Study Of Beamforming And Array Configuration Of Active Phased Antenna Arrays

With the increasing demand and continuous advancement of related technologies,the applications of active phased antenna array(APAA)in military and civil fields are also expanding.Urging engineering demands include space-borne APAA,irregular APAA,dual-band APAA with shared aperture,and so on.In accordance,many new challenges such as beamforming of space-borne APAA,synthesis of irregular active phased linear antenna array with consideration of mutual coupling effect,and the array configuration design of dual-band APAA with shared aperture,have emerged.It is of significant importance to study the underlying physical principles of antenna theory and develop solutions to meet demands of fast analysis,calibration and diagnosis of APAA from practical applications.The main innovations and contributions of this thesis are as follows:1.Fast computation of antenna array pattern based on CZTAs an essential means of evaluating antenna array performance and the basis of antenna array design,numerical computation of antenna array pattern is very important.Computation of antenna array pattern by using straightforward summation is time consuming especially for planar array with many elements.Moreover,in some applications such as antenna array synthesis,huge number of repeated pattern computations is needed that the consumed time is untolerably long.Although the computation can be accelerated by FFT when the elements are equally spaced by half of a wavelength because the array factor and the element excitation currents is a Fourier transform pair,in general,FFT is not applicable.In this thesis,the CZT is introduced to accurately and efficiently compute pattern of general linear or planar antenna arrays.The corresponding parameters of CZT for antenna array factor computation are derived.Computation processes are also explored and given in this thesis.Simulation results prove that it is applicable with high accuracy and efficiency,especially for planar array with equally or unequally spaced elements.2.ICZT and its applications in the inverse problems of antenna arrayBased on the aforementioned study,this thesis further develops ICZT for inverse problems of antenna array and applies it to the calibration,diagnosis and synthesis of APAA.Unlike FFT,which can only be directly used in periodic antenna arrays with a half-wavelength element spacing,ICZT can be used for calibration and diagnosis of periodic antenna arrays with arbitrary element spacings.Combined with the aformentioned fast computation method of antenna array pattern,ICZT can also be applied to fast synthesis of antenna arrays.This proposed method can synthesize periodic antenna arrays with arbitrary element spacings with high convergence speed and less time consumption.It has been successfully applied to different types of missile-borne and space-borne APAAs in practice.3.Study of beamforming method for spaceborne APAAIn a practical APAA,main beam scanning angle(MBSA)-dependent low SLL and gain loss are the ultimate and most critical performances.At some MBSA,extremely low SLL in some local space is needed.The harsh limitation on APAA gain loss further complicates the problem seriously.In this thesis,the main beam scanning space was divided into several subspaces.Instead of applying a single set of weights regardless of the MBSA,a separate set of weights is implemented independently in each subspace.This transforms the nearly unsolvable problem into multiple solvable problems.An array-decomposition approach is proposed to further reduce the number of optimization parameters for each subspace.The entire array is simplified as an assembly of multiple sub-arrays.Each and every sub-array shares the same set of weights.The number of synthesis parameters is therefore reduced to the order of the subarray that the synthesis is much easier to solve without sacrificing too much synthesis performance.The proposed approach has been applied to solve the concerned practical problem successfully.4.Study of synthesis method for irregular active phased linear antenna array with consideration of mutual coupling effectThe synthesis of irregular active phased linear antenna array with consideration of mutual coupling(MC)which plays an important role in the radiation pattern of antenna arrays needs further study.For this study,a synthesis method is proposed in this thesis.For the application of long-ranging detection,the position-only synthesis is performed in step I and step II of this method to suppress PSLL.Among them,an initial array is optimized in step I and without consideration of MC.To avoid the grating lobes and high sidelobes when the main beam is scanning,the patterns with different MBSA are evaluated.In step II,the array is re-optimized with consideration of MC by using an iterative optimization procedure combined with electromagnetic field full-wave simulations.After several iterations,the deterioration of PSLL due to MC effect can be almost compensated.For the application of near-ranging detection,based on the synthesized array layout and AEP method,step III uses phase-only and amplitude-only synthesise to further suppress the PSLL,and then both the amplitudes and phases are used for optimizing scanning flat-top main beams while suppressing PSLL.This study fully considers the array synthesis problem that needs to be solved when applying the irregular array configuration to APAA.5.Study of sparse array configuration for Ku/Ka dual-band APAAs with shared apertureThe dual-band APAAs with shared aperture adopting the form of‘periodic array+sparse array'have many advantages and it can avoid the problems involved in other forms of dual-band APAAs with shared aperture to a certain extent.However,the configuration design of the sparse arrays becomes the key technical problem needs be solved for this kind of APAAs.An array configuration by adopting this form and a design method of sparse array configuration are proposed in this thesis.The problem of array configuration design with strictly location constraints is transformed into one with no location constraints,and hence the difficulty is significantly reduced.For general planar sparse antenna arrays,the SLL of the patterns with main beam steering at broadside is usually higher.Moreover,when the beam main is scanning,the grating lobes or high sidelobes will enter visible region from invisible region,which further deteriorates the performance of array patterns.For the purpose of finding all of the concerned grating lobes or high sidelobes,the calculation frequency of the sparse array pattern is set as fs=(1+sin?s)·f_H.For the optimized Ka sparse antenna array operating in its working band,there are no grating lobes and high side lobes in the visible regions of the patterns with different main beam diretions.