Study On Compact Electromagnetic Bandgap Structure And Reconfigurable Antennas As Well As Multi-mode Filters

With the development of wireless communication, the microwave devices of higher performance are required. Multiband, multifunction and miniaturization are the developing trend of modern microwave devices. More and more novel theories are built and new materials are invented for application. The cross development of multi subject areas introduces innovative ideas and technology for the design of microwave devices. In this dissertation, compact electromagnetic bandgap (EBG) structures, reconfigurable antennas as well as multimode filters are investigated. The main contents and contributions are listed below:1. An improved quasi-static effective medium model of mushroom-like EBG structure is proposed by conformal mapping. The proposed model built a bridge between geometrical parameters and effective medium properties. The effects on the operation frequency and band width by metal vias are involved. The surface-wave bandgap calculated by proposed model is consistent with that of numerical simulation and measured results. The validation of this model is proved.2. The 12 errors model of two ports network in microwave measurement is analyzed, and the calibration setting of measurement by rectangle waveguide is proposed. By analyzing the propagation of TEio mode in rectangle waveguide, the disagreement of in-phase reflection phase between measurement results in waveguide and period unit model simulation results is explained. The errors of reflection phase measured by waveguide are analyzed, and the process to verify the property of EBG reflection phase is present.3. A TEM waveguide measurement system is built, which can operate at C band and X band simultaneously with the frequency from 5.8GHz to 8.2GHz. The TEM waveguide chamber and the feeding structure are carefully designed. The measurement results of propagating wave in the chamber prove the facts that the system can support TEM wave well. The measured result of EBG reflection phase by this system agrees well with simulation result of period unit cell model, which prove the accuracy and availability of proposed method. As a convenient and accurate measuring method, it simplifies the EBG reflection phase measurement.4. The propagation conditions of surface wave are analyzed. By inserting EBG structures around the surface antenna, the surface current and impedance matching of the antenna can be improved. The surface wave antenna operates at the engine frequency of feeding antennas, the impedance matching is improved and the operation bandwidth is broadened.5. A reconfigurable EBG structure is designed. The bandgap of surface wave can be reconfigured by controlled by PIN diodes between metal via of EBG and ground. By inserting this kind of EBG structures around a square patch antenna, the direction of surface wave is controlled. The main beam of proposed antenna can swept at four directions and the maximum gain is as high as 9.3dB.6. A radiation pattern reconfigurable antenna is proposed. The antenna is constructed by a feeding element with four individual parasitic elements. U-slot is etched on the parasitic element to control the surface current. By selection of different elements, the antenna can generate three kinds of radiation pattern. An H slot is employed to supporting bias networks, which reduces the effect of the bias feeding line on the antenna.7. A dual-band bandpass filter is proposed based on stepped impedance resonators (SIRs). The filter operates at 2.4GHz and 5.2GHz respectively, which meets the requirement of WLAN. A stepped impedance line is employed to feeding the resonator as tapped-line. This feeding structure can meet the requirements of two operation bands’out coupling simultaneously, while transmission zeros are introduced in the higher frequency out of passband. The whole size is greatly reduced by folding the resonators. Transmission zeros at lower frequency out of passband is realized by cross coupling between source/load and non-adjacent resonator. All of these transmission zeros improve the isolation of stop-band. The size of filter is reduced by 50%, which successful realize the miniaturization.