| With the complexity of the electromagnetic environment and the diversification of various wireless application scenarios,new requirements have been proposed for the design of radio frequency(RF)systems,such as high performance,miniaturization,low cost,etc.As the frontend subsystem,the antenna performance directly affects the overall function implementation.Thus,research on the high-performance antennas has become an important direction.In particular,the development of phased array technology and digital antenna array has made the beam scanning more flexible and adaptable.Traditional phased array antenna elements are distributed in three-dimensional(3D)space,and the synthesis of radiation field is achieved by controlling the position,excitation amplitude,and phase of antenna elements.However,the realistic application often needs to balance multiple requirements.In order to improve the reconfigurability of the array in varies environments,the concept of unconventional antenna array is proposed.In essence,the multidimensional degree of freedom(Do F)is proposed to seek for improvement of perception and processing capabilities of antennas.When the time is introduced as a fourth-dimensional control parameter for a phased array,it comes to form a time-modulated phased array(TMA),also called a four-dimensional(4D)phsaed array.The periodic time modulation regulated by RF swiches introduces the dynamic excitation of elements,which helps to reduce the complexity of the feeding network to achieve low sidelobe radiation,simultaneous multi-beam,and realtime adaptive beamforming.By this way,it ensures high perfomence while meeting with the requirements of low-cost and compact design.When a small frequency offset(far less than the carrier frequency)between the antenna channels is introduced as a new Do F,it constitutes another type of novel antenna array,a frequency diverse array(FDA).The introduction of the channel frequency offset makes the radiating field changes in 4D space,includes angle dimension(elevation angle,azimuth angle),range dimension and time dimension.Thus,it is conducive to realize the target location and interference suppression in range dimension,and the automatic beam scanning.The research on these advanced antenna technologies is based on the study of traditional phased array.However,the new techniques and new solutions should be proposed in combination with new application scenarios.In this dissertation,the theoretical research and application exploration of these innovative array technologies are carried out on the background of high-performance and miniaturized array system design for practical applications.The main contributions and innovations are summarized as below:1.The multi-domain fusion beamforming algorithm is studied.To avoid anti-jamming deterioration due to insufficient Do F for miniaturized multi-mode co-aperture navigation antennas,a space-polarization fusion processing method using a polarization sensitive array(PSA)is proposed.The polarization filtering is enabled by using dual linearly-polarized antenna.By introducing polarization constraint to the Linear Constraint Minimum Variance algorithm,the adaptive Do F is increased while the reception of navigation signal is ensured.To reduce the hardware complexity of antenna system,a single RF channel beamforming method based on time sequence phased weighting is explored.The Walsh-Hadamard transform of antenna aperture is achieved by weighting in time domain,and the channel information is reconstructed by inverse transform for adaptive processing.By comparing different types of interference signals,it is found that this method is suitable for processing stationary signals without phase modulation,which can greatly reduce the hardware complexity.2.The synthesis of spatially focused spot beampattern for FDA is studied.To solve the problem of three-dimensional periodic radiation pattern(distance,angle,and time)for the linear frequency shifted FDA,an optimization method of both element position and frequency offset parameters is proposed.Based on the analysis from the perspective of array factor,the synthesis of spot-shape focused beampattern in range-angle dimension is proposed by optimization of nonlinear frequency offsets.To ruduce the complexity of both software and hardware design,a sparse FDA with frequency offsets optimization is introduced.At last,a fast-convergent iterative method with variable step size is proposed to find the array with minimum element.3.The application of FDA in range-dependent interference suppression is studied.To overcome the susceptibility to interference due to high sidelobe level(SLL)in range dimension,a multi-stage mixing FDA structure is proposed.By optimizing the amount and value of frequency offsets,the low SLL in both range and angle dimension is achieved.Based on this,the FDA is applied to realize the range-dependent interference suppression.Considering the mismatch of steering vector cused by random channel error,and the high-dynamic changes of interference power caused by random sidelobe,a robust adaptive beamforming method based on eigensubspace projection is proposed for the FDA.The main beam alignment and interference nulling generation in range and angle dimension are achieved by using this method.4.The harmonic beamforming method of the TMA is studied.The multi-beam generation mechanism is analyzed from the perspective of array factor,and the characteristics of harmonic beams generated by different modulating sequence are compared in time and frequency domain.The single-sideband modulation based on pre-processing of rectangular pulse sequence is introduced by using a set of orthogonal cosine harmonics as auxiliary signals.The independent control of each harmonic beam is achieved,thus the beamforming efficiency is enhanced by this way.For the application of simultaneous multi-user charging in far-field wireless power transmission(WPT),the beam alignment between power base stations and terminals is achieved by combination the retrodirectivity technology.And the flexible beamforming makes the power efficiency enhanced.It brings a highly potential insight for far-field WPT by overcoming the spectrum limits of rectangular pulse sequence.5.The application of TMA in simultaneous power transmission and terminal localization is studied.For the far-field WPT,a terminal localization strategy based on intermodulation(IM)feedback is proposed for accurate power feeding.The generation of two-tone multisine by using a TMA is proposed.At terminal side,the IM signal generated spontaneously under two-tone incidence is employed as a feedback.To isolate the downlink and uplink channels,dualpolarized transmission is adopted.The multi-baseline TMA implemented by a two-stage switching network is designed to achieve high-accuracy direction estimation.A compensation method for switches imperfection is proposed.Then the distance can be obtained as well based on the received signal strength indicator method.This method is beneficial for the base station to adjust the beam steering and transmitting power to compensate for the space transmission loss,thereby ensuring the power conversion efficiency of the terminal.The effectiveness is proved by prototype experiments. |
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