Design of Butterfly Shaped Microstrip Antenna for Multi Band Operation

In this paper we have designed butterfly shaped microstrip patch antenna which is used for multiband operation. To increase the bandwidth this antenna structure is loaded by trapezoidal-shaped slot on the radiating patch. Indirect microstrip feed line is provided to excite the trapezoidal shaped slot at its respective optimal feeding position. The designed antenna has compact size of 30*40 mm including the ground plane and substrate (εr = 2.2) of thickness h=1.57 mm. The designed structures were simulated using the HFSS software and the values of simulated return losses obtained were less than -10 dB at resonant frequencies. The results were obtained for three antenna structures having trapezoidal-cut with varying l₁ and l₂ (length of parallel sides) and w(distance between parallel sides). For trapezoidal 1, the value of l₁=12mm, l₂=10mm and w=6mm; for trapezoidal 2, the value of l₁=10mm, l₂=8mm and w=5mm; for trapezoidal 3, the value of l₁=8mm, l₂=6mm and w=4mm. These structures were operated at their quarter wavelength modes and arranged in a compact planar configuration. After simulation of these structures we got four distinct operating frequency bands centred at 3.60 GHz, 7.10GHz, 9.90 GHz and 16.10 GHz with improved return loss. The simulation results show that an acceptable impedance bandwidth is obtained and the resonant frequencies are used in case of multiband antenna and for mobile services.