Testing and Analysis of PIM Performance in a Passive DAS Network - Experimental Approach

Passive intermodulation (PIM) poses a significant challenge in telecommunication networks, with potentially severe impacts on network performance and signal integrity if not addressed during the initial deployment phase. This study investigates PIM levels within a passive distributed antenna system (DAS) network for cellular mobile radio communication across multiple floors of a building. The network comprises coaxial cables, connectors, splitters, combiners, and antennas structured in a systematic plan. This work used the experimental method to test for PIM in the network used for this investigation. Designed as a multicarrier system, it handles RF signals across frequencies of 700/850MHz, 1900MHz, 2100MHz, and 2600MHz. On-site PIM testing was conducted during the network deployment phase to analyze the behavior of high-power RF signals. Utilizing Kaelus iQA-1921C and iQA 850C series PIM analyzers, tests were conducted following known industry codes and standards. High RF power was preset to 43dBm for full band, 35dBm for high bands, and 25dBm for low band. The test equipment was calibrated on high PIM load and low PIM load. Test points were selected at both vertical and horizontal subsystem cabling structures, focusing on riser cables. The standard baseline performance PIM levels was set to -150dBc. The analysis focused on examining the characteristics of PIM signals captured via time-domain PIM traces, investigating the impact of altering the frequency of the two-tone signal on the IM3 frequency component, and highlighting the importance of selecting an appropriate frequency for the two-tone signal that is not positioned near the edges. Results were based on pass or fail test, and resolution measures were taken to mitigate interference.