Study Of Antenna Radiation Pattern And Beam Control By Using Planar Superstrate

In modern microwave field,antennas with different radiation patterns are in demand for different scenarios.In this dissertation the radiation pattern and beam control of these planar superstrate antennas are systematically investigated in depth by using spectral domain Green's function(SDGF),the Huygens equivalence principle,the leaky wave and diffraction mechanism combined with the tools of HFSS plug-in optimizer and the commercial software.Some planar supestrate antennas with very good performances have also been developed which can meet the requirements of many microwave systems.The main contents in this dissertation can be summarized as follows:1.Pattern synthesis of dielectric superstrate antennas based on spectral domain Green's function:(1)For dual-layer homogeneous dielectric superstrate(HDS)dual-band resonant cavity antenna(RCA)with two assigned resonant frequencies,the conventional design method based on resonant cavity model will become inconvenient and inflexible.Facing this problem,the pattern synthesis method based on SDGF is introduced to design the antenna,and the computer time can be reduced by at least two orders.(2)To solve the problem of the optimized relative permittivity(?_r)unavailable from market,the equivalence between perforated dielectric superstrate(PDS)and HDS in spectral domain is investigated.Thus the pattern synthesis based on SDGF for HDS antenna is also applicable for PDS antenna,which reduces the computational cost significantly.Then,the PDS antenna with low side lobe level(SLL)and equal E-and H-plane beamwidth was designed and fabricated.Compared with other feeders of a parabolic reflector used in satellite communications,the fabricated antenna has the advantage of simple structure and good performance.(3)For an antenna,the reduction of gain can be compensated by introducing the low noise amplifier,however the responses of the spatial filters(radiation pattern)are difficult to control and it is also difficult to design microstrip array with both narrow beamwidth and low SLL.Then,the SLL suppression technique using lossy HDS at the cost of gain for robust antenna design is proposed.Compared with lossless HDS microstrip array,by using lossy HDS the SLL at the designed frequency can be reduced from-30.4 d B to-35.6 d B at the cost of gain by 5.6 d B.The designed lossy HDS antenna has narrow beamwidth and its SLL is lower than-32.3 d B within the bandwidth of 1.6%.2.Beam control of planar superstrate antennas based on leaky wave and edge diffractions:(1)Commercial PCBs with removed copper cover are usually used as the HDS,but its?_r and thickness are limited in the market.Facing this problem,the wire metamaterial(WMM)is proposed which is composed by dense arrays of aligned metal rods embedded into3D-printed host dielectric.The equivalence between WMM and HDS in spectral domain is investigated,and the WMM RCA was designed and fabricated.The WMM and 3D-printed PDS can substitute for HDS with higher and lower?_r,respectively.Thus the 3D-printed host dielectric with/without metal rods can substitute for the HDS with almost arbitrarily?_r and thickness.(2)For RCA with its aperture decreased below?₀,the antenna performance tends to converge to that of the primary feed alone.In view of this phenomenon,the optimization by using HFSS plug-in optimizer is introduced,and the HDS electrically small antennas were designed and fabricated for the first time which have good performance.The aperture of the designed antenna is only 0.5?_0,while by using HDS its gain is increased by 3.8 d B.(3)For 1-D beam-scanning linear phased array,the beam of array element in the scanning plane should be wide enough and that in the orthogonal plane should be as narrow as possible.Different from the existing HDS technology,here the HDS is used to satisfy the requirements of the beams in both planes.Using the simple measure,the measured 3.5 d B gain enhancement in the scanning range of±43°has been achieved.3.Beam control of transmitarray antennas based on array-fed mechanism:For electronically beam-scanning lens antenna illuminated by the feeder with movable phase center,it is a challenge to move the phase center continuously.Facing the problem,the linear array with overlapping handover of subarray(OHSA)is proposed,which can produce continuously movable virtual point source based on Huygens equivalence principle.The advantages of the proposed linear array are being less phase shifters,with low cost,and easy control.As the feeder of transmitarray antenna,the proposed OHSA not only enables continuous beam scanning electronically,but also reduces the profile.Based on it,a dual-polarized beam-scanning transmitarray antenna was designed and fabricated,whose operating band and scanning range are 5.3-5.9 GHz and±30°respectively.Moreover,to deal with the conflict between high gain and low profile for transmitarray fed by planar array,the HDS planar array is introduced to provide better illumination of the transmitarray.The simulated results exhibit that by using HDS the gain enhancement is about 2.25 d Bi under the same requirement of profile.4.To tailor the conical beam by using planar superstrate.For conical beam antennas used in“Satcom on the move”,the wider coverage is in conflict with the higher gain.Facing this problem,the planar superstrate is proposed to tailor conical beam,which may provide a good balance of wide coverage and high gain.Moreover,the dielectric superstrate etched with metal ring can also make the conical beam split into dual conical beams.