| Microwave wireless energy transfer is a technology that uses near-field or far-field microwaves radiation as carrier to transmit energy.Compared with other wireless energy transfer technologies such as electromagnetic induction coupling and magnet ic resonance coupling,microwave energy transfer has the advantages of point-to-multipoint transmission,easy deployment,safety and reliability.It has wide application prospects in the fields of solar power stations,wireless energy supply of near-space vehicles,and wireless self-power supply of sensors.Antenna is a kind of electromagnetic structure that realizes the mutual conversion between circuit oscillation energy and electromagnetic wave radiation energy,which is one of the core components of a wireless information/energy transmission system.Its feeding/radiation efficiency and beam transmission characteristics determine the efficiency of the microwave energy transmission link.Therefore,exploring and developing new antenna structures,working mechanisms and design methods with high radiation efficiency and quasi-diffraction-free radiation beams have become a research hotspot in the microwave energy transmission academia and industry areas.However,the traditional self-focusing beam transmitting antenna array and its feeding network have complex architectures and low energy conversion efficiency;the electromagnetic wave dispersion caused by the spherical spreading of energy in isotropic spaces(e.g.,air)is at the origin of the large propagation loss usually experienced by propagating microwaves;the low aperture utilization efficiency of traditional microwave energy transfer transceiver antenna array systems results in the inability to achieve maximum spatial transfer efficiency.To solve the above scientific problems,this dissertation studies high-efficient self-focusing beam radiation mechanism,quasi-non-diffraction beam forming method,and high aperture efficiency and high-density transceiver antenna array system technology,developing the self-focusing beam forming antenna array design and its low insertion loss feed network implementation,independent amplitude and phase design method,quasi-non-diffraction beam forming antenna array design and fast design method for three-level unequal power division feeding networks,as well as high-density transceiver antenna array design and high space transmission efficiency port-excitation methods.The performance of these microwave energy transmission array antennas,their beam forming characteristics,and the spatial transmission efficiency are systematically analyzed.The main research work and innovative contributions of this dissertation are as follows:1.For the complex architecture,large insertion loss,low aperture efficiency and low radiation efficiency of traditional self-focusing beam forming antenna based on rectangular transmitting antenna array and feeding network structures,a self-focusing circular antenna array and its circular equal amplitude and equal phase distribution feeding network architecture based on radial waveguide with TEM mode are proposed to significantly reduce the complexity of beam forming feeding network design and implementation,enhancing the radiation efficiency of the antenna.By loading a metal cylindrical shunt impedance converter at each coupling element in the radial waveguide,the reflection loss at each feeding port as well as the insertion loss of the radial waveguide feeding network are reduced.Through the independent design of coupling unit structure in the circular array within the radial waveguide at different radii and the microstrip transmission line phase shift structure between the coupling unit and the antenna unit,the decoupling regulation of the feeding amplitude and phase of the self-focusing beam forming antenna array is investigated,so as to achieve the required characteristics of Chebyshev amplitude distribution and square law phase distribution,and finally realizing the high-efficient self-focusing beam forming.A 5.8 GHz self-focusing beam forming circular antenna array with an aperture surface diameter of610 mm is designed and developed.The results show that the feeding network insertion loss is 0.46 dB,and the radiation efficiency is 84.5%.When both the receiving and transmitting ends are realized with such antenna array and the distance is 5 m,the measured spatial transmission efficiency of microwave energy transfer can reach 54.5%.The efficiency of the spatial beam transmission is larger than that of the equal-amplitude focus beam and Chebyshev-amplitude equal-phase beam under the same transmission conditions.2.For the large propagation loss of electromagnetic waves which follows a square law with the distance increase due to the beam spreading effect,the idea of using quasi Airy/Bessel microwave beams and array antenna structures for quasi Airy/Bessel microwave beam radiation is proposed.Based on the electromagnetic field distribution on the aperture surface of the quasi-Airy beam and the Nyquist sampling theorem,it is proposed to use the sampled microwave signal(predetermined feed signal amplitude and phase)to feed each array element of a microstrip patch antenna array to radiate a quasi-Airy beam.A three-level asymmetric microstrip line feeding network for quasi-Airy beam forming is rapidly designed through simulated annealing and an iterative algorithm.A 5.8 GHz quasi-Airy beam radiation array structure based on microstrip patch antenna was designed and developed.The power division feeding network can meet the amplitude and phase distribution requirements of the sampling Airy function,and finally realizes the efficient quasi-Airy beam forming based on the microstrip antenna array.The designed and developed 5.8 GHz microstrip antenna array successfully generates a quasi-Airy beam propagating along a parabolic trajectory;its energy loss is 1.46 dB when it propagates from 1 m to 3 m;the synthesized new focused Airy beam propagates from 3.5 m to 4.5 m with an energy loss of 2.14 dB.This loss is lower than the propagation loss of conventional electromagnetic beams,which decay by the square law of distance.The microwave energy transfer characteristics of quasi-Bessel beams with straight-line propagation trajectories are further studied,and concentric circular array antennas are designed by the target field synthesis method to realize quasi-Bessel beam forming.The energy transmission loss of the generated quasi-Bessel beam is 3.66 dB,lower than that of the equal-amplitude focused beam under the same transmission conditions.3.For the low aperture utilization efficiency of microwave energy transmission transceiver antenna array,a high-density array microwave energy transmission transceiver antenna array architecture design idea is proposed.The effect and mechanism of the distance between the array elements on the radiation efficiency of the element and the return loss of the input port of the element,as well as the influence law on the spatial transmission efficiency of the transceiver array are revealed through the analysis and simulation research of infinite array equivalent models.Based on S parameters representation of the N×M-order equivalent network,the excitation coefficient of the transmitting array is derived.The energy space transmission efficiency characteristics between array systems with the same high-density array structures and different excitation coefficient distributions are obtained through simulation,which can effectively guide the design of high-density array antennas with a given aperture size.A5.8 GHz array antenna with 8 × 8 electric LC type antenna element and a dimension of99.2 mm is designed,and its beam energy space transmission efficiency is higher than array antennas with only 3×3/4×4 array elements.This dissertation studies antenna structures,beam forming and design methods for high-efficiency self-focusing beams,quasi non-diffractive beams,and high aperture efficiency,and develops high-efficiency self-focusing beams antenna array and quasi non-diffractive beams antenna array in the microwave regime,which can effectively reduce the space transmission loss of microwave energy,improving the efficiency of microwave energy transmission systems.These research results provide a new engineering way for the realization of high-efficiency microwave energy transmission system,which is beneficial to promote the application of microwave energy transmission technology. |
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