Analysis on active phased antenna array on complex platform using hybrid UTD-ACGF technique

Abstract

When an active phased array antenna array operates on a complex platform, the ideal voltages of the antenna array are significantly distorted by both mutual coupling and platform scattering. This distortion causes performance degradation of the direction of arrival (DOA) algorithms and modification of the beam pattern of the antenna array. Therefore, an analysis of the active phased antenna array on the platform is required.

In this dissertation, a hybrid UTD-ACGF technique is proposed for modeling port voltages of the active phased antenna array on a complex platform, and the hybrid UTD-ACGF technique is applied to DOA searching and beam synthesis issue. The dissertation consists of following five main ideas.

First, the complex platform is modeled based on uniform theory of diffraction (UTD) technique. If the complex platform is electrically larger than the wavelength of an antenna center frequency, the complex platform can be intuitively analyzed based on optical approximation. The complex platform can be precisely designed with only coarse non-uniform rational b-spline (NURBS) surfaces. Using a NURBS-based ray-tracing technique, the scattered electric fields by complex platform are effectively calculated by using the UTD technique.

Second, the antenna array is modeled based on antenna current Green’s function (ACGF). If the antenna array is finely segmented on the basis of the wavelength, the entire ACGF of the segmented antenna array represents an exact mutual coupling effect of the antenna array itself.

Third, electromagnetic modeling, called the hybrid UTD-ACGF technique, is proposed combining scattering effect by the complex platform and mutual coupling by the antenna array. Based on the rigorous mutual coupling perturbation series, the proposed model uses the first-order perturbation series approximation to explain an interaction between the complex platform and the antenna array. The adequacy of the approximation can be validated with comparison between hybrid UTD-ACGF results and method of moment (MoM) results. For a complex structure containing an arbitrary wavelength scale, the proposed model provides both effective and accurate results of port voltages of the active phased antenna array on the complex platform.

Fourth, the proposed electromagnetic model is used as a backbone, and two methods to enhance performance of DOA algorithms are proposed. The first method is a statistical distortion matrix compensation. This method estimate the statistical solution of a distortion matrix related to both mutual coupling and the platform-scattering effect. This statistical distortion matrix is applied to measured signal covariance matrix for distortion compensation. The second method is replacing hybrid UTD-ACGF steering vector to original steering vector of MUSIC algorithm. Through scanning process of MUSIC algorithm, obtained signal DOAs are automatically compensated, because the hybrid UTD-ACGF steering vector reflects both mutual coupling and platform scattering effect. A DOA simulation using the MUSIC algorithm is performed to confirm the compensatory effect of the two proposed compensation methods.

Fifth, a beam synthesis method for the antenna array on the complex platform is proposed, combining active element pattern (AEP) method of receiving mode and hybrid UTD-ACGF technique. This proposed method clearly and mathematically divides the beam pattern with the platform into mutual coupling and platform scattering component. The beamforming and boresight error simulation results using proposed method were verified with the MoM results. The proposed method can efficiently and accurately provide beam pattern reflecting both the mutual coupling effect and the platform scattering effect.