| As an array technique that can improve the ratio of signal to noise and increase the frequency reuse rate effectively, smart antenna has gained a lot of attention for its promising applications especially in 4G and 5G communication systems. Smart antenna has flexible beam-forming methods, which can steer its main lobe to users and radiation null to interference. Smart antenna with its high data transmission capacity and large coverage will be a key technology in future mobile communication.However, there still some problems in conventional smart antenna that remains to be settled: complicated structure, limited array allocation, low radiation efficiency, etc.For that reason, this paper gives a series of research on the design of low profile smart antenna in following aspects:Firstly, the concept of cascaded feeding network is proposed, which can be applied to smart antenna with compact structure and flexible array-distribution. Secondly, a feeding network based on electrically tunable qusi-lumped coupler is analyzed. To improve the transmission efficiency and uniformity, the power recycling model is introduced and a low profile beam switched antenna based on cascaded feeding net work is designed and simulated. Thirdly, the paper proposes a full range electrically tunable coupler providing arbitrary power assignment ratio, then the new type of cascaded feeding network based on it is researched, which is more practical in application of smart antenna. Finally, based on the research of full range electrically tunable coupler, a tri-polarization reconfigurable antenna is designed.The results of numerical calculation and measurements demonstrates that the smart antenna based on cascaded feeding network has simple and compact structure, high degree of freedom in array assignments, providing a novel method in antenna design.The concept and structure proposed in this paper is very promising in the field of beamforming, radiation pattern optimization and multi-beam switching arrays. |
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