A simple design of rectangular microstrip antenna with shorted parasitic strip
is presented for compact and wideband operation. The antenna consists of a
parasitic strip which was looped around the rectangular microstrip patch, and a shorting
strip was placed at the optimum point between the parasitic strip and radiating
patch. From the experimental results, it was observed that 73.97% of large effective
reduction of antenna size was achieved and -10 dB return loss impedance bandwidth was
1.83 times more than that of conventional rectangular microstrip antenna without
change in broadside radiation characteristics. This antenna may find application in
Secondary Surveillance Radar (SSR) systems (1.03-1.09 GHz). Design concepts of
proposed antennas are given and experimental results are discussed.
Microstrip antennas find far-reaching applications in the current communication
systems because of their unique properties like lightweight, ease of fabrication, low
production cost, low profile, etc. However, the field of applications of these antennas is mainly
limited by their inherent disadvantages of narrow impedance bandwidth. Further, it is difficult
to accommodate microstrip antenna in many portable systems, operating at lower
frequencies, because the size of antenna is inversely proportional to its designed frequency.
Several techniques are available in literature for improving the impedance bandwidth and
reducing the effective size of the antenna. Chin-Yu et al. (1998) have reduced the antenna size
to 6% by loading a chip resistor to the conventional microstrip antenna and Das et al. (2006) have loaded the patch with slots and obtained 35% reduction in antenna size. But in
this paper, a simple technique has been proposed by using a parasitic strip covered around
the radiating patch and placing a short at the optimum place between strip and patch.
This technique not only enhances the impedance bandwidth but also reduces the effective
size of antenna to a greater extent than that found earlier (Chin-Yu et al., 1998;
and Das Krishna et al., 2006) without changing the nature of broadside
radiation characteristics, when compared to conventional rectangular microstrip antenna.
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