Reconfigurable OTA Chamber Design Optimization

The reconfigurable over-the-air chamber has been shown capable of synthesizing the field incident on the device under test in over-the-air testing. However, to date, there has been minimal exploration of the chamber complexity required to achieve a specified accuracy of the synthesized fields. This paper uses an analytic solution for the fields in the chamber based on the modal Green's function along with optimization of the antenna locations for synthesizing the desired fields according to three different cost functions. The results show that different cost functions achieve notably different results, with a traditional optimization based on minimizing error producing solutions that exhibit supergain characteristics.

I. Introduction

The reconfigurable over-the-air chamber (ROTAC) is a reverberation chamber whose walls are lined with antennas [1], some of which are excited and the remainder of which are terminated with individually tunable impedances. This design allows the chamber to synthesize the field incident on the device under test (DUT), with prior work confirming that the ROTAC has notable flexibility in the field profiles that can be created. However, this prior work has mostly focused on fixed chamber geometries, and therefore has not considered adequately the relationship between the fidelity of the synthesized field and the number and placement of the ROTAC antennas. This paper connects the antennas to the chamber fields using a rigorous modal analysis and then uses optimization with three different cost functions to design the optimal antenna configuration. The results show that a simple circle packing antenna arrangement provides good performance, and that optimizing to minimize the error between the synthesized and desired field can lead to supergain excitation conditions.