Analysis And Control Of Four-dimensional Antenna Array Radiation

Array antennas are widely used in intelligent and integrated wireless electronic information systems due to their high gain,flexible beam reconfiguration,and quick beam scanning.However,complex beamforming networks,high-cost hardware architectures,and increasing system energy consumption are issues that need to be addressed in the design of array antenna systems.Therefore,the study of low-cost,low-power,high-flexibility,and multi-functional integrated new architecture array antennas has become an inevitable trend.The four-dimensional(4-D)antenna array uses “time” as the fourth-dimensional design variable and features flexible and precise control of the aperture field distribution with a simple hardware architecture.It stands out among the new generation of candidate technologies.This dissertation is focused on four aspects of the 4-D antenna array:fundamental theory,real-time beam scanning method,simultaneous multi-beamforming method,and physical layer secure communication.This dissertation comprises of the following five parts:1.To address the issue that a closed-form formula for sideband power radiation is only applicable to the array factor,closed-form formulas for sideband power radiation of4-D antenna arrays with arbitrary element pattern and arbitrary time-modulated waveform(TMW)are derived,theoretically verifying the uniformity of radiation power in the timeand frequency-domain.This is beneficial for the rapid evaluation of radiation performance and non-ideal TMW modeling of the 4-D antenna array.2.A beam scanning method at the fundamental frequency based on the phase modulation(PM)technique is proposed.Completeness theory research on the traditional PM technology is conducted,deducing the achievable equivalent excitation amplitude and phase coverage under a given number of phase states.This method can be used directly to calculate the corresponding TMWs according to the expected excitation distribution for real-time beamforming.A probability-based 4-D antenna array is also proposed to further suppress sideband radiation,dispersing sideband radiation power to a wider frequency band and obtaining a low sidelobe radiation pattern,thereby significantly suppressing the sideband level(SBL).3.A high-efficiency harmonic beamforming method is proposed utilizing TMWs with a linear phase.The slope of the phase change is related to the amplitude of the harmonic excitation,and the relative time delay between array elements is related to the phase of the harmonic excitation,making it easy to control the target harmonic pattern.An8-element antenna array integrated with 2-bit phase shift in the Ku frequency band is used to build a harmonic beamforming test platform to verify the effectiveness of the method in beam scanning and sidelobe suppression.4.Using the multi-harmonic characteristics of the 4-D antenna array,two methods are explored: forming simultaneous sum and difference beams and forming flexible multibeams.Theoretical analysis of the conditions for forming sum and difference beams leads to a method to form a difference beam at the negative 1st harmonic,form a sum beam at the positive 1st harmonic,and suppress even harmonics.This method improves time modulation efficiency and enhances the transmittable signal bandwidth.Using the genetic algorithm,coded TMWs suitable for 3,4,5,and 7 beams are obtained.Compared with the traditional multi-beam 4-D antenna array that lights-up sequentially,this method shows advantages in flexibility of radiation patterns,efficiency,and power balance between harmonics.5.For physical layer secure communication based on the 4-D antenna array in the baseband domain,an elaboration of the basic theory of directional modulation(DM)is included.This includes conditions for forming DM signals,statistical models of sideband signals,and evaluation metrics(EVM,SER,and secrecy rate).A novel dynamic distributed 4-D antenna array with 2-bit phase control is proposed for implementing continuous beam scanning DM.The element positions of the 4-D antenna array change randomly over time and conform to a Bernoulli distribution,which can be easily implemented via single pole double throw(SPDT)switches and redundant elements.A codebook optimization algorithm is described for continuous beam scanning with 2-bit phase control.