Antenna diversity, also called space diversity, is a scheme that uses two or more antennas to
improve the quality and reliability of a wireless link. Often, especially in urban and indoor
environments, there is no clear line of sight between transmitter and receiver. Instead, the signal
is reflected along multiple paths before finally being received. Each bounce can introduce phase
shifts, time delays, attenuations, and distortions that can destructively interfere with one another
at the aperture of the receiving antenna. Diversity antenna capable devices support multiple
antennas (usually two) in order to combat this phenomenon and minimize its effects.
Diversity antennas are not required for 2G/3G connections; however, they are highly
recommended in order to get the most reliable connection, especially in areas of low coverage.
Identical or very similar antennas should also be used for the best results.
For 4G networks, the second antenna operates as a MIMO (multiple input, multiple output )
antenna, providing a second receive path and a second transmit path. This connection is
required for operation on 4G/LTE networks.
Table 7-1: Recommended antenna separation
Service
Frequency
(MHz)
Wavelength (λ)
(mm)
Best antenna
separation (mm)
(1/2 λ)
Good antenna
separation (mm)
(1/4 λ)
LTE 700 428 214 107
LTE 800 375 187 94
LTE 900 333 167 83
LTE 1800 167 83 42
LTE 2100 143 71 36
LTE 2600 115 58 29
WCDMA 850 353 176 88
WCDMA 900 333 167 83
WCDMA 1900 158 79 39
WCDMA 2100 143 71 36
CDMA/EV-DO 800 375 187 94
CDMA/EV-DO 1900 158 79 39
GSM/GPRS/EDGE 850 353 176 88
GSM/GPRS/EDGE 900 333 167 83
RV50(X) Sierra Wireless AirLink® 4G LTE Cellular Modem 32
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