Using Free-Space Transmission Loss for Evaluating Anechoic Chamber Performance

Performance of a rectangular RF anechoic chamber is evaluated by measuring the relative insertion loss versus separation distance between the sources of chamber illumination and small dipole or open waveguide antennas on a particular measurement axis. Measured data are compared to free-space transmission loss calculated using finite-range source antenna gains. A lack of fit between measured insertion loss and calculated transmission loss is a measure of reflections from chamber surfaces assuming the finiterange gain calculations are exact for the separation distances considered. Experimental results show excellent agreement between a smooth-curve fit to the measured data and the calculated free-space data. Standard fields in this chamber are used for calibrating hazard meters and dipole antennas used for field-strength measurements.