The Microstrip Antennas (MSAs) are most popular and widely used because of their
attractive features such as low volume, low cost, light weight, planar configuration
and compatibility with integrated circuits. However, the major demerit associated
with MSAs is their narrow bandwidth, nearly 1 to 2% (Bahl and Bhartia, 1981) and
single frequency operation which limits their many useful applications. A number
of techniques are mentioned in the literature for enhancing the bandwidth of MSAs.
These include incorporating slots (Steven et al., 2003), use of additional resonators
(Kumar and Gupta, 1984), use of parasitic elements with main radiating patch (Nishiyama
and Aikawa, 2004), use of multilayer structure (Zehforoosh et al., 2006), etc. Among
these, the slot technique is simple and straightforward in enhancing the bandwidth
compared to other techniques available in the literature, because it has the freedom
to add the desired slot on the radiating element and in the ground plane. Further,
the antenna operating at more than one band of frequency is more useful than single
band antenna because each band can be used independently for transmit/receive applications
particularly in Synthetic Aperture Radar (SAR). A variety of methods have been proposed
in the literature to obtain dual band operation. But the antenna operating at two
different bands of frequencies and their enhancement using slot loaded microstrip
array antenna are found rarely in the literature. The array technique improves the
radiation characteristics of the antenna.
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