A Measurement Method for Passive Intermodulation Chamber Performance Evaluation

With emerging wireless communication technology, undesired interference caused by passive intermodulation (PIM) becomes a major obstacle to the network efficiency and the electromagnetic compatibility (EMC) of the devices. Accurate measurement techniques for PIM are fundamental to identify and characterize the electromagnetic interferences (EMIs). Anechoic chambers are commonly used in the antenna PIM test. The noise of PIM test chamber usually determines the accuracy of PIM measurement. The additional PIM sources caused by the chamber can be classified into three classes: those due to the absorbers, those due to the design of the shielded enclosure, and those due to the extraneous signals caused by an ineffective shielding. In this paper, a measurement method is proposed for the performance verification of PIM test chamber. The proposed method has two key points. One is adjusting the measurement distance between antenna and absorbers for gain compensation, which can evaluate the maximum measurable antenna gain of the PIM test chamber. The other is choosing the multiple measurement points according to the beamwidth of antenna, which can define the PIM level in worse case of the chamber. Theoretical analysis of the proposed method and measured results for two PIM chambers by the method are given in this paper.