Research On The Measurement And Simulation Methods For Transfer Impedance Of Shielded Coaxial Cables

With the increasingly complex electromagnetic environment in the rocketengine testing system, there would be produce a variety of EMI during the experi-ment. Once these transient interference with broadband and high amplitude couplesinto the inner conductor of cable, the reliability of equipment connected with thecable will be seriously influenced. Even this will be result in abnormal work of thetesting system. So research on the measurement and simulation methods of shieldedcoaxial cables are vitally important in improving the electromagnetic compatibility ofoverall rocket engine test system, and providing theory support for developing anti-jamming equipment of testing system.Firstly, A new model is presented for the accurate predictions of transferimpedance of braided coaxial cables, from a summary study on the existing modelsproposed. The complicated responses on the braided shields due to the radiation fromthe exterior produced electromagnetic fields are taking into account in the new model.In addition, the diameter of braid is rebuilt to improve the accuracy of inductance.The formulas have a close relationship with the primary parameters of braided shield.The new model is demonstrated valid by studying against the results obtained fromthe existing models and the measurement of several braided cable samples. Then thenew model is applied to research the change rules of transfer impedance with thechange of primary parameters of shield.Secondly, research on the method of establishing finite element numericalmodel in Ansoft HFSS with the simplified structural model and approximatestructural model of braided shielded cable which are established by Pro/Engineersoftware. The validity of the method is verified by studying in several cable samples.The method solves the difficulties of the existing numerical analysis method tocalculate transfer impedance of braided shield cables which are spindly, even smalland complex in partial structure.Finally, a new method for transfer impedance measurement which based on timeresponse is proposed, and the method is made into a simple and easily useexperimental platform. The new method has some technology innovation points. First,it doesn’t need to special process to cables which guarantees the completeness ofshield. Second, it is more close to the true cable application environment by usingfield excitation than the lumped souse excitation the earlier measurement methods.Finally, it is solve the difficulty of impedance matching in the outer loop by designeda circuit to measure the characteristic impedance irregular round-planar transmission line. The validity experimental setup is verified by applied to some examples. At last,the factors influencing to improve the applicable frequency range is analyzed indetail.