RF Exposure revised

FCC ID: JF6-8505U-4

RF Exposure Info

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RF RADIATION
 EXPOSURE


                                                     RF Safety Rules


Based on ET Docket No. 93-62.
       - http://www.fcc.gov/oet/rfsafety

All Details are in OET Bulletin 65
       - http://www.fcc.gov/oet/info/documents/bulletins/#65


                                                                  Parabolic Antennas

? Near-Field or Fresnel Region:
    The radiation is substantially confined within a cylindrical pattern having the same
    diameter as the antenna. This region may be considered to extend out from the antenna
    to a distance of Rnf as defined on the following slide.*

? Transition Region:
    Since the distance to the far-field region is two to three times the length of the near-
    field region, there is a transition region between the two.* Within the transition region
    the power density decreases inversely with distance.

? Far-Field or Fraunhofer Region:
    At a substantial distance from an antenna, the power density begins to decrease in
    proportion to the inverse square of the distance from the antenna. This occurs at a
    distance from a parabolic antenna where the difference in path length between a ray on
    the axis of the beam, and a ray from the edge of the antenna to a given point on the
    beam axis, is less than 1/16 of a wavelength. This region begins at a distance
    designated as Rff as defined on the following slide.


                                                                     Antenna Near & Far Fields

                                                                                                ANTENNA DIAMETER
                                                                                      Freq.      6 foot      10 foot
                                                                                      GHz      Rnf     Rff Rnf     Rff
                                                                                        2      18      44  51      122
                                                                                        6      55     132  153     366
                                                                                       11      101    242  280     671

         D
                                                                                                                 Radiation
                                                                                                                   Axis




                          Near-Field or Fresnel                Transition                     Far-Field or Fraunhofer
                                Region                          Region                                Region
                             Rnf = D2 / 4?           Rnf                    Rff          Rff = ? ?? D2 / ?
                             ???????= D F / 3.934
                                       2
                                                                                         ??????= D2F / 1.639
Rnf = Distance from the antenna to Near-Field boundary (ft).                  Ref.: “Evaluating Compliance with FCC Guidelines
Rff = Distance from the antenna to Far-Field boundary (ft).                   for Human Exposure to Radiofrequency EM Fields”
D = Diameter of antenna (ft).                                                 OET Bulletin 65, Edition 97-01, August 1997.
? = Wavelength (ft).         F = Frequency (GHz).                             FCC Office of Engineering and Technology


                                   Power Density for Parabolic Antennas

? Power density calculations for the Near-Field
 Region of a Parabolic Antenna.
  – The magnitude of the on-axis power density varies with location
    within the near-field. However, the maximum value of the near-
    field power density can be calculated by the following equation:

    Wnf   ? 4? P       ? 16 ? P
                   A              ? D2
    Where: Wnf ? Maximum power density in the Near - Field Region in mW / cm 2
            ? ? Apeture efficiency, typically 50 - 60% for commercially available antennas
            P ? Average transmitter power in mW
            D ? Antenna diameter in cm
            A ? Area of antenna aperture (? D 4 ) in cm2
                                              2


                     Power Density for Parabolic Antennas (Cont.)

? Power density calculations for the Transition
 Region of a Parabolic Antenna.
  – Within the transition region, the magnitude of the on-axis power
    density decreases inversely with distance from the antenna.
    Therefore the power density within this region can be calculated
    the following equation:

  W   t
          ? W nf R nf R


  W h e r e : W t ? Power density in the transition region in mW / cm 2
             W nf ? M a x i m u m power density in the Near - F ield Region in mW / cm
                                                                                       2


             R nf ? D istance from the antenna to N ear - F ield boundary in feet
              R   ? D istance to point of interest in feet


                       Power Density for Parabolic Antennas (Cont.)

? Power density calculations for the Far-Field
 Region of a Parabolic Antenna.
  – The power density in the far-field region decreases inversely as
    the square of the distance from the antenna surface. Within this
    region the power density can be estimated by the following
    equation:
              ?   PG
     W   ff            4? R 2
     Where: W ff ? Maximum power density on axis in the Far - Field Region in mW / cm 2
             P ? Average power fed to the antenna in mW
                  G ? Gain of antenna in the direction of interest relative to an isotropic radiator
                  R ? Distance to the point of interest in cm


                                                   Maximum Permissible Exposure

   FCC Office of Engineering & Technology Bulletin 65
   Edition 97-01 (August 1997) Guidelines for Human
   Exposure to Radiofrequency Electromagnetic Fields
                                           Maximum Permissible Exposure (MPE)
                                                      (mW/cm 2 )
    Frequency Range                      Occupational/                        General Population/
         (MHz)                        Controlled Exposure*                  Uncontrolled Exposure**
    30 -   300                                 1.0                                    0.2
   300    -   1500                              f / 300                                f / 1500
 1500     - 100,000                               5.0                                     1.0
  f = Frequency in MHz
* Controlled Environments - A location where individuals are aware of radiation exposure.
                            (Averaging time 6 min.)
** Uncontrolled Environments - Individuals have no knowledge or control over their exposure.
                               (Averaging time 30 min.)


                                            Power Density Calculation

Exemple:
– Antenna Diameter = 8 ft
– Aperture efficiency = 55%
– Operating frequency = 5.8 GHz
– MW transmitter output = +30 dBm (1Watt)
– Transmission line loss = 0.2 dB (worst case)
Power @ antenna input port = 30 dBm - 0.2 dB = 29.8 dBm
Pmw = 10 Pdbm/10 = 10 2.98 = 954.99 mW
D = 8 ft x m/3.2808 x 100cm/m = 243.84 cm
A =?? ?D2/4 = ? x (243.84)2/4 = 46699.297 cm2
W = Power density in Near - Field Region of example system.
W = 4 ? P/ A = 4 x .55 x 954.99 mW / 46699.297 cm2 = 0.04498 mW/cm2
• Bulletin-65 Maximum allowable power density for 11.2 GHz is 1.0 mW/cm2 ,
  or 22.2 times greater than calculated maximum power density.


                                            Power Density Calculation

Example:
– Antenna Diameter = 2ft
– Aperture efficiency = 62% (for G=29.3dbi)
– Operating frequency = 5.8 GHz
– MW transmitter output = +30 dBm (1Watt)
– Transmission line loss = 0.2 dB (worst case)
Power @ antenna input port = 30 dBm - 0.2 dB = 29.8 dBm
Pmw = 10 Pdbm/10 = 10 2.98 = 954.99 mW
D = 2 ft x m/3.2808 x 100cm/m = 60.96 cm
A =?? ?D2/4 = ? x (60.96)2/4 = 2918.635 cm2
W = Power density in Near - Field Region of example system.
W = 4 ? P/ A = 4 x .62 x 954.99 mW / 2918.63 cm2 = 0.81146 mW/cm2
• Bulletin-65 Maximum allowable power density for 5.8 GHz is 1.0 mW/cm2 .


                                         Power Density Calculations (Cont.)

                   Near-Field Power Density Calculations
           for 2, 6, & 11 GHz MW Radios with High Power PA’s
  Operating       Power into             Antenna      Near-Field    Max Permissible
  Frequency     Antenna-Feeder           Diameter   Power Density   Exposure (MPE)
    (GHz)           Losses                (feet)      (mW/cm2)        (mW/cm2)*
                    (dBm)
    1.96        +30-1.5 = +28.5             6         0.05928            1.00
     5.8        +30-0.2 = +29.8             2         0.81146            1.00

     5.8        +30-0.2 = +29.8             8         0.04498            1.00
     6.2        +33-1.8 = +31.2            10         0.03975            1.00

    11.2        +34-4.6 = +29.4             6         0.07295            1.00
    11.2        +34-4.6 = +29.4            10         0.02626            1.00


* Maximum Permissible Exposure for Uncontrolled Environment from FCC OET
  Bulletin 65, Edition 97-01; Aug. 97.



Document Created: 2019-09-22 10:19:50
Document Modified: 2019-09-22 10:19:50

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