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HUAWEI EM820W HSPA+ PC Embedded Module
Hardware Guide RF Specifications
Issue 01 (2010-12-31)
Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
22
Envelope Correlation Coefficient
The envelope correlation coefficient indicates the correlation between different
antennas in a multi-antenna system (master antenna, diversity antenna, and MIMO
antenna). The correlation coefficient shows the similarity of radiation patterns, that is,
amplitude and phase, of the antennas. The ideal correlation coefficient of a diversity
antenna system or a MIMO antenna system is 0. A small value of the envelope
correlation coefficient between the master antenna and the slave antenna indicates a
high diversity gain. The envelope correlation coefficient depends on the following
factors:
z
Distance between antennas
z
Antenna type
z
Antenna direction
The antenna correlation coefficient differs from the antenna isolation. Sufficient
antenna isolation does not represent a satisfactory correlation coefficient. For this
reason, the two indicators need to be evaluated separately.
For the antennas on laptops, the recommended envelope correlation coefficient
between the master antenna and the diversity antenna is smaller than 0.5.
Radiation Pattern
The radiation pattern of an antenna reflects the radiation features of the antenna in
the remote field region. The radiation pattern of an antenna describes the power or
field strength of the radiated electromagnetic waves in various directions from the
antenna. The power or field strength varies with the angular coordinates (θ and φ),
but is independent of the radial coordinates.
The radiation pattern of half wave dipole antennas is the best option for wireless
terminals. The radiation pattern of half wave dipole antennas is omnidirectional in the
horizontal plane, and the incident waves of base stations are often in the horizontal
plane. For this reason, the reception is optimal.
To improve the performance of diversity antennas, it is recommended that the
radiation pattern of the slave antenna be complementary with that of the master
antenna.
The following radiation patterns are recommended for the antennas on laptops:
z
Master antenna: omnidirectional
z
Slave antenna: complementary with the radiation pattern of the master slave
z
GPS antenna: omnidirectional
z
Wi-Fi antenna: omnidirectional
Gain and Directivity
The radiation pattern of an antenna represents the field strength of the radiated
electromagnetic waves in all directions, but not the power density that the antenna
radiates in the specific direction. The directivity of an antenna, however, measures
the power density that the antenna radiates.
Gain, as another important parameter of antennas, correlates closely to the directivity.
The gain of an antenna takes both the directivity and the efficiency of the antenna