Present era of wireless communication thrust the need of miniaturization and multi-frequency operations to make the devices compact and affordable. To overcome the challenges of multi-frequency operation, in this paper a revised design is proposed for dual band micro strip antenna printed on RT-duroid substrate which can operate in two frequency bands with a single structure. To make the antenna compact the use of defective ground plane is justified as the size of the structure becomes almost one-third in comparison to the structure with full ground plain. The basic principal of its operation is the multiple resonance frequencies, the first frequency band occurs due to first resonance frequency and the second frequency band due to third resonance frequency which is the first odd harmonic of first resonance frequency. Due to the symmetry in the structure the even harmonics are cancelled out. The antenna is designed using 1.2 mm wide metal lines printed on a simple RT-duroid substrate (er=2.22) of thickness (H =15mils) it works like a coplanar wave guide micro-strip line of Z0 =50ohm, the structure is very simple rectangular loop printed as a micro strip line with characteristics impedance. Design is simulated using Electromagnetic simulator. We got exciting results of return loss is less than-30dB at both the resonance frequencies (1.5GHz & 4.2GHz).
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