| Resonance-Based Reflector(RBR)antennas have the advantages of wide band,compact size and unidirectional radiation.Although the reflector of these antennas can achieve in-phase reflection in wide frequency band,they have the disadvantage of low reflection magnitude,especially in high frequency band.It's difficult to achieve wide front-to-back ratio(FBR)bandwidth.In order to resolve this problem,two resonance-based reflectors,ring with three stubs resonance-based reflector(RTS-RBR)and ring with four circles resonance-based reflector(RFC-RBR),which can effectively improve the reflection magnitude,are designed in this paper.Unidirectional antennas based on these two resonance-based reflectors have wider front-to-back ratio bandwidth.In addition,the human body detection technology based microwave is a research hotspot in recent years,which requires high performances for antennas,such as broadband,unidirectional radiation,miniaturization and conformal.In order to meet these requirements,in this paper,resonance-based reflector technology is applied to the design and research of human detection antenna.Moreover,the conformal resonance-based reflector antenna is designed with flexible material for the applications of human brain detections.The main work and contributions of the thesis are listed as follows:1.The theory of transmission lines is briefly introduced.The working principle for resonance-based reflector is elaborated using both the electromagnetic field theory and the circuit theory.Resonance-based reflector is compared with AMC and FSS in their working principle of achieving in-phase reflection and low-profile.Their advantages and disadvantages are analyzed,which indicates the application prospects of resonance-based reflectors in wide frequency band and miniaturization.2.The RTS-RBR and broadband unidirectional antenna are designed and researched.Based on the existing ring-shaped resonance-based reflector,the RTS-RBR,which has a high reflection magnitude in the in-phase reflection band,is designed.The reflection magnitude of the RTS-RBR in the in-phase reflection band of 3.23-6.24 GHz(63.57%)varies between 0 dB and-11.53 dB.A wideband unidirectional antenna is designed with the RTS-RBR and a teardrop-shaped bow-tie antenna.The proposed antenna has a measured impedance band of 3.48 GHz to 6.12 GHz(55.00%)and a measured front-to-back band(FBR > 10 dB)of 3.48 GHz to 6.12 GHz(55.00%).The maximum FBR is up to 20.4 dB and the antenna profile is only 0.15?.Compared to the ring-shaped RBR antenna(37.29%(FBR > 5 dB)),the front-to-back ratio bandwidth of the RTS-RBR antenna is 55%(FBR > 10 dB),which increases by 17.71%.3.The RFC-RBR and broadband unidirectional antenna are designed and researched.In order to reduce the resonance frequency of the reflector and to reduce the size of the antenna while ensuring wide bandwidth,RFC-RBR with almost the same physical size as the RTS-RBR is designed with a lower resonance frequency.The reflection magnitude of the RFC-RBR in the in-phase reflection band of 2.61-5.59 GHz(72.68%)varies between 0 dB and-6.93 dB.The resonance frequency is 2.73 GHz,and it's 620 MHz lower than the resonance frequency of the RTS-RBR(3.35 GHz).Moreover,the reflection magnitude of the RFC-RBR is also larger than the RTS-RBR.Then,an elliptical monopole antenna is used as the radiating element,and it is combined with the RFC-RBR to form a unidirectional antenna.The proposed antenna has a measured impedance band of 2.12-6 GHz(95.57%)and a measured front-to-back ratio band(FBR > 10 dB)of 2.2-4.74 GHz(73.20%)with a maximum FBR of 27.21 dB.The height of the antenna is 0.12?.4.Bio-electromagnetic properties are researched by using non-conformal and conformal resonance-based reflector antennas.The RFC-RBR unidirectional antenna is used as the operating antenna to study the transmission characteristics of electromagnetic wave in human brain detection and the interactions between the human brain and electromagnetic wave,including field distribution analysis and SAR analysis.In addition,flexible material is used to design a conformal resonance-based reflector antenna.The effects of the conformal shape of the RBR are investigated on the unidirectional radiating characteristics and the human brain electromagnetic properties effects,including SAR analysis.The non-conformal and conformal resonance-based reflector antennas have good radiation performance in human brain detection.They meet the safety standards,and have good application value in the field of bio-electromagnetics.However,the conformal antennas adapt to the human body. |
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