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Antennas for WLAN (WiFi) Applications 245

signal-to-noise ratio (SNR) known as array gain. Array gain improves
resistance to noise, thereby improving the coverage of a wireless net-
work. Also, the signal-to-noise-plus-interference ratio (SINR) will be
improved, and as a result, interference in wireless networks can be
mitigated. Reducing interference by increasing the separation between
users and directing the energy toward intended users improves the
coverage and range of a wireless network.
MIMO technology is found in several standards for future wireless
communication systems, especially WLANs and cellular networks. The
standardization of MIMO technology is currently under development.
The IEEE 802.11n, which has yet to be finalized, supports MIMO com-
munications with peak data rates of 600 Mbps. The IEEE 802.16 stan-
dard has been developed for the world interoperability for microwave
access (WiMAX), which is intended to deliver high data rates over long
distances. MIMO communication has been incorporated in the IEEE
802.16e version of this standard, where 2 × 1 and 4 × 4 MIMO configu-
rations are considered. The 3GPP technology, also known as wideband
code division multiple access (W-CDMA), is used for 3G cellular net-
works, and MIMO has been incorporated into this standard, particularly
in Releases 7 and 8. In Release 7, 2 × 1 and 4 × 2 configurations employ-
ing space-time block coding were used, whereas in Release 8 (TSG-
R1(04)0336(2004)), the 2 × 2 and 4 × 4 configurations were employed.
In addition, MIMO is also considered in IEEE 802.20 and IEEE 802.22
standards. The former is used to enable the worldwide deployment of
multivendor interoperable mobile broadband wireless access networks,
whereas the latter is aimed at constructing wireless regional area net-
works (WRANs), utilizing channels that are not employed within the
already allocated television frequency spectrum.

7.2 Design Considerations for Antennas
Generally, the major considerations for WLAN antenna design include
electrical properties such as frequency range/bandwidth in terms of
gain, impedance matching, and polarization, as well as other factors
such as size, cost effectiveness, and mechanical robustness. Fulfilling
the electrical properties of the antenna is a priority, which stems from
system requirements. In addition to an antenna’s electrical perfor-
mance, other factors are also vital for a successful design. For example,
a low-cost antenna product is always preferable for the commercial
market. The relevant cost factors include the material used, manufac-
turing, mechanical tolerance, installation, switching from one standard
to another, and integration with the radio. In addition, the form factor
of the antenna is also an important consideration. Indoor antennas are
generally designed to be compact and less protrusive.