RF Exposure Info

0191-EX-RR-2001 Text Documents

CATERPILLAR OF DELAWARE, INC.

2001-12-21ELS_51906

Radiation Hazard Analysis for Experimental Obstacle
Detection Radar for Caterpillar Inc.

FCC File #: 0191-EX-RR-2001 [Reference Number: 1551]

Description of Experimental Radar Unit
1. Central frequency of transmitter: 77.0 GHz
2. Bandwidth of transmission: 300 MHz centered in above frequency
3. Maximum continuous transmission power: 20 mW (13 dBm)
4. Maximum antenna aperture: 23 cm.
5. Typical antenna aperture 15 cm
6. Type of transmitter: continuous wave
7. Antennas are typically connected to the transmitter.
8. Disassembly of equipment is ALWAYS done by knowledgeable personnel and
with power off.

Assumptions:
1. Type of exposure: Occupational/controlled
2. Antenna efficiency: 0.65 (due to polarization filter and inefficient planar antenna)

Power Calculations:

1. Antenna gain (Ref: Eq (15) in page 28 of OET Bulletin 65)

4πηA 4π (0.65)(15cm * 23cm)
G= = = 17790 (~43 dBi)
λ2 (0.398cm) 2
Experimental value provided by manufacturer G=40 dBi (Antenna Performance
Summary, Millitech)

2. Near field range up to (Ref: Eq (12) in page 27 of OET Bulletin 65):

D2 (23cm) 2
Rnf = = = 332cm
4λ 4 * 0.39cm

3. Power density in the near field region (Ref: Eq (13) in page 28 of OET Bulletin
65)

16ηP 16 * 0.65 * 20mW
Snf = = = 0.125mW / cm 2
πD 2
πD 2

4. Transition field up to (Ref: Eq (16) in page 29 of OET Bulletin 65)

0.6 D 2 0.6(23cm) 2
Rnf = = = 813cm
λ 0.39cm

5. Power density in the transition zone (Ref: Eq (17) in page 29 of OET Bulletin 65)

Snf * Rnf 0.125mW / cm 2 * 332cm
Stf = = = 0.05mW / cm 2
R 812cm

6. Power density in far field zone (Ref: Eq (18) in page 29 of OET Bulletin 65)

PG 20mW *17790
Sff = = = 0.041mW / cm 2
4πR 2
4π 833 2

Exposure Calculations:

The power density has a maximum of 0.125 mW/cm2 for distances within the near
field of the antenna, that is, 332 cm. The power decreases proportional to the
inverse of the distance within the transition zone to 0.05 mW/cm2 at 813 cm from
the sensor. Farther than that, the power density decreases proportional to the
square of the distance. These numbers apply for positions in the main axis of the
antenna. The antenna exhibits sidelobes around 20 dB lower than the main lobe;
therefore, the power density levels for sidelobe exposure are at least 100 times
lower than the aforementioned values.

Conclusions:

The levels of power density are below the Limits for Maximum Permissible
Exposure (MPE) indicated in the Table 1 in page 67 of OET Bulletin 65, which
are: 5 mW/cm2 for the frequency range of 1,500–100,000 MHz (77 GHz is in this
range).

The levels of power density are ALSO below the General
Population/Uncontrolled Exposure limit of 1 mW/cm2. This is not the typical type
of exposure, however.

The type of antennas used and the experimental procedures allow transmitter
power of 40 times more (~30 dBm) under the Occupational/Controlled Exposure
Standards.

Document Created: 2001-12-21 09:54:50
Document Modified: 2001-12-21 09:54:50

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