Research On UWB Photonic Crystal Antenna Based On MEMS Technology

UWB is a radio engineering technology with ultra wide spectrum resource,which is mainly applied in the short-range high speed communication,image transmission,wireless sensor network and so on.The antenna is the energy conversion device of wireless systems,which size and performance have the significant influences on the whole system.When UWB technology is used for terminals of portable mobile systems,antennas should have the advantages including low profile,small size,easy to integration with other circuits and so on.It is great significant that research on UWB antenna with miniaturization and integration.To gain better radiation performance,low dielectric constant materials are generally used for designing UWB antenna.Because of the inverse relation between planar size and dielectric constant,antenna miniaturization is the choke point in design process.This paper utilizes high dielectric constant silicon material as substrates to design miniaturized UWB antennas.The proposed silicon antennas have very compact planar size.The silicon substrate is also used for RF integrated circuits,so silicon antenna and functional circuit can be fabricated together to reduce power loss of isolate elements and improve antenna integration level.Photonic crystal structure is applied in UWB antenna design processes to improve radiation performance of silicon antenna in this paper.Photonic crystal is an artifical electromagnetic material with permittivity periodic distribution,which unique frequency band gap characteristic can restrain surface wave loss of silicon substrate effectively.MEMS is the three dimensional manufacturing technology of micro electromechanical systems with characteristics of micromation,integration and quantity production.In this paper,MEMS technology is used to fabricate silicon antennas,which can realize cavity,through-hole and other subtle and complicated structures accurately.This paper researches on UWB antennas for small volume wireless equipments.The design and implementation methods of new style antennas are studied based on multi-disciplinary analysis,which includes antenna technology,artificial electromagnetic material technology and MEMS technology.The main achievements include these contents.Firstly,the design method of planar monopole UWB antenna is studied based on transmission line modal theory.The wide impedance matching characteristic of antenna isobtained by modifying rectangular radiation patch and CPW feeder.To avoid interference from existing narrowband systems,the UWB antenna with dual band-notched function is proposed.The notched elements,that are two biased T-shaped parasitic elements in the rear side and a window aperture on the radiation patch,are combined to generate resonance phenomena at corresponding frequency bands respectively.The results demonstrate that the proposed antenna prevents narrow band signal interferences from WLAN and WiMAX effectively.Secondly,high dielectric constant silicon is used as substrate to improve miniaturization of UWB antenna.The design method of silicon UWB antenna with back cavity is proposed.The back rectangular cavity is etched to form hybrid structure of silicon and air,which can lower effective dielectric constant and reduce surface wave loss of silicon substrate.The detailed MEMS processing steps are designed to fabricate silicon UWB antenna with photoetching,coating and ICP cavity etching process.The frequency domain and time domain results show the miniaturized MEMS antenna has good omni-direction radiation performance in the UWB frequency band,and high correlation property exists between input signal and response signal via antenna radiation.Then,in order to improve transmission rate and communication reliability of UWB systems,the design methods of UWB-MIMO antennas with two and four elements are proposed based on silicon antenna with back cavity.Limit to small antenna area,the metamaterial MEFSS unit with single negative electromagnetic property is designed to reduce mutual coupling between antennas,which has band-stop filtering function in the entire UWB band.The MEFSS units are arranged longitudinally to compose one-dimensional photonic crystal structure,then placed in UWB-MIMO antennas with two and four elements.Because the working frequency band of MIMO antennas is the same as band gap range of MEFSS unit,coupling coefficients of adjacent antennas and opposite antennas are decreased to improve isolation of UWB-MIMO antennas.Additionally,in order to enhance radiation efficiency of silicon antenna,the design method of photonic crystal UWB antenna is proposed by applying periodical square lattice or triangular lattice.Photonic crystal band gap of energy band structure can decrease electromagnetic wave absorption of silicon substrate,restrain surface wave loss of antenna,and increase electromagnetic wave space radiation.MEMS processes are used to fabricatephotonic crystal antenna with plenty tiny through-holes,which include photoetching,coating,ICP through-hole etching and bonding processes.The results demonstrate the antenna design method can obviously extend antenna working bandwidth based on two dimensional photonic crystal construction.Eventually,in order to restrain interference from irrelevant signals to photonic crystal antenna,the design method of notched UWB antennas with photonic crystal is proposed based on defect band characteristic of photonic crystal defect waveguides.When the periodicity of photonic crystal is broken,the electromagnetic waves propagate along defect direction.In antenna structure,defect waveguide can change surface electromagnetic distribution of substrate,concentrate energy on defect position,and present band notched function of resonance unit.After correct designing of photonic crystal defect waveguides with square lattice and triangular lattice,photonic crystal UWB antennas can respectively restrain signals from X band and Ku band.