Analysis of Synthetic Cylindrical Array Beam-Forming for Semi-Anechoic Chamber Evaluation K. Priandana 1* , J. Takada 1 , M. Ghoraishi 1 , M. Hirose 2 , S. Kurokawa 2 , M. Ameya 2 1 Graduate School of Engineering Tokyo Institute of Technology, 2-12-1-H-105 Ookayama, Meguro-ku, Tokyo 2 National Institute of Advanced Industrial Science and Technology 1-1-1, Umezono, Tsukuba, Ibaraki 305-8563, Japan This paper describes the study of synthetic cylindrical array beam-forming for narrowband signals, under the influence of antenna elements position-error. The required side-lobe level and the physical dimensions of the array are presumed based on the requirements and limitations to evaluate a RF semi-anechoic chamber. Dolph-Chebyshev algorithm is used for beam-forming because of its optimal beam-width for a predefined uniform sidelobe level. Monte-Carlo simulations reveal the sensitivity of the beam-pattern side-lobe level to the elements position-error. 1. Introduction The rapid emergence of electromagnetic (EM) equipments has forced us to carefully conduct the electromagnetic compatibility (EMC) testing, to avoid the possibility of interference. Ideally, EMC testing is conducted in an open-area test site (OATS), an obstacle-free environment. However, it is inconvenient due to the high dependency on the changing factors of the environment. As a result, EMC test is conducted inside a semi-anechoic chamber (SAC): a room having walls and a ceiling equipped with EM absorbers, and a metallic ground. To simulate an OATS, SAC should be free from scattering waves other than the ground-reflected wave. However, in reality, the imperfect absorbers, corners, junctions, etc., may cause the SAC discrepancy from an ideal OATS. Therefore, evaluation of SAC is required. This paper proposes the utilization of beam-forming for SAC evaluation. The final goal of this research is to design the applicable beam-forming methodology for SAC evaluation. In this study, a synthetic cylindrical array antenna will be used. The low side-lobe requirement for SAC evaluation is realized by using Dolph-Chebyshev algorithm. Monte-Carlo simulations were conducted to find the optimal array parameters that can produce minimum side-lobe level at reasonable beam-width, under the antenna elements position-error. 2. Conventional Method of SAC Evaluation Standardized validation methods to evaluate the SAC have been developed by CISPR/A [1]. The validation is established by finding the Site VSWR (S VSWR ) of the SAC. Standing waves voltages are measured at discrete locations of receiving antenna (Fig. 1). By moving the antenna spatially, the phase between the direct and scattering (unwanted) waves will vary. When the waves add constructively, there is a peak response (E max ) between the two antennas and when the waves add destructively, there is a minimum response (E min ). S VSWR is the ratio of the maximum peak to the minimum peak. For SAC of 1-18 GHz, the S VSWR at each frequency of at least 50 MHz steps should be less than 2 (in linear scale) or 6 dB (in logarithmic scale). When there is no reflection (ideal case), the VSWR value will be 1 (0 dB). The disadvantage of this method is the inability to identify the reasons behind the SAC discrepancy from an ideal OATS. This is because of the output: S VSWR with no other information about the source(s) of the scattering waves. Thus, the performance of SAC cannot be improved. Another limitation is that the frequency selective scattering may not be captured by this method. 3. Beam-Forming for SAC Evaluation This paper proposes a new method for SAC evaluation by beam-forming. The method offers an ability to identify the sources of scattering signals, including the frequency selective scattering. These advantages are superior to the standardized Site VSWR method. This method requires a similar measurement system with that of Site VSWR method. However, different measurement positions will be used as a synthetic array antenna. Some assumptions taken are: 1) The chamber discrepancy occurs due to some scattering waves that are caused by discrete points inside the SAC. Each of these points is modeled as an independent signal source, to be identified by beam-forming. 2) The distance between receiving array antenna center and the scattering point(s) are far enough, so that the plane wave approximation can be applied. The near-field analysis will be incorporated by using the spherical-wave radiation in the future. * Responsible author. E-mail: karlisa.p.aa@m.titech.ac.jp Fig.1. S VSWR Measurement Points along 40 cm Line