CPW-fed slot antennas are increasingly popular in modem
wireless communications. They also have many attractive
features including low radiation loss, less dispersion, easy
integration for monolithic microwave integrated circuits
(MMIC's) and a simple configuration with a single metallic
layer. Since no backside processing (via holes) is required for
integration of devices, the designs of these antennas have
recently become more and more attractive. Their main
drawback, however, is essentially a bi-directional radiator,
with the back radiation being undesirable, which not only
directs half of the power in potentially undesired directions
but also increases the sensitivity of the antenna to its
surrounding environment and prohibits the placement of such
slot antennas on the platforms. For example, placing such a
slot antenna in close proximity of a large metallic object, such
as a vehicle, can significantly change the input impedance and
radiation patterns of the antenna. One common technique to
redirect the back radiation forward is to place a conducting
reflector at a fixed distance away from the antenna [1]-[4]. In
practical applications, the antenna has a finite size which is
controlled by its application environment. This truncation of
the ground plane or reflector influences its input impedance
and radiation characteristics.