Research On Direction Finding Based On Microwave Photonics

Direction finding is a process of measuring the direction of radio waves according to the propagation characteristics of the electromagnetic waves.The traditional direction finding system has developed to mature period,but it is difficult to meet the increasing demand of modern electronic warfare for higher frequency band and larger bandwidth.In order to overcome the bottleneck of direction finding technology in working frequency band,working bandwidth,frequency tuning ability and anti-electromagnetic interference ability,microwave photonics technology has attracted the attention of the direction finding field for its intrinsic advantages.The research on the direction finding scheme based on microwave photonics has been going on for several years at home and abroad.In this paper,the application of microwave photonics technology in direction finding is studied,three direction finding schemes based on microwave photonics are put forward.The theoretical derivation and simulation of the proposed schemes are carried out,and the simulation results are analyzed and discussed.The specific research contents are as follows:1.This paper expounds the history and research trend of electronic warfare technology,and introduces the beginning and development of microwave photonics.Then several kinds of typical modulators as the core of the scheme are introduced and the realization principle is explained by theoretical derivation.Representative microwave photonics direction finding schemes published by universities and research institutions at home and abroad in recent years are selected and briefly introduced.Finally,the commonly used phase interferometer structure for direction finding is introduced and the measurement error source is analyzed.2.A new direction finding scheme for microwave photonics is constructed with dual polarization modulator as the core.A single integrated modulator is used to realize the phase detection that supports frequency conversion.Then the interferometer structure is used to implement direction finding,which not only guarantees the stability of the system,but also realizes a high measurement accuracy in large frequency band.3.A microwave photonics direction finding scheme based on the Sagnac loop composed of two parallel phase modulators is proposed and studied by simulation.By using the characteristic of the two signals in the ring structure which have the same amplitude but a opposite phase,the optical carrier can be completely suppressed by the two signals canceling each other,and the operating frequency range of the system is extended by using the modulator structure of the lower circuit.The phase discrimination in the range of-168~168° is realized by simulation,and the error is less than 0.5°.4.A microwave photonics direction finding scheme based on a double drive Mach-Zehnder modulator and stimulated Brillouin scattering effect is proposed and studied by simulation.The phase difference information is modulated into the sideband and the carrier is suppressed by the modulator.The optical fiber is used as the medium to generate SBS and its attenuation spectrum is used to completely suppress the carrier.Finally,the phase difference is calculated according to the measured optical power.The feasibility of the idea is verified by simulation,and a ideal measurement accuracy is obtained.