Research On Technology Of Multiband And Miniaturized Terminal Antennas For Wireless Communications

The design of multi-band and miniaturization for terminal antennas is a research hot in recent years.The development of wireless communication technology sets higher requirement for antenna design.The main problem for terminal antenna is to cover a wide band or multiple bands in a limited volume.It is also an important research direction in the future.Many traditional methods cannot be applied any more,that is because of the complicated electromagnetic environment caused by the highly integrated and miniaturized wireless communication devices.Thus as a result,new breakthroughs are required.In this dissertation,the problems of miniaturization and multi-band operation are studied.From the point of basic working principles of antenna,some new methods are introduced and feasible specific designs are also presented.Besides,the reconfiguration technique and artificial magnetic conductor(AMC)are studied and some new ideas are proposed.The applications in terminal antennas validate the effectiveness of the proposed methods in obtaining the desired radiation characteristics.This thesis can be divided into the following parts.Firstly,muti-band techniques for terminal antennas are studied.Based on multi-band monopole antennas,the method of merging multiple modes is analyzed and the design principles are given.Based on the method of merging multiple modes,specific design techniques are also presented for different cases,including the problems of multi-band operation,small size,wide and narrow band combination,etc.For compact multi-band multiple input and multiple output(MIMO)antennas,the methods of using pattern diversity and polarization diversity are studied,aiming at designing dual antennas in a small volume.For the mobile communication antenna,a dual-element antenna with limited ground clearance is proposed,which meets the requirement of multi-band operation and low mutual coupling.On the other hand,for the dual-band wireless local area network(WLAN)antenna,bidirectional pattern is achieved by combing monopole and wide slot.The method of isolation improvement is also introduced.For mobile communication terminal antennas,a compact smartphone antenna is designed.By using multi-mode monopole and bezel mode,the hepta-band for the fourth generation mobile communication is covered with unbroken bezel and size-reduced ground clearance.Opposite bezel modes are obtained by introducing capacitively loading method,and as a result,the bandwidth for the low band is widen.For the high band,a threedimensional metal structure is designed,combing multiple resonant modes,providing a wideband coverage with good radiation performance.The proposed antenna has advantages of complete bezel,low profile and small ground clearance,which make it to be a good potential candidate for commercial applications.For ultra-wideband(UWB)communication terminal antennas,a new deign method using wideband slot antenna is introduced.Different from traditional wideband design with multiple resonances,the proposed antenna utilizes the current distribution characteristics of slot strcture,and further generating the traveling-wave mode.Benefited from the travelling-wave mode,wide band and stable radiation performances are achieved.The fidelity of transmitted and received time domain impulse signals are also guaranteed.The proposed UWB slot antenna has narrow slot width,compact size,simple structure and stable radiation characteristics,making it appropriate for various wireless communication devices.At last,two emerging techniques,reconfiguration and artificial magnetic conductor(AMC)are studied and applied to terminal antenna design.The main innovations are as follows.Firstly,a pattern reconfiguration method based on loading parasitic loop pair is proposed.When the parasitic loop pair is loaded to a single slot antenna,two additional end-fire modes are generated apart from the original broadside mode.Multiple switchable radiation modes meet the requirement for applications in multi-environment.Secondly,the pattern reconfigurable circular patch antenna is studied.By exciting a single-layer circular radiator with a direct-differential hybrid feeding network,switchable conical and broadside patterns are achieved.The antenna has simple structure and good radiation performance.At last,a novel AMC structure based on slow-wave surface is proposed.The size of the unit cell is reduced,which is appropriate as antenna reflector,giving good performance for the design of compactness and directional patterns.