Study On Planar Near-field Antenna Measurement And Multi-Beam Antenna

Being associated with research projects,this dissertation mainly focus on the planar near-field antenna measurement technology and multi-beam antenna design.This dissertation presents the measurement of wide-angle scanning antenna,near-field array diagnosis,mode filtering technique applying to the suppression of multi-path effect,and multi-beam microstrip antenna array.The author's major contributions are summarized as follows:1.The measurement method of wide-angle scanning antenna based coordinate transform is studied.Firstly,the question occurring during the measurement of wide-angle scanning antenna is analyzed.It is found that the truncation level cannot meet the requirement of PNF,and this is the reason why the measured results obtained with the traditional PNF measurement is seriously different from the real performance of the AUT.Secondly,the PNF measurement method based on coordinate transformation is proposed according to the uniqueness theorems of electromagnetic field,which needs to rotate the AUT with a certain angle before the PNF measurement so as to get a lower truncation level.After the PNF measurement,the pattern which is relative to the measurement coordinate system is obtained,and the pattern relative to the antenna CS can be obtained with the use of the relationship between the measurement CS and the antenna CS.Finally,the PNF measurement method based coordinate transformation is verified with numerical simulation experiments and practical measurement experiments.Under the existing conditions,a 2 X 8 helical antenna array is machined as the AUT for the practical measurement experiments.Both the numerical simulated results and practical measured results show that the wide-angle scanning antenna can be precisely measured with the proposed PNF measurement method based on coordinate transformation.2.The near-field diagnoses technology based on PWS(plane wave spectrum)is studied.Firstly,the aperture holographic diagnose is studied.It is a transformation from near-field to aperture-field,and the feeding current amplitude and phase of array can be obtained from the aperture field distribution.Secondly,the diagnose technique based on theory of PWS and LSM(least square method)is studied.It means to get the array factor from the measured near-field data with the use of theory of plane wave spectrum,and the least square solution of the feeding current can be obtained for a given array configuration.Taking the element factor into consideration and a good solution can be obtained,which is better than the method of aperture holographic.3.The application of mode filtering technique to the multi-path effect suppression is studied.The basic concept of mode filtering technique is stated.The theory of spherical wave is discussed,and the expansion of electromagnetic field radiating from antenna is given.On the basis of the theory of spherical wave,the principle of mode filtering technique is stated,and it is proved that mode filtering technique is complete in mathematically.A series of simulation experiments are carried out to verify the performance of mode filtering technique to the multi-path effect suppression,four different additional radiating sources outside of the array aperture are studied respectively.The simulated results show that the multi-path effect suppression is quite obvious within the scope of the main beam.4.Two multi-beam antenna arrays are designed.At first,a four-element array is designed,which is used as interrogator antenna and can radiate a sum beam and a difference beam.Four air-filled microstrip patches are used as radiating units,and the feeding network consists of a 3dB branch-line coupler and two T-shape power dividers which is designed appropriately to maintain the difference beam cover the sum beam within,the vast majority of space.The network and units are cascaded to radiate two different beams,and the radiating beam is controlled through changing two inputs.The antenna is fabricated and measured to verify the design method.Secondly,an antenna array based on butler matrix is designed which can radiate three beams in three different directions.The modified L-shape probe feeding patches are used as the array units,and the feeding network is composed of branch-line couplers,wideband 90° phase shifters and a Wilkinson power divider.As the wideband performance of the feeding network components,the feeding network can provide stable output amplitude and phase across a quite wide frequency band.With the three inputs are fed in turn,the antenna array can radiate L-beam,R-beam and BS-beam,respectively.