Studies On The Techniques Of Directional Modulation And Direction Finding Based On Four Dimensional Antenna Arrays

With the rapid progress in radar and communication technology, radio electronicsystems are pushing their antennas to develop towards the directions ofhigh-performance, multi-function, low-cost, miniaturization, etc. The antennas areplaying an important or even decisive role in system performance. Traditionalhigh-performance antenna designs are facing challenging difficulties which are hard tosolve, such as complex feed structure, high manufacturing cost. By introducing time asa fourth design freedom, the four dimensional (4D) antenna array can be formed. Afterextensive study of about ten years,4D antenna arrays reveal great potential insimplifying feed structure, improving antenna performance while cutting down themanufacturing cost, and scientists have been paying great attention to this promisingtechnology.Due to the effects of time modulation, signals radiated or received by4D antennaarrays possess some unique properties. Through the in-depth study of these properties,one could not only make up for the deficiencies of the traditional antenna designtechniques, but also find the ideas of some novel applications. This thesis focuses onthese unique properties of the time-modulated signal and carries out the studies on thebasics of engineering applications. The outlines are summarized as follows:1. The time-domain analysis of the4D antenna array is studied. Using theequivalent complex baseband representation, the original signal of4D antenna array canbe represented with a much reduced sampling rate and a much smaller storage spacewhile still gives insight into the physical mechanism. Representing the radiated orreceived signal in the time domain provides an easy way for the analysis the4D antennaarray in the presence of noise, interference signal and other cascaded systems, andprovides an effective means for the systematical level analysis of the4D antenna array.2. The directional modulation technique and4D antenna array are combined toform the secure communication system. This method makes use of pattern’stime-varying feature of the4D antenna array, and the4D antenna array acts not only asa radiating device but also as a modulating device. A QPSK modulation system and a spread-spectrum modulation system adopting the aforementioned method are proposedand investigated. Simulated results show that the two proposed systems not onlysimplify the transmitter architecture and but also realize spatial encryption, whichmeans useful information could be formed only in the desired direction.3.4D antenna array are combined with the monopulse technique to form a noveldirection-finding system. Firstly, differential evolutionary algorithm is used to optimizethe time sequence of the4D antenna array to generate multi-beams. Secondly, thegenerated multi-beams are subtracted and summed to form sum-difference patterns atdifferent spatial angles. This novel direction-finding system retains the high data rate ofmonopulse radar while improves the ability of dealing with multiple targets within largeangular space. The simulated and experimental results validate the effectiveness of theproposed method.