Attachment Wales Rad Haz

This document pretains to SES-LIC-20180809-02198 for License on a Satellite Earth Station filing.

IBFS_SESLIC2018080902198_1487336

                                                                                            Page 1 of 5




                      Radiation Hazard Study

3.8m Offset Feed Earth Station C-band Antenna

This analysis predicts the radiation levels around a earth station comprised of one aperture (reflector)
type antenna. 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, Section 2 Prediction Methods, Aperture Antennas, 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 unuseable.



Earth Station Technical Parameters

Antenna diameter                 3.8 m
Antenna Isotropic gain           46.5 dBi
Maximum Transmit Power           50 Watts
Number of carriers               1
Nominal Frequency                6.1 GHz (frequency for the 46.5 dBi in FCC312 E42)


In the following sections, the power density in the above regions, as well as other critically important
areas will be calculated and evaluated.




X2nsat Inc.                      Radiation Hazard Study – 3.8m C-band       1 August 2018


                                                                                             Page 2 of 5




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 given by the
equation (1).

(1) Lnf = D²/(4λ)

Where Lnf = length to end of the near field,

Where D = antenna diameter

Where λ = wavelength at 6.1 GHz = 49.0 x10-3 meters or 49 mm

From equation (1) it is found that the distance to the end of the near field is 73 meters.


The maximum power flux density in the near field PDnf is given by:

(2) PDnf = 16 Pt ŋ/(πD²)

Where Pt is the maximum power transmitted by the amplifier (50 Watts).

Where ŋ = Antenna Efficiency

Antenna efficiency can be estimated, or a reasonable approximation for circular apertures can be
obtained from the ratio of the effective aperture area to the physical area as follows:

          ŋ = (Gλ²/4π)/(πD²/4) = Gλ²/(π²D²) = 0.76

Where G = the on-axis gain of the antenna (46.5 dBi at 6.1 GHz)

From equation (2), we see that

                           PDnf = 1.34 mW/cm²

Evaluation

         Controlled Environment           Complies with FCC Limit of 5 milliwatts per square centimeter

The power density in the region on-axis near-field is conceded to be in excess of the limit for
Uncontrolled Environment. This area will not be accessible to the general public. Operators
and technicians have received training specifying this area as a Controlled Environment.




X2nsat Inc.                       Radiation Hazard Study – 3.8m C-band       1 August 2018


                                                                                              Page 3 of 5




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 power density in the near field region, as shown above, will not exceed 1.34 mW/cm².

Evaluation

         Controlled Environment            Complies with FCC Limit of 5 milliwatts per square centimeter

The power density in the region on-axis transition is conceded to be in excess of the limit for
Uncontrolled Environment. This area will not be accessible to the general public. Operators
and technicians have received training specifying this area as a Controlled Environment.




On-axis Far-Field Region
Free-space power density is maximum on-axis, varies inversely with the square of the of the distance
and may be calculated from equation (3).

(3) PDff = GPt/(4π R²)

Where PDff = the power flux density on-axis in the far field,

R = the distance to the far field region and is found from equation (4).

(4) R = 0.6D²/λ

From equation (4) it is found that the distance to the far field is 176 meters.

And, PDff is found from equation (3) as follows:

                                                    PDff = 0.57 mW/cm²

Evaluation

         Uncontrolled Environment          Complies with FCC Limit of 1 milliwatt per square centimeter
         Controlled Environment            Complies with FCC Limit of 5 milliwatts per square centimeter




Off-axis Levels at the Far Field 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 on-axis center line and the point of interest. The on-
axis main-beam will be the location of the greatest of these maxima. The on-axis power density
calculated above represent the maximum exposure levels that the system can produce. Off-axis power
densities will be considerably less and hence comply with FCC limits.




X2nsat Inc.                       Radiation Hazard Study – 3.8m C-band        1 August 2018


                                                                                          Page 4 of 5




Region Between Feed Flange and Reflector

Transmissions from the feed horn are directed toward the reflector surface, and are confined within a
conical shape defined by the feed. The energy between the feed and reflector surface can be calculated
by determining the power density at the feed flange. This can be accomplished as follows:

Power Density at Feed Flange, PDfeed = 4*Pt/Fa

Where Fa = Area of Feed Window = π*Df²/4

Where Df = 19 cm

Fa = 283 cm²

                                  PDfeed = 706 mW/cm²

The energy between the feed horn and reflector 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
have received training specifying this area as a high exposure area. Procedures are established that
assure that the transmitter is turned off before access by maintenance personnel to this area.




Main Reflector Region
The power density in the main reflector region is determined in the same manner as the power density at
the feed flange, above, but the area is now the area of the reflector aperture:

Power Density at Reflector Surface, PDreflector = 4*Pt/Sa

Where Sa = Surface Area of Reflector = 11 m²

                                  PDreflector = 1.76 mW/cm²


Evaluation

         Controlled Environment           Complies with FCC Limit of 5 milliwatts per square centimeter

The power density in the main reflector region is conceded to be in excess of the limit for
Uncontrolled Environment. This area will not be accessible to the general public. Operators
and technicians have received training specifying this area as a Controlled Environment.




X2nsat Inc.                       Radiation Hazard Study – 3.8m C-band    1 August 2018


                                                                                            Page 5 of 5




Off-axis Levels at the Near Field and in the Transition Region
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 (20dB) 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 = 0.013 mW/cm²

Evaluation

         Uncontrolled Environment         Complies with FCC Limit of 1 milliwatt per square centimeter
         Controlled Environment           Complies with FCC Limit of 5 milliwatts per square centimeter




Conclusion
This antenna area will not be accessible to the general public.

Based on the above analysis it is concluded that harmful levels of radiation will not exist in regions
accessible to the general public or to the earth station’s operating personnel.

The controlled environment not to be accessed by maintenance personnel without the transmitter being
turned off is the area between the feed horn and the reflector.




Study Prepared by:       x2nsat Engineer




X2nsat Inc.                      Radiation Hazard Study – 3.8m C-band       1 August 2018



Document Created: 2018-08-01 16:59:36
Document Modified: 2018-08-01 16:59:36

© 2024 FCC.report
This site is not affiliated with or endorsed by the FCC