Research On IPD Measurement Techniques For The Wave-transparent Components With Complex Shapes

The wave-transparent component is a kind of electromagnetic dielectric shell to protect the antenna from the harsh external environment,and has been widely used in various antenna systems.However,when the electromagnetic wave passes through the wave-transparent component,the phase will change significantly,which influences the detection accuracy of the antenna system.In order to evaluate the electric performance of the antenna system,it is necessary to accurately measure the IPD(Insert Phase Delay)distribution of the wave-transparent component.To realize the high-precision,no-blind-area IPD measurement of the wave-transparent components with complex shapes,this paper studied the measurement method combining transmission and reflection,carried out a free-space method for permittivity extraction applied to oblique incidence.The microwave measurement system is established.The calibration and data processing method are introduced in detail.Firstly,this paper abstracts the wave-transparent component as a two-port network,and establishes the mathematical relationship between the material parameters and the scattering parameters.On the basis of this mathematical relationship,a free-space method for permittivity extraction applied to oblique incidence is proposed.In this method,the cubic spline interpolation is applied to establish the correlation between the complex permittivity and the frequency of the electromagnetic field.The complex permittivity is extracted by using the improved PSO(Particle Swarm Optimization)method to minimize the distance between the measured and the calculated transmission coefficients.This method solves the problem of contactless measurement of complex permittivity for wave-transparent components with complex shapes.Secondly,a microwave measurement system is established.In order to ensure the measurement accuracy,the error source of the entire measurement system is analyzed.The TRL(Through-Relect-Line)calibration is applied to eliminate the error caused by the impedance mismatch between the vector network analyzer,cable,and antenna,as well as the error caused by the standing wave effect of the antenna and the multiple reflections between the emitting and receiving antennas.The time-domain filtering algorithm is developed to filter out the interference component caused by external space reflection.Next,a plate structure sample was utilized to validate the effectiveness of the free-space permitticity extraction menthod under oblique incidence.The experiment results show that the proposed extraction method is compatible with commercial rectangular waveguide method.Also,the influence of the curvature of the measured area on the measurement accuracy is studied using a rotating body wave-transparent component.The ralationship between the relative permittivity,frequency and curvature of the measured area is established.On the basis of the relationship,the measurement accuracy criterion is clarified.The reasonable suggestions for improving the measurement accuracy of the relative permittivity of the wave-transparent components are carried out.Finally,to realize the high-precision,no-blind-area IPD measurement of the wave-transparent components with complex shapes,a measurement method combining transmission and reflection is proposed.The transmission measurement is performed in the relatively wide area of the internal space of the wave-transparent component.When the internal space is too narrow that cannot be measured by the transmission method,the reflection can be performed.The experimental results show that the IPD measurement method based on the combination of transmission and reflection proposed in this paper can realize the high-precision and no-blind-area IPD measurement of the wave-transparent components with complex shapes.