Anechoic Chamber Clean Zone Analysis with Angle Dependent Reflection Coefficients

An important part of a radio frequency (RF) anechoic chamber design process is the selection and placement of absorbers to make the quiet zone devoid of unwanted electromagnetic (EM) waves. Due to their nature, absorbers have different reflection coefficient values depending on the incidence angle and frequency of operation, albeit the reflection coefficient values depending on the angles are seldom shown on the specification sheets of commercially available absorbers. In this study, a chamber illuminated with a semi-isotropic antenna is simulated to calculate the incidence angles of the EM waves on the absorbers. The obtained results are presented as a percentage distribution of incidence angles. It is seen that, most of the reflections occur at angles far from normal incidence. Quiet zone analyses with and without angle dependent reflection coefficient values are carried out to quantify the error made by assuming a constant reflection coefficient. It has been quantitatively shown by three examples that a better isolation level estimation can be made if the angle dependent reflection coefficient values are taken into account.