Blind direction-of-arrival estimation algorithm for conformal array antenna with respect to polarisation diversity

Owing to the curvature of the conformal carrier, the polarisation diversity of element patterns is one of the most distinct characteristics of conformal array manifolds. Consequently, direction-of-arrival (DOA) estimation with conformal array antennas always couples with the estimation of the polarisation. Based on the fourth-order cumulants of the array outputs and an elaborately designed array structure, an estimation of signal parameters via rotational invariance techniques-based blind DOA estimation algorithm with respect to polarisation diversity is proposed for conformal array antennas, in which the displacement vectors required by ESPRIT are acquired by utilising 'virtual array elements' derived from actual array elements by 'virtual cross-correlation computation'. Owing to the fact that these distance vectors used in algorithm implementation are not affected by element patterns and source polarisation, the 2D DOA estimates are decoupled from polarisation and obtained with no need for exact knowledge of array element polarised patterns. The proposed method achieves high-resolution 2D DOA estimation and is applicable to cylindrical, conical and spherical conformal carriers. The array set-up examples of conical, cylindrical and spherical carriers are presented for demonstration and the Monte-Carlo simulation results of DOA estimation with cylindrical conformal array are also provided to illustrate the effectiveness of the proposed algorithm.