Research On Vector Sum Microwave Photonic Phase Shifter

Phased array radar can meet some new requirements on radar in the present world.And comparing with all-electric-controlled phased array radar, optically controlled phased array radar owns many advantages.Optically controlled phased array technology gains a great deal of global attention in the field of research on phased array antennas.Optically controlled phased array antennas have such advantages as simple structure,high stability,strong anti-interference ability,etc.Phase-shifting technique is a key of optically phased array antennas.Therefore,research on MPPS applied in optically controlled phased array radar that can make microwave phase change continuously is of great use.So far as the status, research on MPPS is mainly based on the following three technologies.They are the real-time optical delay line(OTTD),heterodyne mixing technique and vector sum technique.VSMPPS is usually designed as follows, Mach-Zehnder modulator(MZM) is used to make the optical wave modulated by the microwave signal,and then the modulated signal is split, attenuated,coupled and detected,etc.At last,the phase-shifted microwave signal is obtained.The main concept of this paper can be summarized as follows:researching the VSMPPS that can make phase shift range be 90 degrees,analyzing the relationship between the phase shift of microwave and the control variable which is called the amplitude ratio of the signals in the two optical branches,on which to determine the length of the branches,putting forward the design of VSMPPS owning 360 degrees phase shift range.In this paper,chapter one is abriefly introduction to the applications present condition of VSMPPS;character two introduces electro optical modulation that is a part of optoelectronie technology,because it is an important link to load the microwave on the optical signal and it is necessary for us to know the signal in the VSMPPS clearly.Character three introduces the theory research on the designed VSMPPS that works in ideal state via mathematical derivation and the use of Matlab,some useful conclusions are obtained.In character four,simulation using optisystem3.0 and experiments with discrete devices are described,which mean to verify the conclusions got in character three;The current research work is summarized and future research directions is prospected in character five.In the theory research,via the use of Matlab,some figures showing the relationships among the phase shift caused by VSMPPS and the parameters of VSMPPS are drawn.After research on the figures,it is known that if the VSMPPS designed can satisfy some requirements(they areφ₂=κ₀△x=2κπ,φ₁=κ_RF△X=2κπ+π/2,where k is an integer,△x is the optical length difference between the optical branches,κ_RF andκ₀ are the wavenumbers of microwave and optical signal),the VSMPPS can make the microwave get phase shift continuously,the phase shift range be 90 degrees,the relationship between the phase shift and the amplitude ratio be most linear,the phase shift error caused by the production error of optical waveguide branch be minimum.Via the use of Optisystem3.0,the simulation shows that some conclusions of theoretical studies have been verified.However,due to the limitations of simulation software and theoretical studies dealing with some simplification,the results of simulation analysis and theory research can not be fully consistent.One of the key issues is the output signal of the photo detectors of the microwave signal contains some component outside of the fundamental frequency,in some cases it can not be ignored and the influence on the output signal waveform is serious.In the experiments using discrete devices,although excessive losses have never been overcome and the output signal of the phase shifter is so weak that its phase is quite unstable, it can be seen to some extent that the optical length difference between the two optical branches determines the phase shift range,and via grossly observation,it is seen that the range in time is equivalent to the time difference that the signal spent in passing the two branches.It is also known that the phase shift can be changed by regulating the magnitude of the signal in an optic branch.As some problems exist in simulation and experiments,in order to obtain more detailed and valuable results,future work in these areas need to be improved.After the research on the VSPPS owing 90-degree phase shift range,the design of VSPPS owing 360-degree phase shift range is put forward.Some basic requirements on it are shown in this paper.By adjusting the variable optical attenuator to change the magnitude of signals in the four branches, we can make the microwave signal get continuous 360-degree phase shift.In short,after the theoretical research on VSPPS,simulation analysis and experiments using discrete devices,we get some valuable conclusions, which supply some theoretical basis for designing of monolithic integrated VSPPS.And this paper has a certain guiding significance for it.