Methods for anechoic chamber certification at VHF/UHF frequencies

This paper describes joint efforts undertaken by Penn State University Applied Research Laboratory, the National Institute of Standards, and the Microwave Vision Group, which includes ORBIT/FR Inc. and Satimo. The purpose of this research was to characterize a selected certification method for the performance of the test zone in a large anechoic chamber. The Applied Research Laboratory´s chamber in Warminster, PA was selected for this research. The anechoic chamber is described in [1] and has the following internal dimensions: 100´ (L) × 40´ (W) × 40´ (H). The Quiet Zone is designed to have a cylindrical shape with a diameter of at least 12´. The chamber offers antenna measurement services over a broad frequency range. Although the chamber was designed to operate at VHF/UHF frequencies as low as 100 MHz, it has never been thoroughly characterized at these frequencies. There was also a desire to verify the chamber and absorber performance after many years of operation. The main challenge was the fact that conventional methods of chamber Quiet Zone characterization [2-5] which have been successfully implemented at microwave frequencies starting at 1 GHz and above are less practical at VHF/UHF frequencies in chambers with large Quiet Zone volumes, as in the Penn State anechoic chamber. Therefore, there was a need to carefully consider the pros and cons of different methods as applied to the specific case of the anechoic chamber at Penn State. The paper describes the trade offs between different methods, their pros and cons, and justifies the choice of the method applied for the Quiet Zone characterization in this case.