INVESTIGATIONS ON CIRCULARLY POLARIZED INVERTED STACKED PATCH CIRCULAR MICROSTRIP ANTENNA

Abstract

In this dissertation, the design of a circularly polarized, inverted stacked patch, circular microstrip antenna is described. Size reduction has been achieved by choosing circular ring structure. Circular polarization has been achieved with a conducting strip across the diameter of inner circle of the circular ring. It is found that the circular polarization operation depends heavily on the inner radius and the conducting strip width. For further size reduction, an angular stub loading at the outer periphery of the circular ring has been proposed. An air-gap has been used to achieve a larger VSWR and AR bandwidth. Air-gap also helps in impedance matching of the linearly polarized, inverted stacked patch, circular ring antenna. However, it was found that for circularly polarized, inverted stacked patch, circular ring antenna, a A/4 transformer is necessary to achieve a VSWR bandwidth over the desired frequency range. First of all, the effects of various main parameters for single patch antenna have been studied. Next; the antenna element with only the conducting strip has been optimized for large axial ratio bandwidth covering 2.5 GHz - 2.7 GHz. The antenna has single feed structure with microstrip line edge-feeding. The simulated 3-dB axial ratio bandwidth achieved is 7.7 % with centre frequency of 2.6 GHz. Thereafter, an inverted stacked patch antenna with an angular . stub loading has been optimized for a large 3-dB axial ratio bandwidth, which has a smaller size than the antenna element with only the conducting strip. It can further be optimized for more size reduction with a larger angular length of the stub and for more bandwidth with a larger. air-gap. Finally, sequentially rotated 2 x 2 array using optimized elements with only the conducting strip, has been designed. Effect of inter-element distance on various characteristics of the 2 x 2 array has been studied. A 15.7 %axial ratio bandwidth has been obtained from the optimized simulated 2 x 2 array. The antenna element with only the conducting strip and the 2 x 2 array have been fabricated. A comparison of simulated and experiment results has also been presented.