Research On Wideband Antennas And Shaped-beam Array Antennas

With the rapid development of modern communication technology, the sizes ofcommunication electronic equipments are increasingly miniaturized, and their ability toprocess information is also increasingly intelligent and broadband. In order to adapt tothe fast growth of modern wireless communication, there is no doubt that broadband,multi-frequency and miniaturization technology for antennas must be developed. In thisdissertation, based on the research projects, wideband sleeve antenna, multi-frequencyprinted antenna, ultra-wideband antenna and broadband beam-shaped array antennahave been studied intensively so as to obtain the designed antennas with characteristicsof miniaturization, multi-band and wideband and the array antenna with broadband. Theauthor’s major contributions are as follows:1. Broadband low profile sleeve monopole antennas are studied. Aiming at digitalTV band, a broadband low profile tapered sleeve monopole antenna is designed with theproposed disc top loading technology, by a shorting probe connecting top loading discand ground to achieve low profile effectively and tapered sleeve to achieve broadband.For mobile communication and wireless communication band, a broadband low profilering sleeve monopole antenna is designed, with the top loading disc, tapered lineargradient structure and shorting probe to reduce the antenna’s height and size, byadjusting the tapered angle to improve input impedance and the ring’s structure tocontrol its working mode at high frequencies and widen impedance bandwidth greatly.After that, a broadband low-profile double sleeve monopole antenna is studied, withopened sleeve structure to produce a third incentive mode at high frequencies so as tofurther expand the working band.2. Broadband bow-tie antennas are investigated. The impedance bandwidth of thiskind antenna can be broadened effectively by a space electromagnetic coupled-fedbalun structure and feeding the end shorted bow-tie antenna. But the radiation pattern athigh frequencies becomes split, and the inverted L-shaped leading junction structure isintroduced to improve its radiation characteristics. Based on these, a broadbandcircularly polarized antenna is investigated, focusing on the effects of some parameterson the axial ratio characteristics. Also, it is given an end equivalent bow-tie antennawith broadband characteristic by adopting end equivalent form to match the impedanceat low frequencies and electromagnetic coupled-fed balun to adjust impedance over the whole band. Meanwhile, an ultra-wideband bow-tie antenna with back cavity isproposed, using parasitic leading junction and ring structure together to improve theradiation characteristics within operating band.3. Broadband and multi-band printed antennas are presented and studied. Abroadband printed dipole antenna is given by employing electromagnetic coupled-fed, aG-shaped printed monopole antenna, by introducing branches and electromagneticcoupled-fed to obtain dual-band and broadband, and a multi-branch monopole antenna,by loading symmetric L-shaped slots in the ground to adjust the impendence withinentire band. At the same time, a monopole antenna with parasitic bending is designed,through parasitic coupled branch from ground to achieve multi-band performance, andbending radiator to extend the current path in order to obtain low profile andminiaturization. Then, by combination of round and ladder radiator, giving a smoothcrossover of each resonant mode, to achieve ultra-wideband, and loading U-shaped slotsin radiator and V-shaped slots in ground respectively to reach double notchescharacteristic, a ultra-wideband printed antenna with notch performance is presented,which gives compatibility among ultra-wideband wireless communication systems,WLAN and WiMAX systems.4. Broadband beam-shaped array antennas are investigated. A wideband arrayantenna flat-top beam-shaped is studied using adaptive differential evolution algorithmdominating its research status at the present stage. It is proposed to put patterns of eachunit and each frequency into the optimization process to overcome the neglect oftraditional array mutual coupled during the optimization process, which improves thereliability of the calculation results. What’s more, there are designed the broadbandcircularly polarized antenna elements, and feed network with broadband phasedifference by the introduction of phase comparator. Finally, the prototype of antenna isfabricated and its measured results of far-field radiation show the design method isreasonable and valid in this paper.