Research On The Technology Of High-focused Space-feed Antennas

With the rapid development of wireless communication system,the spectrum re-sources of microwave low frequency band are increasingly crowded,and the mutual in-terference between the systems becomes serious.The millimeter wave(MMW)band has rich spectrum resources,making it possible for future communication systems to transmit information with high capacity and high rate.However,the atmospheric transmission loss of MMW is serious,and the attenuation is great under the influence of rain and fog.In order to solve this problem,the antenna is usually required to have a strong ability to focus the radiation energy.The space-feed array antenna,inheriting the advantages of space-feed antenna and microstrip arrays,can flexibly modulate the electromagnetic wave from the feed source,to achieve the desired beampattern.It owns the advantages of strong focusing ability,simple feed and flexible design,which has been drawn more and more attention by researchers.The transmitarray(TA)antenna is taken as the main research object in this dissertation,and the low-profile design,conformal design and bidirectional radiation characteristics are studied.At the same time,the near field shaping and focus control of the TA antenna are also discussed in detail.The main research contents and innovation points of this dissertation are as follows:1.A novel design method of low-profile TA antenna is presented.Three different methods are proposed to design the transmitting surface,namely,planar medium phase shifting element,double-layer phase shifting element loaded through hole and double-layer phase shifting element combined with multiple FSS types.Then,the transmitting surface is directly loaded on the aperture of a profile-reduced horn,forming the TA an-tenna with compact size.Simulation and experimental results demonstrate that,the profile reduction of the designed TA antenna is 42.3%,45.9%and 50.7%compared with the stan-dard horn antenna,respectively,while the peak gains are maintained at the same level.2.A novel design method of high gain transmit-reflect-array(TRA)antenna is pre-sented.Firstly,the design method based on sparse array is discussed.The phase shifting surface integrates both transmission and reflection units,which is then optimized by the multi-population genetic algorithm,realizing the independent adjustment of the radiation characteristics such as the peak gain and beam pointing of the bidirectional beams.Several simulations are introduced for verification.Then the amplitude-phase modulation(APM)unit is designed based on the multilayer FSS structure.A high-gain TRA antenna with bidirectional beams of the same polarization properties pointing to 0?/170?is developed,achieving a peak gain of 21.4/24.4 d Bi and a 1-d B gain bandwidth of 6.7%/9.3%.Finally,an APM unit with polarization rotation characteristics is proposed.Based on this,a TRA antenna with orthogonally polarized bidirectional beams is developed,obtaining a peak gain of 24.1/24.0 d Bi and a 1-d B gain bandwidth of 16.2%/13.1%,respectively,for the transmission and reflection beams.Literature investigation demonstrates that this is the first time that the sparse array method is applied to the space-feed array antenna.3.A high gain broadband wide-angle scanning conformal TA antenna is proposed.Firstly,the limitation of beam scanning range of the single focal conformal TA antenna is analyzed.Then,the bifocal concave cylindrical conformal TA antenna is designed.A peak gain of 25.8d Bi and±30?beam scanning range are achieved,and the maximum gain attenuation is only 1.0d B.In order to further expand the beam scanning range,a bifocal convex cylindrical conformal TA antenna is developed.The beam scanning range reached±70?with a maximum gain fluctuation of 4.5d B.4.A wideband TA antenna with near-field(NF)focus frequency sweep characteristic is proposed.Firstly,the frequency sweep characteristics of the NF focused TA antenna are analyzed theoretically.Then,a TA antenna is developed and verified experimentally.The results show that the focal point is scanned from z=59mm to z=197mm in the frequency range of 24?36GHz.5.An efficient NF shaping method based on the TA antenna is proposed.Firstly,the NF shaping problem is modeled and then Powell~?s Dog-leg(DL)nonlinear optimization algorithm is introduced to optimize the problem.The design process of the NF shaping problem is established by discussing the different two cases:the amplitude-phase op-timization simultaneously and phase optimization only.Furthermore,the optimization method of 2-D and 3-D shaping problem is proposed.A number of simulation experi-ments are carried out to verify the effectiveness and robustness of the algorithm.Finally,TA antennas with flat?top pattern and multiple focuses are developed.The experimental results are in good agreement with the simulation,which verifies the effectiveness of the algorithm.