenna gain       Power output, in a particular direction,        compared to that produced in any direc...
Antenna Gain   Antenna gain is the measure in dB how    much more power an antenna will    radiate in a certain direction...
Antenna Gain   Relationship between antenna gain and effective    area                                          2        ...
Propagation Modes   Ground-wave propagation   Sky-wave propagation   Line-of-sight propagation
Ground Wave Propagation
Ground Wave Propagation   Follows contour of the earth   Can Propagate considerable distances   Frequencies up to 2 MHz...
Sky Wave Propagation
Sky Wave Propagation   Signal reflected from ionized layer of atmosphere    back down to earth   Signal can travel a num...
Line-of-Sight Propagation
Line-of-Sight Propagation   Transmitting and receiving antennas must be    within line of sight       Satellite communic...
Line-of-Sight Equations   Optical line of sight                d     3.57 h   Effective, or radio, line of sight        ...
Line-of-Sight Equations   Maximum distance between two antennas    for LOS propagation:            3.57         h1       ...
LOS Wireless Transmission Impairments   Attenuation and attenuation distortion   Free space loss   Noise   Atmospheric...
Thermal Noise   Thermal noise due to agitation of electrons   Present in all electronic devices and    transmission medi...
Noise Terminology   Intermodulation noise – occurs if signals with    different frequencies share the same medium       ...
Other Impairments   Atmospheric absorption – water vapor and    oxygen contribute to attenuation   Multipath – obstacles...
Multipath Propagation
Multipath Propagation   Reflection - occurs when signal encounters a    surface that is large relative to the wavelength ...
The Effects of Multipath              Propagation   Multiple copies of a signal may arrive at    different phases       ...
Types of Fading   Fast fading   Slow fading   Flat fading   Selective fading   Rayleigh fading   Rician fading
Error Compensation Mechanisms   Forward error correction   Adaptive equalization   Diversity techniques
Forward Error Correction   Transmitter adds error-correcting code to data    block       Code is a function of the data ...
Adaptive Equalization   Can be applied to transmissions that carry analog    or digital information       Analog voice o...
Antenna Height   Antenna height above the ground is directly    related to radiation resistance. Ground    reflections ca...
Smart Antennas
Smart Antennas   smart antennas are base station antennas    with a pattern that is not fixed, but adapts to    the curre...
Smart Antennas-cont’d   Major drawbacks and cost factors    include increased transceiver complexity    and more complex ...
Smart Antennas-cont’d   The idea of smart antennas is to use base    station                      that are         , but ...
Smart Antennas-cont’d   Smart antennas add a new way of separating    users, namely by space, through SDMA    (space divi...
Elements of a Smart Antenna   Smart antennas consists of a number of    radiating elements, a combining/dividing    netwo...
Phased Array Antenna   Phased   Array     antennas are a    combination of antennas in which    there is a control of the...
Types of Intelligent Antennas   Switched lobe (SL): This is also called    switched beam. It is the simplest    technique...
Intelligent Antennas-cont’d   Dynamically phased array (PA): By    including a direction of arrival (DoA)    algorithm fo...
Intelligent Antennas-cont’d   Adaptive array (AA): In this case, a DoA    algorithm for determining the direction toward ...
SMDA   Space Division Multiple Access (SDMA)    implies that more than one user can be    allocated to the same physical ...
SMDA-cont’d   In systems providing full SDMA, there    will be much more intracell handovers    than in conventional TDMA...
Antenna Installation Considerations   Safety      standard operating procedure priority   Grounding      lightning str...
Antenna Installation Considerations-               cont’d   Adaptive array antenna placement    needs to be considered di...
Antenna Installation Considerations   Base, mast, and supporting    structure needs clearance,    serviceability (access)...
11 basic antenna theory and concepts ممتازة عن الهوائيات
11 basic antenna theory and concepts ممتازة عن الهوائيات
11 basic antenna theory and concepts ممتازة عن الهوائيات
11 basic antenna theory and concepts ممتازة عن الهوائيات
11 basic antenna theory and concepts ممتازة عن الهوائيات
11 basic antenna theory and concepts ممتازة عن الهوائيات
11 basic antenna theory and concepts ممتازة عن الهوائيات
11 basic antenna theory and concepts ممتازة عن الهوائيات
11 basic antenna theory and concepts ممتازة عن الهوائيات
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11 basic antenna theory and concepts ممتازة عن الهوائيات

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Transcript of "11 basic antenna theory and concepts ممتازة عن الهوائيات"

  1. 1. Introduction An antenna is an electrical conductor or system of conductors  Transmission - radiates electromagnetic energy into space  Reception - collects electromagnetic energy from space In two-way communication, the same antenna can be used for transmission and reception
  2. 2. Antenna Definition An antenna is a circuit element that provides a transition form a guided wave on a transmission line to a free space wave and it provides for the collection of electromagnetic energy.
  3. 3. Antenna Definition-cont’d In transmit systems the RF signal is generated, amplified, modulated and applied to the antenna In receive systems the antenna collects electromagnetic waves that are “cutting” through the antenna and induce alternating currents that are used by the receiver
  4. 4. Reciprocity An antenna ability to transfer energy form the atmosphere to its receiver with the same efficiency with which it transfers energy from the transmitter into the atmosphere Antenna characteristics are essentially the same regardless of whether an antenna is sending or receiving electromagnetic energy
  5. 5. Polarization Polarization is the direction of the electric field and is the same as the physical attitude of the antenna  A vertical antenna will transmit a vertically polarized wave The receive and transmit antennas need to possess the same polarization
  6. 6. Types of Antennas Isotropic antenna (idealized)  Radiates power equally in all directions Dipole antennas  Half-wave dipole antenna (or Hertz antenna)  Quarter-wave vertical antenna (or Marconi antenna) Parabolic Reflective Antenna
  7. 7. Directional Antenna beamwidthMax power • A Radiated energy is focused in a specific directionantenna 2 dipole Power 3dB down from maximum point A
  8. 8. Beamwidth Beamwidth is the angular separation of the half-power points of the radiated pattern
  9. 9. Half-wave Dipole (Hertz) Antenna An antenna having a physical length that is one-half wavelength of the applied frequency is called a Hertz antenna or a half-wave dipole antenna. Hertz antennas are not found at frequencies below 2MHz because of the physical size needed of the antenna to represent a half-wave
  10. 10. Vertical (Marconi) Antenna Vertical Antennas are used for frequencies under 2 MHz. It uses a conducting path to ground that acts as ¼ wavelength portion the antenna above the ground. The above ground structure represents a /4 wavelength
  11. 11. Vertical (Marconi) Antenna – cont’d Poor grounding conditions of the earth/soil surrounding the antenna can result in serious signal attenuation. This problem is alleviated by installing a counterpoise
  12. 12. Counterpoise Counterpoise is a grounding grid established where the earth grounding cannot satisfy electrical requirements for circuit completion. It is designed to be non-resonant at the operating frequency
  13. 13. Counterpoise-cont’d radius = ¼ antenna supports
  14. 14. Antenna Array Antenna array is a group of antennas or antenna elements arranged to provide the desired directional characteristics. Generally any combination of elements can form an array. However, equal elements in a regular geometry are usually used.
  15. 15. Yagi-Uda Antenna The Yagi-Uda antenna is a simple form of a directional antenna based off of a reflector placed /4 from the dipole antenna’s placement. Complex analysis to define the radiated patterns are experimental rather than theoretical calculations
  16. 16. Yagi-Uda Antenna-cont’dreflector /4 dipole antenna
  17. 17. Radiated Directed Signalantenna 2 dipole radiated signal 2 dipole radiated signal without reflector with reflector
  18. 18. The Antenna Formula c 186,000 mi sec frequency of the signal•c is the speed of light is the wavelength of the signal use 3 x 108 when dealing in meters for the speed of light
  19. 19. The Antenna Formula - applied If a half-wave dipole antenna needed to be constructed for a 60 Hz signal, how large would it need to be? c 186,000 mi sec = 3100 mi 602 = 1550 miles!
  20. 20. Radiation & Induction Fields The mechanics launching radio frequencies from an antenna are not full understood. The RF fields that are created around the antenna have specific properties that affect the signals transmission. The radiated field field is known as the (surprisingly!) radiation field
  21. 21. Radiation & Induction Fields-cont’d There are two induction fields or areas where signals collapse and radiate from the antenna. They are known as the near field and far field. The distance that antenna inductance has on the transmitted signal is directly proportional to antenna height and the dimensions of the wave 2 R 2D
  22. 22. Radiation & Induction Fields-cont’d 2 R 2DWhere: R = the distance from the antenna D = dimension of the antenna = wavelength of the transmitted signal
  23. 23. Radiation Resistance Radiation Resistance is the portion of the antenna’s impedance that results in power radiated into space (i.e., the effective resistance that is related to the power radiated by the antenna. Radiation resistance varies with antenna length. Resistance increases as the increases
  24. 24. Effective Radiated Power (ERP) ERP is the power input value and the gain of the antenna multiplied together  dBi = isotropic radiator gain  dBd = dipole antenna gain
  25. 25. Radiation Pattern Radiation pattern is an indication of radiated field strength around the antenna. Power radiated from a /2 dipole occurs at right angles to the antenna with no power emitting from the ends of the antenna. Optimum signal strength occurs at right angles or 180 from opposite the antenna
  26. 26. Radiation Patterns Radiation pattern  Graphical representation of radiation properties of an antenna  Depicted as two-dimensional cross section Beam width (or half-power beam width)  Measure of directivity of antenna Reception pattern  Receiving antenna’s equivalent to radiation pattern
  27. 27. Radiation Pattern for Vertical Antennas /4/2 antenna
  28. 28. Antenna Gain Antenna gain  Power output, in a particular direction, compared to that produced in any direction by a perfect omnidirectional antenna (isotropic antenna) Effective area  Related to physical size and shape of antenna
  29. 29. Antenna Gain Antenna gain is the measure in dB how much more power an antenna will radiate in a certain direction with respect to that which would be radiated by a reference antenna
  30. 30. Antenna Gain Relationship between antenna gain and effective area 2 4 Ae 4 f Ae G 2 2 c  G = antenna gain  Ae = effective area  f = carrier frequency  c = speed of light (» 3 ´ 108 m/s)  = carrier wavelength
  31. 31. Propagation Modes Ground-wave propagation Sky-wave propagation Line-of-sight propagation
  32. 32. Ground Wave Propagation
  33. 33. Ground Wave Propagation Follows contour of the earth Can Propagate considerable distances Frequencies up to 2 MHz Example  AM radio
  34. 34. Sky Wave Propagation
  35. 35. Sky Wave Propagation Signal reflected from ionized layer of atmosphere back down to earth Signal can travel a number of hops, back and forth between ionosphere and earth’s surface Reflection effect caused by refraction Examples  Amateur radio  CB radio
  36. 36. Line-of-Sight Propagation
  37. 37. Line-of-Sight Propagation Transmitting and receiving antennas must be within line of sight  Satellite communication – signal above 30 MHz not reflected by ionosphere  Ground communication – antennas within effective line of site due to refraction Refraction – bending of microwaves by the atmosphere  Velocity of electromagnetic wave is a function of the density of the medium  When wave changes medium, speed changes  Wave bends at the boundary between mediums
  38. 38. Line-of-Sight Equations Optical line of sight d 3.57 h Effective, or radio, line of sight d 3.57 h  d = distance between antenna and horizon (km)  h = antenna height (m)  K = adjustment factor to account for refraction, rule of thumb K = 4/3
  39. 39. Line-of-Sight Equations Maximum distance between two antennas for LOS propagation: 3.57 h1 h2  h1 = height of antenna one  h2 = height of antenna two
  40. 40. LOS Wireless Transmission Impairments Attenuation and attenuation distortion Free space loss Noise Atmospheric absorption Multipath Refraction Thermal noise
  41. 41. Thermal Noise Thermal noise due to agitation of electrons Present in all electronic devices and transmission media Cannot be eliminated Function of temperature Particularly significant for satellite communication
  42. 42. Noise Terminology Intermodulation noise – occurs if signals with different frequencies share the same medium  Interference caused by a signal produced at a frequency that is the sum or difference of original frequencies Crosstalk – unwanted coupling between signal paths Impulse noise – irregular pulses or noise spikes  Short duration and of relatively high amplitude  Caused by external electromagnetic disturbances, or faults and flaws in the communications system
  43. 43. Other Impairments Atmospheric absorption – water vapor and oxygen contribute to attenuation Multipath – obstacles reflect signals so that multiple copies with varying delays are received Refraction – bending of radio waves as they propagate through the atmosphere
  44. 44. Multipath Propagation
  45. 45. Multipath Propagation Reflection - occurs when signal encounters a surface that is large relative to the wavelength of the signal Diffraction - occurs at the edge of an impenetrable body that is large compared to wavelength of radio wave Scattering – occurs when incoming signal hits an object whose size in the order of the wavelength of the signal or less
  46. 46. The Effects of Multipath Propagation Multiple copies of a signal may arrive at different phases  If phases add destructively, the signal level relative to noise declines, making detection more difficult Intersymbol interference (ISI)  One or more delayed copies of a pulse may arrive at the same time as the primary pulse for a subsequent bit
  47. 47. Types of Fading Fast fading Slow fading Flat fading Selective fading Rayleigh fading Rician fading
  48. 48. Error Compensation Mechanisms Forward error correction Adaptive equalization Diversity techniques
  49. 49. Forward Error Correction Transmitter adds error-correcting code to data block  Code is a function of the data bits Receiver calculates error-correcting code from incoming data bits  If calculated code matches incoming code, no error occurred  If error-correcting codes don’t match, receiver attempts to determine bits in error and correct
  50. 50. Adaptive Equalization Can be applied to transmissions that carry analog or digital information  Analog voice or video  Digital data, digitized voice or video Used to combat intersymbol interference Involves gathering dispersed symbol energy back into its original time interval Techniques  Lumped analog circuits  Sophisticated digital signal processing algorithms
  51. 51. Antenna Height Antenna height above the ground is directly related to radiation resistance. Ground reflections causing out-of-phase signals to be radiated to receiving antennas will degrade the transmission. Physical length and electrical length of most antennas are approximately 95% of the physical length. Ideal antenna height is usually based on trial and error procedures
  52. 52. Smart Antennas
  53. 53. Smart Antennas smart antennas are base station antennas with a pattern that is not fixed, but adapts to the current radio conditions smart antennas have the possibility for a large increase in capacity: an increase of three times for TDMA systems and five times for CDMA systems has been reported.
  54. 54. Smart Antennas-cont’d Major drawbacks and cost factors include increased transceiver complexity and more complex radio resource management
  55. 55. Smart Antennas-cont’d The idea of smart antennas is to use base station that are , but adapt to the current radio conditions. This can be visualized as the antenna directing a beam toward the communication partner only
  56. 56. Smart Antennas-cont’d Smart antennas add a new way of separating users, namely by space, through SDMA (space division multiple access) By maximizing the antenna gain in the desired direction and simultaneously placing minimal radiation pattern in the directions of the interferers, the quality of the communication link can be significantly improved
  57. 57. Elements of a Smart Antenna Smart antennas consists of a number of radiating elements, a combining/dividing network and a control unit
  58. 58. Phased Array Antenna Phased Array antennas are a combination of antennas in which there is a control of the phase and power of the signal applied at each antenna resulting in a wide variety of possible radiation patterns
  59. 59. Types of Intelligent Antennas Switched lobe (SL): This is also called switched beam. It is the simplest technique, and comprises only a basic switching function between separate directive antennas or predefined beams of an array. The setting that gives the best performance, usually in terms of received power, is chosen
  60. 60. Intelligent Antennas-cont’d Dynamically phased array (PA): By including a direction of arrival (DoA) algorithm for the signal received from the user, continuous tracking can be achieved and it can be viewed as a generalization of the switched lobe concept
  61. 61. Intelligent Antennas-cont’d Adaptive array (AA): In this case, a DoA algorithm for determining the direction toward interference sources (e.g., other users) is added. The radiation pattern can then be adjusted to null out the interferers. In addition, by using special algorithms and space diversity techniques, the radiation pattern can be adapted to receive multipath signals which can be combined. These techniques will maximize the signal to interference ratio (SIR)
  62. 62. SMDA Space Division Multiple Access (SDMA) implies that more than one user can be allocated to the same physical communications channel simultaneously in the same cell, only separated by angle. In a TDMA system, two users will be allocated to the same time slot and carrier frequency at the same time and in the same cell
  63. 63. SMDA-cont’d In systems providing full SDMA, there will be much more intracell handovers than in conventional TDMA or CDMA systems, and more monitoring by the network is necessary
  64. 64. Antenna Installation Considerations Safety  standard operating procedure priority Grounding  lightning strikes  static charges Surge protection  lightning searches for a second path to ground
  65. 65. Antenna Installation Considerations- cont’d Adaptive array antenna placement needs to be considered differently than current technologies serving the mobile environment. They need to be place so they have a greater angular approach to the receiving units. Existing tower placement with close proximity to roads and highways would need to be reconsidered.
  66. 66. Antenna Installation Considerations Base, mast, and supporting structure needs clearance, serviceability (access), and complies with state, federal, and municipal guidelines
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