Research On Low Complexity Beamforming Algorithm For Frequency Diversity Array

As the most front-end equipment of wireless system,antenna has experienced a long-term development process.With the development of mechanical scanning antenna and electric scanning antenna,the efficiency and accuracy of beam scanning are gradually and rapidly improved.Although phased array antenna has many advantages such as flexible beam control,it also has some disadvantages.For example,range dimension interference cannot be effectively suppressed,and the beam pattern lacks range dimension information.In contrast,as a new array antenna proposed in recent years,frequency diverse array antenna obtains more flexible beam control ability by designing the signal frequency difference between array elements.It can produce range-angle-dependent beampattern,so it has gradually attracted extensive interest of relevant researchers.Frequency diverse array has very broad application prospects in radar imaging,interference suppression and elimination,joint positioning and so on.For frequency diverse receiving array,range angle decoupling and better beam pattern performance are often achieved by full frequency reception.However,it usually brings huge amount of calculation and memory,as well as high performance requirements for front-end hardware,especially array antenna devices.Therefore,there is great trouble in practical application.In order to obtain high resolution beam pattern with lower complexity and ensure efficient decoupling ability,the following researches is carried out in this thesis:(1)The kern optimization algorithm of compressed sensing based on information theory is studied,so as to realize the beamforming algorithm with low data transmission and storage.As a data independent scheme,the traditional compressed sensing algorithm based on random compressed measurement matrix has certain robustness.A beamforming algorithm based on orthogonal matching pursuit is proposed.This algorithm can not only reduce the amount of data transmission,but also ensure high range dimension resolution.However,it will still bring a large amount of calculation in signal reconstruction.Aiming at the optimization problem of compressed measurement matrix,an iterative optimization method based on the prior distribution information of the target is proposed to maximize the Shannon mutual information between the compressed sensing core and the two-dimensional spatial position distribution information.Then,the position parameters of the target are estimated by searching the compressed sensing minimum variance distortionless response spatial spectrum.Since the compressed signal is directly used to realize the positioning function,the original signal does not need to be reconstructed and the overall computational complexity is reduced.Compared with the random compressed sensing kernel commonly used,the proposed method can effectively distinguish multiple targets while significantly reducing the measurement size.The result is to form a beam pattern with narrower main lobe width and higher resolution,so as to achieve better Joint DOA and range estimation.(2)The range dependent beamforming algorithm based on space-frequency virtual differential array is studied.Aiming at the problem of angle distance coupling existing in the existing beamforming algorithms and the defects of high hardware requirements of the front-end signal receiver,a method based on the sparsity of coprime array and the decoupling ability of random frequency diverse array is proposed.It is proposed to organically combine the prime number properties in the design of array element position,which breaks through the limitation of Nyquist sampling rate and realizes the under sampling of signal.Therefore,a larger aperture can be achieved with only a small number of array elements,and a higher degree of freedom can also be obtained.By combining the coprime array with the frequency diverse array model,a one-dimensional linear virtual array is constructed in the virtual domain by using the second-order statistics.Using the theory of random frequency offset array,the virtual frequency is randomly selected from the second-order statistics and assigned to each virtual array element.Thus,the hardware complexity and computational overhead are reduced when the range angle decoupling is effectively carried out and the energy focused beam pattern is formed.(3)The beamforming algorithm of improved frequency diverse array based on padded coprime array is studied.The number of array elements,array aperture and degree of freedom of the scheme are analyzed and studied.An optimized padded coprime frequency diversity array structure is proposed.By combining the padded subarrays into a tailored coprime array with displaced subarrays,the continuous linear segments are amplified in the differential common array.Then,the virtual frequency is randomly selected from the second-order statistics of the received signal from the frequency diverse padded coprime array and assigned to each virtual array element to realize the range-angle decoupling and focused beam pattern.The proposed scheme expands the virtual array without increasing the number of physical units,and can obtain more focused beam patterns and higher degrees of freedom in the virtual domain.