System with magnetic film for reducing passive intermodulation

Abstract

A wireless communication system includes a transmitter configured to transmit at least first and second electromagnetic waves having different frequencies F1 and F2, respectively; a first substantially linear passive medium; a first substantially nonlinear passive medium disposed adjacent to the first substantially linear passive medium; and a first magnetic film covering at least a portion of the first substantially linear passive medium. When the transmitter transmits the first and second electromagnetic waves, the first substantially linear passive medium and the first substantially nonlinear passive medium receive the first and second electromagnetic waves and generate first and second signals propagating therethrough at the respective frequencies F1 and F2. At least one intermodulation signal having a frequency F3 equal to nF1 + mF2 (m and n are positive or negative integers) is generated in the first substantially nonlinear passive medium. The first magnetic film reduces the at least one intermodulation signal by at least 2 dB.

Description

[Background technology]

[0001] As wireless communication networks evolve, signal quality (more specifically, signal-to-noise ratio, or SNR) becomes increasingly important. To achieve very high data rates, higher-order modulation is used, requiring correspondingly higher levels of SNR. A common cause of SNR degradation is passive intermodulation (PIM) distortion, which can significantly reduce network performance and capacity. PIM distortion is generated when multiple frequencies encounter nonlinear materials or features, which then generate sum and difference combinations (products) of fundamental frequencies and their harmonics. The resulting products often occur in uplink / receive frequency bands where the signal of interest is very weak, making coherent reception very difficult or impossible.

[0002] There are many mechanisms that can create or propagate PIM. Typically, the interaction and interconnection of conductive mechanical components within a system can create nonlinear elements within the system. In some cases, nonlinearities can occur due to poor metal-to-metal contact at the location of the antenna mounting bracket, or if the bracket contains a joint between dissimilar materials. Other sources of nonlinearities can be contamination, loose connections, nearby metal objects, or a variety of other causes. Summary of the Invention

[0003] This specification relates generally to systems, such as wireless communication systems, that include at least one magnetic film. The magnetic film may be included to mitigate the effects of passive intermodulation distortion in wireless communication systems.

[0004] In some aspects of the present disclosure, a wireless communication system is provided. The wireless communication system includes: a transmitter configured to transmit at least first and second electromagnetic waves having different frequencies F1 and F2, a first electrically conductive substantially linear passive medium; a first electrically conductive substantially nonlinear passive medium disposed proximate the first substantially linear passive medium; and a first magnetic film covering at least a first portion of the first substantially linear passive medium and approximately 20% or less of any electrically conductive substantially nonlinear passive medium. When the transmitter transmits the first and second electromagnetic waves, the first and first substantially linear passive medium receive the first and second electromagnetic waves and generate first and second signals propagating therethrough at respective frequencies F1 and F2. At least one intermodulation signal is generated from the first and second signals in the first substantially nonlinear passive medium. The at least one intermodulation signal has a frequency F3 equal to nF1+mF2, where m and n are positive or negative integers. The first magnetic film reduces the occurrence of the at least one intermodulation signal by at least 2 dB.

[0005] In some aspects of the present disclosure, a wireless communication system is provided. The wireless communication system includes: a transmitter configured to transmit at least first and second electromagnetic waves having different frequencies F1 and F2, a first substantially nonlinear passive medium portion; and a first substantially linear passive medium portion disposed proximate to the first substantially nonlinear passive medium portion, the first substantially linear passive medium portion receiving the first and second electromagnetic waves and generating first and second signals at the respective frequencies F1 and F2 when the transmitter transmits the first and second electromagnetic waves. The first and second signals propagate through the first substantially linear passive medium portion along a first path toward the first substantially nonlinear passive medium portion. An intermodulation signal is generated from the first and second signals in the first substantially nonlinear passive medium portion. The intermodulation signal has a frequency F3 equal to nF1 + mF2, where m and n are positive or negative integers. The wireless communication system further includes a first magnetic film positioned to cover at least a first portion of the first substantially linear passive medium portion along a first path and to attenuate the generated first and second signals propagating through the first substantially linear passive medium portion to a greater extent than an intermodulation signal generated in the first substantially nonlinear passive medium portion.

[0006] In some aspects of the present disclosure, a system for reducing passive intermodulation is provided. The system includes a first, substantially linear, electrically conductive passive medium configured to receive first and second electromagnetic waves having different frequencies F1 and F2, respectively, and to generate first and second signals at the respective frequencies F1 and F2. The first and second signals propagate through the first, substantially linear, passive medium along a first path toward the first, substantially nonlinear, electrically conductive passive medium. An intermodulation signal is generated from the first and second signals in the first, substantially nonlinear, passive medium. The intermodulation signal has a frequency F3 equal to nF1 + mF2, where m and n are positive or negative integers. The system further includes a first magnetic film covering at least a first portion of the first, substantially linear, passive medium along the first path and covering no more than about 20% of the first, substantially nonlinear, passive medium.

[0007] In some aspects of the present disclosure, a system for reducing passive intermodulation is provided. The system includes a first, substantially linear, electrically conductive passive medium configured to receive first and second electromagnetic waves having different frequencies F1 and F2, respectively, and to generate first and second signals at the respective frequencies F1 and F2. The first and second signals propagate through the first, substantially linear, passive medium along a first path toward the first, substantially nonlinear, electrically conductive passive medium. An intermodulation signal is generated from the first and second signals in the first, substantially nonlinear, passive medium. The intermodulation signal has a frequency F3 equal to nF1 + mF2, where m and n are positive or negative integers. The system further includes a first magnetic film covering a first portion of the first, substantially linear, passive medium along the first path and leaving a second portion of the first, substantially linear, passive medium exposed. The first magnetic film faces the first substantially nonlinear passive medium and the second portion faces an opposite side from the first substantially nonlinear passive medium.

[0008] These and other aspects will become apparent from the following detailed description. In no event, however, should this brief summary be construed as limiting the claimed subject matter. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic side view of a wireless communication system according to an embodiment of the present disclosure; [Figure 2] 1 is a schematic side view of a conductive passive medium through which signals may propagate in a wireless communication system according to an embodiment of the present disclosure; [Figure 3] 1 is a schematic side view of a conductive passive medium having a magnetically absorbing film according to an embodiment herein; [Figure 4] FIG. 2 is a schematic side view of a conductive passive medium showing a junction between a first conductive portion and a second conductive portion according to an embodiment herein. [Figure 5] FIG. 10 is a schematic side view of a conductive passive medium showing a junction between a metal and a metal oxide according to an alternative embodiment herein. [Figure 6] FIG. 10 is a schematic side view of a conductive passive medium exhibiting metal corrosion according to an alternative embodiment herein. [Figure 7] 1 is a schematic graph illustrating transmission frequencies and intermodulation frequencies of a wireless communication system according to an embodiment herein; [Figure 8A] FIG. 1 is a schematic diagram of a system for reducing passive modulation, according to some embodiments herein. [Figure 8B] FIG. 1 is a schematic diagram of a system for reducing passive modulation, according to some embodiments herein. [Figure 8C] FIG. 1 is a schematic diagram of a system for reducing passive modulation, according to some embodiments herein. [Figure 8D] FIG. 1 is a schematic diagram of a system for reducing passive modulation, according to some embodiments herein. [Figure 8E] FIG. 1 is a schematic diagram of a system for reducing passive modulation, according to some embodiments herein. [Figure 8F] FIG. 1 is a schematic diagram of a system for reducing passive modulation, according to some embodiments herein. [Figure 9] 1 is a plot of magnetic permeability versus frequency for a magnetic film, according to some embodiments herein. [Figure 10] 1 is a plot of magnetic permeability versus frequency for a magnetic film, according to some embodiments herein. DETAILED DESCRIPTION OF THE INVENTION

[0010] In the following description, reference is made to the accompanying drawings, which form a part hereof, and in which are shown by way of illustration various embodiments. The drawings are not necessarily to scale. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present disclosure. Accordingly, the following detailed description is not to be taken in a limiting sense.

[0011] As wireless communication networks evolve, signal quality (more specifically, signal-to-noise ratio, or SNR) becomes increasingly important. To achieve very high data rates, higher-order modulation (e.g., 64QAM, 256QAM) is used, requiring correspondingly higher levels of SNR. A common cause of SNR degradation is passive intermodulation (PIM) distortion, which can significantly reduce network performance and capacity. PIM distortion (abbreviated as "PIM") is generated when multiple frequencies encounter nonlinear materials or features, which then generate sum and difference combinations (products) of fundamental frequencies and their harmonics. The resulting products, typically third-, fifth-, and / or seventh-order products, often occur in uplink / receive frequency bands where the signal of interest is very weak, making coherent reception very difficult or impossible.

[0012] PIM is a form of electromagnetic interference that occurs in wireless communication systems when the system simultaneously transmits signals at multiple frequencies through passive devices such as cables, connectors, antennas, mounting brackets, and other objects in or near the system's transmission path. PIM interference is particularly noticeable in nodes transmitting at high power, such as cellular base station antennas. PIM occurs when two or more signals at different frequencies mix with each other due to nonlinearities in the system's mechanical components. When two signals are combined (through amplitude modulation), sum and difference signals are generated within the operating band of the wireless system, including within the signal harmonics, which can cause interference.

[0013] There are many mechanisms that can create or propagate PIM. Typically, the interaction and interconnection of conductive mechanical components within a system can create nonlinear elements within the system. In some cases, nonlinearities can occur due to poor metal-to-metal contact at the location of the antenna mounting bracket or if the bracket contains a joint between dissimilar materials. For example, the fundamental frequencies (e.g., F1 and F2) of a cellular base station can be radiated by an antenna mounted on a galvanized steel mast. When signals (e.g., currents and / or voltages) are induced in the steel mast at these frequencies, they encounter the mounting bracket (i.e., the nonlinearity) and can mix within the nonlinearity to form a third signal (i.e., an intermodulation signal) at a new frequency, F3. The intermodulation signal can radiate from the bracket as PIM and / or be conducted away from the bracket by a conductive linear portion, which acts as an antenna for the PIM and can radiate PIM with even better efficiency than the nonlinear bracket. Although a conductive shield is often applied to encapsulate the bracket and prevent it from radiating PIM, intermodulation signals (e.g., currents) can still travel from the bracket throughout the structure and to other antennas, eventually being re-radiated and degrading the network.

[0014] Other causes of nonlinearity (and therefore PIM) can be contamination (e.g., rust, corrosion, dirt, oxidation, etc.), loose connections, nearby metal objects (e.g., guy wires, anchors, roof flashing, pipes, etc.), or a variety of other causes.

[0015] According to some aspects of the present disclosure, a wireless communication system (e.g., a system including a cellular base station as a component) includes a conductive passive medium (e.g., a metallic structure of an antenna mast) along which first and second electromagnetic signals of different frequencies F1 and F2, respectively, can simultaneously propagate. In some embodiments, at least one of the first and second signals includes a current. In some embodiments, at least one of the first and second signals includes a voltage. In some embodiments, the first and second signals may be generated by two radio frequency (RF) signals transmitted at similar but different frequencies (i.e., F1 and F2). In some embodiments, each of F1 and F2 is between about 100 MHz and about 10 GHz, between about 200 MHz and about 5 GHz, or between about 300 MHz and about 3 GHz. In some such or other embodiments, the difference between F1 and F2 is between about 5 MHz and about 1 GHz, between about 10 MHz and about 900 MHz, between about 10 MHz and about 800 MHz, or between about 10 MHz and about 700 MHz.

[0016] For example, in one embodiment, F1 may be 869 MHz and F2 may be 894 MHz, with an adjacent receive band for signals returned from an external device (e.g., a mobile device). For example, the adjacent receive band may be 824-849 MHz. Another receive band may be adjacent to a frequency range above the transmit band (i.e., frequencies above the range of transmit band frequencies). These fundamental frequencies may be mixed to generate new frequency products according to the formula nF1 + mF2, where m and n are positive or negative integers. Simple addition of the modulated signals in this example (e.g., when both m and n are +1) produces a signal of 869 + 894 = 1763 MHz, and the difference between the signals (e.g., when n is +1 and m is -1) is 894 - 869 = 25 MHz. Both 25 MHz and 1763 MHz are outside the intended receive band of a cellular system, and therefore these signals are not a concern for that particular cellular system (however, these frequencies may be within the intended receive band or receive spectrum of another nearby system and therefore may cause PIM interference in that system). However, when these signals combine to form third-order products (when the sum of the absolute values ​​of m and n equals 3), and sometimes higher-order products, they can generate PIM signals within the intended receive band. For example, 2F1-F2 (844 MHz) and 2F2-F1 (919 MHz) generate third-order products within the receive portion of the cellular band that can lead to PIM distortion.

[0017] In some embodiments, the electrically conductive passive medium includes a first, substantially linear, electrically conductive passive medium portion adjacent to a first, substantially nonlinear, electrically conductive passive medium portion. An intermodulation signal may be generated from the first and second signals in the first, substantially nonlinear, passive medium portion. The intermodulation signal may be generated based on a nonlinear interaction between the first and second signals (e.g., an indirect interaction resulting from the first and second signals interacting with the first, substantially nonlinear, passive medium). For example, in some embodiments, the first, substantially linear, electrically conductive passive medium portion may be a metal mast (e.g., a galvanized steel mast) to which a cellular antenna is attached, and the first, substantially nonlinear, electrically conductive passive medium portion may be a mounting bracket made of dissimilar metals. This junction or confluence of dissimilar materials may create a nonlinearity that acts similar to a diode, mixing the first and second signals (at frequencies F1 and F2) to generate an intermodulation signal (PIM) at a new frequency. In some embodiments, the nonlinearity may be created by a junction between two dissimilar metals. In some embodiments, the nonlinearity may be generated by a junction between a metal and a metal oxide (e.g., a metal oxide resulting from oxidation effects). In some embodiments, the nonlinearity may respond to areas of corrosion or contamination (e.g., areas of rust, contaminants such as dirt, poor contact between metals, etc.).

[0018] A medium portion is a portion of a medium. The medium portion can be, for example, the medium or a contact or junction between adjacent materials. A contact or junction between adjacent materials can define a substantially nonlinear medium as a medium that includes the junction and has electrical properties significantly affected by the junction or junction. For example, in some embodiments, for a nonlinearity created by a junction between two metals with different Fermi levels, a transfer of charge across the junction occurs, equalizing the Fermi levels and creating a dipole that significantly affects the electrical properties of a thin region (e.g., having a thickness small compared to the overall dimensions of the metals but that may be large compared to the atomic lattice spacing of the metals) around the junction, thereby defining the substantially nonlinear medium. The first (and, if included, second, third, etc., respectively) substantially linear passive medium portion can be a first (and, if included, second, third, etc., respectively) substantially linear passive medium. This is because a portion of a medium can be considered a medium, and similarly, a first (and if included, second, third, etc., respectively) substantially nonlinear passive medium portion can be a first (and if included, second, third, etc., respectively) substantially nonlinear passive medium.

[0019] In some embodiments, a first magnetic film may be disposed proximate to a conductive outer surface of the first substantially linear portion. In some embodiments, the wireless communication system may further include a conductive second substantially linear passive medium portion adjacent to the conductive first substantially nonlinear passive medium portion on an opposite side of the first substantially linear passive medium portion (e.g., the substantially nonlinear portion may be "sandwiched" between the first substantially linear portion and the second substantially linear portion). In some embodiments, a second magnetic film may be disposed proximate to a conductive outer surface of the second substantially linear portion, and the first magnetic film reduces generation of intermodulation signals in the first substantially nonlinear portion by absorbing at least a portion of the first signal and the second signal when the first signal and the second signal propagate along the first substantially linear portion toward the substantially nonlinear portion. In some embodiments, at least a portion of the remaining portions of the first and second signals mix in the first substantially nonlinear portion to generate an intermodulation signal that propagates through the first substantially nonlinear portion and the second linear portion, and the intermodulation signal is at least partially absorbed by the second magnetic film.

[0020] In some embodiments, the first and second signals may be induced by electromagnetic radiation transmitted from an antenna coupled to a conductive, substantially linear passive medium. In some embodiments, the first and second signals may be induced by electromagnetic radiation radiated from a second, substantially nonlinear passive medium coupled to a first, substantially linear passive medium portion. That is, PIM distortion may be generated in a second, substantially nonlinear portion coupled to the substantially linear portion and radiated from the second, substantially nonlinear portion, induced to induce a signal in the substantially linear portion.

[0021] In some embodiments, the intermodulation signal propagating along the first substantially nonlinear passive medium may have a frequency F3 equal to nF1 + mF2, where m and n are positive or negative integers. For example, as discussed elsewhere herein, n may be 2 and m may be −1, or n may be −1 and m may be 2. These values ​​are merely examples, and other values ​​of n and m are possible. In some embodiments, one of m and n is a negative integer and the other of m and n is a positive integer. In some embodiments, n may be equal to −1 and m may be equal to +2, and thus F3 is equal to 2F2 − F1. In some embodiments, n may be equal to +2 and m may be equal to −1, and thus F3 is equal to 2F1 − F2. In some embodiments, n may be equal to +1 and m may be equal to +1, and thus F3 is equal to F1 + F2. In some embodiments, n may be equal to +2 and m may be equal to +2, such that F3 is equal to 2F1 + 2F2. In some embodiments, F1 and F2 are both less than about 6 GHz. In some embodiments, F1 and F2 are both between about 600 MHz and 4 GHz. In some embodiments, F1 and F2 are both between about 600 MHz and 800 MHz. In some embodiments, F1 and F2 are frequencies that are less than about 100 MHz apart, or less than about 50 MHz apart.

[0022] In some embodiments, the first magnetic film is disposed proximate to the conductive outer surface of the first substantially linear medium portion such that when the first and second signals propagate along the first substantially linear passive medium portion toward the first substantially nonlinear passive medium portion, the magnetic film attenuates at least a portion of the first and second signals, thereby reducing the generation of intermodulation currents in the first substantially nonlinear passive medium (e.g., preventing the propagation of the signals through the corresponding structure). In some embodiments, the magnetic film may reduce the intensity of intermodulation emissions generated by and radiated from the first substantially nonlinear passive medium portion by at least 2 dB, at least 3 dB, at least 3.5 dB, at least 4 dB, at least 5 dB, or at least 6 dB (e.g., between 2 dB and 100 dB, or between 3 dB and 50 dB).

[0023] The magnetic film may have a relative permeability with a real part greater than about 10 for at least one frequency in the range of about 100 MHz to about 10 GHz. The magnetic film may have a relative permeability with an imaginary part greater than about 5 for at least one frequency in the range of about 100 MHz to about 10 GHz, or within any range described elsewhere herein. The magnetic film may be conductive or include a conductive layer, or the magnetic film may be non-conductive. A non-conductive film may have an electrical resistivity (evaluated at low frequencies (e.g., about 1 kHz or less) or static (DC)) of 0 Ω-m to at least 100 Ω-m along each direction (e.g., along mutually orthogonal in-plane directions and along the thickness direction), and for each layer of the film in some embodiments where the film has two or more layers. A non-conductive film may also be referred to as an electrically insulating film.

[0024] In some embodiments, the first magnetic film or another magnetic film may be a magnetic absorber. One example of a magnetic absorber is the 3M™ EMI Shielding Absorber AB6000HF series of shielding films manufactured by 3M Company (St. Paul, MN). Other suitable magnetic absorbers include 3M™ Flux Field Direction Material (FFDM), such as 3M™ FFDM EM25TP, available from 3M Company. In some embodiments, the magnetic film includes a conductive layer (e.g., 3M™ EMI Shielding Absorber AB6000HF film includes a conductive shielding layer). In other embodiments, a conductive layer is not included (e.g., 3M™ Flux Field Direction Material (FFDM) EM25TP film is available without a conductive layer).

[0025] In some embodiments, the magnetic film may attenuate the first and second signals by absorbing at least a portion of the magnetic fields generated by the first and second signals. In some embodiments, the first magnetic film does not cover any portion of the first substantially nonlinear medium or does not cover any portion of any substantially nonlinear medium. In some embodiments, the first magnetic film covers at least a first portion of the first substantially linear passive medium (e.g., along a first path), covering no more than about 50% of the first substantially nonlinear passive medium, or no more than about 50% of any electrically conductive substantially nonlinear passive medium. In some embodiments, the first magnetic film covers at least a first portion of the first substantially linear passive medium (e.g., along a first path), covering no more than about 20% of the first substantially nonlinear passive medium, or no more than about 20% of any electrically conductive substantially nonlinear passive medium. In some embodiments, the first magnetic film covers at least a first portion of the first substantially linear passive medium (e.g., along a first path) and covers no more than about 10% of the first substantially nonlinear passive medium, or no more than about 10% of any electrically conductive substantially nonlinear passive medium. X% (e.g., 50%, 20%, or 10%) of the electrically conductive substantially nonlinear passive medium refers to X% of the entire continuous nonlinear portion of the electrically conductive passive medium, not just X% of a portion of the nonlinear portion. For example, in an embodiment in which the rusted portion of the first mounting bracket is the substantially nonlinear medium, X% of the electrically conductive substantially nonlinear passive medium refers to X% of the entire rusted portion of the first mounting bracket. As another example, in an embodiment where a first continuous rusted portion of a first mounting bracket is a first substantially nonlinear medium, and a second continuous rusted portion of the first mounting bracket or a second mounting bracket is a second substantially nonlinear medium, and the first and second rusted portions are spaced apart from one another (i.e., the first and second rusted portions are not contiguous with one another), covering no more than about X% of any electrically conductive substantially nonlinear passive medium means that no more than X% of the entire first rusted portion is covered and no more than X% of the entire second rusted portion is covered.Covering X% of a conductive substantially nonlinear passive medium with a magnetic film may be understood to mean covering X% of the area of ​​the substantially nonlinear medium facing the magnetic film. For example, in an embodiment where the nonlinear medium is a mounting bracket, covering X% of the substantially nonlinear medium may be understood to mean covering X% of the area of ​​the outer surface of the mounting bracket. As another example, in an embodiment where the substantially nonlinear medium is defined by a junction, covering X% of the substantially nonlinear medium may be understood to mean covering X% of the area of ​​the junction.

[0026] According to some aspects herein, a wireless communication system includes an antenna (e.g., a cellular antenna) and an electrically conductive substantially linear passive medium portion electrically interconnected with an electrically conductive substantially nonlinear passive medium portion (e.g., a junction of two dissimilar materials, such as a mounting bracket and an antenna mast), wherein when the antenna radiates first and second electromagnetic waves at different frequencies F and F, respectively, the first and second electromagnetic waves induce respective first and second signals that propagate through the first substantially nonlinear passive medium portion, and the first substantially nonlinear passive medium portion mixes the first and second signals to generate a third signal (i.e., intermodulation current, or PIM) having a frequency n+mF and that propagates along the substantially nonlinear passive medium portion and the substantially linear passive medium portion, where m and n are integers that can be either positive or negative. In some embodiments, a magnetic film is disposed in the substantially linear passive medium portion but not in the substantially nonlinear passive medium portion to absorb at least a portion of the third signal. For example, in some embodiments, the magnetic film may be a magnetically absorbing film wrapped around the antenna mast (substantially linear medium portion) adjacent to and within the propagation path, before the attached antenna mounting bracket (substantially nonlinear medium portion). In some embodiments, disposing the magnetic film in the substantially linear medium portion may prevent propagation of signals that may contribute to PIM interference (e.g., by attenuating the signals due at least in part to absorbing magnetic fields generated by the signals). In some embodiments, the magnetic film may be disposed in both the substantially linear passive medium portion and a portion of the substantially nonlinear passive medium portion. Attenuating the signals in the substantially linear passive medium may result in a reduction of intermodulation signals in the substantially nonlinear medium portion. The reduction of intermodulation signals in the substantially nonlinear medium portion may be greater than the reduction of signals in the substantially linear medium portion.For example, for a third-order (|m|+|n|=3) intermodulation signal, approximately a 3 dB reduction in the power of the intermodulation signal in the substantially nonlinear medium portion can occur for every 1 dB reduction in the power of the signal in the substantially linear medium portion. In some embodiments, the magnetic film is positioned to primarily attenuate at least a portion of the first and second signals propagating through the first substantially linear passive medium portion. A magnetic film covering only a portion of the substantially linear passive medium portion, or a magnetic film covering a portion of the substantially linear passive medium portion and a portion of the substantially nonlinear passive medium portion, which attenuates at least a portion of the first and second signals propagating through the substantially linear passive medium portion more than it attenuates at least a portion of the signal in the substantially nonlinear passive medium portion, thereby resulting in greater attenuation of the intermodulation signal, can be described as being primarily positioned to attenuate at least a portion of the first and second signals propagating through the first substantially linear passive medium portion.

[0027] According to some aspects herein, a wireless communication system (e.g., a cellular base station) may include one or more antennas, a plurality of spaced-apart conductive first sections (e.g., one or more mounting brackets or irregular welds), and a plurality of conductive second sections (e.g., sections of an antenna mast) interconnected with the first sections such that when the one or more antennas radiate first and second electromagnetic waves at different frequencies F1 and F2, respectively, the first and second electromagnetic waves may propagate through the first and second sections to induce first and second signals at respective frequencies F1 and F2. In some embodiments, the first section may generate a third signal (e.g., an intermodulation signal) at a frequency F3 different from F1 and F2 by mixing (e.g., combining by amplitude modulation) the first and second signals. In some embodiments, the generated third signal may propagate along the first and second sections, generating a new signal at frequency F3 in the first section but not in the second section, which may propagate along the second section and then radiate electromagnetic energy at frequency F3. In some embodiments, the second section may also generate an electrical signal at frequency F3 that may contribute to the radiated electromagnetic energy. In some embodiments, this "mixing" of signals may be caused by nonlinearities in the first section. For example, corrosion of a mounting bracket, a loose connection, or any number of other causes may cause nonlinearities in the first section, causing the first section to act as a signal (e.g., current or voltage) mixer, generating a third (intermodulation) signal based on the first and second signals and their respective frequencies. In some embodiments, a magnetic film (e.g., a magnetic absorber) may be disposed on the conductive surface of each second section (e.g., wrapped around or disposed on the outer surface of the section) to absorb at least a portion of the third signal propagating along the second section.

[0028] According to some aspects of the present disclosure, a wireless communication system is provided, including one or more antennas (e.g., multiple cellular antennas on a cellular base station), one or more transceivers (e.g., transceivers housed in a base transceiver station, or BTS, used to facilitate wireless communication between mobile devices and a cellular network) coupled to the one or more antennas, multiple conductive substantially linear passive medium portions interconnected with multiple conductive nonlinear passive medium portions, and a magnetic film (e.g., a magnetic absorber) disposed on at least a portion of the substantially linear medium portions but not on the substantially nonlinear medium portions. In some embodiments, the substantially linear medium portions and the substantially nonlinear medium portions may each be capable of simultaneously propagating a first electromagnetic signal and a second electromagnetic signal at different frequencies F and F, respectively. In some embodiments, each of the substantially nonlinear passive portions may be capable of mixing or otherwise combining the first and second signals to generate a third signal having a frequency n+mF, where m and n are positive or negative integers, while the substantially linear passive portion is not capable of generating the third signal. In some embodiments, the third signal propagates along the substantially nonlinear passive medium portion and / or along the substantially linear passive portion. In some embodiments, a magnetic absorber disposed in the linear portion may prevent the formation of a signal in the substantially linear portion that may otherwise contribute to the generation of the third signal (e.g., a PIM signal) when encountering the substantially nonlinear portion. In some embodiments, the PIM signal may cause PIM emissions that increase the overall noise level within a frequency band (e.g., a cellular band) used by the transceiver, leading to degradation or distortion of the communication signal.

[0029] A substantially linear medium or medium portion and a substantially nonlinear medium or medium portion can be understood as follows: when a first signal and a second signal are induced in a medium or medium portion and a modulation signal or at least one intermodulation signal arises from the first signal and the second signal in a first substantially nonlinear passive medium or medium portion in the substantially nonlinear medium or medium portion (e.g., based on a nonlinear interaction between the first signal and the second signal), any intermodulation signal arising from the first signal and the second signal in the substantially linear medium (e.g., based on a nonlinear interaction between the first signal and the second signal) has an amplitude A, and the intermodulation signal or at least one intermodulation signal arising in the substantially nonlinear passive medium has an amplitude B, where B is at least 2.5 dB greater than A. In some embodiments, a system includes a first electrically conductive substantially linear passive medium or medium portion and a first electrically conductive substantially nonlinear passive medium or medium portion. In some embodiments, any intermodulation signal generated in the first substantially linear passive medium or medium portion (e.g., due to a nonlinear interaction between the first signal and the second signal) has an amplitude A, and the intermodulation signal or at least one intermodulation signal generated in the first substantially nonlinear passive medium or medium portion has an amplitude B, where B is at least 3 dB, at least 4 dB, at least 5 dB, at least 6 dB, at least 8 dB, at least 10 dB, at least 15 dB, or at least 20 dB greater than A.

[0030] According to some aspects of the present disclosure, there is provided a wireless communication system including: a transmitter configured to transmit at least first and second electromagnetic waves having different frequencies F1 and F2, a first electrically conductive substantially linear passive medium; a first electrically conductive substantially nonlinear passive medium disposed proximate to the first substantially linear passive medium; and a first magnetic film covering at least a first portion of the first substantially linear passive medium, and in some embodiments covering no more than about 20% of any electrically conductive substantially nonlinear passive medium, wherein when the transmitter transmits the first and second electromagnetic waves, the first substantially linear passive medium and the first substantially nonlinear passive medium receive the first and second electromagnetic waves and generate first and second signals propagating therethrough at the respective frequencies F1 and F2. In some embodiments, at least one intermodulation signal is generated from the first and second signals in the first substantially nonlinear passive medium. At least one intermodulation signal may be generated in the first substantially nonlinear passive medium based on a nonlinear interaction between the first signal and the second signal. The nonlinear interaction may be direct or indirect. For example, the nonlinear effect may be mediated by the first substantially nonlinear passive medium. In some embodiments, the first signal and the second signal interact with the first substantially nonlinear passive medium to generate at least one intermodulation signal. The at least one intermodulation signal has a frequency F3 equal to nF1 + mF2, where m and n are positive or negative integers. In some embodiments, the first magnetic film reduces the generation of the at least one intermodulation signal by at least 2 dB, or by an amount within a range described elsewhere. In some embodiments, the at least one intermodulation signal propagates through a substantially nonlinear medium and / or a substantially linear medium (e.g., the at least one intermodulation signal may be generated in a substantially nonlinear medium, propagate through the substantially nonlinear medium into a substantially linear medium, and then propagate through the substantially linear medium).In some embodiments, any intermodulation signal arising from the first signal and the second signal in the first substantially linear passive medium has an amplitude A, and at least one intermodulation signal arising in the first substantially nonlinear passive medium has an amplitude B, where B is greater than A by at least 3 dB, or by an amount described elsewhere.

[0031] According to some aspects of the present disclosure, there is provided a wireless communication system including: a transmitter configured to transmit at least first and second electromagnetic waves having different frequencies F1 and F2, respectively; a first substantially nonlinear passive medium portion; and a first substantially linear passive medium portion disposed proximate to the first substantially nonlinear passive medium portion, the first substantially linear passive medium portion receiving the first and second electromagnetic waves and generating first and second signals at the respective frequencies F1 and F2 when the transmitter transmits the first and second electromagnetic waves. The first and second signals propagate along a first path through the first substantially linear passive medium portion toward the first substantially nonlinear passive medium portion. In some embodiments, an intermodulation signal (or at least one intermodulation signal or at least two intermodulation signals) is generated from the first and second signals in the first substantially nonlinear passive medium portion. In some embodiments, an intermodulation signal is generated in the first substantially nonlinear passive medium portion based on a nonlinear interaction between the first signal and the second signal. In some embodiments, the first signal and the second signal interact with the first substantially nonlinear passive medium portion (e.g., resulting in an indirect nonlinear interaction between the first signal and the second signal) to generate the intermodulation signal. The intermodulation signal has a frequency F3 equal to nF1 + mF2, where m and n are positive or negative integers. The wireless communication system further includes a first magnetic film disposed to cover at least a first portion of the first substantially linear passive medium portion along a first path and to attenuate the generated first and second signals propagating through the first substantially linear passive medium portion to a greater extent than the intermodulation signal generated in the first substantially nonlinear passive medium portion. For example, attenuating a signal propagating through the first substantially linear passive medium portion can substantially result in a substantial reduction of intermodulation signals occurring in the first substantially nonlinear passive medium portion, even if little or substantially no intermodulation signals are attenuated (e.g., absorbed).This is because the reduction may occur due to a reduction in the generation of the intermodulation signal rather than due to attenuation of the generated intermodulation signal. In some embodiments, the first magnetic film may also partially attenuate the intermodulation signal. For example, in some embodiments, the first magnetic film may also cover a portion of the first substantially nonlinear passive medium portion so that the intermodulation signal generated in the first substantially nonlinear passive medium portion is somewhat attenuated. In some embodiments, any intermodulation signal generated from the first signal and the second signal in the first substantially linear passive medium portion has an amplitude A, and the amplitude of the intermodulation signal generated in the first substantially nonlinear passive medium portion is B, where B is at least 3 dB greater than A, or by an amount described elsewhere. The conductive passive medium may include a conductive first substantially nonlinear passive medium portion and a conductive first substantially linear passive medium portion.

[0032] According to some aspects of the present disclosure, a system for reducing passive intermodulation is provided, the system including a first substantially linear conductive passive medium configured to receive first and second electromagnetic waves having different frequencies F1 and F2, respectively, and generate first and second signals at the respective frequencies F1 and F2, where the first and second signals propagate along a first path through the first substantially linear passive medium toward a first substantially nonlinear conductive passive medium. The first substantially linear conductive passive medium may be configured to receive the first and second electromagnetic waves and generate the first and second signals, for example, by being made of a material (e.g., steel or other metal) capable of generating signals from the received electromagnetic waves. A suitable substantially linear passive medium configured to receive the first and second electromagnetic waves and generate the first and second signals includes a structural element (e.g., an antenna mast) for supporting a transmitter (e.g., made of metal). In some embodiments, an intermodulation signal (or at least one intermodulation signal or at least two intermodulation signals) is generated from a first signal and a second signal in a first substantially nonlinear passive medium. In some embodiments, the intermodulation signal is generated in the first substantially nonlinear passive medium based on a nonlinear interaction between the first signal and the second signal. For example, in some embodiments, the first signal and the second signal interact with the first substantially nonlinear passive medium to generate the intermodulation signal. The intermodulation signal has a frequency F3 equal to nF1 + mF2, where m and n are positive or negative integers. The system includes a first magnetic film covering at least a first of the first substantially linear passive media along a first path. In some embodiments, the first magnetic film covers no more than about 20% of the first substantially nonlinear passive medium, or no more than about 20% of any of the substantially nonlinear passive media. In some embodiments, the first magnetic film covers a first portion of the first substantially linear passive medium along a first path and leaves a second portion of the first substantially linear passive medium exposed, with the first magnetic film facing the first substantially nonlinear passive medium and the second portion facing an opposite side from the first substantially nonlinear passive medium.In some embodiments, the first magnetic film reduces the intermodulation signal by at least 2 dB, or by an amount within a range as described elsewhere. In some embodiments, any intermodulation signal generated from the first signal and the second signal in the first substantially linear passive medium has an amplitude A, and the amplitude of the intermodulation signal generated in the first substantially nonlinear passive medium is B, where B is greater than A by at least 3 dB, or by an amount as described elsewhere.

[0033] Referring now to the figures, FIG. 1 is a side view of a wireless communication system according to some embodiments herein. In some embodiments, the wireless communication system 200 includes one or more antennas 50 disposed on (e.g., mounted on, supported by) a conductive passive medium 10 (e.g., a metallic antenna mast or mounting structure). In some embodiments, the conductive passive medium 10 may include two distinct portions: a conductive linear passive portion 11 (e.g., a major substantially dissimilar element of the mounting structure, such as a main shaft) and a conductive nonlinear passive portion 12 (e.g., a mounting bracket, weld bead, or other connecting structure). Note that the nonlinear portion 12 may be created by the presence of different materials and / or different conditions for the linear portion 11. That is, nonlinear elements may be created at the interface between two dissimilar metals (e.g., between the galvanized steel of an antenna mast and the metal used in a mounting bracket attached to the mast), by loose or broken connector points or cables, by rust, corrosion, dirt, oxidation, etc., by nearby metal objects such as roof flashing or pipes, or by any of a number of other causes. For illustrative purposes, Figure 1 shows nonlinear element 12 coinciding with the antenna's mounting bracket, but in fact it could be any suitable nonlinearity of any suitable cause or condition.

[0034] In some embodiments, wireless communication system 200 may also include one or more transceivers 60 (e.g., transceivers housed in a base transceiver station for a cellular base station) coupled to antenna 50. In some embodiments, transceiver 60 may be used to facilitate wireless communication between external devices and a wireless network. In some embodiments, transceiver 60 may be a high-power transceiver (e.g., 20 W or greater).

[0035] In operation, in some embodiments, the transceiver 60 of the wireless communication system 200 may generate two or more radio frequency (RF) signals, each at a unique frequency. The signals propagate through a transmission line (e.g., a coaxial cable or an optical fiber) and are broadcast / radiated as electromagnetic radiation 40 from an antenna 50 (e.g., a first antenna 50a). In some embodiments, the electromagnetic radiation 40 may include a first electromagnetic wave 40a radiating at a frequency F1 and a second electromagnetic wave 40b radiating at a frequency F2. In some embodiments, when the first electromagnetic wave 40a and the second electromagnetic wave 40b impinge on a structure comprising a linear portion 11 and a nonlinear portion 12, respectively, the first electromagnetic wave 40a and the second electromagnetic wave 40b may induce a first signal 20 and a second signal 21 at corresponding frequencies F1 and F2, respectively, in the nonlinear portion 12 (the first signal 20 and the second signal 21 are shown in FIG. 2 ). In some embodiments, the nonlinear section 12 may function as a mixer that combines the first signal 20 and the second signal 21 to generate a third signal (i.e., an intermodulation signal) 22 at a third frequency F3. The third signal 22 (as well as the first signal 20 and the second signal 21) may then propagate throughout the conductive passive medium 10 (e.g., flowing through a metal antenna mast path), possibly flowing back to the transceiver 60 or one or more antennas 50, or returning to one or more antennas 50 by being re-radiated into space as second electromagnetic radiation 41 at a new frequency F3. In some embodiments, the second antenna 50b may retransmit or receive the RF signals (having fundamental frequencies F1 and F2) originally generated at the first antenna 50a, including the PIM signals at frequency F3 generated in the one or more nonlinear sections 12 / 12a. These RF signals (especially F3 signals) can be seen as increased noise in the transceiver 60, significantly reducing the SNR of the signal of interest.

[0036] To mitigate the effects of PIM, one or more magnetic films 30 (including 30a and 30b in some embodiments) may be disposed on or near the conductive outer surface 13 of the linear medium portion 11. In some embodiments, the magnetic film 30 may reduce or prevent the generation of the intermodulation signal 22 in the nonlinear portion 12. In some embodiments, the intermodulation signal 22 may be reduced by the magnetic film 30 in several ways. In some embodiments, the magnetic film 30 may attenuate one or both of the first signal and the second signal before they enter the nonlinear portion 12, thereby eliminating or significantly reducing the generation of the intermodulation signal 22. In some embodiments, the magnetic film 30 may block the signal or radiated energy from the nonlinear portion 12 before it exits the nonlinear portion 12 and enters the linear portion 11 / 11a / 11b. In some embodiments, additional magnetic films 30 (such as films 30a and / or 30b) may be placed in or adjacent to the additional linear portions 11 (such as portions 11a and / or 11b) to help attenuate signals induced in or passing through the structure. In some embodiments, magnetic films 30 (e.g., magnetic absorbers) may be placed in the linear portions 11 on either side of the nonlinear portion 12, for example, to attenuate and / or eliminate signals originating in or exiting the nonlinear portion 12.

[0037] FIG. 2 is a side view of the conductive passive medium 10 of FIG. 1 , showing further details regarding the generation of intermodulation signals. Electromagnetic radiation (RF signals) broadcast by a nearby antenna or radiated by another conductive structure (as shown in FIG. 1 ) induces a first signal 20 (corresponding to an RF signal having a fundamental frequency F1) and a second signal 21 (corresponding to an RF signal having a fundamental frequency F2) in the conductive passive medium 10 (e.g., a metallic portion of an antenna mast). In some embodiments, the first signal 20 and the second signal 21 may be induced in the conductive linear passive portion 11 of the conductive passive medium 10 and then travel throughout the rest of the structure. In these embodiments, the first signal 20 and the second signal 21 may propagate through the conductive linear passive portion 11 until encountering the conductive nonlinear passive portion 12. As described elsewhere herein, nonlinear portion 12 can be created by several things, including, but not limited to, joints between dissimilar materials, loose connections between mechanical parts, corroded or damaged areas, the proximity of other conductive components (e.g., pipes or roof flashing), etc. When first signal 20 and second signal 21 enter nonlinear portion 12, the nonlinearity can cause first signal 20 and second signal 21 to mix and generate a new signal having a new frequency. In some embodiments, at least a third signal 22 is generated, which has a frequency F3 that can represent the third harmonic of F1 and F2, which can be calculated, for example, using the formula F3 = nF1 + mF2, where n and m can be positive or negative integers. In other words, the third signal may be an intermodulation signal having frequency F3, which, when radiated from an antenna or other structure, may be received by antenna 50 in a frequency range intended to receive signals from external devices (e.g., mobile devices such as cellular telephones), thereby increasing the noise level and reducing the fidelity of the received signal. This, in turn, may reduce the rate at which information can be transferred from the mobile device to antenna 50, or may result in a loss of connection from the mobile device to the antenna (i.e., a "dropped call").In other embodiments, first signal 20 and second signal 21 may be induced directly in nonlinear section 12 (rather than originating in linear section 11 and propagating to nonlinear section 12). In these embodiments, each of signals 20 and 21, as well as intermodulation signal 22, may exit nonlinear section 12 and propagate away to adjacent linear section 11.

[0038] In some embodiments, the magnetic film 30 may be disposed on the linear portion 11 of the conductive passive medium 10 adjacent to the nonlinear portion 12 (e.g., disposed on the exterior surface or wrapped around the linear portion 11). In some embodiments, the magnetic film 30 may be a magnetic absorber that at least partially attenuates the first signal 20 and the second signal 21, and at least a portion of any electromagnetic fields generated by the signals 20 and 21 (through absorption of the magnetic fields generated by the signals 20 and 21 adjacent to the linear section), before the signals enter the nonlinear portion 12. By reducing or eliminating the first signal 20 and the second signal 21 before they enter the nonlinear portion 12, the generation of the third (intermodulation) signal 22 can be prevented or significantly reduced. In some embodiments, when the first signal 20 and the second signal 21 are initially generated in the nonlinear portion 12, the magnetic film 30 can limit or eliminate any signals (e.g., currents), including the first signal 20, the second signal 21, and the third signal 22, from exiting the nonlinear portion 12.

[0039] In some embodiments, two or more magnetic films 30 may be disposed on multiple linear portions 11 (e.g., on the shaft of an antenna mast that extends both above and below a nonlinear portion, such as a mounting bracket) to prevent or reduce PIM signals that may occur in the nonlinear portion 12 from propagating throughout other portions of the conductive passive medium 10. FIG. 3 is a side cutaway view of a conductive passive medium 10 having a magnetic absorbing film, according to one embodiment of the present disclosure. In the illustrated embodiment, the conductive passive medium 10 includes a conductive first linear passive medium portion 11 (or “first linear portion”) and a conductive second linear passive portion 11a (or “second linear portion”), both of which are adjacent to the conductive first nonlinear passive medium portion 12 (or “nonlinear portion”). That is, the first linear portion 11 and the second linear portion 11a are disposed on opposite sides of the nonlinear portion 12. The first magnetic film 30 is disposed proximate to the conductive outer surface 13 of the first linear portion 11 (e.g., wrapped around the first linear portion 11), and the second magnetic film 30a is disposed proximate to the conductive outer surface 13a of the second linear portion 11a. In some embodiments, at least one of the first magnetic film 30 and the second magnetic film 30a substantially conforms to at least a portion of the respective outer surface 13, 13a. In some embodiments, the first guided signal 20 and the second guided signal 21 propagate along the first linear portion 11 and enter the nonlinear portion 12. Upon entering the nonlinear portion 12, the first signal 20 and the second signal 21 mix to generate a third signal or intermodulation signal 22, which may then propagate out of the nonlinear portion 12 as a surface wave. By placing the first magnetic film 30 and the second magnetic film 30a on either side of the nonlinear section (i.e., on the first linear section 11 and the second linear section 11a), the magnetic films 30 and 30a can absorb either any electrical signals attempting to enter the nonlinear section 12 (which may mix to create a new signal at a new frequency) or any electrical signals attempting to exit the nonlinear section 12.By absorbing these signals (including any generated PIM signals), as well as absorbing the electromagnetic fields resulting from the signals or preventing the formation of electromagnetic fields, magnetic films 30 and 30a can eliminate or significantly reduce PIM interference.

[0040] The exemplary nonlinearity shown in FIG. 3 (i.e., nonlinearity 12) may be created by a mounting bracket or mounting hardware made of a material sufficiently different from, or loosely connected to, the conductive passive medium 10, whereby the difference results in a nonlinear component. In another example, the nonlinearity may be a rusted bolt or other fastener connecting two portions of the conductive passive medium 10 or connecting two portions of a material sufficiently different from the passive medium 10. FIGS. 4, 5, and 6 provide side cutaway views of similar embodiments of wireless communication systems, in which various components and / or conditions create nonlinearities and potentially lead to the generation of PIM interference as described herein. FIGS. 4, 5, and 6 each include similarly numbered elements that are common to FIG. 3 and perform similar functions. Similar numbered elements already described with respect to FIG. 3 may not be discussed again with respect to FIGS. 4, 5, and 6, except where necessary.

[0041] In some embodiments, the magnetic film is non-conductive. In some such or other embodiments, the magnetic film (e.g., first magnetic film 30) has a first major surface (e.g., major surface 31) that contacts a first portion of the first substantially linear passive medium and an opposing second major surface (e.g., major surface 32) that is at least partially exposed. For example, more than 50% of the area of ​​the second major surface may be exposed (e.g., not covered by an additional layer, such as a conductive layer).

[0042] 4 is a side cutaway view of a conductive passive medium 10 in which a nonlinearity 12-1 is created by a junction 14 between a first metal 11 and a second, dissimilar metal 15. For example, the surface contact area between the first metal 11 and the second, dissimilar metal 15 may have different electrochemical potentials, creating a nonlinear I / V curve (nonlinear junction). The use of one or more magnetic films 30 / 30a disposed on the outer surface 13 / 13a adjacent to the nonlinearity 12-1 can absorb / mitigate inductive signals propagating to the nonlinear junction and intermodulation signals propagating away from the nonlinear junction that may contribute to the creation of PIM effects.

[0043] FIG. 5 is a side view of conductive passive medium 10, in which nonlinearity 12-2 is created by a junction between metal 11 and metal oxide 17. For example, in some embodiments, in the presence of oxygen, an ionic chemical reaction can occur on the exposed metal surface, transferring electrons from the metal to oxygen molecules and creating negative oxygen ions that can create an oxide surface on the metal. The interface between the original metal and the created metal oxide can be a PIM source. Placing one or more magnetic films 30 adjacent to nonlinearity 12-2 can help mitigate the creation of PIM distortion, as described herein.

[0044] 6 is a side view of the conductive passive medium 10 in which a nonlinearity 12-3 is created by a rust region 18 in the conductive passive medium 10. Other conditions that can result in the creation of a nonlinearity include, but are not limited to, contaminants (e.g., dirty connections), loose connections, irregular metal-to-metal contact (e.g., a poor weld bead), and uneven contact surfaces. Placing one or more magnetic films 30 adjacent to the nonlinearity 12-3 can help mitigate the creation of PIM distortion, as described herein.

[0045] FIG. 7 is a graph illustrating the frequencies of transmitted and intermodulated signals in a wireless communication system, as described herein. The y-axis shows the relative amplitude (strength) of the signals, and the x-axis shows the relative frequency bands of the signals. In the center of the graph, the transmit band, or Tx band (in this example), includes two signals for intended transmission, labeled based on their corresponding frequencies, F1 and F2, as described elsewhere herein. Moving in either direction from the Tx band signals, there are an odd number of passive intermodulation signals that can arise from mixing of the Tx band signals. Moving from the F1 signal to the left side of the page, there are third-order intermodulations, fifth-order intermodulations, seventh-order intermodulations, etc. Moving from the F2 signal to the right side of the page, there are another third-order intermodulation, fifth-order intermodulation, seventh-order intermodulation, etc. For example, the signal immediately to the left of the F1 signal is third-order passive intermodulation emissions (PIM) generated by the equation nF1 + mF2 when n = +2 and m = -1 (i.e., 2F1 - F2). As can be seen in Figure 7, this third-order intermodulation falls within one of the intended receive bands, or Rx bands, used by the wireless communication system, and the amplitude of the signal is still relatively high. These types of PIM signals can interfere with the reception of legitimate intended signals by increasing the noise level and reducing the signal-to-noise ratio (SNR) of the signal. The use of a magnetic absorber as described herein can help mitigate the generation of these PIM distortion signals and improve the SNR of the intended wireless system signals.

[0046] 8A-8F are schematic diagrams of wireless communication systems according to some embodiments of the present disclosure. The wireless communication systems 500, 500′, 500″, 500′″, and 500′″ include a transmitter 150 (e.g., an antenna), a conductive first substantially linear passive medium 111 (sometimes referred to as a conductive first substantially linear passive medium portion), a conductive first substantially nonlinear passive medium 112 (sometimes referred to as a conductive first substantially nonlinear passive medium portion) disposed proximate to the first substantially linear passive medium 111, and a first magnetic film 130, 130′, 130″, 131, 130′″, and 130′″ covering at least a first portion of the first substantially linear passive medium 111 and about 20% or less of any conductive substantially nonlinear passive medium. Wireless communication system 500, 500', 500'', 500''', 500'''', or a system without transmitter 150, may be referred to as a system for reducing passive intermodulation. In some embodiments, the first magnetic film (e.g., 130, 130', 130'', 131, 130''', 130'''') substantially conforms to at least a first portion of the first substantially linear passive medium (e.g., nominally conforms, or conforms to a scale variation of no more than about three times the thickness of the magnetic film, or conforms to a scale variation of no more than about 20% or no more than about 10% of the largest dimension or diameter of the first portion). FIG. 8A is a schematic side view of wireless communication system 500, and FIG. 8B is a schematic rear view of wireless communication system 500. FIGS. 8C-8F are schematic rear views of wireless communication systems 500', 500'', 500''', and 500''', respectively, which correspond to wireless communication system 500 except for the placement of the magnetic film. In some embodiments, the first substantially linear passive medium 111 is part of a support structure 122 for supporting the transmitter 150, and the first substantially nonlinear passive medium 112 is attached to the support structure 122. In the illustrated embodiment, the support structure 122 is or includes an antenna mast 121, and the first substantially linear passive medium 111 is part of the antenna mast 121 and the first substantially nonlinear passive medium 112 is attached to the antenna mast 121.In other embodiments, the support structure may be other structures, such as those used to support antennas, within a cellular base station. In the illustrated embodiment, transmitter 150 is mounted to antenna mast 121 by first mounting bracket 141 and second mounting bracket 142. In other embodiments, a single mounting bracket may be used, or more than two mounting brackets may be used. One or more of the mounting brackets may be a substantially nonlinear medium, or the joint between mast 121 and one or more of the mounting brackets may be a substantially nonlinear medium, or rust on one or more of the mounting brackets, or rust on antenna mast 121 adjacent to one or more of the antenna masts (shown schematically in FIG. 8A on mounting bracket 141), may be a substantially nonlinear medium 112.

[0047] In some embodiments, the first magnetic film is at least partially wrapped around the first substantially linear passive medium. In the embodiment of Figures 8A-8B, the first magnetic film 130 is only partially wrapped around the first substantially linear passive medium 111. In some embodiments, the electrically conductive first substantially linear passive medium 111 is configured to receive first and second electromagnetic waves (e.g., corresponding to radiation 40 and 41) having different frequencies F1 and F2, respectively, and to generate first and second signals (e.g., corresponding to signals 20 and 21) at the respective frequencies F1 and F2, which propagate along a first path 113 through the first substantially linear passive medium 111 toward the electrically conductive first substantially nonlinear passive medium 112. In some embodiments, the first magnetic film 130 covers a first portion of the first substantially linear passive medium 111 along the first path 113, leaving a second portion 116 of the first substantially linear passive medium 111 exposed, with the first magnetic film 130 facing the first substantially nonlinear passive medium 112 and the second portion 116 facing away from the first substantially nonlinear passive medium 112. In some embodiments, the first magnetic film 130 wraps only partially around the first substantially linear passive medium 111, leaving the portion 116 of the substantially linear passive medium exposed between opposing ends 117 and 119 of the first magnetic film 130, with the exposed portion 116 facing away from the first substantially nonlinear passive medium 112.

[0048] In the embodiment of FIG. 8C , the first magnetic film 130′ completely wraps around the first substantially linear passive medium 111. In the illustrated embodiment, the ends of the magnetic film 130′ overlap each other. In some embodiments, the system 500″ includes the first magnetic film 130″ and further includes a second magnetic film 131 covering at least a second portion of the first substantially linear passive medium 111 and no more than about 20% of any electrically conductive substantially nonlinear passive medium. In the embodiment shown in FIGS. 8E-8F , the first magnetic films 130′″, 130′″ are helically wrapped around the first substantially linear passive medium. In some embodiments, the first magnetic film 130′″ is helically wrapped around the first substantially linear passive medium without overlapping. The magnetic film 130''' can be wrapped helically and without overlap around the first substantially linear passive medium 111, with or without gaps between adjacent wraps. It has been found that having no gaps between adjacent wraps facing the substantially nonlinear medium 112 results in improved reduction of intermodulation signals. In some embodiments, the first magnetic film 130'''' wraps helically and with overlap around the first substantially linear passive medium 111. In the embodiment shown in FIG. 8E, the first magnetic film 130''' covers a portion of the mounting bracket 141, which may be the substantially nonlinear medium. However, in some embodiments, the first magnetic film 130''' covers about 20% or less of the mounting bracket 141. In some embodiments, the first magnetic film 130''' (or magnetic film 130', 130'', 130'''', 131) covers at least a first portion of the first substantially linear passive medium or medium portion along the first path 113 and is positioned to attenuate the generated first and second signals propagating through the first substantially linear passive medium or medium portion more than the intermodulation signals generated in the first substantially nonlinear passive medium or medium portion.

[0049] As further described elsewhere herein, transmitter 150 is configured to transmit at least first and second electromagnetic waves 240 and 241 having different frequencies F1 and F2, respectively. When transmitter 150 transmits first and second electromagnetic waves 240 and 241, a first substantially linear passive medium or medium portion and a first substantially nonlinear passive medium or medium portion receive first and second electromagnetic waves 240 and 241 and generate first and second signals (e.g., corresponding to signals 20 and 21) propagating therethrough at respective frequencies F1 and F2. An intermodulation signal (e.g., corresponding to signal 22) or at least one intermodulation signal is generated from the first and second signals in the first substantially nonlinear passive medium or medium portion. The intermodulation signal or at least one intermodulation signal has a frequency F3 equal to nF1 + mF2, where m and n are positive or negative integers. In some embodiments, the first magnetic film reduces the occurrence of the intermodulation signal or at least one intermodulation signal by at least 2 dB, at least 3 dB, at least 3.5 dB, at least 4 dB, at least 5 dB, or at least 6 dB (e.g., 2 dB to 100 dB or 3 to 50 dB). In some embodiments, at least the first intermodulation signal and the second intermodulation signal are generated or produced from the first signal and the second signal in a first substantially nonlinear passive medium or medium portion. The first intermodulation signal and the second intermodulation signal have different frequencies F3 and F3', respectively. Each of F3 and F3' is equal to nF1 + mF2, where m and n are positive or negative integers. For example, the first intermodulation signal can correspond to one of the PIM signals schematically shown in Figure 7 (e.g., a signal having a frequency 2F1-F2), and the second intermodulation signal can correspond to a different one of the PIM signals schematically shown in Figure 7 (e.g., a signal having a frequency 3F1-2F2 or a signal having a frequency 2F2-F1). In some embodiments, the first magnetic film reduces each of the first intermodulation signal and the second intermodulation signal by at least 2 dB, at least 3 dB, at least 3.5 dB, at least 4 dB, at least 5 dB, or at least 6 dB (e.g., 2 dB to 100 dB or 3 dB to 50 dB).

[0050] In some embodiments, system 500, 500′, 500″, 500′″, 500″″ may include receiver 160, wherein when an intermodulation signal (e.g., corresponding to signal 22) or at least one intermodulation signal occurs or is generated in first substantially nonlinear passive medium 112, the intermodulation signal or at least one intermodulation signal radiates electromagnetic waves 242 at frequency F3, and receiver 160 detects the radiated electromagnetic waves 242. In some embodiments, a first magnetic film (e.g., 130, 130′, 130″, 130′″, 130′″, 131) or a combination of one or more magnetic films (e.g., 130″ and 131) reduces the radiated electromagnetic waves detected by the receiver by at least 2 dB. In some embodiments, the magnetic film reduces the radiated electromagnetic waves detected by the receiver by at least 3 dB, at least 3.5 dB, at least 4 dB, at least 5 dB, or at least 6 dB (e.g., between 3 dB and 100 dB or between 3.5 dB and 50 dB).

[0051] 9-10 are plots of permeability versus frequency for various magnetic films. FIG. 9 shows the permeability of 3M™ Flux Field Direction Material (FFDM) EM25TP-0100 (with a 100 micrometer thick composite magnetic FFDM layer). FIG. 10 shows the permeability of a related magnetic film including a magnetic absorbing layer with magnetic filler in a carrier resin. The real (μ) and imaginary (μ) portions of the permeability are shown. In some embodiments, the magnetic film has a relative permeability for at least one of F1 or F2 with an imaginary part of at least about 5, at least about 10, at least about 15, or at least about 20. In some such embodiments or other embodiments, the magnetic film has a relative permeability for F3 with an imaginary part of at least about 5, at least about 10, at least about 15, or at least about 20. In some embodiments, the relative permeability has an imaginary part of at least about 5, at least about 10, at least about 15, or at least about 20 for each of F1, F2, and F3. In some embodiments, the magnetic film includes a magnetic absorbing layer having an average thickness in the range of about 25 micrometers to about 1 mm, or in the range of about 40 micrometers to about 500 micrometers. In some embodiments, thinner absorbing layers may be used if the absorbing layer has high μ″ (e.g., at least about 10) and / or magnetic loss tangent (e.g., μ″ / μ′ of at least about 2) for F1 and / or F2, and thicker absorbing layers may be used if the μ″ and / or magnetic loss tangent of the layer are lower.

[0052] Examples / Comparative Examples A wireless communication system including an antenna (COMMSCOPE LNX-6513DS-A1M, available from CommScope, Inc., Hickory, NC) attached to an antenna mast (galvanized steel pole) using clamps with two mounting brackets (see, e.g., Figures 8A-8E) was placed in an anechoic chamber. The antenna height was approximately 4.5 feet, and the outer diameter of the antenna mast was approximately 2 inches. The antenna was positioned to radiate primarily away from the antenna mast. A PIM analyzer (SummiTek iQA850B, available from Kaelus, Spokane Valley, WA) was attached to the antenna's ports with coaxial cables. Two 43 dBm (20 W) continuous wave (CW) carriers at 871 MHz and 894 MHz were input to a single port of the antenna, and the reflected PIM signal at 848 MHz (2 * 871 MHz - 894 MHz) was measured by the PIM analyzer through the same port. In the absence of an external PIM source, the PIM analyzer reported a PIM signal of -126.9 dBm, corresponding to -169.9 dBc at 43 dBm input power, indicating a low noise floor that remained stable for at least 5 minutes. Experiments conducted using magnetic film involved placing the PIM source (e.g., steel wool), applying the magnetic film, and then removing the magnetic film, thus reestablishing a baseline in the absence of the magnetic film. This procedure ensured that the PIM source was not disturbed during the experiment.

[0053] A PIM signal was generated by placing steel wool on top of the lower mounting bracket, and then a 13-inch (vertical dimension parallel to the antenna mast) wide magnetic film was wrapped around the antenna mast near the lower mounting bracket. For magnetic films with the permeabilities shown in Figures 9-10, changing the width of the magnetic film from 13 inches to 6.5 inches and / or shifting the film's position approximately 4 inches up the mast (away from the lower mounting bracket) did not significantly change the PIM signal.

[0054] Steel wool was then placed on each of the upper and lower brackets. A magnetic film (a 6.5-inch-wide strip of 3M™ FFDM EM25TP-0150, a multilayer magnetic film with a total thickness of approximately 250 μm, including a liner, an adhesive layer, and a 150 μm-thick magnetically absorbing layer) was wrapped around the antenna mast at the top or bottom of the upper bracket and / or the top or bottom of the lower bracket. Placing a magnetic film on the top of the upper bracket had little effect on the PIM signal. Placing another magnetic film on the top of the lower bracket reduced the PIM signal by approximately 10 dB compared to when the magnetic film was not present. Removing these magnetic films and reestablishing the baseline without the magnetic film, and then placing a magnetic film on the bottom of the upper bracket and on the top of the lower bracket reduced the PIM signal by approximately 14 dB. By removing these magnetic films and re-establishing the baseline without the magnetic films, and then placing magnetic films above and below the upper bracket and above and below the lower bracket, the PIM signal was reduced by approximately 15 dB.

[0055] In another experiment, steel wool was placed on top of each of the upper and lower brackets, and then 3.5-inch, 2.5-inch, or 1-inch wide magnetic film (3M™ FFDM EM25TP-0150) was wrapped around the antenna mast at the top of the lower mounting bracket. With the 3.5-inch and 2.5-inch widths, the PIM signal was reduced by 9-10 dB. With the 1-inch width, the PIM signal was reduced by approximately 8 dB.

[0056] In another experiment, steel wool was placed on top of the lower bracket, and then a 3.5-inch-wide strip of 3M™ FFDM EM25TP-0150 was wrapped around the antenna mast at the top of the lower bracket, testing various wrap ratios. The magnetic film resulted in a 7-8 dB reduction in PIM signal at 100% wrap. Similar results were found for 30%, 50%, and 90% wrap ratios when the magnetic film faced the steel wool and the uncovered portion of the mast faced away from the steel wool. Significantly less reduction in PIM signal was observed when the uncovered portion of the mast faced the steel wool, or when using a spiral wrap with gaps between wraps and gaps between spiral wraps facing the steel wool.

[0057] In another experiment, steel wool was placed on top of the lower bracket, and then a 3.5-inch wide strip of 3M™ FFDM EM25TP was wrapped around the antenna mast at the top of the lower bracket (one complete revolution). Various thicknesses of magnetic absorbing layers were tested: EM25TP-0025 with a 25 μm thick magnetic absorbing layer, EM25TP-0050 with a 50 μm thick magnetic absorbing layer, EM25TP-0100 with a 100 μm thick magnetic absorbing layer, and EM25TP-0150 with a 150 μm thick magnetic absorbing layer. A 1-2 dB reduction in PIM signal was observed with the 25 μm and 50 μm thick magnetic absorbing layers, and a 4-5 dB reduction was observed with the 100 μm and 150 μm thick magnetic absorbing layers.

[0058] In another experiment, steel wool was placed on top of the lower bracket, and then a 3.5-inch wide strip of magnetic film was wrapped completely around the antenna mast twice on top of the lower bracket. 3M™ FFDM EM25TP-0150 and a magnetic film having a 60 μm thick magnetic absorbing layer and the permeability shown in FIG. 10 were tested. The magnetic film with the 60 μm thick magnetic absorbing layer also included a 10 μm thick adhesive layer. A 6 dB reduction in PIM signal was observed with 3M™ FFDM EM25TP-0150, while a 2 dB reduction was observed with the magnetic film having the permeability shown in FIG. 10.

[0059] In another experiment, steel wool was placed on top of the lower bracket, and then a 3.5-inch wide strip of magnetic film was wrapped completely around the antenna mast twice on top of the lower bracket. The magnetic films tested included 3M™ FFDM EM25TP-0150, a magnetic film having a 10 μm thick adhesive layer and a 60 μm thick magnetic absorbing layer with the permeability shown in FIG. 10, and a magnetic film formed from a laminate of two magnetic films, each having a 10 μm thick adhesive layer and a 60 μm thick magnetic absorbing layer with the permeability shown in FIG. 10. A reduction of approximately 4 to 5 dB in PIM signal was observed with the 3M™ FFDM EM25TP-0150 film, while a reduction of 2 to 3 dB was observed with the film having two 60 μm thick magnetic absorbing layers, and a reduction of 1 to 2 dB was observed with the magnetic film having one 60 μm thick magnetic absorbing layer.

[0060] Terms such as "about" will be understood by those of ordinary skill in the art in the context in which they are used and described herein. Unless otherwise clear to those of ordinary skill in the art in the context in which they are used and described herein, the use of "about" as applied to quantities expressing feature sizes, amounts, and physical characteristics will be understood to mean within 10 percent of a particular value. A quantity given as about or approximately a particular value may be the exact particular value. For example, unless otherwise clear to those of ordinary skill in the art in the context in which they are used and described herein, an amount having a value of about 1 means that the amount has a value between 0.9 and 1.1, and may even be 1.

[0061] All references, patents, or patent applications referenced above are hereby incorporated by reference in their entirety. In the event of any inconsistency or contradiction between any portion of the incorporated reference and this application, the information in the foregoing statement shall prevail.

[0062] Descriptions of elements in the figures should be understood to apply equally to corresponding elements in other figures unless otherwise indicated. While specific embodiments have been illustrated and described herein, those skilled in the art will recognize that the specific embodiments illustrated and described may be replaced by various alternative and / or equivalent embodiments without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Accordingly, the present disclosure is intended to be limited only by the claims and equivalents thereof. In addition to the embodiments, the following aspects will be noted. (Appendix 1) 1. A wireless communication system, comprising: a transmitter configured to transmit at least a first electromagnetic wave and a second electromagnetic wave having different frequencies F1 and F2, respectively; an electrically conductive first substantially linear passive medium; an electrically conductive first substantially nonlinear passive medium disposed proximate to the first substantially linear passive medium; a first magnetic film covering at least a first portion of the first substantially linear passive medium and no more than about 20% of any electrically conductive substantially nonlinear passive medium, wherein when the transmitter transmits the first electromagnetic wave and the second electromagnetic wave, the first substantially linear passive medium and the first substantially nonlinear passive medium receive the first electromagnetic wave and the second electromagnetic wave and generate first and second signals propagating therethrough at the respective frequencies F1 and F2, at least one intermodulation signal generates in the first substantially nonlinear passive medium from the first and second signals, the at least one intermodulation signal having a frequency F3 equal to nF1 + mF2, where m and n are positive or negative integers, and the first magnetic film reduces the generation of the at least one intermodulation signal by at least 2 dB. (Appendix 2) 2. The wireless communication system of claim 1, wherein any intermodulation signal generated from the first signal and the second signal in the first substantially linear passive medium has an amplitude A, and the amplitude of at least one intermodulation signal generated in the first substantially nonlinear passive medium is B, and B is at least 3 dB greater than A. (Appendix 3) 3. The wireless communication system of claim 1 or 2, wherein the first magnetic film is at least partially wrapped around the first substantially linear passive medium. (Appendix 4) 4. The wireless communication system of claim 1, wherein the first magnetic film is only partially wrapped around the first substantially linear passive medium, leaving a portion of the substantially linear passive medium exposed between opposite ends of the first magnetic film, the exposed portion facing away from the first substantially nonlinear passive medium. (Appendix 5) 4. The wireless communication system of claim 1, wherein the first magnetic film is spirally wrapped around the first substantially linear passive medium. (Appendix 6) 6. A wireless communication system according to any one of claims 1 to 5, wherein the first substantially linear passive medium is part of a support structure for supporting the transmitter, and the first substantially nonlinear passive medium is attached to the support structure. (Appendix 7) 1. A wireless communication system, comprising: a transmitter configured to transmit at least a first electromagnetic wave and a second electromagnetic wave having different frequencies F1 and F2, respectively; a conductive first substantially nonlinear passive medium portion; a conductive first substantially linear passive medium portion disposed proximate to the first substantially nonlinear passive medium portion, the conductive first substantially linear passive medium portion receiving the first electromagnetic wave and the second electromagnetic wave when the transmitter transmits the first electromagnetic wave and the second electromagnetic wave, and generating first and second signals at the frequencies F1 and F2, respectively, the first and second signals propagating along a first path through the first substantially linear passive medium portion toward the conductive first substantially nonlinear passive medium portion, an intermodulation signal being generated from the first and second signals in the first substantially nonlinear passive medium portion, the intermodulation signal having a frequency F3 equal to nF1+mF2, where m and n are positive or negative integers; a first magnetic film arranged to cover at least a first portion of the first substantially linear passive medium portion along the first path and to attenuate the generated first and second signals propagating through the first substantially linear passive medium portion to a greater extent than the intermodulation signal generated in the first substantially nonlinear passive medium portion; 2. A wireless communication system comprising: (Appendix 8) 8. The wireless communication system of claim 7, wherein any intermodulation signal generated from the first signal and the second signal in the first substantially linear passive medium section has an amplitude A, and the amplitude of the intermodulation signal generated in the first substantially nonlinear passive medium section is B, and B is at least 3 dB greater than A. (Appendix 9) 9. The wireless communication system of claim 7 or 8, wherein at least the first intermodulation signal and the second intermodulation signal generate from the first signal and the second signal in the first substantially nonlinear passive medium portion, the first intermodulation signal and the second intermodulation signal having different frequencies F3 and F3', respectively, where F3 and F3' are each equal to nF1 + mF2, where m and n are positive or negative integers, and the first magnetic film reduces the first intermodulation signal and the second intermodulation signal each by at least 2 dB. (Appendix 10) 10. The wireless communication system according to any one of appendices 1 to 9, wherein the difference between F1 and F2 is about 5 MHz to about 1 GHz. (Appendix 11) 11. The wireless communication system according to any one of appendices 1 to 10, wherein each of F1 and F2 is about 100 MHz to about 10 GHz. (Appendix 12) 1. A system for reducing passive intermodulation, comprising: a first substantially linear passive medium that is electrically conductive and configured to receive first and second electromagnetic waves having different frequencies F1 and F2, respectively, and to generate first and second signals at the respective frequencies F1 and F2, wherein the first and second signals propagate along a first path through the first substantially linear passive medium toward a first substantially nonlinear passive medium, and an intermodulation signal is generated from the first and second signals in the first substantially nonlinear passive medium, the intermodulation signal having a frequency F3 equal to nF1+mF2, where m and n are positive or negative integers; a first magnetic film covering at least a first portion of the first substantially linear passive medium along the first path and covering no more than about 20% of the first substantially nonlinear passive medium; Including, the system. (Appendix 13) 1. A system for reducing passive intermodulation, comprising: a first substantially linear passive medium that is electrically conductive and configured to receive first and second electromagnetic waves having different frequencies F1 and F2, respectively, and to generate first and second signals at the respective frequencies F1 and F2, wherein the first and second signals propagate along a first path through the first substantially linear passive medium toward a first substantially nonlinear passive medium, and an intermodulation signal is generated from the first and second signals in the first substantially nonlinear passive medium, the intermodulation signal having a frequency F3 equal to nF1+mF2, where m and n are positive or negative integers; a first magnetic film covering a first portion of the first substantially linear passive medium along the first path and leaving a second portion of the first substantially linear passive medium exposed, the first magnetic film facing the first substantially nonlinear passive medium and the second portion facing an opposite side from the first substantially nonlinear passive medium; Including, the system. (Appendix 14) 14. The system of claim 12 or 13, wherein any intermodulation signal generated from the first signal and the second signal in the first substantially linear passive medium has an amplitude A, and the amplitude of the intermodulation signal generated in the first substantially nonlinear passive medium is B, and B is at least 3 dB greater than A. (Appendix 15) 15. The system of any one of claims 12 to 14, further comprising a receiver, wherein when the intermodulation signal is generated, the intermodulation signal radiates an electromagnetic wave at a frequency F3, the receiver detects the radiated electromagnetic wave, and the first magnetic film reduces the radiated electromagnetic wave detected by the receiver by at least 2 dB.

Claims

1. 1. A wireless communication system, comprising: a transmitter configured to transmit at least a first electromagnetic wave and a second electromagnetic wave having different frequencies F1 and F2, respectively; a first substantially linear passive medium that is electrically conductive; an electrically conductive first substantially nonlinear passive medium disposed proximate to the first substantially linear passive medium; a first magnetic film covering at least a first portion of the first substantially linear passive medium and no more than about 20% of any electrically conductive substantially nonlinear passive medium, wherein when the transmitter transmits the first electromagnetic wave and the second electromagnetic wave, the first substantially linear passive medium and the first substantially nonlinear passive medium receive the first electromagnetic wave and the second electromagnetic wave and generate first and second signals propagating therethrough at the respective frequencies F1 and F2, at least one intermodulation signal generates in the first substantially nonlinear passive medium from the first and second signals, the at least one intermodulation signal having a frequency F3 equal to nF1 + mF2, where m and n are positive or negative integers, and the first magnetic film reduces the generation of the at least one intermodulation signal by at least 2 dB.

2. 2. The wireless communication system of claim 1, wherein any intermodulation signal generated from the first signal and the second signal in the first substantially linear passive medium has an amplitude A, and the at least one intermodulation signal generated in the first substantially nonlinear passive medium has an amplitude B, where B is at least 3 dB greater than A.

3. 3. The wireless communication system of claim 1, wherein the first magnetic film is at least partially wrapped around the first substantially linear passive medium.

4. 4. The wireless communication system of claim 1, wherein the first magnetic film is only partially wrapped around the first substantially linear passive medium, leaving a portion of the substantially linear passive medium exposed between opposite ends of the first magnetic film, the exposed portion facing away from the first substantially nonlinear passive medium.

5. 4. The wireless communication system according to claim 1, wherein the first magnetic film is spirally wrapped around the first substantially linear passive medium.

6. 6. A wireless communication system according to claim 1, wherein the first substantially linear passive medium is part of a support structure for supporting the transmitter, and the first substantially nonlinear passive medium is attached to the support structure.

7. 1. A wireless communication system, comprising: a transmitter configured to transmit at least a first electromagnetic wave and a second electromagnetic wave having different frequencies F1 and F2, respectively; a first substantially nonlinear passive medium portion that is electrically conductive; a first substantially linear passive medium portion of an electrically conductive medium disposed proximate to the first substantially nonlinear passive medium portion, the first substantially linear passive medium portion receiving the first electromagnetic wave and the second electromagnetic wave when the transmitter transmits the first electromagnetic wave and the second electromagnetic wave, and generating a first signal and a second signal at the respective frequencies F1 and F2, the first signal and the second signal propagating along a first path through the first substantially linear passive medium portion toward the first substantially nonlinear passive medium portion, an intermodulation signal being generated from the first signal and the second signal in the first substantially nonlinear passive medium portion, the intermodulation signal having a frequency F3 equal to nF1 + mF2, where m and n are positive or negative integers; a first magnetic film arranged to cover at least a first portion of the first substantially linear passive medium portion along the first path and to attenuate the generated first and second signals propagating through the first substantially linear passive medium portion to a greater extent than the intermodulation signals generated in the first substantially nonlinear passive medium portion; 2. A wireless communication system comprising:

8. 8. The wireless communication system of claim 7, wherein any intermodulation signal generated from the first signal and the second signal in the first substantially linear passive medium section has an amplitude A, and the amplitude of the intermodulation signal generated in the first substantially nonlinear passive medium section is B, and B is at least 3 dB greater than A.

9. 9. The wireless communication system of claim 7, wherein at least a first intermodulation signal and a second intermodulation signal are generated from the first signal and the second signal in the first substantially nonlinear passive medium portion, the first intermodulation signal and the second intermodulation signal having different frequencies F3 and F3', respectively, F3 and F3' each equal to nF1+mF2, where m and n are positive or negative integers, and the first magnetic film reduces the first intermodulation signal and the second intermodulation signal by at least 2 dB, respectively.

10. 10. A wireless communication system according to any one of claims 1 to 9, wherein the difference between F1 and F2 is between about 5 MHz and about 1 GHz.

11. 11. The wireless communication system according to claim 1, wherein each of F1 and F2 is between about 100 MHz and about 10 GHz.

12. 1. A system for reducing passive intermodulation, comprising: a first substantially linear passive medium that is electrically conductive and configured to receive first and second electromagnetic waves having different frequencies F1 and F2, respectively, and to generate first and second signals at the respective frequencies F1 and F2, wherein the first and second signals propagate along a first path through the first substantially linear passive medium toward a first substantially nonlinear passive medium, and an intermodulation signal is generated from the first and second signals in the first substantially nonlinear passive medium, the intermodulation signal having a frequency F3 equal to nF1 + mF2, where m and n are positive or negative integers; a first magnetic film covering at least a first portion of the first substantially linear passive medium along the first path and covering no more than about 20% of the first substantially nonlinear passive medium; Including, the system.

13. 1. A system for reducing passive intermodulation, comprising: a first substantially linear passive medium that is electrically conductive and configured to receive first and second electromagnetic waves having different frequencies F1 and F2, respectively, and to generate first and second signals at the respective frequencies F1 and F2, wherein the first and second signals propagate along a first path through the first substantially linear passive medium toward a first substantially nonlinear passive medium, and an intermodulation signal is generated from the first and second signals in the first substantially nonlinear passive medium, the intermodulation signal having a frequency F3 equal to nF1 + mF2, where m and n are positive or negative integers; a first magnetic film covering a first portion of the first substantially linear passive medium along the first path and leaving a second portion of the first substantially linear passive medium exposed, the first magnetic film facing the first substantially nonlinear passive medium and the second portion facing an opposite side from the first substantially nonlinear passive medium; Including, the system.

14. 14. The system of claim 12 or 13, wherein any intermodulation signal generated from the first signal and the second signal in the first substantially linear passive medium has an amplitude A, and the amplitude of the intermodulation signal generated in the first substantially nonlinear passive medium is B, and B is at least 3 dB greater than A.

15. 15. The system of claim 12, further comprising a receiver, wherein when the intermodulation signal is generated, the intermodulation signal radiates an electromagnetic wave at a frequency F3, the receiver detects the radiated electromagnetic wave, and the first magnetic film reduces the radiated electromagnetic wave detected by the receiver by at least 2 dB.

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