Attachment Radiation Hazard Ana

This document pretains to SES-LIC-20051205-01684 for License on a Satellite Earth Station filing.

IBFS_SESLIC2005120501684_469317

Radiation Hazard Analysis
This analysis predicts the radiation levels around a proposed earth station complex, comprised of one or more
aperture (reflector) type antennas. This report is developed in accordance with the prediction methods contained in
OET Bulletin No. 65, Evaluating Compliance with FCC Guidelines for Human Exposure to Radio Frequency
Electromagnetic Fields, Edition 97-01, pp 26-30. The maximum level of non-ionizing radiation to which employees
may be exposed is limited to a power density level of 5 milliwatts per square centimeter (5 mW/cm2) averaged over
any 6 minute period in a controlled environment and the maximum level of non-ionizing radiation to which the
general public is exposed is limited to a power density level of 1 milliwatt per square centimeter (1 mW/cm2)
averaged over any 30 minute period in a uncontrolled evironment. Note that the worse-case radiation hazards exist
along the beam axis. Under normal circumstances, it is highly unlikely that the antenna axis will be aligned with any
occupied area since that would represent a blockage to the desired signals, thus rendering the link unuseable.

Earth Station Technical Parameter Table
Antenna Actual Diameter                                         2.4 meters
Antenna Surface Area                                            4.5 sq. meters
Antenna Isotropic Gain                                          48.8 dBi
Number of Identical Adjacent Antennas*                          0
Nominal Antenna Efficiency (ε)                                  59%
Nominal Frequency                                               14250 MHz
Nominal Wavelength (λ)                                          0.0211 meters
Maximum Transmit Power / Carrier                                300 Watts
Number of Carriers                                              1
Total Transmit Power                                            300 Watts
W/G Loss from Transmitter to Feed                               3 dB
Total Feed Input Power                                          150 Watts
Near Field Limit                                                Rnf = D²/4λ = 68 meters
Far Field Limit                                                 Rff = 0.6 D²/λ = 164 meters
Transition Region                                               Rnf to Rff
* The Radiation Levels will be increased directly by the number of antennas indicated, on the assumption that all
antennas may illuminate the same area.
In the following sections, the power density in the above regions, as well as other critically important areas will be
calculated and evaluated. The calculations are done in the order discussed in OET Bulletin 65. In addition to the
input parameters above, input cells are provided below for the user to evaluate the power density at specific
distances or angles.
1.0 At the Antenna Surface
The power density at the reflector surface can be calculated from the expression:
 PDrefl =     4P/A =             13.29 mW/cm² (1)
 Where:       P = total power at feed, milliwatts
              A = Total area of reflector, sq. cm
In the normal range of transmit powers for satellite antennas, the power densities at or around the reflector surface is
expected to exceed safe levels. This area will not be accessible to the general public. Operators and technicians
should receive training specifying this area as a high exposure area. Procedures must be established that will assure
that all transmitters are rerouted or turned off before access by maintenance personnel to this area is possible.
2.0 On-Axis Near Field Region
The geometrical limits of the radiated power in the near field approximate a cylindrical volume with a diameter
equal to that of the antenna. In the near field, the power density is neither uniform nor does its value vary uniformly
with distance from the antenna. For the purpose of considering radiation hazard it is assumed that the on-axis flux
density is at its maximum value throughout the length of this region. The length of this region, i.e., the distance from
the antenna to the end of the near field, is computed as Rnf above.
The maximum power density in the near field is given by:
        PDnf = (16ε P)/(π D²) =                      0 mW/cm² (2)
                                                     from 0 to 68 meters
Evaluation


 Uncontrolled Environment:                        Complies to FCC Limits
 Controlled Environment:                          Complies to FCC Limits
3.0 On-Axis Transition Region
The transition region is located between the near and far field regions. As stated in Bulletin 65, the power density
begins to vary inversely with distance in the transition region. The maximum power density in the transition region
will not exceed that calculated for the near field region, and the transition region begins at that value. The maximum
value for a given distance within the transition region may be computed for the point of interest according to:
   PDt =               (PDnf)(Rnf)/R = dependent on R (3)
   where:              PDnf = near field power density
                       Rnf = near field distance
                       R = distance to point of interest
   For:                68 < R < 164 meters
We use Eq (3) to determine the safe on-axis distances required for the two occupancy conditions:
Evaluation
  Uncontrolled Environment Safe Operating Distance,(meters), Rsafeu:              0
  Controlled Environment Safe Operating Distance,(meters), Rsafec:                0
4.0 On-Axis Far-Field Region
The on- axis power density in the far field region (PDff) varies inversely with the square of the distance as follows:
  PDff = PG/(4πR²) = dependent on R (4)
  where: P = total power at feed
           G = Numeric Antenna gain in the direction of interest relative to isotropic radiator
           R = distance to the point of interest
  For: R > Rff = 164 meters
           PDff = 0 mW/cm² at Rff
We use Eq (4) to determine the safe on-axis distances required for the two occupancy conditions:
Evaluation
  Uncontrolled Environment Safe Operating Distance,(meters), Rsafeu :              See Section 3
  Controlled Environment Safe Operating Distance,(meters), Rsafec :                See Section 3
5.0 Off-Axis Levels at the FarField Limit and Beyond
Ipn the far field region, the power is distributed in a pattern of maxima and minima (sidelobes) as a function of the
off-axis angle between the antenna center line and the point of interest. Off-axis power density in the far field can be
estimated using the antenna radiation patterns prescribed for the antenna in use. Usually this will correspond to the
antenna gain pattern envelope defined by the FCC or the ITU, which takes the form of:
 Goff = 32 - 25log(Θ)
 for Θ from 1 to 48 degrees; -10 dBi from 48 to 180 degrees
 (Applicable for commonly used satellite transmit antennas)
Considering that satellite antenna beams are aimed skyward, power density in the far field will usually not be a
problem except at low look angles. In these cases, the off axis gain reduction may be used to further reduce the
power density levels.
For example: At one (1) degree off axis At the far-field limit, we can calculate the power density as:
Goff = 32 - 25log(1) = 32 - 0 dBi = 1585 numeric
 PD1 deg off-axis = PDffx 1585/G = 0 mW/cm² (5)
6.0 Off-Axis power density in the Near Field and Transitional Regions
According to Bulletin 65, off-axis calculations in the near field may be performed as follows: assuming that the
point of interest is at least one antenna diameter removed from the center of the main beam, the power density at that
point is at least a factor of 100 (20 dB) less than the value calculated for the equivalent on-axis power density in the
main beam. Therefore, for regions at least D meters away from the center line of the dish, whether behind, below, or
in front under of the antenna's main beam, the power density exposure is at least 20 dB below the main beam level
as follows:
 PDnf(off-axis) = PDnf /100 = 0 mW/cm² at D off axis (6)
See page 5 for the calculation of the distance vs elevation angle required to achieve this rule for a given object
height.
7.0 Region Between the Feed Horn and Sub-reflector
Transmissions from the feed horn are directed toward the subreflector surface, and are confined within a conical
shape defined by the feed horn. The energy between the feed horn and subreflector is conceded to be in excess of


any limits for maximum permissible exposure. This area will not be accessible to the general public. Operators and
technicians should receive training specifying this area as a high exposure area. Procedures must be established that
will assure that all transmitters are rerouted or turned off before access by maintenance personnel to this area is
possible.
Note 1:
Mitigation of the radiation level may take several forms. First, check the distance from the antenna to the nearest
potentially occupied area that the antenna could be pointed toward, and compare to the distances appearing in
Sections 2, 3 & 4. If those distances lie within the potentially hazardous regions, then the most common solution
would be to take steps to insure that the antenna(s) are not capable of being pointed at those areas while RF is being
transmitted. This may be accomplished by setting the tracking system to not allow the antenna be pointed below
certain elevation angles. Other techniques, such as shielding may also be used effectively.
Evaluation of Safe Occupancy Area in Front of Antenna
The distance (S) from a vertical axis passing through the dish center to a safe off axis location in front of the antenna
can be determined based on the dish diameter rule (Item 6.0). Assuming a flat terrain in front of the antenna, the
relationship is:
 S = (D/ sin α) + (2h - D - 2)/(2 tan α) (7)
 Where:                           α = minimum elevation angle of antenna
                                  D = dish diameter in meters
                                  h = maximum height of object to be cleared, meters
For distances equal or greater than determined by equation (7), the radiation hazard will be below safe levels for all
but the most powerful stations (> 4 kilowatts RF at the feed).
          For              D=                2.4 meters
                           h=                4 meters
          Then:
                           α                 S
                           10                24 meters
                           15                16 meters
                           20                12 meters
                           25                9.5 meters
                           30                7.9 meters
                           48                4.9 meters
                           180               185696130131465 meters
Suitable fencing or other barrier should be provided to prevent casual occupancy of the area in front of the antenna
within the limits prescribed above at the lowest elevation angle required.



Document Created: 2005-12-05 15:18:29
Document Modified: 2005-12-05 15:18:29

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