Passive Intermodulation Products Research Articles

Digital cancellation of multi-band passive inter-modulation based on Wiener-Hammerstein model

Utilizing multi-band and multi-carrier techniques enhances throughput and capacity in Long-Term Evolution (LTE)-Advanced and 5G New Radio (NR) mobile networks. However, these techniques introduce Passive Inter-Modulation (PIM) interference in Frequency-Division Duplexing (FDD) systems. In this paper, a novel multi-band Wiener-Hammerstein model is presented to digitally reconstruct PIM interference signals, thereby achieving effective PIM Cancellation (PIMC) in multi-band scenarios. In the model, transmitted signals are independently processed to simulate Inter-Modulation Distortions (IMDs) and Cross-Modulation Distortions (CMDs). Furthermore, the Finite Impulse Response (FIR) filter, basis function generation, and B-spline function are applied for precise PIM product estimation and generation in multi-band scenarios. Simulations involving 4 carrier components from diverse NR frequency bands at varying transmitting powers validate the feasibility of the model for multi-band PIMC, achieving up to 19 dB in PIMC performance. Compared to other models, this approach offers superior PIMC performance, exceeding them by more than 5 dB in high transmitting power scenarios. Additionally, its lower sampling rate requirement reduces the hardware complexity associated with implementing multi-band PIMC.

Via Impact on Passive Intermodulation Distortion in Planar Circuits

This work presents the passive intermodulation (PIM) induced by vias in microwave circuits. An analytical model combining the equivalent nonlinear source theory and the vector superposition principle is established to evaluate the PIM product of the vias array, which is influenced by the combination effect of the vias location, diameter, and number. The proposed model is verified and evaluated at 2.6 GHz. Good agreement between theory and experiment proves the logic and practicability of modeling. This work provides guidance for the low PIM optimization design of vias.

Air-Induced PIM Cancellation in FDD MIMO Transceivers

In this letter, air-induced passive intermodulation (PIM) modeling and cancellation schemes are presented in a multiple-input multiple-output (MIMO) frequency-division duplexing (FDD) transceiver context. PIM is distortion generated by nonlinear passive devices either within the transmitter chain or outside the transceiver system, as is the case in air-induced PIM. In FDD systems, the PIM products may lie on the receiver band, thus possibly desensitizing the receiver chain. Unlike previous PIM cancellation works, we consider a challenging rank-2 dual-carrier MIMO transceiver scenario, with two spatially multiplexed signals per component carrier (CC). Stemming from the PIM modeling, we first present a cancellation method based on a complete set of identified basis functions (BFs). Additionally, to relax the processing complexity, we propose an alternative canceller solution with a reduced number of BFs, inspired by the problem modeling. RF measurements conducted with real-life equipment indicate favorable PIM suppression levels of up to 20 dB using both introduced techniques.

Passive Intermodulation at Contacts of Rough Conductors

Passive intermodulation (PIM) is a niggling phenomenon that debilitates the performance of modern communications and navigation systems. PIM products interfere with information signals and cause their nonlinear distortion. The sources and basic mechanisms of PIM have been studied in the literature but PIM remains a serious problem of signal integrity. In this paper, the main sources and mechanisms of PIM generation by joints of good conductors are discussed. It is shown that the passive electrical, thermal and mechanical nonlinearities are intrinsically linked despite their distinctively different time scales. The roughness of the contact surfaces plays an important role in PIM generation by conductor joints. A review of the PIM phenomenology at the contacts of the good conductors suggests that novel multiphysics models are necessary for the analysis and reliable prediction of PIM products generated by several concurrent nonlinearities of a diverse physical nature.

Waveguide Cell With Water Filling for Passive Intermodulation Localization on Planar Circuits

This work presents a novel miniaturized waveguide cell with water filling for passive intermodulation (PIM) localization on planar circuits. The planar circuit as printed circuit board (PCB) is excited in a small waveguide, while its PIM product is detected simultaneously. The waveguide width is minimized by water filling (high permittivity dielectric), and the localization resolution is enhanced. During test, the PCB only needs move through the waveguide twice, once along its <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$X$ </tex-math></inline-formula> -direction and once along its <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Y$ </tex-math></inline-formula> -direction. By crossing the peak PIM distribution line along two directions together, the regions on PCB have PIM responses that can be decided. The proposed method is intended for the planer PCB and other normal PCB with surface mount components.

Novel cost-effective passive intermodulation measurement technique using a single power amplifier

The growing number of cellular devices and the introduction of high-speed data affect the network performance of mobile communication systems. Evaluation of passive intermodulation (PIM) phenomenon in the field of microwaves and mobile communications improve system performance. Typically, the PIM of the device-under-test (DUT) is measured using a set-up that involves two power amplifiers (PA), making it an expensive measurement set-up. This research aims to make PIM measurements cost-effective by using a single PA. Reflected (RFL) PIM distortion measured for two different DUTs, i.e., circulator and a microstrip (MS) line containing radio frequency interference (RFI) shielding gasket, using the presented and standard techniques. The presented PIM analyzer has a residue PIM of -104.5dBm. Comparison and error analysis suggested that the presented single PA method is feasible for DUTs having PIM between -60 and -94.5dBm at 43dBm input power. The residual PIM of the presented analyzer is high compared to the standard PIM analyzers; it is investigated that IM generated by the PA is the leading cause of this higher residual PIM product (RPIM). The proposed method will reduce overall system cost and size; it will also improve the battery efficiency of portable and desktop PIM analyzers.

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.

Directional passive intermodulation effect by distributed nonlinearities in two‐port network

AbstractThis work demonstrated the directional passive intermodulation (PIM) product distribution effect in a microwave two‐port network using a distributed nonlinear model. The analysis is demonstrated through the comparison of PIM products at the double ends of a general two‐port network by a microstrip line. The reverse and forward PIM products are compared with the nonlinear source distribution and carrier frequency, the model and experiment demonstrates that the directional PIM effect (the difference by reverse and forward PIM) is caused by the PIM accumulation effect from multiple nonlinear sources, what is more, the frequency dependent phase relation can be one reason for the frequency dependent PIM product on wideband transmission line.

Simulation analysis of passive intermodulation mechanism of transceiver link

The electromagnetic environment of modern battle-field is complex and the interference intensity is large. Under the influence of high field electromagnetic interference, airborne RF equipment becomes the short board of electromagnetic environment adaptability of aircraft. Because of the wide application of military aircraft platform, the external climate and electromagnetic environment are very complex. At the same time, the interior space of military aircraft is narrow and there are many high-power frequency equipment, which lead to a very complex electromagnetic environment inside the aircraft. Under the irradiation of high-power electromagnetic field, passive intermodulation products will be produced in the receiving antenna, transmission line, connector, filter and even some non-metallic conductive materials and aircraft skin under certain conditions. The passive intermodulation products will cause great interference to the airborne high sensitivity receiving equipment, and even burn the receiving equipment in extreme conditions. Therefore, the research on passive intermodulation products of airborne equipment is very urgent.

Calculation of passive intermodulation product on nonlinear area source using reciprocity principle

AbstractA compact passive intermodulation calculation method for the nonlinear source with noticeable size is proposed and demonstrated. By approximating the transmission factors of linear carrier and nonlinear passive intermodulation to be the non‐dimensional ratios between the current and power based on the reciprocal calculation principle, the PIM synthetize on a nonlinear source with notable size can ignore the complicated microwave characteristic analysis, while just need the accumulation of each PIM product of each nonlinear cell, which significantly simplifies the calculation process for the passive intermodulation product on a practical microwave device. The study proposed a compact solution to solve PIM product from the nonlinear source with big scale, which can be extended to the PIM analysis of practical microwave device with unevenly distributed PIM product.

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.

Mitigation Methods for Passive Intermodulation Distortion in Circuit Systems Using Signal Compensation

An equivalent circuit model of a passive system with nonlinear characteristics was developed to simulate the forward and reversed passive intermodulation product (PIMP) powers. Mitigation methods based on signal compensation were proposed and used to reduce the interferences of passive intermodulation (PIM). The cancellation phenomena of third-order PIMP powers were observed both in the active and passive signal compensation simulations, followed by some theoretical analysis. The advantages and disadvantages of each mitigation method were discussed in detail, providing flexible selections in low-PIM design and PIM elimination in specific applications.

Error Vector Magnitude, Intermodulation, and Radiation Characteristics of a Bandwidth- and Pattern-Reconfigurable Antenna

This letter presents the error vector magnitude (EVM), intermodulation (IM), and radiation performances of a reconfigurable antenna capable of varying its bandwidth between 3.4–3.6 and 3.1–3.9 GHz bands, and steering its main beam into three directions pertaining to $\theta \in \lbrace -30^{\circ },0^{\circ },30^{\circ }\rbrace$ and $\phi \in \lbrace 0^{\circ }\rbrace$ for each band. Two parasitically coupled reconfigurable layers located on top of a driven antenna used in conjunction with a reconfigurable feed layer employing p-i-n diode switches enable a concurrent configuration of an impedance bandwidth and a radiation pattern. The maximum realized gain of $\sim$ 9 dB has been achieved for all modes of operation as shown by measurements and simulations. Measurements indicated less than $-$ 25 dB ( $5.6\%$ ) EVM for input powers up to 30 dBm and revealed that the combined effects of loose solder joints and large nonlinear response of p-i-n diodes are the main factors resulting in passive IM products.

A Composite Exponential Model to Characterize Nonlinearity Causing Passive Intermodulation Interference

Passive intermodulation (PIM) interference that occurs in communication systems could limit the communication capacity and increase the manufacturing and maintenance costs. In this letter, a composite exponential model is developed to characterize the weak nonlinearity of passive components that causes PIM generation accurately. This proposed model fully considers the correlation between the PIM products on each order and the relation of PIM products with variation of carrier powers. For verification, a microwave filter is given to demonstrate the effectiveness of this composite model, and the reliability of this model is proved by the sensitivity analysis due to measurement uncertainty. Besides, the good agreement between the calculated powers of PIM products and the measured data shows that it can provide a theoretical guidance for PIM performance assessment in engineering application, thereby evaluating the influence of PIM interference on communication quality effectively.

Modeling of Passive Intermodulation in Connectors With Coating Material and Iron Content in Base Brass

Ferromagnetic materials in coaxial connectors are one of the main contributors to passive intermodulation (PIM) in radio frequency systems. In this paper, the effects of coating materials and iron content in base brass on PIM performance were theoretically modeled and analyzed, and the results experimentally verified. A finite-element analysis model for a cross section of the inner conductor was developed to evaluate the current density distribution in connectors with different materials, coating thickness, and iron content in the base copper alloy. Simulation calculations were performed to study the nonlinear characteristics induced by ferromagnetic materials in the communication frequency band. The relationship between the PIM products power and the current density distributions was investigated based on the theory of microwave electromagnetic fields and nonlinear mathematical modeling. This model was used to theoretically predict the intermodulation (IM) products power resulting from connectors with various material properties. In addition, a series of experiments based on two-tone testing was conducted to measure IM products of specific connectors. Good agreement was observed between experimental measurements and the predictions of the analytical model, validating the PIM analysis method and results.

A Segmented Polynomial Model to Evaluate Passive Intermodulation Products From Low-Order PIM Measurements

In this letter, a segmented polynomial model is developed to accurately calculate the powers of high-order passive intermodulation (PIM) products from the measurement data of low-order PIM product. This proposed model fully considers the dependence of dominant PIM generation mechanism on carrier power. An example of a microstrip transmission line is given to verify the effectiveness of this model, and excellent agreement between the measured data and calculated results has been achieved. Compared to the common-used polynomial model, not only the order adopted in the segmented model is much lower but also the number of measured data required for evaluation is much less. Moreover, this presented model can calculate the more accurate high-order PIM products than any other model. Thus, it can provide a theoretical guidance for PIM performance assessment in engineering application.

Passive Intermodulation Interference in Helicopter Platform RF Communication System

This paper discusses the research status of Passive Intermodulation (PIM) on helicopter platforms, and mainly analyzes the reasons for the formation of PIM interference on it. RF devices that may generate PIM interference are analyzed at the same time. Taking the PIM interference of L-band antenna as an example, the existence of PIM problem on the helicopter platform was verified by means of electromagnetic simulation. The PIM Product (PIMP) of the RF device commonly used on the helicopter was tested to further prove that the PIM problem on it should be taken seriously.

Behavior modeling of passive intermodulation distortion with multiple nonlinear sources

AbstractA modified passive intermodulation (PIM) model with multiple nonlinear sources and lossy transmission is developed to evaluate the reflected passive intermodulation products (PIMP) in case of series connection. Equivalent circuit models are proposed for demonstrating the effect of length between nonlinear sources and number of connections on the PIM behaviors, followed by some experimental validation. The measurement results agree well with the theoretical calculations and circuit simulations, having a mean difference within 0.5 dB.

Numerical simulation and analysis of passive intermodulation caused by multipaction

In this paper, emphasis is put on passive intermodulation (PIM) caused by multipaction. The results are calculated by particle-in-cell simulation under the conditions of 2-tone and 4-tone carriers. A temporal evolution of the number of particles with different carrier powers is presented. The input and output signals in the time domain and the power spectrum densities of these signals in the frequency domain under different conditions are compared. The relationship between multipaction and PIM interference is discussed. It shows that the appearance of the PIM phenomenon follows the occurrence of saturation of multipactor discharge and the powers of PIM products basically increase as the carrier powers grow. In addition, to suppress the occurrence of PIM interference, an external magnetic field is added in the direction perpendicular to the electric field, which is a practical way to inhibit multipaction, and the effectiveness and the reliability of this method are also verified by simulation.

Nonlinear Characterization for Microstrip Circuits With Low Passive Intermodulation

Products of passive intermodulation (PIM) generated by weak nonlinearities of passive circuits subjected to relatively high transmit power of multicarrier signals may cause strong interference in emerging broadband and multiradio communication systems. This paper presents a new approach to a characterization of distributed nonlinearities in printed circuits fabricated on commercial grade microwave laminate materials. An efficient procedure for PIM characterization has been devised using the commercial RF-CAD software. The phenomenological model has been developed to take into account concurrent distributed nonlinearities of printed transmission lines and to evaluate PIM products of arbitrary order. It has been observed for the first time that the sources of nonlinearity in typical microstrip circuits may have highly uneven distributions which require a different means for PIM characterization and modeling. The proposed methodology has been validated by accurate predictions of the PIM response of complex circuit layouts. The results of this paper pave the way to a holistic approach to the design of planar microwave circuits and devices under given linearity constraints.