Attachment Radhaz Argyle.pdf

This document pretains to SES-LIC-20070801-01016 for License on a Satellite Earth Station filing.

IBFS_SESLIC2007080101016_579342

                                   Radiation Hazard Analysis
                                    Cross Timbers Church
                                            Argyle, TX


This analysis predicts the radiation levels around a proposed earth station complex, comprised of
one (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 environment. 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 unusable.

Earth Station Technical Parameter Table
Antenna Actual Diameter               2.4 meters
Antenna Surface Area                  4.5 sq. meters
Antenna Isotropic Gain                49.4 dBi
Number of Identical Adjacent Antennas 1
Nominal Antenna Efficiency (ε)        67.50%
Nominal Frequency                     14.25 GHz
Nominal Wavelength (λ)                0.0211 meters
Maximum Transmit Power / Carrier      14.0 Watts
Number of Carriers                    1
Total Transmit Power                  14.0 Watts
W/G Loss from Transmitter to Feed     1.0 dB
Total Feed Input Power                11.08 Watts
Near Field Limit                      Rnf = D²/4λ =68.40 meters
Far Field Limit                       Rff = 0.6 D²/λ = 164.16 meters
Transition Region                     Rnf to Rff

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.

1.0 At the Antenna Surface

The power density at the reflector surface can be calculated from the expression:

 PDrefl = 4P/A = 0.980 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 shall receive training specifying this area as a high exposure


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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) =     0.661 mW/cm² (2)
                             from 0 to 68.40 meters
Evaluation
 Uncontrolled Environment:        Meets Uncontrolled Limits
 Controlled Environment:          Meets Controlled 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:        68.40 < R < 164.2 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:          45.2
 Controlled Environment Safe Operating Distance,(meters), Rsafec:            9.0

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



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         R = distance to the point of interest
 For:    R > Rff = 164.2 meters
         PDff = 0.283 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

In 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 = 0.052 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 = 0.00661 mW/cm² at D off axis (6)

See Section 8 for the calculation of the distance vs. elevation angle required to achieve this rule
for a given object height.




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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 shall 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.

8.0 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=            2.0 meters
   Then:
               α             S
               10            12.7 meters
               15            8.5meters
               20            6.5 meters
               25            5.2 meters
               30            4.5 meters


Suitable fencing or other barrier may 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.




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Document Created: 2007-07-23 16:13:13
Document Modified: 2007-07-23 16:13:13

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