Passive Intermodulation Analyzers vs. Network Analyzers

Vector network analyzers operate on the assumption that the system under test is linear. A VNA transmits low-power stimulus signals—typically in the range of 0 dBm to 10 dBm—and monitors the amplitude and phase of the reflected or transmitted signal. This low power is highly effective for characterizing impedance, VSWR, return loss, and cable attenuation.\n\nHowever, passive intermodulation behaves as a non-linear effect that only becomes measurable under high RF power levels. In a low-power environment, a corroding connector or loose coaxial junction will perform linearly, leading a VNA to report a perfectly matched, fault-free transmission line. When high carrier power from cellular base station transmitters passes through these same faulty junctions, intermodulation products are generated that can blind the base station receiver.

PIM analyzers employ a dual-transmitter architecture that sends two high-power RF test tones into the line under test. This high power mimics the stress experienced during peak cellular traffic. The Anritsu MW82119A PIM Master, for instance, provides a carrier power output range of 20 dBm to 46 dBm (0.1 W to 40 W) per transmitter, with a resolution of 0.1 dB and an accuracy of plus or minus 0.5 dB at 43 dBm.\n\nIf non-linearities exist in the transmission path, the two high-power carriers mix and generate intermodulation products. The receiver portion of the analyzer then filters and measures these weak intermodulation signals. Depending on the selected band option, the receive frequency range for the MW82119A spans 698 MHz to 2570 MHz, enabling the detection of PIM signals down to a measurement range of -130 dBm to -70 dBm.

Beyond detecting whether PIM is present, field technicians must locate the physical source of the non-linearity. A VNA uses distance-to-fault (DTF) algorithms based on frequency domain reflectometry to locate impedance mismatches. It cannot, however, locate the non-linear junctions that cause PIM.\n\nPIM analyzers resolve this issue by offering specialized diagnostic modes. The MW82119A supports measurements such as Distance-to-PIM (DTP), PIM vs. Time, Noise Floor, and Swept PIM. Distance-to-PIM allows the technician to find the exact distance of the intermodulation source relative to the instrument's RF output port connector. Because these tests are conducted outdoors, the MW82119A is engineered as a portable unit weighing 9.0 kg to 12.2 kg depending on the band, operating in temperatures from -10 degrees Celsius to +55 degrees Celsius, and featuring an 8.4-inch diagonal daylight-viewable color resistive touchscreen with an 800 x 600 resolution.