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In this work, a novel use of the Non-Uniform Fast Fourier Transform (NUFFT) in reflectarray antenna analysis is proposed to greatly accelerate the computation of radiation patterns using a non-uniform, reduced and adaptive grid in the spectral domain. The proposed methodology is very useful for very large reflectarrays, which have very narrow beamwidths due to their large directivity, and shaped-beam reflectarrays for satellite applications such as Direct Broadcast Satellite (DBS), which might require a compliance analysis in very small angular regions. In those cases, high resolution in the radiation pattern is required, while a low resolution could be enough elsewhere to account for side lobes. However, current analysis techniques for such reflectarrays present limitations regarding large memory footprints or slow computations. The methodology presented in this work allows to overcome those limitations by performing computations in a non-uniform, reduced and adaptive grid in the transformed UV domain, achieving faster computations using considerably less memory. Numerical examples for current applications of interest are provided to assess the capabilities of the technique. In particular, the use of the NUFFT allows to compute efficiently the radiation pattern in any principal plane with improved resolution for multibeam applications. Also, compliance analyses for DBS applications may be improved with the use of a reduced, multiresolution grid and the NUFFT. The proposed technique is thus suitable to greatly accelerate optimization algorithms. [ABSTRACT FROM AUTHOR]

This paper presents a technique for the acceleration of gradient-based algorithms that employ finite differences in the calculation of the gradient for the optimization of array antennas. It is based on differential contributions, which takes advantage of the fact that when an array is optimized, each element is analyzed independently of the rest. Thus, the computation of the gradient of the cost function, which is typically the most time-consuming operation of the algorithm, can be accelerated. A time cost study is presented and the technique is implemented, as an example, in the generalized intersection approach algorithm for array optimization in near and far fields. Several syntheses are performed to assess the improvement of this technique. In the far field, it is compared with periodic and aperiodic arrays using different approaches for the computation of the gradient, including the analytic derivative. A reflectarray is also optimized in the near field with the goal of improving its quiet zone. The technique of differential contributions shows the important reductions in the time per iteration in all three syntheses, especially in that of aperiodic arrays and near-field optimization, where the time saved in the evaluation of the gradient is greater than 99%. [ABSTRACT FROM AUTHOR]

A method for the optimization of the crosspolar component of dual-polarized reflectarrays using full-wave analysis at the element level is described and demonstrated. The reflectarray full-wave analysis is based on local periodicity (LP) and integrated within the optimization process in order to accurately characterize the crosspolar far field. The proposed method is based on the generalized Intersection Approach framework using the Levenberg–Marquardt Algorithm as backward projector, and the employed full-wave analysis is based on the Method of Moments assuming Local Periodicity (MoM-LP). Several strategies to accelerate the computations are exploited, such as the parallelization of all the algorithm building blocks. To minimize the impact of MoM-LP in the optimization process, a strategy to reduce the number of MoM-LP calls is described, further accelerating the algorithm. Moreover, the convergence is improved by working with the squared field amplitude, alleviating the trap problem of local optimizers. This method allows to optimize the crosspolar component in the whole visible region or only in the coverage zone to facilitate the convergence, reducing computing time and memory usage. Two test cases are provided to validate the technique, one with an isoflux pattern for global Earth coverage and another with European coverage for direct broadcast satellite application. [ABSTRACT FROM PUBLISHER]

A new efficient method for broadband antenna characterization from phaseless acquisitions in the frequency-domain (FD) is presented. The phase-retrieval technique is based on an extrapolation of the off-axis indirect holography. In common with the conventional approach, the power of the interferometric field of the antenna under test (AUT) and a reference antenna, whose field is known in advance, as well as the power of the AUT alone, is measured at the desired frequencies. Nevertheless, the phase retrieval is accomplished independently at each spatial point by filtering in the time-domain (TD) rather than in the k-space. Thus, the dependency of the phase retrieval on the position accuracy is reduced and it can be accomplished simultaneously at all frequencies without resorting to iterative schemes. Moreover, it yields a less dense sampling and a phase-retrieval algorithm not dependent on the geometry of the acquisition. The method is illustrated with a numerical example in the $W$-band as well as with two near-field (NF) measurement examples in the $K_a$- and $W$-bands. [ABSTRACT FROM PUBLISHER]

An extended formulation of the intersection approach (IA) algorithm is presented to synthesize matrices of complex reflection coefficients for dual-polarized reflectarrays. The synthesis of complex reflection coefficients allows to impose copolar as well as cross-polar specifications, since these coefficients fully characterize the behavior of the unit cell. The implementation of the algorithm is based on the use of the fast Fourier transform (FFT) in both the forward and backward projectors of the IA, allowing for a highly efficient and fast synthesis process of dual-polarized reflectarrays. Although arbitrary restrictions can be enforced in the reflection coefficients, they might not be feasible for passive antennas. Hence, the unit cell is analyzed as a lossless and lossy passive two-port network and the restriction equations are derived for both cases involving amplitudes and phases of the reflection coefficients. The lossless constraints proved to be too restrictive so lossy restrictions should be applied to achieve feasible reflection coefficients for passive array design. Test cases are provided, which confirm that the algorithm is able to synthesize with success radiation patterns with copolar and cross-polar requirements with restrictions applied to the reflection coefficients. [ABSTRACT FROM PUBLISHER]

We present a multilevel version to the characteristic basis function method (CBFM). This technique extends the range of applicability of the conventional CBFM and allows a direct solution of problems even when they exceed 250,000 degrees of freedom. In this paper, it is shown how we can use the multilevel CBFM, which is a natural extension of the conventional approach and which saves both time and memory, and yet retains excellent accuracy in the computed far fields. Also, the adaptive cross algorithm is used for fast calculation of the interaction between the blocks in the process of generating the reduced matrix. [ABSTRACT FROM AUTHOR]

This article presents an acceleration technique for the fast calculation of the impedance matrix elements in the method of moments in the case of using characteristic basis functions (CBFs). This technique is based on taking advantage of the smooth amplitude and phase behaviors of the fields generated by a CBF when the distance is sufficiently large. Computational efficiency is realized by calculating the reaction between a source-CBF and a test-CBF by first evaluating a sampling of the field at a sparse set of points, and then computing the fields at the rest via the use of interpolation. Thus, this procedure avoids the highly expensive integration in the source domain that is needed to calculate the radiated field in the entire test domain when following the conventional procedure. Phase unwrap prior to interpolation and the fast sample calculation scheme are detailed in the article. The technique has been validated by considering several examples involving Radar Cross Section computations. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1818–1824, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24478 [ABSTRACT FROM AUTHOR]

This article presents two practical applications of the Sources Reconstruction Method for antenna diagnostics and antenna manufacturing errors detection. The goal is to show the SRM capabilities to determine defective elements in antenna arrays as well as to detect irregularities in the surface of reflector antennas from the analysis of the aperture fields. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1664–1668, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24416 [ABSTRACT FROM AUTHOR]

Addresses a near-field to far-field transformation for the case of spherical scanning using equivalent magnetic currents and matrix methods. Equivalent current reconstruction from spherical data; Radial electric field retrieval algorithm; Results and conclusion.

This article deals with the issue of convergence of the Adaptive Cross Algorithm (ACA) and argues that the stopping criterion used in this algorithm can lead to a premature stop, and yield inaccurate results as a consequence. A multiple restart, which is simple and effective, is proposed to improve the robustness. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2458–2460, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24637 [ABSTRACT FROM AUTHOR]