Iterative Fourier Technique Research Articles

Peak-to-Average Power Ratio Reduction for High-Mobility Massive MIMO With Angle-Domain Doppler Suppression

Doppler suppression techniques with angle-domain Doppler compensation target reducing the time fluctuations of time-varying channel for high-mobility massive MIMO communications. However, the existing Doppler suppression solutions suffer from high peak-to-average power ratio (PAPR). In this letter, we propose a PAPR reduction scheme for Doppler suppression, where an optimization problem is formulated to minimize the Doppler spread under a constraint of tolerable PAPR level. We further develop a suboptimal solution which decomposes the original joint optimization problem into two steps. First, an iterative Fourier technique is employed and the idea of basis expansion model (BEM) is proposed to reduce the computational complexity. Then, the antenna weighting vector is optimized which takes into consideration both Doppler spread and PAPR. Simulation results are provided to demonstrate that the proposed scheme can substantially outperform the existing schemes.

Adaptive Learning of Probability Density Taper for Large Planar Array Thinning

This article presents a novel optimization algorithm to design a probability density taper for large array thinning. This novel algorithm is based on the iterative Fourier technique (IFT) integrated with an innovative adaptive learning mechanism and denoted as the probability learning IFT (PLIFT) here. With successive forward and backward Fourier transforms, the traditional IFT can be capable of thinning large arrays with high convergence rates, but easily get trapped in local optima. The proposed PLIFT utilizes the probability estimation to describe the elements with possible states of “ON” and “OFF” in a thinned array. A probability model is then adopted to determine the locations of elements in the thinned array featuring minimum sidelobe level. In this PLIFT, on the one hand, the probability model of density taper is learned in optimization process and gradually trained to approach the global optima. With the previous information being honored, the probability model taper proves to be reliable and effective in generating diverse competitive seeds, which, in turn, helps training an optimal probability distribution to best-fit the design goal. Several representative examples of large planar arrays thinning are provided to demonstrate the validity, highlighted global searching ability and increased robustness of the PLIFT.

Linear Array Thinning Using Probability Density Tapering Approach

In this letter, a novel synthesis algorithm is presented by using a probability density tapering approach in determining element distributions in a thinned array. The probability density tapering is carried out with the iterative Fourier technique (IFT) in array thinning, since the IFT method is proved effective in large array thinning, but the traditional IFT often easily gets trapped in local optima. In the proposed method, namely the probability tapering IFT (PTIFT), the element locations are determined by probability estimation. Then, a probability density taper is used to model the element distributions across the aperture. With iterations, the probability model taper is optimized to approach the global optimal solution. The efficiency of the PTIFT method was validated by some representative examples of array thinning with minimum peak sidelobe level. In addition, null placement in the uniformly illuminated thinned array with low sidelobes was investigated by utilizing the PTIFT.

Monopulse time‐modulated antenna array using iterative Fourier technique

SummaryThe iterative Fourier technique (IFT) is applied to design monopulse radar tracking system using time‐modulated linear antenna array (TMLA). IFT is used to modify the time sequences of the radio‐frequency switches connected to the antennas to generate sum and difference patterns with suppressed interference‐plus‐noise signal while constraining the power losses associated with side‐band radiation (SBR). The time modulation allows quick and precise control of the excitation distribution, which increases the tracking accuracy. To obtain best angle sensitivity, the article computes the tradeoff among side‐lobe level (SLL), half power beam width, directivity, and dynamic efficiency. The approach is proved successful to handle several design constraints through adaption in radiation domain as well as in aperture domain. Authors illustrate additional representative TMLA examples where the time sequences of the selected elements are prefixed to enhance the dynamic efficiency and directivity for different SLL and side‐band level (SBL). Application of IFT saves the computational cost significantly with respect to existing state‐of‐the‐art optimization techniques. Introduction of the symmetric switching sequences simplifies the feed network greatly. The proposed design solution is validated with a fabricated TMLA prototype consisting of two time‐switched printed dipoles with microstrip via‐hole balun at 2.45 GHz. Copyright © 2016 John Wiley & Sons, Ltd.

Synthesis of multiple‐pattern planar arrays with A hybrid generalised iterative fast Fourier transform algorithm

This study investigates the synthesis of multiple-pattern periodic phase-only control planar arrays. A hybrid generalised iterative Fourier technique is proposed to iteratively derive the array element excitations efficiently from the prescribed array factor, in which the two-dimensional Woodward-Lawson method is employed in order to generate good initial values. During the synthesis process, the phase-only control reconfigurable array is obtained by changing the corresponding phase for different array patterns while keeping the excitation amplitude constant. The robustness of the proposed algorithm has been testified by investigating the sensitivity of the radiation pattern affected by the amplitude and phase errors. Furthermore, three totally different types of reconfigurable numerical examples are discussed to validate the proposed method. Simulation results reveal the superior performance, the efficiency and the robustness of the proposed algorithm in dealing with multiple-pattern arrays.

Design of Wideband Multifunction Antenna Array Based on Multiple Interleaved Subarrays

A new Modified Iterative Fourier Technique (MIFT) is proposed for the design of interleaved linear antenna arrays which operate at different frequencies with no grating lobes, low-sidelobe levels, and wide bandwidths. In view of the Fourier transform mapping between the element excitations and array factor of uniform linear antenna array, the spectrum of the array factor is first acquired with FFT and its energy distributions are investigated thoroughly. The relationship between the carrier frequency and the element excitation is obtained by the density-weighting theory. In the following steps, the element excitations of interleaved subarrays are carefully selected in an alternate manner, which ensures that similar patterns can be achieved for interleaved subarrays. The Peak Sidelobe Levels (PSLs) of the interleaved subarrays are further reduced by the iterative Fourier transform algorithm. Numerical simulation results show that favorable design of the interleaved linear antenna arrays with different carrier frequencies can be obtained by the proposed method with favorable pattern similarity, low PSL, and wide bandwidths.

Design of Single-Feed Multi-Beam Reflectarray Using Iterative Fourier Techniques

Reflectarray antenna with multiple simultaneous beams is a promising antenna candidate for the multiple beam applications. A comprehensive and systematic study on the design of single-feed multi-beam reflectarray antenna is presented in this paper. The traditional direct design method, called aperture field superposition method, is investigated first. It is demonstrated that although this method can generate a multi-beam pattern, it cannot provide satisfactory performances, mainly because of high side lobe level, gain loss and beam deviation. The iterative Fourier technique is then applied to optimize the performances of the multi-beam reflectarray antenna. The required mask and cost function for multi-beam design and the flow of the iterative Fourier techniques are represented. Finally, a Ku-band four beam reflectarray with a single feed is designed using the iterative Fourier techniques and the radiation performances are analyzed and compared with that of single beam, as reference case, and multiple beam designed by aperture field superposition. The numerical results show that a good four beam performance can be obtained by using the iterative Fourier techniques, which suggests that the iterative Fourier technique is suitable for the design of the multi-beam reflectarray antenna with a single-feed.

Synthesis of Large Thinned Planar Arrays Using a Modified Iterative Fourier Technique

A modified iterative Fourier technique (MIFT) is proposed for the synthesis of large thinned planar arrays generating a pattern with lower sidelobe level (SLL). This technique is based on the iterative Fourier technique (IFT), and a variable filling factor is introduced to avoid the local minima in the optimization. Numerical results for several circular thinned planar arrays demonstrate that when the array's filling factor is larger than 40%, the MIFT allows one to find the optimum element distribution that yields a pattern with the minimum sidelobe level and almost the same beamwidth as the one obtainable using the IFT and a deterministic approach (DA). An approach for identifying the most appropriate sidelobe level threshold (SLT) suitable for the MIFT for synthesizing a large thinned planar array is also proposed.

SYNTHESIS OF LARGE PLANAR THINNED ARRAYS USING IWO-IFT ALGORITHM

The iterative Fourier technique (IFT) is a high e-ciency method that was proposed in recent past for the synthesis of large planar thinned arrays with isotropic radiating elements. However, the selection mechanism of IFT cannot always include the most useful elements in the \turned ON families, which make the method trap in some local minima. Therefore, in this paper, inspired by invasive weed optimization (IWO) algorithm, a developed version of the iterative Fourier technique (IFT), IWO-IFT, is proposed for thinning large planar arrays. In this new method, the initial weeds are produced by IFT, and are further perturbed by IWO through repeatedly reproduction, dispersion, and exclusion over search space to flnd better weeds. Numerical results for synthesizing difierent circular thinned arrays demonstrated the superiority of IWO-IFT over the IFT method.

Phaseless Measurements Over Nonrectangular Planar Near-Field Systems Without Probe Corotation

The need for acquiring the near-field phase with a high precision has imposed a stringent condition for measuring the antennas pattern at high frequencies in indoor facilities. The phaseless near-field techniques are introduced to overcome the necessity of operating with costly high frequency vector instruments. Many algorithms are proposed by the researchers and among them the Iterative Fourier technique is proved a viable solution for planar near-field systems. This paper discusses a difficulty in implementing this technique in nonrectangular facilities, such as plane-polar and bipolar, and introduces an iterative algorithm to alleviate it. The measurement of the co and cross-polarized field necessitates the corotation of the probe with the antenna under test to maintain the polarization, for all the nonrectangular planar systems. The corotation increases the hardware complexity of these measurement systems. Therefore the proposed algorithm which alleviates the probe corotation can significantly simplify the hardware involved. The convergence and stability of the proposed algorithm is studied and it is shown how one can control them. The developed algorithm is implemented using simulated near-field for two different types of antennas. The applicability of this algorithm is also assessed by employing a bipolar phaseless near-field measurement.

Fractal-Based Thinned Planar-Array Design Utilizing Iterative FFT Technique

This paper investigated the synthesis problem of fractal-based thinned planar arrays by using the iterative Fourier technique (IFT). Since an inverse discrete Fourier transform relationship exists between the array factor and the element excitations for a periodic array antenna, an iterative Fourier technique is introduced to derive the array element excitation from the prescribed array factor based on this peculiar property. However, considering the IFT technique is sensitive to the initial values, the fractal-thinned array technique is employed and combined in the synthesis process to exploit the advantages of these two techniques. Moreover, the DRR of the excitation amplitude is controlled to achieve a reduction of the cost of the feeding network. Numerical examples have been carried out to validate the proposed approach.

GRADUAL THINNING SYNTHESIS FOR LINEAR ARRAY BASED ON ITERATIVE FOURIER TECHNIQUES

In this paper, a modifled iterative fourier technique (MIFT) for thinning uniformly spaced linear arrays featuring a minimum sidelobe level as well as narrow beam is presented. Since IFT is a thinning procedure which has to be performed many trial times with difierent initial element distributions to get the optimum solution, it is, to some extent, time consuming. Moreover, in each trial of IFT, the number of iterations is usually low, which makes the method tend to be trapped in local solution even with a large number of trials. Therefore, the similar procedures for both MIFT and IFT are to derive the element excitations from the prescribed array factor using successive forward and backward Fourier transforms, and array thinning is accomplished by setting the amplitudes of a predetermined number of the largest element excitations to unity while the others to zero during each iteration cycle. Furthermore, in MIFT, based on the idea of gradual thinning which is inspired by perturbation theory, an adaptively changed flll factor is proposed to modify IFT with the purpose of accelerating computational speed and facilitating convergence. The immediate result caused by this modifled flll factor can be embodied in two points. One point is that unlike the random number of iterations contained in difierent trials of IFT, the number of iterations in all trials of MIFT is a flxed value and only predetermined by the array inherent features (symmetrical or asymmetrical) and flll factor. Therefore, su-cient iterations are ensured in each trial to efiectively help the algorithm avoid trapping. The other point is that when MIFT is performed, the array elements are gradually truncated, which maintains the most useful element excitations while maximally excludes the bad excitations, so that the optimum solution

Weighted Thinned Linear Array Design With the Iterative FFT Technique

A version of the iterative Fourier technique (IFT) for the design of thinned antenna arrays with weighted elements is presented. The structure of the algorithm means that it is well suited to the design of weighted thinned arrays with low current taper ratios (CTRs). A number of test problems from the literature are considered, and in each case, the IFT produces results with improved sidelobe level (SLL) at lower CTR.

Synthesis of thinned linear antenna arrays using bees algorithm

AbstractIn this article, we propose a method based on the bees algorithm (BA) to synthesize thinned linear antenna arrays with low sidelobe level.The BA is an optimization algorithm inspired by the behavior of the honey bees to find the optimal way of harvesting food resources around the hive. Several examples with different thinning percentages are given to show the effectiveness of the proposed method. The results of BA are compared with the results of real coded genetic algorithm, ant colony optimization, and iterative Fourier technique. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:795–799, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25850

Resilience to Probe-Positioning Errors in Planar Phaseless Near-Field Measurements

The phaseless techniques have been discussed in the antenna measurements community and the theories behind these techniques are well explained in literature. The issue of the noise and the presence of measurement errors are not investigated in details to provide strong impetus to the importance of phaseless measurements. In this paper the near-fields of a number of different types of antennas with high, medium and low side lobes are simulated to create some realistic cases. The probe positioning error effects are investigated by implementing random errors in the position of the simulated probe samples along different axes. A novel method is also adopted to incorporate the probe-height positioning error in an actual near-field measurement of an array antenna. It is also illustrated how the positioning errors can distort the phase distributions. Through detailed characterizations of the constructed far-field patterns, robustness of the Iterative Fourier technique even at the presence of very high probe positioning errors is demonstrated. It is shown how the utilization of a phaseless technique can significantly reduce the effects of probe positioning errors. The results are compared with the results extracted from the commonly used amplitude and phase near-field measurement techniques and the clear improvements are illustrated.

FFT Synthesis of Radiation Patterns With Wide Nulls Using Tapered Leaky-Wave Antennas

The ability of tapered leaky-wave antennas (LWAs) to synthesize directive radiation diagrams with suppression of the radiation in prescribed angular regions is studied in this work. The synthesis is based on an iterative Fourier technique that has been adapted for the case of LWAs, taking into account that the far field is related to the antenna illumination through an inverse Fourier transform. Results show that the simultaneous tapering of both phase and leakage constants of the leaky mode allow to obtain wide and deep radiation nulls while maintaining the high-gain scanning pattern of LWAs. The limitations of this unconventional tapering technique are also reported, and a practical design is validated with simulations.

Large Planar Array Thinning Using Iterative FFT Techniques

A new approach for the synthesis of thinned periodic planar arrays featuring a minimum sidelobe level is presented. The method is based on the iterative Fourier technique to derive the array element excitations from the prescribed array factor using successive forward and backward Fourier transforms. Array thinning is accomplished by setting the amplitudes of a predetermined number of largest element excitations to unity and the others to zero during each iteration cycle. Basically it is the same method successfully applied earlier to the thinning of periodic linear arrays. The effectiveness of the iterative Fourier technique for thinning periodic planar arrays will be demonstrated for a number of large arrays (> 1500 element positions) with a circular aperture using various degree of thinning.

Low-Sidelobe Pattern Synthesis Using Iterative Fourier Techniques Coded in MATLAB [EM Programmer's Notebook

The iterative Fourier technique for the synthesis of low-sidelobe patterns for linear arrays with uniform element spacing is described. The method uses the property that for a linear array with uniform element spacing, an inverse Fourier transform relationship exists between the array factor and the element excitations. This property is used in an iterative way to derive the array element excitations from the prescribed array factor. A brief outline of the iterative Fourier technique for the synthesis of low-sidelobe patterns for linear arrays will be given. The effectiveness of this method for realizing low-sidelobe sum and difference patterns will be demonstrated for linear arrays equipped with 50 and 80 elements. This demonstration of effectiveness also involves the recovery of the original low-sidelobe patterns, as close as possible, in case of element failures. Included is a program listing of this synthesis method, coded in MATLABtrade. With a few minor modifications/additions, the included MATLAB program can also be used for the design of thinned linear arrays having a periodic element spacing. Since the computational part of the included MATLAB program is coded using vector/matrix operations, this program can easily be extended for the synthesis of low-sidelobe patterns of planar arrays with a periodic element spacing, including pattern recovery in the case of defective elements.

Polarization Extraction in Planar Near-Field Phaseless Measurements

Near-field measurements typically require both amplitude and phase information to correctly predict the far-field. Unfortunately, there are situations in which the phase data is not available or impractical to obtain. That is why there has been a need for the development of phaseless techniques. Up until now, a number of remarkable solutions to this problem have been proposed by the researcher in different disciplines. Unfortunately, the complete vectorial representation of the field is not investigated in depth. The evaluated cases are usually linearly polarized and only the dominant polarization is investigated while the cross polarized field is usually neglected. This paper addresses the polarization issue in a two-component approach and then proposes a solution to the problem. A searching mechanism, for the incorporation of an appropriate initial guess, is integrated into the well-known, iterative Fourier technique (plane-to-plane) to enhance the algorithm response. Then, using two sets of measured orthogonal information data gathered by two linearly and orthogonally polarized probes, it is shown that with the aid of only a single point amplitude measurement, the polarization characteristics of the antenna can be extracted up to an inherent ambiguity of the right- and left-handedness. In order to have an assessment of the applicability of the proposed method, both linearly and circularly polarized antennas are simulated. Additionally, the method of extracting the polarization from the phaseless data is also verified through a bi-polar near-field measurement.

Linear Array Thinning Using Iterative FFT Techniques

A new approach for the synthesis of thinned uniformly spaced linear arrays featuring a minimum sidelobe level is presented. The method is based on the iterative Fourier technique to derive element excitations from the prescribed array factor using successive forward and backward Fourier transforms. Array thinning is accomplished by setting the amplitudes of the largest element excitations to unity and the others to zero during each iteration cycle. The number of turned on elements depends on the array filling factor and the total count of element positions. The effectiveness of the new method will be demonstrated for various 200-element linear arrays and compared with published results.