Dip Angle And Complex Permittivity Estimation Based On Passive Millimeter-wave Polarization Measurement

The polarization of electromagnetic wave is transformed after being reflected on the surface of objects.Such transformation is determined by object’s surface inclination,electromagnetic parameters,and the background,which can be harnessed for object detection.Thanks to the relatively small wavelength,the polarization of reflected millimeter wave signals provides more fine-grained information,which facilitates accurate object detection.As a result,sampling the reflected millimeter wave signal using radiometers for polarization analysis,i.e.,passive millimeter wave(PMMW)polarization measurement,becomes a new object detection technique,which can be widely applied to security inspection,military investigation,topographical survey,etc.As a promising detection technique,PMMW polarization measurement has the characteristics of high safety/concealment,maintains good penetration,and is able to operate all-day and in all-weather conditions.It serves as a good complement to other object detection techniques,such as visible light-,infra-red-,and radar-based detection.A theoretical investigation on how to extract more object information from the reflected millimeter signals is of significance.Yet,most of the existing research works focus on the the design and implementation of the PMMW system,theoretic knowledge on the transformed polarization of reflected millimeter wave signals remains largely unknown.In specific,the impact of object’s surface inclination and granularity,as well as its electromagnetic feature and background temperature,on the reflected polarization require in-depth investigation.This paper focuses on the theory of millimeter wave signal polarization,analyzes the innate correlation between object’s physic parameters(namely,complex permittivity)and the reflective polarization.In order to effectively extract useful object information from the reflected signal,we define a feature concept named reflective degree of polarization(RDo P).The RDo P is able to eliminate the interference from background conditions.Based on the RDo P,we established a theoretic model,for the first time,between the brightness temperature and the polarization of reflected signals.Then,we propose a modified RDo P,which successfully characterizes the non-linear relationship between the measured brightness temperature,object’s electromagnetic feature,and the measurement angle.Based on such relationship,we design a multi-angle polarization-based object information extract method.The simulation results show that the target dip angle inversion results have high accuracy.The distribution of complex permittivity obtained by inversion is consistent with the theoretical analysis and can be used to classify and identify targets.Extensive numerical analysis and experiments have confirmed the effectiveness and advantages of the proposed method.In practice,the established model and the proposed method can be applied to target detection and topographical survey.