A beamforming approach to the self-calibration of phased arrays

In this paper, we propose a beamforming method for the calibration of the direction-independent gain of the analog chains of aperture arrays. The gain estimates are obtained by cross-correlating the output voltage of each antenna with a voltage beamformed using the other antennas of the array. When the beamforming weights are equal to the average cross-correlated power, a relation is drawn with the StEFCal algorithm. An example illustrates this approach for few point sources and a 256-element array

Fast and Accurate Simulation Technique for Large Irregular Arrays

A fast full-wave simulation technique is presented for the analysis of large irregular planar arrays of identical 3-D metallic antennas. The solution method relies on the Macro Basis Functions (MBF) approach and an interpolatory technique to compute the interactions between MBFs. The Harmonic-polynomial (HARP) model is established for the near-field interactions in a modified system of coordinates. For extremely large arrays made of complex antennas, two approaches assuming a limited radius of influence for mutual coupling are considered: one is based on a sparse-matrix LU decomposition and the other one on a tessellation of the array in the form of overlapping sub-arrays. The computation of all embedded element patterns is sped up with the help of the non-uniform FFT algorithm. Extensive validations are shown for arrays of log-periodic antennas envisaged for the low-frequency SKA (Square Kilometer Array) radio-telescope. The analysis of SKA stations with such a large number of elements has not been treated yet in the literature. Validations include comparison with results obtained with commercial software and with experiments. The proposed method is particularly well suited to array synthesis, in which several orders of magnitude can be saved in terms of computation time.Comment: The paper was submitted to IEEE Transaction on Antennas and Propagation on 01 - Feb.- 2017. The paper is 12 pages with 18 figure

Inhomogeneous plane-wave spectrum based Physical Optics for the simulation of urban radio propagation

Characterizing the radio propagation in urban environment has become essential to the design, assessment and installation of future wireless communication systems. Benefiting from the progress in the fields of computer graphics and computational electromagnetics, the deterministic simulations have gain significant interest in the last decade since they offer the advantage of providing accurate results, thereby replacing the need for costly and complicated measurement campaigns. In this thesis, we started from an accurate method, the Physical Optics (PO), and tried to reduce its computational cost. The PO radiation integral is known to accurately capture the truncation effect due to the finite dimension of scatterers. However, at Ultra High Frequencies (UHF), the numerical integration of highly-oscillating currents is extremely time-consuming. Hence, we have developed a fast algorithm which combines the efficiency of a Fast Fourier Transform and the simplicity of an inhomogeneous plane-wave representation of the scattered fields. It substantially accelerates the computation of the radiation integrals over quasi-planar building walls at UHF down to seconds. This is a step forward towards more accurate predictions of radio propagation at cm-waves in large and complex urban environments.(FSA - Sciences de l'ingénieur) -- UCL, 201

Sampling rules for an inhomogeneous plane-wave representation of scattered fields

Inhomogeneous plane waves (IPWs) based on a linear contour deformation provide an accurate and concise field representation for scattering problems in which source and observation domains are visible within a limited angular sector. Given an error level, we derive closed-form expressions for the truncation limit, the sampling step, and the contour slope that minimize the number of plane waves. A relation is drawn between the required number of plane waves and the degrees of freedom of the field, defined as the minimum number of orthonormal basis functions that represents scattered fields. The sampling rules are then applied to an efficient evaluation of the physical optics radiation integral

Modeling the Phase Correlation of Effective Diffuse Scattering From Surfaces for Radio Propagation Prediction With Antennas at Refined Separation

Diffuse scattering (DS), mostly caused by macroscopically rough surfaces, can be modeled by an effective roughness (ER) approach. In the ER approach, the object surface is divided into tiles, and the DS field amplitude associated with each tile is given. Assuming that the transmit antenna (or emitted field) is fixed and the phases associated with different tiles are independent, this paper proposes a phase evolution model based on the relative spatial locations of the receive antenna (Rx) to each tile. The proposed model contains two parts: the deterministic part that depends on the variation of the distance from Rx to tile center, and the correlated random part that depends on the variation of the angle between the Rx and the normal vector of tile. The correlation of the tile field phases resulting from the angular variation is modeled by the exponentially damped cosine correlation function. The proposed phase evolution model is evaluated by being applied to the ER approach to predict the DS component of radio channel transfer function (CTF). The predicted DS-CTF is compared with the reference (simulated data by physical optics and measured data in well-controlled environment) in terms of the spatial autocorrelation as well as the spatial Doppler spectrum

Mutual coupling analysis of large irregular arrays: from multipole to interpolatory methods

A novel formulation is proposed for the multipole expansion, called Laurent series formulation. It finds applications to the fast calculations of integral reactions between Macro Basis Functions in large planar irregular arrays of identical elements. Indeed, it automatically provides the coefficients of the harmonic-polynomial model of the reactions. A better understanding is also achieved for the minimized impact of the so-called low-frequency breakdown when computing interactions at small distances with the interpolatory method

Validation of the HARP method for simulation ofmutual coupling between SKALA antennas

The low-frequency instrument of the SKA radiotelescope will be made of large arrays of log-periodic antennas. Their mutual coupling may be strong and needs to be modeled in terms of em- bedded element patterns. The HARP method is based on Macro Basis Functions and computes their interactions versus relative positions, based on a lim- ited number of explicit calculations in the near eld. This paper shows results of this method in the low and medium range of the foreseen frequency spec- trum, considering the SKALA (SKA Log-Periodic Antennas) designed for this new telescope