In this article, a decoupled source current reconstruction method (SRM) for noisy and reactive near-field (NF) to far-field (FF) transformation is introduced. It is shown that the traditional SRM for NF/FF transformation shows instability in the regions that the amounts of noise or reactive radiations are noticeable. Therefore, in these regions, equivalent currents should be determined from a Tikhonov SRM equation. However, this equation increases the computational cost of the SRM. To simplify the Tikhonov SRM equation, a Tikhonov radial field retrieval algorithm is also proposed. In this algorithm, the Tikhonov integral equation is decoupled by considering and retrieving the radial components of the electric field. Results of far-field calculation with both the proposed Tikhonov SRM equation and Tikhonov radial field retrieval algorithm with three different antennas are presented and compared with those of the full-wave simulation and measurements. The results show more accurate field transformation with the proposed algorithms. K E Y W O R D Sfield transformation, reactive near-field, source current reconstruction, Tikhonov inverse problem | I NT ROD UCTI ONAdvanced and accurate measurement of the antenna radiating characteristics in a controlled environment has attracted considerable attentions in the recent years. Measuring the nearfields of the antenna under test (AUT) and reconstructing the far-field (FF) radiation is one of the most widely used advanced measurement techniques. 1-14 Near-field (NF) measurements have dramatically reduced the dimensions of test facilities and test costs and increased measurement speeds.Recently, measuring the field data in the close proximity of the radiator is also possible with the electro-optic field technology. [12][13][14][15] Although measuring the reactive near-field radiation of an AUT is a big step forward for further reducing the cost and speed of the antenna measurements, these measurement systems are applicable when a method for accurately transforming the reactive near-field to far-field radiations is also being developed. However, up to the authors' knowledge, most of the available NF to FF transformation method are placed in the region that the reactive radiations are negligible and the effects of evanescent modes on the field transformation procedure have not already studied. [1][2][3][4][5][6][7][8] For NF to FF transformation, two main methods have already been reported over the past years. The oldest method which has been used widely is the modal techniques. 1,2 Brief reports about the reactive near-field transformation with modal techniques can be found in Refs. 13 and 14. In these papers, a stable field transformation is obtained by optimizing the field sampling positions of the AUT in a way that creates a transformation matrix with the most convenient singular values. This reduces the effects of reactive radiation as will be discussed in this article.The newest method for NF to FF transformation which is more flexible but has a higher computatio...

A novel hybrid finite-element time-domain (FETD) finite-difference time-domain (FDTD) formulation is presented. Numerical results show that the proposed method is stable even for very large time steps. Thus, from the implementation aspect, the method can be considered as an unconditionally stable scheme.The key to the successful hybridization of them is identical equivalence between alternating-direction implicit (ADI)-FDTD and ADI-FETD on rectangular mass-lumped elements. The stability and accuracy of the proposed method are validated by a numerical example. In addition, the proposed method has overcome some of the accuracy drawbacks of the pure ADI-FDTD method.Index Terms-Alternating-direction implicit (ADI) technique, finite-difference time-domain (FDTD) method, finite-element time-domain (FETD) method, hybrid formulation, unconditionally stable.

Abstract-This paper describes the concept and design of a novel compact self-supported cup feed antenna for parabolic reflectors. The feed antenna consists of an open waveguide cup which is excited by a disk loaded dipole. This structure is fed by a coaxial waveguide through a split-coaxial balun and has a rear radiation pattern toward the reflector antenna. Two different types of this configuration are designed in this paper: a linearly-polarized grid reflector antenna fed by a single dipole excitation, and a circularly-polarized solid reflector antenna fed by a cross dipole excitation. The measurement is done for the former, and simulation results of the latter via two different software packages CST and HFSS are compared in this paper. Analyzing the results shows that both types of cup feed antenna have an excellent aperture efficiency and low side lobe level.

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