Element Antenna Vector Pattern Measurement And Antenna Array Synthesis And Optimization

High-performance array antennas are widely used in various wireless applications,such as 5G wireless communications,phased array radar,aerospace,and radio astronomy observations.The advantage of the array antenna is that it can perform flexible beam forming and beam scanning.The architecture types of array antennas mainly include analog,digital,and analog-to-digital hybrid arrays.Regardless of the array type,some problems still affect the synthesis and optimization performance of the array antenna,such as the inconsistency of the element antenna radiation pattern,mutual coupling between antenna elements and crosstalk between receiving channels,etc.This dissertation mainly studies the fast and high-precision measurement of the element antenna vector pattern in the hybrid array,and the synthesis and optimization method of the array antenna based on the phase-normalized vector pattern.The main contributions of this dissertation are as follows:(1)The Time-Division-Sampling(TDS)method for measuring the vector pattern of the element antenna in the array is proposed and realized.Due to the difference of the relative positions of the element antennas in the array and the existence of mutual coupling between elements,the radiation patterns of different element antennas in the array are always different.If the influence of these factors is not considered,it is impossible to realize an ultra-low side lobe beamforming.To achieve high-precision array synthesis,the radiation pattern information of each element antenna in the array must be considered.However,in an actual array,the phase of each element is time-varying,which requires the use of complex phase-coherent measurement channels to complete the phase-coherent measurement,so it is generally difficult to measure the vector radiation pattern containing both amplitude and phase information.Since there is no reference channel in some arrays which do array synthesis in the analog domain,this problem is more prominent.In this dissertation,the method of Time-Division-Sampling(TDS)is used to measure the phase relationship between every two elements,and the time domain waveform obtained by time-division-sampling is subjected to FFT transformation to calculate the phase difference between the waveforms,and then the phase delay caused by different sampling moments is calculated through the sampling time difference.Finally,the phase relationship between the elements can be restored by compensating the phase difference of the waveform with the phase delay caused by the sampling time difference.Therefore,the proposed TDS method can solve the key technical problem of high-precision array synthesis and can realize the simultaneous measurement of the amplitude and phase of all elements under the same rotation angle,so as to realize the rapid and high-precision measurement of the phasenormalized vector pattern;In addition,this method ensures the phase coherence between multiple channels through the known time interval,and does not require complex hardware circuits to achieve phase synchronization,which greatly simplifies the complexity of the system;Besides,the system does not require additional coherent channels for phase measurement,which makes this method can also be used for analog arrays or hybrid arrays that only output one analog signal after all elements are combined in the analog domain,so this method has strong versatility.(2)An array synthesis and optimization method based on the phase-normalized vector radiation pattern is proposed and validated.Since the radiation pattern of each element antenna of the array contains amplitude and phase information,the radiation pattern of the array antenna can be obtained by vector summation of all element vector radiation patterns according to the specified array coefficients.The initial value of the array coefficient can be calculated according to typical array synthesis algorithms such as Taylor or Chebyshev synthesis algorithms,and then the array radiation pattern for the specified performance(such as ultra-low sidelobe or multi-beam)can be optimized through the array optimization algorithm.The advantage of this method is that the element radiation patterns used in the optimization process are all the vector radiation patterns measured in the actual environment,which not only contain the difference of the radiation patterns of elements but also include the mutual coupling between elements and other non-ideal factors,so there is no need to repeatedly consider the influence of these factors in the array optimization process.This can ensure that the simulation results of the array pattern optimized by this method can be more consistent with the measured results.(3)A hybrid array antenna system with ultra-low sidelobe scanning beam is realized.The array antenna uses the genetic algorithm to perform array synthesis and optimization based on phase-normalized vector element patterns.Cooperating with the multi-channel receiving system with high amplitude and phase adjustment accuracy,this method reduced the influence of factors such as different element patterns and mutual coupling elements on the array pattern,with achieving ultra-low sidelobe beam scanning characteristics.The measured sidelobe level of the array pattern can reach-33 d B at the beam direction of 0 degree and can achieve-30 d B ultra-low sidelobe beam scanning within the scanning range of +/-50 degree.This verified the normalized vector pattern measurement method and the effectiveness of comprehensive optimization algorithms.Due to the limitation of the measurement accuracy of the microwave anechoic chamber,it is impossible to accurately measure the sidelobe level below-35 d B.The amplitude and phase adjustment accuracy of the array antenna system and the accuracy of the array synthesis method can actually achieve lower sidelobe levels and other beam performance.This dissertation realized the rapid measurement of vector element pattern through timedivision-sampling and phase recovery method,and the synthesis and optimization of the array based on the vector element pattern;solved other key technical issues such as mutual coupling that affect the overall performance of the array;realized ultra-low-sidelobe synthesis and optimization of the array pattern,and can be used to achieve the array synthesis and optimization with other pattern performance such as multi-beam,difference beam,and custom radiation patterns.