Pattern compensation for DOA estimation by electromagnetic vector sensors

Vector sensors are made of electric dipoles and magnetic loops. A full six vector sensor can measure the complete six electric and magnetic field components at one point in the space. Vector sensor concept was proposed from signal processing community and associated direction of arrival (DOA) estimation algorithm was based on isotropic radiation model. This paper shows that the radiation pattern compensation of sensor element is necessary for practical DOA application with improved accuracy, from more than 12° to about 1° for a realistic signal of 10 dB SNR. As a useful example, we consider a simpler yet more popular low-grazing angle application with a reduced vector sensor of two magnetic loop sensor elements for DOA estimation of a low-grazing angle source with vertical polarization. The reduced vector sensor can greatly simplify the system design, fabrication, measurement, and data processing.

I. Introduction

Vector sensor for source localization has been researched since 1991 [1]. A vector sensor antenna is made of electric dipoles and magnetic loops. A full six vector sensor antenna measures the complete six components of electric field and magnetic field at one point in the space (three dipoles measure three electric field components and three loops measure three magnetic field components) [1]. Such vector sensor is normally referred to as a 6-dimensional (6-D) vector sensor since its output data is a 6-D vector. With the complete electric and magnetic information, a single 6-D vector sensor is able to estimate the DOA information of one source [1] or even two sources [2]. Besides DOA estimation, a vector sensor can also be used in the polarization diversity applications, in which it helps to improve the performances of wireless communication or radar systems [3], [4]. The DOA estimation algorithms associated with a 6-D vector sensor include a Cross-Product-Based DOA estimator [1], [5] and an Adaptive Cross-Product algorithm [6]. These algorithms utilize the property of the Poynting vector in plane waves and achieve the direction estimation by computing the full electric and magnetic field components. However, these algorithms have not considered the actual pattern variations of the antenna components, which can have large effect on the DOA estimation accuracy in practical situations.