Studies On The Basic Applications Of Space-Time Four-Dimensional Antenna Arrays In Wireless Communication

The antenna array is an indispensable building block of wireless communication systems,playing an important role in improving system performances.Mordern communication and radar systems have posed new requirements for antenna arrays,e.g.,low/ultralow sidelobes,fast beam scanning,fast beamforming,multi-beam forming and adaptive nulling.Convetionally,these functions can be achieved by precisely controlling the amplitude and phase excitations of each antenna element in an antenna array.However,the complicated feed network and the expensive phase and power tuners not only increase the difficulty in design and fabrication but also greatly limits the implementations of above mechinsim for practical antenna arrays or systems.By time-modulating the radio frequency(RF)switch,the four-dimensional(4D)antenna array can form an equivalent amplitude weight at the center operating frequency and produce equivalent amplitude weighting and phase weighting in the sidebands,weakening the dependences of the traditional array antenna upon the excitation amplitude phase.The precise radiation control of the antenna array is realized at a lower amplitude dynamic range ratio,which greatly simplifies the feeding network and saves cost.Meanwhile,the 4D antenna array has high efficiency.Even with fixed structures,the functionalities of 4D antenna arrays can be reconfigured to work in multiple scenarios by simply changing the time sequences,which is highly demanded in many applications.The work of this dissertation starts from the nature of the 4D antenna array in both time domain and frequency domains,and investigated the applications of the 4D antenna array in the field of wireless communication under different signal bandwidth and modulation frequency.First,an improved phase modulation technique based on 4D antenna array is proposed to realize more precise and simple radiation control of array center frequency radiation characteristics.Secondly,with both numerical simulation and experimental results,the advantages of 4D antenna array in Orbital Angular Momentum(OAM)communication are verified.Furthermore,a physical layer secure communication system based on 4D Retro-Directive Antenna array(4D-RDA)is proposed.The proposed 4D RDA overcomes the limitations on the locations and the number of legitimate receivers in the traditional physical layer secure communication systems,and improves performance of secure communication.The main content of this dissertation is summarized as the following three parts:1.An improved phase modulation technique based on 4D antenna arrays is proposed in this dissertation.The modified control unit consists of two single-pole double-throw(SPDT)switches and four different delay lines(0°,180°,90° and 270°).Each control unit connects the feed network with the antenna array element.The proposed architecture generates simultaneously effective real and imaginary excitation weighings at the carrier frequency.Numerical simulations indicate that the proposed architecture allows for arbitrary-angle beam steering and beam-forming by adjusting the time sequence of the switches,without using conventional phase shifters.It is worthy to point out that all the switches in the proposed scheme are always in the “ON” state.As a result,the radiation efficiency of the 4D antenna array using the proposed phase modulation technique is also improved significantly and new opportunities to radiation pattern synthesis are brought into 4D antenna arrays.2.It is demonstrated for the first time that multiple orbital angular momentums can be simultaneously generated by the 4D antenna array.By optimizing the time sequence under different switch types,the efficiency of the OAM waves generated by the 4D ring array is improved,and the energy of each mode is significantly enhanced.Moreover,the advantages of this scheme are verified by the novel near-field phase test method which is first proposed in this dissertation for the scenario in which the transmitting antenna and the receiving antenna operate at different frequencies.Meanwhile,it is demonstrated that the 4D circular antenna array can also receive and demodulate a variety of original signals carrying the OAM mode.The ability of the 4D circular array in receiving and demodulating multiple OAM-carrying BPSK signals is validated through the filter and bit error rate(BER)simulations.3.A secure communication technology based on 4D retrodirective antenna array is proposed.This technology benefits from the unique property of the retrodirective antenna array,which does not require the information of the incoming wave incident angle,and does not require complex digital signal operations.It can redirect the transmitting beam of the array to the direction of the incoming wave justing using its own hardware processing.The secure transmission of communication information in any desired direction can be realized without using phase shifters and attenuators,and the security performance is significantly improved under optimized time sequence.In addition,it is verified by both numerical simulations and experiments that the proposed 4D antenna array is also applicable to multiple legitimate receiver scenarios with different receiver directions.