Abstract
Abstract. The characterization of antenna radiation patterns by transformed near-field measurements requires accurate amplitude and phase data. This represents a problem since expensive measurement equipment is required, especially at millimeter and submillimeter wavelengths (Isernia et al., 1996). Amplitude-only antenna field measurements are theoretically sufficient for the unique determination of antenna far-fields. Therefore, phaseless techniques are of special interest. However, the required field transformations are extremely challenging, since they are nonlinear and strongly ill-posed. In this work, the amplitude-only or phaseless near-field far-field transformation problem is formulated as a nonlinear optimization problem. The linear radiation operator within the nonlinear formulation is evaluated using the fast irregular antenna field transformation algorithm (FIAFTA). A hybrid solution procedure is described which combines a genetic algorithm with an iterative conjugate gradient (CG) search method. Numerical results prove the efficiency and flexibility of the formulation and it is shown that the algorithm remains stable when the noise level in the measurements is moderate. Nevertheless, regularization techniques might be beneficial to further improve the robustness of the algorithm.
Highlights
Near-field far-field transformations of antenna measurements with amplitude and phase data are well established (Yaghjian, 1986)
The well-known methods for planar, cylindrical and spherical measurements are widely employed in practical applications. These canonical transformation algorithms correspond to solving a linear equation system efficiently by applying the fast Fourier transform (FFT)
Formulating the problem in a general way leads to a nonlinear optimization problem in contrast to the linear one in case of available phase information
Summary
Near-field far-field transformations of antenna measurements with amplitude and phase data are well established (Yaghjian, 1986). Much research has been performed on this topic and under certain conditions it is possible to guarantee convergence (Pierri et al, 1999) Global optimization strategies such as genetic algorithms have been applied to find the correct solution (Regue et al, 2001). Schnattinger et al.: Antenna field transformation for phaseless and irregular measurements based on multi-level fast multipole method (MLFMM) principles (Chew et al, 2001). It supports arbitrary measurement positions and orientations with full consideration of arbitrary probe characteristics. The topic of this paper is to utilize these advantages for improved transformations of phaseless near-field measurement data by using a CG method in combination with a genetic algorithm. For the phaseless transformation approach it is assumed that the matrix A can be only evaluated through the matrix-vector products and the entries of the matrix A cannot be accessed directly
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
