The near tofar field transformation feature is demonstrated using four different examples. This technique is associated with a threedimensional finitedifference timedomain fdtd model, which solves the maxwell equations in the time domain. Glisson, fellow, ieee abstractsa near to far eld transformation ntft based on the rwg basis function is proposed for a 2d triangulargrid. Nearfield and farfield modeling of scattered surface. Capoglu and di zhang, and is currently maintained by di zhang. Tests with different scenarios show that a computation gain of.
A timedomain near to farfield transformation for fdtd. On the fdtd neartofarfield transformations for weakly. According to the time domain calculation sequence in fdtd, the contribution of ss to ls is transferred directly to far zone observation point. In the present work, a model based on the finite difference time domain fdtd method and the near field to far field nftff transformation for electromagnetic waves propagation is presented. The main fdtd volume is left as is in the classical fdtd method, but the task of the near tofar field transformation ntfft module is distributed. Near to farfield transformation in the aperiodic fourier. We propose a simple yet effective modification to significantly improve the accuracy of the finitedifference timedomain fdtd near tofar field ntff transformation for calculating the. The first technique used to perform the nfff transformation could only be applied to a single frequency analysis 1, 3. Osa implementing the near to farfield transformation. Abstract fdtd based radar cross section rcs and antenna simulations is discussed. It is based on the finitedifference timedomain fdtd method, which is one of the most popular approaches for solving maxwells equations of electrodynamics.
The transformation of the near field to the corresponding far field is a key step involved in the application of the finitedifference timedomain fdtd technique to the scattering of an electromagnetic wave by a dielectric particle. Compared to conventional near tofar field transformation techniques, the proposal allows one to easily evaluate the guidedmode radiation diagrams, even if material dissipation is present in the stack, and thus to simultaneously track the coupling of light to all channels i. On the otherhand, because of theapproximations appliedto the surface integrals, the standard transformation typically used within the finitedifference timedomain fdtd method 15 is strictly a near to far field transform. When the finitedifference timedomain fdtd method is applied to lightscattering computations, the far fields can be obtained by means of integrating the near fields either over the volume bounded by the particles surface or on a regular surface encompassing the scatterer.
When radiation pattern of an antenna or scattering pattern of radar crosssection rcs is measured, its characteristics is usually evaluated in the far field area. A new neartofarfield transformation that combines the fdtd and the series solution is presented. A new neartofarfield transformation algorithm for threedimensional finitedifferent timedomain is presented in this article. Fast fourier transform of the results new algorithms.
A hybrid technique combining fdtd and series solution for. Matlab how to do a near field far field transformation. Timedomain near to farfield transformation for fdtd in two dimensions article in microwave and optical technology letters 276. Pier online fdtdtdpo hybrid approach for analysis of. A timedomain near to farfield transformation for fdtd in two. Fdtd is very efficient when making near field calculations, while for the far field it is necessary to use an additional method to perform a near tofar field nfff transformation. Simple near field to far field transformation method using antenna arrayfactor hirokazu kobayashi, yoshio yamaguchi, yi cui department of information engineering, niigata university, niigata, 2118121, japan. Hello everyone, im trying to implement near to far field transformation frequency domain for my fdtd code in matlab following tafloves books but it doesnt work. Ramahi, member, ieee abstract kirchhoffs surface integral representation ksir is used to calculate the near and far. There are three steps involved in this type of calculation. First, the near surfaces is defined as a set of surfaces capturing all outgoing radiation in the desired directions.
Hologram analysis can also be used to study near field communication nfc antennas. Osa finitedifference timedomain and nearfieldtofar. The book begins with two chapters that introduce the basic concepts of the 3d cartesian fdtd method, followed by discussions of advanced fdtd methods such as conformal techniques, dispersive media, circuit elements, and near tofar field transformation. Timedomain near to farfield transformation for fdtd in. This paper proposes an algorithm based on the equi alence principle to calculate, straightforwardly in the time domain, the transient far field response of a twodimensional structure. Index termsfdtd methods, finite difference methods, finite element methods, nearfield farfield transformation.
We present the study of a spectraldomain near field tofar field nftff transformation, taking into account an interface in the vicinity of a particle. This report describes nafdtd, a nearfield finite difference time domain software package developed at the u. As we have seen, the fdtd method provides the fields throughout some finite region of space. Course syllabus elct 863 computational electromagnetics. Note that the far field calculation point can be still in the computational volume of fdtd, so you can directly compare the field values from yees algorithm and from nfff transformation for the same point in space. Nearfield to farfield transformation for antenna measurements nf2ff. Code for scattering from frequencyindependent dielectric materials by john h. Timedomain near to farfield transformation for fdtd. Does anybody have a 3d2d working code and be so nice to share it. By using a near to far field transformation, far fields can be determined from the near fields. Simple nearfield to farfield transformation method using. Characterization of the radiation pattern of antennas via. Recently published papers on the near tofar field ntff transformation in the finitedifference timedomain fdtd method have demonstrated accuracy improvements for weakly scattering objects. Wide angle far field transform is based on the fresnelkirchhoff diffraction formula 1.
Near to far field transformation algorithm with the fdtd technique, the direct evaluation of the far field calls for an excessively large computational domain, which is not practical in applications. The template nonfaulty near field of an array is simulated numerically fullwave fdtd solver or fem ansoftansys hfss solver at the same distance an alternative is. The algorithm implementation in ol es the numerical e aluation of a time integral along the near to far field con ersion. On the use of the geometric mean in fdtd neartofarfield transformations. Near tofar field transformation body of revolution fdtd algorithm for horn antenna design fdtd modeling of highspeed electronic circuits metamaterials and applications moment method mm point matching method, galerkins method, basis functions, weighting functions. The finite difference time domain fdtd technique models. The first technique used to perform the nfff transformation could. A frequencydomain nearfieldtofarfield transform for planar. Instead, the far zone electromagnetic fields are computed from the near field fdtd data through near field to far field nfff transformation. In general, farfield ranges are a better choice for lower. With this data, i can display a plane that shows the near e field of my microstrip antenna at z 5mm. Near and farfield calculations in fdtd simulations using. The far field position can be expressed with far field angle the far field.
Near field to far field transformation 18, 19 pouvant prendre en. Total field scattered field wave generation technique. Near and far field calculations in fdtd simulations using kirchhoff surface integral representation omar m. Neartofarfield transformations require the tangential electric and magnetic fields over a surface, which we call the integration boundary. Pdf modified fdtd neartofarfield transformation for. Fdtd is very efficient when making near field calculations, while for the far field it is necessary to use an additional method to perform a neartofarfield nfff transformation. Electromagnetic simulation techniques based on the fdtd. This paper presents a simple and practical method and measurement results of transformation by using the idea of arrayfactor for direct far field prediction from the near field data of antenna and rcs in cylindrical scanning system. Where r is the vector from near field to far field. How can i do neartofar field transformation using fdtd. I would like to do a near field far field transformation with matlab. I am using the software tool feko to model my patch antenna and to get the near field data. Differential near field holography for small antenna.
A modification to the near field to far field transformation scheme by luebbers et al. Unlike afdtd, which is designed for radar signature analysis in the far field, nafdtd is an. Abstract when the finitedifference timedomain fdtd method is applied to lightscattering computations, the far fields can be obtained by means of integrating the near fields either over the volume bounded by the particles surface or on a regular surface encompassing the scatterer. On the fdtd near tofar field transformations for weakly scattering objects abstract. This paper presents a simple and practical method and measurement results of transformation by using the idea. There are significant cost, size, and complexity details which will lead to a recommendation of one type over the other. Every modeling technique has strengths and weaknesses, and the fdtd method is. This model has been validated by studying the electromagnetic field of a. It therefore eliminates the numerical errors originating from the spatial offset of the e and h fields, inherent in the standard near tofar field. Huygens surface, obtained with the finitedifference timedomain fdtd method. I honestly dont understand where im doing wrong because im following the books step by step. This program is based on the finite difference time domain fdtd method and is related to the afdtd software. On the otherhand, because of theapproximations appliedto the surface integrals, the standard transformation typically used within the finitedifference time domain fdtd method 15 is strictly a near to farfield transform.
When dealing with the coupling of ss to ls, the near to near field extrapolation technique based on kirchhoffs surface integral representation is used and a sequential transfer method is developed. For a worst case scenario, results indicate an improvement in the accuracy of the calculated far field responses and radar crosssection rcs in comparison to the original algorithm. Angora is a free, opensource software package that computes numerical solutions to electromagnetic radiation and scattering problems. Tutorialneartofar field spectra meep documentation. Near to far field transformation for a fdtd bor with pml abc. However, the staggered nature of the finitedifference timedomain grid is problematic in that the electric and magnetic fields are not collocated in either space or time.
Near field 11 near field vs farfield any antenna can be successfully measured on either a near field or farfield range, with appropriate implementation. Finally, given that the farfield spectra is derived from the fouriertransformed fields which includes an arbitrary constant factor, we should expect an overall scale and phase difference in the results obtained using the neartofarfield feature with those from a corresponding simulation involving the full computational volume. Citeseerx document details isaac councill, lee giles, pradeep teregowda. This is also how the performance of nfff is tested in gsvit examples.
This report describes nafdtd, a near field finite difference time domain software package developed at the u. What is the best near field to far field transformation method for. This new approach is based directly on the polarization current of the scatterer, not the scattered near fields. On the use of the geometric mean in fdtd neartofarfield. Abstract neartofarfield transformations require the tangential electric and magnetic fields over a surface, which we call the integration boundary. The boundary condition is applied to a virtual surface, which encloses arbitrarily shaped scatterers.
Nafdtd a nearfield finite difference time domain solver. The program is designed for quick and efficient programming of fdtd simulations and for extending the available fdtd algorithms with new techniques and features. Pdf on sep 1, 2008, parham mokhtari and others published efficient computation of hrtfs at any distance by fdtd simulation with near to far field transformation find, read and cite all the. Implementing the near to farfield transformation in the. A full wave analysis of antenna using 3d fdtd with cpml. While the fdtd technique computes electromagnetic fields within a compact spatial region, scattered andor radiated far fields can be obtained via near tofar field transformations. Figure 22 far field angle the red region is the near field fresnelkirchhoff diffraction formula. Instead, the farzone electromagnetic fields are computed from the nearfield fdtd data through nearfield to far field nfff. Pdf finitedifference timedomain and nearfieldtofarfield.
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