Generalized Cylindrical Mode Filtered Site VSWR for Above 18 GHz EMC Site Evaluation Using Compressed Sensing

Site Voltage Standing Wave Ratio (SVSWR), as defined in CISPR 16-1-4 or ANSI C63.25.1, has been established as the de facto standard for evaluating the performance of an EMC test site from 1 GHz to 18 GHz. There is a growing need to develop a similar standard for the 18 GHz to 40 GHz range. Researches have shown that the existing methods below 18 GHz do not extrapolate well to the higher frequencies. A new method based cylindrical mode filtered SVSWR was introduced recently to address the limitations of the previous methods. In the mode filtered method, an omni-directional transmit antenna is placed at the edge of the quiet zone, and a single cut antenna pattern is measured. The data is then processed, transformed into cylindrical modes, and then filtered to obtain the "clean" reference pattern. The Mode Filtered SVSWR implementation had previously relied on equally-spaced angular sampling to compute the Cylindrical Mode Coefficients (CMCs) via Fast Fourier Transform (FFT). In this paper, we expand the methodology to a much more general case to allow undersampled data (below the Nyquist rate) and on an unequally-spaced abscissa. CMCs are then accurately computed using the Compressed Sensing (CS) algorithm. Measured results show the validity and effectiveness of the new algorithm.