Theory Of Multi-mode Resonator For Small Antenna Design

The antenna is the device for microwave transmitting and receiving, and goodperformance of antenna can be obtained with sufficient volume. However, the antennais unable to operate in a space-limited system. Therefore, the volume of mobile devicecan’t be minimized due to the limitation of antennas. In this thesis, we have studied thetheory of multi-mode resonators in the view of small antenna design. In this theory, newmodes are constructed in the origin antenna structure. The antenna performance hasbeen improved due to the new added modes without increasing the antenna dimensions.Compared with the conventional small antenna design strategy, the “mode” resource hasbeen added as another design freedom for the enhancement of performance, such asimpedance bandwidth, radiation efficiency and so on. The proposed theory can beadopted in the antenna applications of small-volume mobile terminal, base station andmillimeter wave array.For the mobile antenna design, we have constructed different modes in the antennaelement. By coupling and switching the antenna modes, achieved is multi-bandapplication and dimension minimization of antenna. We have proposed a feedingswitchable IFA antenna, for the purpose of small antenna dimension and quad-bandcoverage. What’s more, a shorting switchable loop antenna is designed with smallervolume and more bands coverage. In order to enhance the radiation efficiency withoutthe increase of antenna dimension, a hepta-band IFA-loop antenna is presented underthe multi-mode resonator theory, and the dimension of this antenna is only5560mm3.We also adopted the multi-mode resonator theory in the design of matching network.The series modes and discrete modes matching network are also designed for antennaminimization.For the base station antenna design, the thesis is focused on the topic of multipleantenna design in space-limited system. We have constructed two orthogonal modes toprovide dual polarizations with high ports isolation. We use the dual-polarized antennain order to take the place of two space-isolated single polarized antennas. Firstly, wehave proposed a dual-polarized slot antenna with dual-mode CPW feeding. For theantenna dimension minimization, the loop element is adopted instead of the slot element. Further more, we have used3-D structure to design a CPW-based dual-polarizedantenna. In order to enhance the isolation between two polarization modes, we haveproposed a slot-monopole antenna. We also designed a slender cylinder type dual-slotantenna, for the purposed of horizontal omnidirectional coverage.In the design of millimeter wave antenna, we have proposed a wideband circularlypolarized antenna element with the strategy of modes coupling. The mutual couplingbetween two antenna elements is also studied in the array design and new decouplingmethod is proposed to achieve good performance. Finally, we have completed a LTCCbased44-element60-GHz SIW-fed circularly polarized antenna array, with theimpedance bandwidth and axial ratio bandwidth both covering the60GHz band of57-64GHz.