Passive Intermodulation Test Research Articles

Novel Coupling Coaxial Adapter for Portable Passive Intermodulation Test of Coaxial Cable

Novel Coupling Coaxial Adapter for Portable Passive Intermodulation Test of Coaxial Cable

Empirical Passive Intermodulation Multiphysics Modeling Using Design of Experiment Method

This work presents a numerical modeling of passive intermodulation (PIM) product on contact junction under the multiphysics condition. The carrier power, temperature, and pressure impacts are combined into the model using design of experiment method. Based on several sets of optimized PIM test conditions, an empirical PIM model versus multiphysics can be established. The experiment demonstrates that the proposed PIM modeling method can predict PIM product with the max error of 7 dB.

Small Anechoic Chamber Design Method for On-Line and On-Site Passive Intermodulation Measurement

A design method is proposed in this article for on-line (online measurement: measurement when producing devices) and on-site (on-site measurement: measurement when using devices) passive intermodulation (PIM) measurement with a small-size anechoic chamber. In a PIM measurement, the role of an anechoic chamber is to shield extraneous electromagnetic signal and reduce reflection, so that an accurate measurement result can be obtained. However, the chamber itself may introduce new PIM sources due to the nonlinearity in absorbing material and shielding enclosure. The traditional method to lower the influence of chamber to PIM measurement is to design a large-size PIM test chamber in order to reduce the PIM level by path loss. In this article, an innovative design concept of the PIM test chamber is presented by controlling the PIM source level of the anechoic chamber instead of increasing the size of the chamber. It can significantly reduce the chamber size using this method, particularly suitable for on-line and on-site PIM measurement. To implement the concept, absorbing material and shielding enclosure structure with extremely low PIM are developed. The design concept includes defining the worst-case reflection level, estimating the PIM level due to reflected signals, and determining the smallest size of the chamber that meets the design specifications. Finally, two PIM test chambers are built to demonstrate the design concept. PIM measurement results are given to verify the theoretical analysis.

Passive intermodulation of printed dipole antennas: Modeling, evaluation, and experiment

A theoretical treatment of electro-thermally induced passive intermodulation (PIM) is developed for printed dipole antennas, yielding an expression of third-order intermodulation distortion based on the surface current distribution. The simulation procedure of third-order PIM products with the full-wave frequency-domain method was given to evaluate the PIM level. In particular, the PIM dependencies on input power, two-tone frequency separation, and substrate parameters are analyzed leading to design guidelines for low distortion antennas. It is shown in this paper that the thermal factors have a noticeable impact on the PIM power generated by printed dipole antennas. Finally, two antenna samples are fabricated on different substrates, Rogers 5880 and FR4, and a two-tone test at 2-GHz band using a reflective PIM test system is reported. The PIM evaluation method and the design guidelines to reduce the PIM on printed antennas proposed in this paper are of great significance for telecommunication systems.

Experimental Study of Electrical Contact Nonlinearity and its Passive Intermodulation Effect

In this article, the single-point electrical contact nonlinearity of the oxidation enhanced copper and its induced passive intermodulation (PIM) effect were systematically investigated. First, based on the composition analysis of the intentionally oxidized copper samples and the pristine ones, the electron potential barrier model across the contact interface was built. Then, based on an equivalent circuit model concluding a linear and nonlinear resistance, a total current equation based on the thermal emission mechanism was deduced and verified by performing a series of I–V measurements. When an oxide film is integrated, the linear current and the nonlinear current are comparable; when the oxide film was broken under an external force, the nonlinear current changes lightly, while the linear current increases sharply by more than two orders of magnitude. Therefore, we observed the transition process from the obvious nonlinear I–V characteristics to the dominant linear curves. Finally, the induced PIM behavior of the pristine and thermal oxidized single-point copper joints was investigated utilizing a specially designed near-field coupling PIM test system. As the pressure increases, the PIM level decrease with the joint pressure increases because both the contact resistance and the nonlinear current decrease. The measured PIM results are consistent with the obtained linear–nonlinear relation from the contact characteristics experiments. Experimentally, the total nonlinear current as the function of voltage drop across the contact interface, which is caused by the linear current, determines the induced PIM level.

TDR Prediction Method for PIM Distortion in Loose Contact Coaxial Connectors

This paper proposes a new method to comprehensively predict the passive intermodulation (PIM) distortion in loose contact coaxial connectors by the time-domain reflectometry (TDR) test. The proposed approach treats the insulating film current and the electrothermal (ET) coupling as PIM sources. An ET coupling model is introduced to analyze the generating process of the PIM caused by the ET coupling in the loose contact coaxial connectors. The simulation and measurement results show good agreement. The proposed method is a cost-effective approach for the evaluation of the PIM distortion, because it uses a common TDR method to replace professional PIM test instruments. The proposed method can also be extended to all the loose metallic contact cases.

Notice of Retraction: 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.

Passive Intermodulation of Contact Nonlinearity on Microwave Connectors

For the passive intermodulation (PIM) problem of nonlinear contact on microwave connectors, an effective method is presented to improve the computational accuracy of PIM. First of all, the contact stress distribution on contact surface is analyzed by finite-element method based on the Weierstrass-Mandelbrot model. The contact stress and real area of contact are evaluated under different loading conditions. Then, the electrical parameters of physical effects of nonlinear contact are derived based on the electric contact theory and the physical effects of metal-metal microcontact. Finally, the nonlinear I-V relation is established from the microcontact equivalent circuit, and the third-order PIM power level generated by contact nonlinearity is revealed in analytic form. The analytic results are verified by the PIM test experiments. This work provides a novel way for PIM calculation of rough surface contact.

How to measure test repeatability when stability and constant variance are not observed

Passive intermodulation (PIM) is a critical measurement for radio frequency (RF) communication networks. Yet PIM measurement inherently has very poor repeatability, which makes product assessment unreliable. The RF industry struggles with the issue since there are no known solutions. With the increasing demand for low-PIM performance, there are pressing demands to address the challenge. Two fundamental problems make traditional gage R&R study invalid for PIM: (1) PIM in nature is unstable and unrepeatable; (2) PIM measurement has inherently inconstant variance at different PIM levels, which is primarily due to limited capability of PIM analyzer. This resulted in several less-known issues significantly impacting the estimation of PIM test repeatability, including sample selection, one-sided spec and differences between test R&R and gage R&R. The paper proposed two fundamental changes when studying R&R of PIM test or tests in general violating constant variance assumptions: (1) sample selection; (2) what measurement to use to better estimate and represent the test repeatability. Special sampling is proposed to minimize the impact of inconstant variance. A more direct R&R measurement, margin of error (MOE), also known as study variation, is proposed to replace traditional gage R&R metrics to more meaningfully represent PIM test R&R. Several statistically based techniques to improve the repeatability and reliability of PIM measurement are also discussed. The study and proposed solutions apply to not only PIM test but also tests in general violating constant variance assumptions.

Reconfigurable Passive Intermodulation Behavior on Nickel-Coated Cell Array

This paper presents a phenomenological study about the passive intermodulation (PIM) behavior on a reconfigurable nickel-coated cell array. An artificial transmission line with reconfigurable nonlinearity is employed for demonstrating PIM generation and propagation behavior. This test fixture gets rid of metal contact distortion by using coupled power to stimulate nonlinear sources. Using the finite element analysis, the simulated magnetic field intensity is compared with the tested PIM data. A set of nonanalytic PIM models directed toward nickel-coated distributed PIM sources is demonstrated. Based on the proposed PIM fixture, a novel PIM reconfiguration method using nonlinearity array is proposed and a strength predictable PIM standard is obtained. The proposed test fixture can work as a practical PIM building-block to provide stable PIM reference. In the demo cases concerning three PIM test frequency spots, the minimal PIM of this device can reach below -112 dBm @ 2 × 43 dBm, while its maximal PIM dynamic range can reach about 20 dB. It exhibited a rudiment of PIM standard that can be applied in practical PIM test calibration field.

Broadband Dual-Port Intermodulation Generator for Passive Intermodulation Measurements

A dual-port tunable intermodulation (IM) generator is reported. This IM generator employs a coupling network to distribute carrier waves and IM. The proposed coupling network is constructed by cascading four parallel-coupled directional couplers, while a Schottky diode is working as a tunable IM source. By adjusting the IM performance of diode using bias voltage and distributing IM along symmetrical IM paths, a pair of tunable IM signals is introduced into passive IM (PIM) test loop simultaneously, they can serve as bidirectional IM reference in dual-port PIM measurements. The provided IM3 can be tuned to be lower than −112 dBm at $2 \times 43$ dBm at either 710 or 2550 MHz, while their dynamic IM3 range can reach about 20 dB at $2 \times 43$ dBm. The work promotes the application of IM predistortion techniques and provides a solution to realize dual-port dynamic IM calibration in PIM test.

On‐line passive intermodulation test method for conductive coatings

An on-line passive intermodulation test method for conductive coating is presented. A split-type rectangular coaxial line is working as test fixture. As the standing wave of this test fixture can stay small in the replacement of coating samples, passive intermodulation test can always continue. By using this test method, several coatings are rapidly distinguished from their different passive intermodulation performance. A fast passive intermodulation test method for coatings is demonstrated.

Connector-less test setup for measurement of passive inter-modulation products at UHF band

This paper describes the establishment of a test setup for measurement of passive inter-modulation (PIM) products generated by various device(s) under test (DUT(s)) (filters, coaxial cables etc.) at ultra high frequency (UHF) band. The paper begins with a brief discussion of an ideal PIM test setup using a quiet load. It then discusses the establishment of the setup in the absence of quiet load and demonstrates a PIM level of −192 dBc of the test setup. Finally it shows the PIM performance of a band-stop filter, a flexible cable, cascade of band-stop filter, and flexible cable, measured using the established test setup. These components are required for UHF payload of a communication satellite.

Passive intermodulation products control and verification activities in a multicarrier L-band satellite system for mobile communications: The italsat F2/EMS experience

The Italsat F2 satellite has been launched in August 1996: in addition to the domestic mission in Ka-band it embarks the L-band mobile payload (European Mobile System). Passive InterModulation (PIM) products generation is a very critical aspect for L-band payloads working in a multicarrier environment, so the EMS payload was designed to cope with stringent PIM Products requirements, while the spacecraft design, as derived from the first Italsat flight unit, did not focus on PIM aspects. PIM generation is basically caused by currents flowing in components with a non linear voltage-current behaviour, and may occur at equipment, s/s and system level. The EMS payload performance can be affected by the intermodulations generated by two L-band Tx carriers, that could fall in the EMS L-band Rx section; from the EMS frequency plan, the minimum order of these PIM products are the 7th and the 9th. This paper describes the activities carried out from equipment up to satellite level to eliminate as much as possible PIM effects, and the results of the final spacecraft PIM test campaign. The paper is composed by three main pans. The first pan deal with the technological aspects of the design and the production of the EMS components considered critical from PIM generation point of view. The second pan describes the PIM control strategy applied at spacecraft level, and in the third part the spacecraft PIM test campaign results are presented.