Studies On Electromagnetic Radiation Manipulation Techniques In Antenna Arrays Based On Space-Time Modulation Theory

Antenna arrays have become crucial components in various wireless electronic systems,owing to their advantages of high gain,low sidelobe,flexible beamforming capability,etc.With the increasingly complex electromagnetic environment,modern radar,communication and electronic countermeasure systems have imposed extremely stringent performance requirements for their antenna arrays.Due to the lack of design degree of freedom,traditional phased arrays have exposed serious problems such as low accuracy,high complexity and high cost for radiation manipulation.These problems become obstacles for the development of wireless technology.Therefore,it has been highly demanded to explore new mechanisms of radiation control and beamforming from the perspective of increasing the design degree of freedom of antenna arrays.The space-time modulation theory is a novel theory that introduces the “time” factor as an additional design degree of freedom for antenna array radiation manipulation.Benefited from the “time” design degree of freedom,space-time modulated antenna arrays can simultaneously manipulate electromagnetic radiation in the space,time,and frequency domains.In this way,space-time modulated antenna arrays have great advantages for improving the array-level beamforming capability,as well as the systemlevel performances.However,the current space-time modulation theory encounters great challenges,such as beam scanning,sideband suppression,and application integration.The main purpose of this dissertation is to tackle the aforementioned challenges,and provide theoretical and key technical support for the development of next-generation high-performance wireless electronic systems.With this purpose,a variety of innovative studies on radiation manipulation techniques in space-time modulated antenna arrays are carried out in this dissertation.A systematic theoretical and technical framework,which covers theoretical principles,analysis methods,hardware implementations,array integrations and system-level applications,is established.The main contents of this dissertation can be summarized in the following four aspects:1.Studies on high-precision,integrated control techniques for amplitude-phase weightings in antenna arrays based on space-time modulation theory.To address the problem of sideband radiation suppression in amplitude-phase control based on periodic space-time modulation,a novel multiple-branch amplitude-phase integrated control technique is proposed.With this technique,the problem of sideband suppression can be decomposed into two sub-problems.The first one is the suppression of unwanted harmonic signals in radio-frequency(RF)channels,while the second one is the harmonic beamforming in antenna arrays.By introducing the parallel modulation circuit topology,most of the unwanted sidebands can be effectively suppressed in RF front-end channels thoroughly before power is delivered to antenna arrays,thus realizing integrated control of amplitudes and phases in antenna arrays with significantly suppressed sideband radiations.To minimize the performance deviation of amplitudephase integrated control caused by the nonidealities in practical modulation modules,a nonideal mathematical model that considers the practical nonidealities of amplitude unbalances,static phase errors,and status switching time is then developed.It further improves the amplitude-phase control precision of practical time modulation modules.2.Studies on high-efficiency phase modulation techniques based on space-time modulation theory.Due to power absorption and inherent multiple harmonic characteristics,the spacetime modulation inevitably causes lower efficiency in antenna array developments.To solve this problem,a novel ascending phase modulation technique is proposed.By periodically modulating the status of antenna elements with an ascending phase sequence of 0°,90°,180°,and 270°,the modulation efficiency can be improved from the theoretical upper bound(50.0%)in the existing literature to 81.1%.On this basis,an array-level nonideal ascending phase modulation model is developed to minimize the performance discrepancy between the fabricated prototype and the ideal theoretical models.The proposed model can comprehensively consider the nonideal characteristics of rising edge and falling edge of RF switches,amplitude and phase imbalances among RF channels,and mutual coupling of antenna elements for radiation manipulation.It provides a reliable way to accurately predict the radiation performance of a realistic nonideal antenna array.3.Studies on space-time pseudorandom modulation techniques for radiation manipulation in antenna arrays.An insight into previous periodic modulation techniques shows a trade-off among sideband levels(SBLs)and the complexity of modulation modules and optimization algorithms.A slightly lower SBL is achieved at the expense of the significantly increased hardware and computation complexity.To address this problem,a space-time pseudorandom modulation model is proposed.Different from traditional periodic time modulation that introduces sideband radiations at a multiple of discrete harmonic frequencies,the proposed model distributes the sideband power over a continuous spectrum,which significantly reduces the radiated power at a single sideband frequency and then realizes efficient SBL suppressions.On this basis,a novel aperture-interpolation pseudorandom amplitude modulation technique is proposed by combining the theory of pseudorandom “0/1” amplitude modulation with the idea of amplitude-control beam scanning.By performing interpolation computation at the antenna array level,highprecision beam scanning can be realized with pseudorandom “0/1” time modulation.To overcome the deficiency of phase control in pseudorandom “0/1” modulation,a novel pseudorandom hybrid phase-amplitude modulation technique is then proposed.By combining the “phase” and “amplitude” pseudorandom modulation objects,the proposed technique can achieve real-time control of amplitudes and phases in antenna elements,simultaneously,with low SBLs and high accuracy.4.Studies on the applications of space-time modulation theory in wireless secure communication systems.Traditional space-time modulation techniques suffer from the deficiencies of poor randomness,poor beam scanning capability,and low efficiency for wireless secure transmission.To solve these problems,two new secure communication techniques are proposed based on the innovative findings of the previous chapters of this dissertation.The first one is a pseudorandom ascending phase(PS-AP)modulation technique,while the second one is a chaotic-enabled phase(CP)modulation technique.The PS-AP modulation jointly considers the anti-interception advantages of the pseudorandom modulation and the high-efficiency beam scanning advantages of the ascending phase modulation.The “time” degree of freedom is utilized to maximize the signal radiation power in desired directions while increasing channel randomness in other undesired directions simultaneously.It provides a low-cost and high-performance directional modulation solution for physical-layer secure communication.The CP modulation offers the chaos features of high randomness,unpredictability,and initial condition sensitive characteristic,to increase the information uncertainty for eavesdropping receivers,thus significantly improving the transmission security.