Theory And Study Of Microstrip Antennas With Fractional-order Cavity Resonant Modes

This thesis is devoted to the study of fractional-order resonant modes in the circular sector cavity antenna,and it attempts to design antennas with different radiation characteristics using single or multiple fractional-order resonant modes in the cavity,such as planar quasi-isotropic antennas,broadband patch antennas and so on.The main content of this thesis includes:1.A planar quasi-isotropic antenna is designed by using a single fractional mode in a cavity.Firstly,the design idea of a basic U-shaped quarter-wavelength radiator evolving into a planar quasi-isotropic antenna is explored.Then,the far-field distribution of the designed antenna is deduced from the cavity model theory.According to the field distribution,the closed-form expression of the far-field radiation of the antenna is obtained so as to determine the flared angle of the circular sector,which is the important design parameter of the antenna.The flared angle should be 270 degrees for the quasi-isotropic radiation performance with the TM_2/3,1 mode.Ansoft HFSS is used to optimize the other design parameters and verify the theoretical method.The prototype antenna designed at the 2.45GHz is fabricated and measured by Agilent's 8720ET vector network analyzer and Satimo's Starlab near field antenna measurement system.To minimize the possible radiation interference caused by the feeding cable,a quarter-wavelength choke sleeve is used.The measured results are in good agreement with the simulation the actual measurement,which fully proved the correctness of the design approach.2.Based on the above evolution process,a similar design method is derived by using the multiple fractional-order modes in the circular sector cavity to design a broadband patch antenna.The 1.5-wavelength magnetic dipole as the basic radiator is evolved into a planar circular sector patch antenna.According to the three constraints,the flared angle is determined as 270 degrees for the broadband radiation,and the corresponding operational modes are TM_4/3,1 and TM_8/3,1 modes.A set of closed-form expressions of the far-fields corresponding to different resonance modes is derived to numerically validate the radiation patterns.The modal analytical and numerical results agree well with each other.A pair of tuning stubs is employed to simultaneously perturb the required two resonant modes to achieve broadband radiation characteristics.Through the parameters analysis,the optimal design parameters and verify the correctness of the theoretical method.Finally,the prototype antenna designed on air substrate and at the 3.25GHz is fabricated and measured,and the measured results are in good agreement with the simulation validating the correctness and effectiveness of the design approach.3.To further prove the design approach,a printed version is implemented on a thin dielectric substrate.Based on the above approach,a 270-degree circular sector patch antenna with dual-mode wideband radiation is designed on a F4B substrate with the dielectric constant of 2.65,and the prototype at the center frequency of 3.55GHz is fabricated.The measured results show that the antenna still own the stable broadband radiation characteristic,which more fully proves the design method.Finally,the printed antennas have been used as the high-performance receiving antennas in synchronized multi-way wireless channel sounding system for future 5G mobile communications.