A theoretical analysis of a gap-coupled stacked annular ringmicrostrip antenna with superstrate is performed in order to obtain wider bandwidth operation. The effects of air gap, superstrate thickness and feedingpoint location on the antenna performance are analyzed in TM11 mode usingequivalent circuit concept. It is noted that the proposed antenna is very sensitive to the feedingpoint location in TM11 mode while annular ringmicrostrip patch antenna is independent of feed point in that mode. The optimized proposed antenna shows an impedance bandwidth of 13.96% whereas the antenna without air-gap has 8.75% bandwidth and without superstrate it has bandwidth of 10.89%. The theoretical results are compared with simulated and experimental results.
Microstrip patch antennas are becomingpopular because of their numerous advantages such as their low profile, conformability, low fabrication cost, mechanical robustness, polarization agility, compatibility/easy integration with microstrip circuits/solid state devices and adaptability to active antenna elements. Although, in principle, the patch may be of any shape yet, in practice, only simple geometries like rectangular, square and circular structures are commonly employed. Like rectangular and circular patches, the annular ringmicrostrip antenna (ARMSA) has received the considerable attention of several investigators [1–8] due to its many salient features such as small size and broader bandwidth compared to other conventional patches. However, the main obstacle that restricts its wide applications in various fields is its inherent narrow bandwidth and low gain

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