Study On Multi-Mode Electro-Magnetic Dipole Combined Antennas

With the advent of high-rising buildings and densely populated indoor environment, wireless communication environment has becoming more and more complicated. Furthermore, the indoor wireless signal coverage sets higher demands to the antenna’s performance of operational bands, dimensions and gain. Thus, the development of directional antennas with simple structure and high performance has important practical significance. Based on the basic theory of complementary antennas, two kinds of multi-mode magnetic-electric combined antennas have been proposed. The design approaches and the operation principles are analyzed in details. The main content of this thesis is organized as follows:1. Based on the classical Huygens principle, by combination of microstrip slot and aperture-dipole elements, a multi-band directional antenna is proposed. Then modeling and simulation have been taken by using Ansoft HFSS. Fractional-order modes of electro-magnetic dipole combined antennas have been explored by analysising the current distribution and radiation pattern. Furthermore, formulas at different resonat frequencies are deduced to valiate the operation principles.2. Multiple modes theory of ideal square loop antenna: A squre loop antenna under even mode operation is investigated. An approximate model based on equivalent multiple sources is developed to describe its radiation characteristics at first. The calculated results of the proposed model are validated by a few classical analytical models. Then, the proposed model is applied to analyze traditional linearly-polarized(LP) and circularly-polarized(CP) loop antennas. Finally, it is further used to design a new loop-dipole combined antenna in the step-by-step procedure. It is theoretically exhibited that a square loop antenna under even-mode excitation can work together with a conventional dipole antenna under odd-mode feeding to form a new complementary antenna with cardiac-shaped radiation pattern.3. Based on the proposed antenna above, parameters of the antenna are analyzed and the optimal size is confirmed. Then, the antenna is simulated and permance optimized by Ansoft HFSS. Antenna prototypes are fabricated to experimentally verify principle of the design, and finally measured by Agilent’s 8720 ET vector network analyzer and Satimo Starlab system. The measured results matched well with the simulation, and the odd mode theroy of loop antenna is well verified. The operation frequency of the antenna is 2.37-3.05 GHz, the average gain is 5.5dBi, and the antenna has quasi-directional pattern, which makes it used in the indoor directional antenna system.