Researches On Quasi-Optical Monopulse Antenna At Sub-Millimeter Wavelengths

Since sub-millimeter wave band is between microwave or millimeter wave band and infrared wave band,it posses the advantages of millimeter wave and infrared wave and can overcome their shortcomings simulta-neously.Therefore it has important scientific value and broad application potential in communication,target detection,precision guidance,space remote sensing,and so on.Monopulse technique is a kind of precision angle measurement technique and has been widely applied to many satellite communication and precision guidance radar systems.In recent years,monopulse antennas in microwave and millimeter wave band have been deeply investigated.However,few monopulse antennas that operate in sub-millimeter wave band have been reported in the literature.Based on this situation,some related research work about monopulse an-tenna operating at sub-millimeter wave band are carried out in this paper.It is well meaningful to develop monopulse antenna at sub-millimeter wave band.The main contents of this paper are listed as follows:1)The basic operational principle of quasi-optical(QO)sum-difference comparator is illustrated in detail.And the performance of QO comparator is simulated and further optimized by using accurate numerical method based on Finite-Difference Time-Domain(FDTD).Then a monopulse antenna operating at sub-millimeter wave band is designed based on QO technology.By using the dielectric prisms to control the aperture field distribution,the sum-difference radiation performance is well improved,especially in suppressing the side-lobe levels of sum patterns.Finally,the designed monopulse antenna had been manufactured and measured.The presented measurement results agree well with the simulated results.2)Research on the improvement about radiation patterns of QO monopulse antenna at sub-millimeter wave based on dielectric lens and diffractive optical elements(DOE).Firstly,by developing the selection,crossover,mutation operator of standard genetic algorithm(SGA),an improved genetic algorithm(I-GA)with better global searching ability and converging speed is proposed.Then,combining with the FDTD method and Stratton-Chu formulas,a modified hyperbolic dielectric lens and diffractive optical element are designed to improve the sum-difference radiation performance of QO monopulse antenna.3)The methodology design and implementation of a monopulse antenna based on QO technology is pro-posed at sum-millimeter wave band.The proposed monopulse antenna is composed of QO sum-difference comparator,beam-waveguide(BWG)feeding systems and cassegrain dual-reflector.Four ellipsoid re-flector mirrors are employed for the BWG feeding system,which can implement beam propagation with low-losses,high efficiency and beam waist transformation.The designed cassegrian dual-reflector can realize good radiation performance,which has high gain and low side-lobe levels.Finally,a prototype of the proposed monopulse antenna was manufactured and measured.The presented measurement results agree well with the corresponding simulated results and validate the effectiveness of design.4)A two-dimensional QO monopulse antenna is researched and designed at sub-millimeter wave band,which can achieve sum-difference radiation performance in azimuth and elevation plane simultaneously.At first,characteristics of the QO faraday rotator is analysed based on the matrix theory and Fourier-transformation techniques.The QO circulator is designed to apply for isolation between receive and transmit channel.Secondly,a 3-dB beam splitter that can operate with dual-polarized wave is proposed and applied to design two-dimensional QO sum-difference comparator.Then,based on genetic algorithm,a dielectric lens is designed to improve the radiation performance of the designed monopulse antenna.In the end,structure design of the proposed monopulse antenna is completed to establish foundation for the following experimental validation.