User's Manual

UltraWAVE Micro BTS Installation and Commissioning Guide, Version B 59
Connecting Antennas
(50 W). The UltraWAVE base station transmitters operate in the U.S. cellular band
of 869 to 894 MHz.
As the UltraWAVE is intended to be operated in cellular service, each of its
transmitters is typically connected to a 65 - 120 degree sector antenna or omni
directional antenna. For the purpose of the MPE calculations, it will be assumed
that the UltraWAVE is fully equipped with six transceivers, and that two different
transmitters are used in each 120 degree sector. For the MPE calculations this
would be the worst case radiation levels as the equivalent RF power of +50 dBm
(100 Watt) would be transmitted into a 120 degree sector.
The typical gain of 65 - 120 degree sector antenna is in the range of +6 to +18 dBi.
However, there is the highest ERP limitation on the Part22 requirement which is
500 Watt (57 dBd).
The duty cycle of the transmitter is 100%. Assuming two transmitters are
operating into the same 120 degree sector, a maximum of +47 dBm of RF energy
would be transmitted into two antennas, with total EIRP=61 dBi would be the
worst case.
RF power density can be calculated with the equation: S = P * G / 4p R
2
, where
S = power density in mW/cm, P = power input to the antenna in mW, G = power
gain of the antenna, and R = distance to the center of radiation of the antenna in
cm. By rearranging this equation, the relationship between distance (R) and Power
Density (S) can be found.
Rearranging R = sqrt (PG/4pS), and solving for the maximum limits of
2.90 mW/cm
2
, and 0.58 mW/cm
2
we have:
R(2.90 mW/cm
2
) = sqrt (1,260,000 mW/4p*2.90) = 186 cm, or 73 inches.
R(0.58 mW/cm
2
) = sqrt (1,260,000 mW/4p*0.58) = 416 cm, or 164 inches.
These results show that the general population RF exposure limits are not
exceeded as long as the general population is kept 164 inches from the feed point
of the antenna.
The propagation characteristics at 870 MHz dictate a line-of-sight type of RF path.
As such, typical installation locations are up on rooftops or masts to get above
ground level path obstructions. When the UltraWAVE antennas are installed in
this manner, the general population will be further than 164 inches from the
antenna, and RF exposure limits will be met.
1,260,000 mW is used to account for two 50,000 mW
transmitters operating into each 120 degree sector.