Research On The Microwave Planar Periodic Structures And Their Applications

In this dissertation, microwave planar periodic structures are researched. Theyinclude: composite right/left handed transmission lines (CRLH TLs), electromagneticband-gap (EBG) structures and zeroth-order resonator (ZOR) antennas, etc. The theories,research methodology, simulation techniques and engineering applications of theperiodic structures are investigated. Besides, a clue to link the researched periodicstructures is the CRLH theory. Specific research contents include:1. The development, electromagnetic characteristics and research progress ofdifferent kinds of microwave planar periodic structures are introduced, and theirrelations are discussed. These periodic structures include: frequency selective surface(FSS), soft/hard surface, left-handed material (LHM), composite right/left handedtransmission line (CRLH TL), defected ground structure (DGS), photonic band-gap(PBG) and electromagnetic band-gap (EBG) structure.2. The theory, development and applications of CRLH TL (or metamaterial TL) arestudied. First, several concepts related to CRLH TL are stated follow by the simple andclear introductions of characteristics of conventional CRLH TL (C-CRLH TL) and dualCRLH TL (D-CRLH TL). Then, a new TL that composite C-CRLH and D-CRLHcharacteristics is proposed and investigated. The new TL is utilized to design low-passfilter (LPF). The proposed LPF has a3dB cut-off frequency at2.38GHz, and its size is16mm*16mm (0.13λg*0.13λg，and λgis the free space wavelength of the cut-offfrequency). The concept of CRLH TL is also used to design compact wide-stop-bandband-pass filter (BPF). The3dB band-width of the proposed BPF ranges from1.04-1.34GHz (25.2%bandwidth), and its size is20mm*17mm (0.080λg*0.068λg，and λgis the free space wavelength of the center frequency).3. EBG structures are researched. First, the operational mechanism of conventionalmushroom-type EBG (CMT-EBG) structure and its relationship with CRLH TL isdiscussd. Three simulation techniques for EBG structures are discussed, then, a newsimulation approach for CMT-EBG structure’s band-gap frequencies detection areproposed based on CRLH and ZOR theories. The new approach are proposed according to the conclusion that band-gap of CMT-EBG can be delimited by resonant frequenciesfshand fse. Boundary conditions for the new approach are deduced and two microstripline based models are designed to calculate the band-gap frequencies. Research foundthe proposed approach have the advantages of good accuracy, simple model, easyfabrication and measurement. According to electromagnetic system’s requirements ofcompactness and multi-band, compact multi-band EBG structures are designed. OneEBG design is based on complementary split ring resonator (CSRR), and its size is28%smaller than the CMT-EBG structure. Another EBG design (DAU-EBG) is morecompact: its size is74.1%smaller than the CMT-EBG structure, and three and twoband-gaps are happened at x and y directions, respectively.4. The applications of EBG structures on ultra-wideband (UWB) antennas fornotches design are investigated. The approach of utilizing EBG structures couple tomicrostrip feeding ling of UWB antennas for single, double and triple band-gaps arestudied. Research found the proposed UWB band-notched design approach can conquerthe two main problems of notch design: high-efficiency multi-notches design and notchwidth control. Besides, the introduction of EBG structures has little effect on UWBantennas’ pass-band characteristics. Time domain characteristics of the UWBband-notched antennas are researched by group delay, waveform response, correlationcoefficient, and pulse width stretch ratio (SR). Research found the introduction of EBGstructure have very small effect on the antennas’ time domain characteristics, therefore,the proposed notch design approach is good for maintain UWB antennas’ time domaincharacteristics.5. A new ZOR (the MZR-EZR resonator) is proposed, and its applications areinvestigated. First, conventional ZORs that deduced from CRLH TL are introduced, andthe classification of ZORs is derived: mu-zero resonator (MZR) and epsilon-zeroresonator (EZR). Then, an approach to deduce the boundary conditions of ZORs wasproposed by simple circuit model. According to the necessary boundary conditions andfields distributions of EZR and MZR, a new resonator, composite the characteristics ofMZR and EZR, is designed. The resonator is MZR-EZR resonator. Research foundcoupling feeding system would be a better way for impedance matching when theresonator used as antenna, and the antenna has a wide HPBW. The MZR-EZRresonators are also utilized as parasitic resonators to enhance microstrip antennas’ bandwidth. Research found microstrip antennas’ bandwidth can be increased from2.2%to5.1%. Research also found the proposed MZR-EZR resonator has two orthogonalpolarized fields, and the phase difference between the fields is fixed to be900. Thus,four MZR-EZR resonators are form in a circular way to make both the polarizationsradiate omni-directionally. From field distributions of the circular polarized antenna, itis found that the antenna acts like an electric dipole in certain phase, and acts like amagnetic dipole in a900phase difference. Then, a low-profile omni-directional circularpolarized antenna is obtained.