Design Of Several Multiple-Band CPW-Fed Printed Antennas

As a key component of wireless communication systems, the antenna withbroadband and miniaturization characteristics has become the main development trend,with the development of radio technology. Printed antennas with low cost, easyfabrication, good performance, small size and other features have attracted muchattention over years. As a kind of printed antennas, coplanar-waveguide-fed antennasalso have some special advantages. In this thesis, by using the coplanar waveguidefeeding structures, some multiple-band omnidirectional and directional printed antennasare designed.First, a multi-band coplanar-waveguide-fed antenna with L-shaped and U-shapedslots covering the PCS, Bluetooth, WiMax and Broadway HIPERLAN/2bands isdesigned. Using Ansoft HFSS simulation software, effect of the slot lengths andpositions on the antenna stopband is analyzed, and the structural parameters of theantenna are determined. According to the simulation results，the antenna prototype isfabricated. The measured results show that the reflection coefficients of the antenna atthe working frequency are less than-10dB.Then, based on electromagnetic symmetry properties, the size of the proposedantenna is reduced to half. According to the impedance matching theory, an L-shapedmatching arm and the linear gradual structure are added. Using Ansoft HFSS simulationsoftware, effect of the structural parameters on the surface current distribution isanalyzed, a set of optimum parameters are determined, and the reflection coefficients ofthe antenna in the operating frequency band are greatly improved. The simulationresults show that the reflection coefficients in the working frequency band are less than-10dB.Finally, a planar Quasi-Yagi antenna covering PCS, WLAN, ISM, TD-LTE andWiMAX band is designed. Three dipoles are excited by CPW through a CPW-to-CPStransition, which can excite the odd-mode electric fields with a180degree phaseshifter. Using Ansoft HFSS simulation software, effect of the structural parameters ofthe antenna on its performance is analyzed. The surface current distribution of theantenna is also simulated. The equivalent circuit model of the antenna is provided toanalyze the working principle of three dipoles for1.85-2.00GHz and2.25-3.05GHzand3.35-3.85GHz bands. According to the simulation results, the antenna model is fabricated. The measured results are in good agreement with the simulated results. Themeasured front-to-back ratios of the antenna patterns are about10dB in the workingfrequency.