Multipath mitigation method based on Gaussian mixture model in RF relative measurement

Radio Frequency(RF) technology represents a high-precision relative navigation solution that has significant potential for application to earth-orbiting satellites. In precision applications, multipath errors dominate the total error because observables, which are used to estimate carrier-phase integer ambiguity, are not always subject to a Gaussian distribution when dualfrequency ambiguity estimation methods are used in the presence of multipath. As it has been shown that ranging observables obey a Gaussian mixture distribution, this study proposes improvements to the accuracy of estimation based on multipath mitigation founded on the Gaussian mixture model. To this end, such a model is created for integer ambiguity resolution in the presence of multipath, using which the theoretical error in dual-frequency ambiguity estimation is derived.Expectation Maximization(EM), which aids dual-frequency ambiguity estimation, is subsequently proposed to reduce the effect of multipath errors. Finally, two experimental scenarios are implemented to test the performance of the proposed method. The results show that EM-aided dualfrequency ambiguity estimation reduces the range error to approximately 20% in comparison with simple dual-frequency ambiguity estimation. Therefore the proposed technique is effective for multipath mitigation in RF relative measurement.

Design,fabrication,and cold-test results of C-band spherical RF pulse compressor prototype

Purpose Pulse compressor is a useful and common RF structure for Free Electron Laser and Linear Collider Facilities, whichcan improve the input power of accelerating structures significantly.Methods In this study, we designed, fabricated and tested a prototype of a compact C-band spherical pulse compressor.This pulse compressor utilizes one high Q0 spherical RF resonant cavity that works with two degenerated TE1,1,3modes anda dual-mode polarized coupler. The cavity and coupler were designed and machined separately and then brazed together.The prototype was tested carefully using vector network analyzer, and a cold-test system was set up to check the workingconditions of the spherical pulse compressor with inversed input powerResults Associated with the C-band high-gradient accelerating structures, the peak power gain and energy multiply factorcan be as high as 6.1 and 1.85, respectively, in theory. The average power gain is 3.8 in the first 0.372 μs after the phasereverse, which is the accelerator filling time. During the cold test, a peak power multiply factor of 6.04 and an energy multiplyfactor of 1.83 were achieved.Conclusions The test results agreed with the design well. The prototype was successfully made as a pre-research for thefuture energy multiplying scheme of SXFEL.