Characteristics and design of microstrip square ring antennas

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Mousavi Bafrooei, Seyed Pedram
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In this thesis a method for miniaturisation of a microstrip patch antenna without degrading its radiation characteristics is investigated. It involves perforating the patch to form a microstrip square ring antenna, which is investigated numerically and experimentally. The ring geometry introduces additional parameters to the antenna that can be used to control its impedance, resonance frequency, and bandwidth. For a single square ring increasing the size of perforation increases its input impedance, but decreases the resonance frequency and bandwidth. It has no effect on directivity of the antenna. A novel transmission-line model is also developed to predict the resonance frequency of a single layer ring antenna. The results of this model show good agreement with those generated by Ensemble software. With the help of the transmission-line model the possibility of using a single stub to decrease the resonance frequency of the patch is also investigated. To match the antenna to a transmission line and also enhance its bandwidth, the ring is stacked by a square patch or another square ring. The computed results are compared with experimental data and again good agreement is obtained.