The Experts below are selected from a list of 75480 Experts worldwide ranked by ideXlab platform
W P M N Keizer - One of the best experts on this subject based on the ideXlab platform.
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linear Array thinning using iterative fft techniques
IEEE Transactions on Antennas and Propagation, 2008Co-Authors: W P M N KeizerAbstract: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.
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fast low sidelobe synthesis for large planar Array antennas utilizing successive fast fourier transforms of the Array Factor
IEEE Transactions on Antennas and Propagation, 2007Co-Authors: W P M N KeizerAbstract:A new and very fast low-sidelobe pattern synthesis method for planar Array antennas with periodic element spacing is described. The basic idea of the method is that since the Array Factor is related to the element excitations through an inverse Fourier transform, the element excitations can be derived from the Array Factor through a direct Fourier transform. Starting with an initial set of suitable element excitations the Array Factor is calculated. After matching the Array Factor to the prescribed pattern, an updated set of excitations is obtained through a direct Fourier transform performed on the matched Array Factor. From this updated set, only the samples associated with the aperture are retained, where after a new Array Factor is calculated. The whole process is repeated until the updated Array Factor does not violate any longer the pattern requirements. The proposed synthesis method provides significant improvements in terms of performance, computational speed, flexibility, and ease of implementation in software to the methods described in reviewed literature. A number of representative examples are presented to demonstrate the various unique capabilities of the method. The results include sum and difference patterns for circular and elliptical aperture shapes featuring uniform ultra low sidelobes
Li Feng - One of the best experts on this subject based on the ideXlab platform.
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relationship between mirrored aperture synthesis radiometers and aperture synthesis radiometers
IEEE Geoscience and Remote Sensing Letters, 2017Co-Authors: Li FengAbstract:The mirrored aperture synthesis radiometer (MASR) has been proposed as a new technique for high-resolution observation. Compared with ASRs, MASRs have the advantage of lower system complexity. However, the relationship between MASRs and ASRs has not been studied. In order to thoroughly study MASRs, it is necessary to establish the relationship between MASRs and ASRs. In this letter, the Array Factor of 1-D MASRs in the discrete cosine transform domain (DCT-domain) is defined. The reconstructed image for a 1-D MASR is a symmetric convolution of the observed brightness temperature distribution and the defined Array Factor in the DCT domain. Since a symmetric convolution can be turned into a linear convolution, the relationship between 1-D MASRs and 1-D ASRs can be established. A 1-D MASR is equivalent to a 1-D ASR that has a mirrored window. Additionally, for the equivalent 1-D ASR, its observed scene is a symmetrically extended real scene. This established relationship is validated by the simulation results. In practical applications, a MASR can be understood as an ASR.
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Array Factor forming for image reconstruction of one dimensional nonuniform aperture synthesis radiometers
IEEE Geoscience and Remote Sensing Letters, 2016Co-Authors: Li Feng, Ke Chen, Jing Tong, Honggang XieAbstract:Nonuniform aperture synthesis radiometers (NASRs) have the advantage of flexibility in practical applications. However, the main limitation of NASRs for Earth observation is the poor reconstruction quality. In this letter, the Array Factor of 1-D NASR is analyzed. Array Factor forming (AFF) is introduced to improve the reconstruction quality of 1-D NASRs. The limitations of the AFF on Array configurations are given. The NASR that meets the given limitations is called the optimizable NASR (ONASR). The numerical results and experimental results demonstrate that the AFF is able to improve the reconstruction quality of 1-D ONASRs. To assess the performance of the AFF thoroughly, the comparisons are made against the linear interpolation and the regularized G-matrix method. Meanwhile, the comparisons between the AFF-based 1-D ONASRs and the 1-D uniform ASRs are also made. The comparison results demonstrate that the AFF can obtain better reconstruction quality than the linear interpolation and the regularized G-matrix method. Additionally, the comparison results also demonstrate that the reconstruction quality of AFF-based 1-D ONASRs can approach that of 1-D uniform ASRs.
W Keizer - One of the best experts on this subject based on the ideXlab platform.
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large planar Array thinning using iterative fft techniques
IEEE Transactions on Antennas and Propagation, 2009Co-Authors: W KeizerAbstract: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.
Mojtaba Fallahpour - One of the best experts on this subject based on the ideXlab platform.
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sum difference and shaped beam pattern synthesis by non uniform spacing and phase control
IEEE Transactions on Antennas and Propagation, 2011Co-Authors: Homayoon Oraizi, Mojtaba FallahpourAbstract:A design procedure for the synthesis of non-uniformly spaced linear Arrays is presented, which uses the Poisson sum expansion of the Array Factor introduced in the literature. By considering the nonzero phase term in the existent formula and using the appropriate line source pattern synthesis methods, a general design procedure is obtained to synthesize any type of pattern, such as sum, difference and shaped beams. This approach converts the nonlinear complex problem of pattern synthesis for non-uniformly spaced linear Arrays to a simple problem, which makes it fast and easy to implement. Moreover, an extra optimization process is added to the synthesis procedure to improve final pattern and provide control on computed parameters.
J A R Azevedo - One of the best experts on this subject based on the ideXlab platform.
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adapted raised cosine window function for Array Factor control with dynamic range ratio limitation
European Conference on Antennas and Propagation, 2017Co-Authors: F E S Santos, J A R AzevedoAbstract:The use of window functions to improve the side lobe level of antenna Arrays is hindered by high value of excitation currents dynamic range ratio. This paper proposes a fast and iterative window function generation strategy aimed at achieving improved side lobe level starting from a preset current dynamic range ratio. Based on this strategy a new window function is developed for standard set of conditions.
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synthesis of non uniformly spaced Arrays using the fourier transform and window techniques
Iet Microwaves Antennas & Propagation, 2009Co-Authors: J A R Azevedo, A M E S CasimiroAbstract:Under the Fourier relation between the Array Factor and its corresponding source distribution, synthesis approaches of non-uniformly spaced Arrays (NUSAs) are proposed. Using the Fourier transform and synthesis concepts of space-tapered Arrays, the optimum patterns like Chebyshev are used to synthesise NUSAs with uniform amplitude, whose Array Factors have the performance approximated to the chosen patterns. The Fourier transform properties can be used to control the Array Factor so that the proposed approaches are applied in different synthesis specifications. Based on the synthesised NUSAs with uniform amplitude and window techniques, under the sampling theorem, NUSAs with non-uniform amplitude can be easily obtained to improve the performance of the Array Factor, mainly in the reduction of sidelobe level. Synthesis examples show the advantages of the presented methods.
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SHAPED BEAM PATTERN SYNTHESIS WITH NON-UNIFORM SAMPLE PHASES
Progress In Electromagnetics Research B, 2008Co-Authors: J A R AzevedoAbstract:For a long time power pattern synthesis has been considered to produce shaped beam patterns due to the number of degrees of freedom when compared with field pattern synthesis. However, severaladvantages exist if synthesis techniques are based on field patterns, since the relationship between the Array Factor and the source distribution is a Fourier transform. In this case, quicker and efficient algorithms are obtained with the Fast Fourier Transform (FFT) to perform the calculations. Therefore, this work presents a new technique that synthesizes shaped beam patterns through the control of non-uniformly samples of the Array Factor, both in amplitude and phase. The sample phases increase the number of degrees of freedom. To produce complex patterns, the sample phases of the shaped beam region are used to create more oscillations in the ripple structure than the ones produced with the realpatterns. Not onl y this procedure yields a narrower transition region between the beam zone and the sidelobe zone but also smaller dynamic range ratios are obtained. Furthermore, it is described how to impose nulls in prescribed directions of the complex patterns. Some examples are presented to demonstrate the application of the synthesis technique.