Recent years, there is rapid development of
applications using 2.4 GHz band of IEEE 802. lIb and 5.0
GHz band of 802.11 n WLAN standard.
Multiple-input multiple-output (MIMO) antenna
system can provide a tremendous increase in the capacity
of wireless systems [1], particularly important in radio
communications systems, such as UMTS and high data
rate wireless local area networks (WLAN). Planar
monopole antennas have been widely used and studied for
a long time due to their attractive merits such as wide
impedance bandwidth, simple structure and nearly omnidirectional
radiation patterns [2], [3]. In addition, printed
CPW-fed monopole antennas have been introduced for
compact size, low cost and ease to integrate with
microwave circuit [4]. Obviously, a printed monopole
antenna with improved pulse preserving capabilities is
urgently demanded and would become an indispensable
part of radio communications systems.
The WLAN systems have been widely adopted and
incorporated in commercial merchandise such as laptop
computers or personal digital assistants (PDAs).
Therefore, the increasing need of dual-band antennas
with light weight and low profile has stimulated
comprehensive researches to pursue cost effective
antenna designs.