Huawei Airbridge BTS3612A-1900 Technical Manual page 51

Technical Manual
Airbridge BTS3612A CDMA Base Station
I. Antenna gain
Antenna gain is the capability of the antenna to radiate the input power in specific
directions. Normally, in the direction where the radiation intensity of the antenna is the
strongest, the higher the gain is, the stronger the field intensity will be in a faraway
place and the larger the effective coverage area will be. But there may be blind areas in
the vicinity.
II. Antenna pattern
Antenna pattern describes the radiation intensity of the antenna in all directions. The
horizontal antenna pattern is often used. It is also used as a standard to classify the
antennae
The BTS antenna is categorized in two types: omni antenna and directional antenna.
The directional antenna includes the following types: 120°, 90°, 65° and 33°.
III. Polarization
Polarization is used to describe the change path of the direction of the electric field. The
mobile communication system often uses uni-polarization antennas. Bi-polarization
antennae have been used recently. It is an antenna with two cross-over antenna
polarization directions. The isolation is above 30dB for both the +45
The adoption of the bi-polarization antenna can save antennae, as one bi-polarization
antenna can replace two sets of independent uni-polarization antennae.
Normally bi-polarization directional antenna is used in directional cell. Compared with
the uni-polarization directional antenna, the bi-polarization directional antenna is
cost-effective, space saving and easy to install. However, uni-polarization omni
antenna is still adopted in omni cell.
IV. Diversity technology
Electrical wave propagation in urban area has the following features:
Field intensity value changes slowly with places and time. It changes in the rule of
logarithmic normal distribution, which is called the slow attenuation.
Field intensity transient value attenuates selectively due to the multi-path
transmission. The attenuation rules falls into Rayleigh distribution, which is called
the fast attenuation.
The fast attenuation, slow attenuation, multi-path effect, and shadow effect will impair
the quality of communication or even interrupts the conversation. Diversity technology
is one of the most effective technologies to tackle the attenuation problem. Diversity
receiving and combining technology can be used to minimize the attenuation when
there is little correlation between the two attenuated signals.
Chapter 4 Antenna & Feeder Subsystem
4-2
System Principle
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and -45 antennae.