Experimental study of passive intermodulation in coaxial cavities for cellular base stations duplexers

This paper presents an experimental investigation of passive intermodulation (PIM) generated inside coaxial cavities employed in filters and duplexers for cellular base stations. A simple non-linear equivalent circuit for the cavities employed in the filters is first introduced. Using this model, the main cavity parameters affecting PIM generation arc found out. Several cavities have been then built having different values for such parameters. PIM produced by each cavity has been measured and the results obtained compared with the model estimations; suitable guidelines for the cavities construction have been so derived. Some aspects of PIM generation not well reproduced by the model are finally pointed out.