Research On Test Method Of Aircraft HIRF Low Level Swept Field

High Intensity Radiated Fields(HIRF)are formed by ground,shipborne or airborne radar,radio,television,and other radio frequency transmitting devices.In addition,it has a longer operating time and a wider frequency band for the aircraft,and its frequency range is10KHz-40 GHz.With the extensive use of modern airborne electronic systems and the increasing proportion of airframe composite materials,the increasing HIRF environment has become a key factor in flight safety.At present,the HIRF test has become a key verifying project in the airworthiness verification of civil aircraft,but the study on the HIRF test is on the start-up phase in our country.This paper takes the low-level swept field test method in the aircraft-level HIRF test as the study object,and a combination approach of test and simulation methods is adopt to study the shielding characteristics of the airframe under HIRF environment,and the variation rule and influence mechanism of shielding effectivenessof the airframe under different antenna polarization,airframe structure and radiation direction are analyzed.The main study contents are as follows:1.A low-level swept field test study on a certain type of helicopter were carried out by using an aircraft-level HIRF test system.The results show that the shielding effectiveness at the test position in the airframe varies with the working conditions of the transmitting antenna polarization,airframe structure,and radiation direction.Finally,it is concluded that the aperture structure is the main coupling path for electromagnetic energy to enter the airframe in the low-level swept field test frequency band.2.With the electromagnetic simulation software CST,the corresponding model of rectangular cavity is established for the aperture structure.First,the validity of the simulation method is verified.Next,the influence on the shielding effectiveness of the cavity imposed by the polarization mode of incident wave,test point position,aperture shape,aperture orientation,multi-apertures form and different materials is analyzed.Finally,the above mechanism was analyzed for its influence mechanism and causes.3.By establishing a full-scale helicopter airframe simulation model and simplifying the airframe model,which ignores seats and luggage racks,etc.,and only retain the external structural features.And setting the aperture streamlined equivalent model on the airframe.Thevariation rule of the shielding effectiveness at the test position in the airframe under different conditions is studied.Through comparing test and simulation results,it is found that the variation rule of the shielding effectiveness of the airframe obtained by simulation is close to the test,which verified the validity of the airframe simulation model and its parameters in this paper.In summary,test and simulation aspects of the low-level swept-field test method have been systematically studied in this paper.The results can provide a reference for domestic HIRF test study and the formulation of standard specifications,which has practical engineering significance for improving domestic HIRF airworthiness verification technology for civil aircraft.