System with magnetic film for reducing passive intermodulation

Abstract

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

Description

BACKGROUND

[0001] As wireless communication networks evolve, signal quality (and more specifically, signal-to-noise ratio or SNR) becomes increasingly important. High order modulation is used to achieve very high data rates and requires a corresponding higher level of SNR. One common cause of SNR degradation is passive intermodulation (PIM) distortion, which can significantly degrade the performance and capacity of a network. PIM distortion is formed when multiple frequencies encounter a non-linear material or feature, which then generates sum and difference combinations (products) of the fundamental and its harmonics. The resulting products often appear in the uplink / receive band where the signals of interest are very weak, making coherent reception very difficult or impossible.

[0002] There are many mechanisms by which PIM can be formed or propagated. Generally, the interaction and interconnection of electrically conductive mechanical components in a system can form non-linear elements in the system. In some cases, non-linearity can be caused by poor intermetallic contact at the location of an antenna mounting bracket, or where the bracket includes a joint between dissimilar materials. Other causes of non-linearity can be contamination, loose connections, nearby metal objects, or various other causes. SUMMARY

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

[0004] In some aspects of the specification, a wireless communication system is provided. The wireless communication system includes a transmitter configured to transmit at least a first radio wave and a second radio wave having respective different frequencies Fl and F2; an electrically conductive first passive linear medium; an electrically conductive first passive non-linear medium disposed proximate the first passive linear medium; and a first magnetic film covering at least a first portion of the first passive linear medium and no more than about 20% of any electrically conductive passive non-linear medium. When the transmitter transmits the first radio wave and the second radio wave, the first passive linear medium and the first passive non-linear medium receive the first radio wave and the second radio wave and generate first and second signals propagating therein at respective frequencies Fl and F2. At least one intermodulation signal is generated in the first passive non-linear medium from the first and second signals. The at least one intermodulation signal has a frequency F3 equal to nFl + mF2, where m and n are positive or negative integers. The first magnetic film reduces the generation of the at least one intermodulation signal by at least 2 dB.

[0005] In some aspects of the description, a wireless communication system is provided. The wireless communication system includes a transmitter configured to transmit at least a first radio wave and a second radio wave having respective different frequencies Fl and F2; a conductive first passive substantially nonlinear medium portion; and a conductive first passive substantially linear medium portion disposed proximate to the first passive substantially nonlinear medium portion such that, when the transmitter transmits the first radio wave and the second radio wave, the first passive substantially linear medium portion receives the first radio wave and the second radio wave and generates the first signal and the second signal at the respective frequencies Fl and F2. The first signal and the second signal propagate in the first passive substantially linear medium portion along a first path toward the conductive first passive substantially nonlinear medium portion. An intermodulation signal is generated in the first passive substantially nonlinear medium portion from the first signal and the second signal. The intermodulation signal has a frequency F3 equal to nFl + mF2, where m and n are positive or negative integers. The wireless communication system further includes a first magnetic film covering at least a first portion of the first passive substantially linear medium portion along the first path and disposed to attenuate the generated first signal and second signal propagating in the first passive substantially linear medium portion more than the generated intermodulation signal in the first passive substantially nonlinear medium portion.

[0006] In some aspects of the description, a system for reducing passive intermodulation is provided. The system includes a conductive first passive substantially linear medium configured to receive a first radio wave and a second radio wave having respective different frequencies Fl and F2 and generate a first signal and a second signal at the respective frequencies Fl and F2. The first signal and the second signal propagate in the first passive substantially linear medium along a first path toward the conductive first passive substantially nonlinear medium. An intermodulation signal is generated in the first passive substantially nonlinear medium from the first signal and the second signal. The intermodulation signal has a frequency F3 equal to nFl + 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 passive substantially linear medium and no more than about 20% of the first passive substantially nonlinear medium along the first path.

[0007] In some aspects of the description, a system for reducing passive intermodulation is provided. The system includes a conductive first passive linear medium configured to receive first and second radio waves having respective different frequencies F1 and F2 and generate first and second signals at the respective frequencies F1 and F2. The first and second signals propagate in the first passive linear medium along a first path towards the conductive first passive non-linear medium. An intermodulation signal is generated in the first passive non-linear medium from the first and second signals. 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 passive linear medium along the first path and exposing a second portion of the first passive linear medium. The first magnetic film faces the first passive non-linear medium and the second portion faces away from the first passive non-linear medium.

[0008] These and other aspects will become apparent from the following detailed description. However, in any case, this brief summary should not be construed to limit the claimed subject matter. BRIEF DESCRIPTION OF DRAWINGS

[0009] Figure 1 Schematic side view of a wireless communication system according to one embodiment of the description;

[0010] Figure 2 Schematic side view of a conductive passive medium capable of propagating signals in a wireless communication system according to one embodiment of the description;

[0011] Figure 3 Schematic side view of a conductive passive medium having a magnetic absorbing film according to one embodiment of the description;

[0012] Figure 4 Schematic side view of a conductive passive medium according to one embodiment of the description showing a junction between a first conductive portion and a second conductive portion;

[0013] Figure 5 Schematic side view of a conductive passive medium according to an alternative embodiment of the description showing a junction between a metal and a metal oxide;

[0014] Figure 6 Schematic side view of a conductive passive medium according to an alternative embodiment of the description showing metal corrosion;

[0015] Figure 7 Schematic view showing transmission and intermodulation frequencies of a wireless communication system according to one embodiment of the description;

[0016] Figures 8A-8F is a graph of magnetic permeability versus frequency for a magnetic film according to some embodiments of the present specification; and

[0017] Figures 9-10 is a graph of magnetic permeability versus frequency for a magnetic film according to some embodiments of the present specification. DETAILED DESCRIPTION

[0018] In the following description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration various embodiments. The drawings are not necessarily to scale. It is to be understood that other embodiments can be utilized and structural or logical changes can be made without departing from the scope or spirit of the present specification. The following detailed description, therefore, is not to be taken in a limiting sense.

[0019] As wireless communication networks evolve, signal quality (and more specifically, signal-to-noise ratio or SNR) becomes increasingly important. High order modulation (64QAM, 256QAM, etc.) is used to achieve very high data rates, and requires a corresponding higher level of SNR. One common cause of SNR degradation is passive intermodulation (PIM) distortion, which can significantly degrade the performance and capacity of a network. PIM distortion (simply “PIM”) is formed when multiple frequencies encounter a non-linear material or feature, which subsequently produces sum and difference combinations (products) of the base frequencies and their harmonics. The resulting products (especially 3rd, 5th, and / or 7th order products) often fall in the uplink / receive band where the signals of interest are very weak, making coherent reception very difficult or impossible.

[0020] PIM is a form of electromagnetic interference that occurs in a wireless communication system 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 transmit path of the system. PIM interference becomes particularly pronounced in nodes that transmit at high power, such as cellular base station antennas. PIM is generated when two or more signals at different frequencies mix with each other due to non-linearity in mechanical components of the system. The two signals can combine (through amplitude modulation) to produce sum and difference signals (including within harmonics of the signals) within the operating band of the wireless system, causing interference.

[0021] There are many mechanisms that can be used to create or propagate PIM. Generally, the interaction and interconnection of electrically conductive mechanical components in a system can create nonlinear elements in the system. In some cases, the nonlinearity can be caused by poor metal-to-metal contact at the location of an antenna mounting bracket, or where the bracket includes a joint between dissimilar materials. For example, the fundamental frequencies (e.g., Fl 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 can encounter the mounting bracket (i.e., a nonlinearity), and can mix within the nonlinearity to create a third signal at a new frequency F3 (i.e., an intermodulation signal). The intermodulation signal can be radiated from the bracket as PIM, and / or conducted away from the bracket through electrically conductive linear portions that can act as antennas for the PIM and radiate the PIM out with better efficiency than the non-linear bracket. An electrically conductive shield is often used to encase the bracket, preventing PIM from being radiated by the bracket, but the intermodulation signal (e.g., current) can still travel through the structure from the bracket and to other antennas, ultimately re-radiating and degrading the network.

[0022] Other causes of nonlinearity (and, thus, PIM) can be contamination (e.g., rust, corrosion, dirt, oxidation, etc.), loose connections, nearby metal objects (e.g., guy wires, anchors, roof shingles, pipes, etc.), or a variety of other causes.

[0023] According to some aspects of the present specification, a wireless communication system (e.g., a system including a cellular base station as a component) includes an electrically conductive passive medium (e.g., a metal structure of an antenna mast) capable of simultaneously propagating first and second electromagnetic signals at different respective frequencies Fl and F2 along the same. 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 can be generated from two radio frequency (RF) signals transmitted at similar but different frequencies (i.e., Fl and F2). In some embodiments, each of Fl and F2 is between about 100 MHz and about 10 GHz, or between about 200 MHz and about 5 GHz, or between about 300 MHz and about 3 GHz. In some such embodiments or in other embodiments, the difference between Fl and F2 is between about 5 MHz and about 1 GHz, or between about 10 MHz and about 900 MHz, or between about 10 MHz and about 800 MHz, or between about 10 MHz and about 700 MHz.

[0024] For example, in one embodiment, F1 can be 869 MHz and F2 can be 894 MHz, where the adjacent receive band is used for signals returned from external devices (e.g., mobile devices). For example, the adjacent receive band can be between 824 MHz and 849 MHz. Another receive band can be adjacent at a range of frequencies above the transmit band (i.e., frequencies higher than the transmit band frequency range). These base frequencies can mix to form products at new frequencies based on the equation nF1 + mF2, where m and n can be positive or negative integers. In this example, a simple addition of modulated signals (e.g., when m and n are both +1) would yield a signal of 869 + 894 = 1763 MHz, and a difference between signals (e.g., when n is +1 and m is -1) would be 894 - 869 = 25 MHz. Both 25 MHz and 1763 MHz are outside the receive band of interest for a cellular system, so these signals would be meaningless to that particular cellular system (but these frequencies can fall within a receive band or spectrum of interest for another adjacent system, so can still cause PIM interference in those systems). However, when these signals combine to form 3rd order (when the sum of the absolute values of m and n is 3) and sometimes higher order products, these signals can generate PIM signals within the receive band of interest. For example, 2F1 - F2 (844 MHz) and 2F2 - F1 (919 MHz) produce 3rd order products within the receive portion of the cellular band that can cause PIM distortion.

[0025] In some embodiments, the electrically conductive passive medium includes an electrically conductive first passive substantially linear medium portion adjacent to an electrically conductive first passive substantially nonlinear medium portion. An intermodulation signal can be generated in the first passive substantially nonlinear medium portion from a first signal and a second signal. The intermodulation signal can be generated based on a nonlinear interaction between the first signal and the second signal (e.g., an indirect interaction resulting from the first signal and the second signal interacting with the first passive substantially nonlinear medium). For example, in some embodiments, the electrically conductive first passive substantially linear medium portion can be a metal pole (e.g., a galvanized steel pole) to which a cellular antenna is mounted, and the electrically conductive first passive substantially nonlinear medium portion can be a mounting bracket of a dissimilar metal. This junction or meeting point of dissimilar materials can form a nonlinearity similar to a diode, which causes the first signal and the second signal (at frequencies F1 and F2) to mix to form an intermodulation signal (PIM) at a new frequency. In some embodiments, the nonlinearity can be formed by a junction between two dissimilar metals. In some embodiments, the nonlinearity can be formed by a junction between a metal and a metal oxide (e.g., a metal oxide resulting from oxidation). In some embodiments, the nonlinearity can be reactive through a corrosion or contamination area (e.g., a rusted area, a contaminant such as dirt, a poor metal-to-metal contact, etc.).

[0026] A medium portion is a portion of a medium. For example, a medium portion can be a contact or junction between a medium and an adjacent material. A contact or junction between adjacent materials can define a substantially nonlinear medium as including the junction or contact and having electrical properties that are significantly affected by the junction or contact. For example, in some embodiments, for a nonlinearity formed by a junction between two metals having different Fermi levels, a charge transfer occurs across the junction to form a dipole that equalizes the Fermi levels and significantly affects the electrical properties of a thin region around the junction (e.g., small in thickness compared to the overall size of the metal, but possibly large compared to the atomic lattice spacing of the metal), such that the region defines a substantially nonlinear medium. A first (respectively, second, third, etc.) passive substantially linear medium portion can be a first (respectively, second, third, etc.) passive substantially linear medium because a portion of a medium can be considered a medium, and similarly, a first (respectively, second, third, etc.) passive substantially nonlinear medium portion can be a first (respectively, second, third, etc.) passive substantially nonlinear medium.

[0027] In some embodiments, a first magnetic film can be disposed proximate to a conductive outer surface of the first substantially linear portion. In some embodiments, the wireless communication system can further include a conductive second passive substantially linear medium portion adjacent to the conductive first passive substantially nonlinear medium portion, opposite the first passive substantially linear medium portion (e.g., the substantially nonlinear portion can be “sandwiched” between the first substantially linear portion and the second substantially linear portion). In some embodiments, a second magnetic film can be disposed proximate to a conductive outer surface of the second substantially linear portion, such that when the first signal and the second signal propagate along the first linear portion toward the substantially nonlinear portion, the first magnetic film reduces generation of intermodulation signals in the first substantially nonlinear portion by absorbing a portion of the first signal and the second signal. In some embodiments, at least some of the remaining portions of the first signal and the second signal can mix in the first substantially nonlinear portion, generating intermodulation signals that propagate through the first substantially nonlinear portion and the second linear portion, where the intermodulation signals are at least partially absorbed by the second magnetic film.

[0028] In some embodiments, the first signal and the second signal can be induced by electromagnetic radiation emitted from an antenna coupled to the conductive passive linear medium. In some embodiments, the first signal and the second signal can be induced by electromagnetic radiation radiated from a second passive substantially nonlinear medium coupled to the first passive substantially linear medium portion. That is, PIM distortion can be generated in and radiate from a second substantially nonlinear portion coupled to a substantially linear portion, causing signals to be induced in the substantially linear portion.

[0029] In some embodiments, the intermodulation signal can have a frequency F3 equal to nFl + mF2, which propagates along the first passive substantially nonlinear medium, where m and n can be positive or negative integers. For example, as discussed elsewhere herein, n can be 2 and m can be -1, or n can be -1 and m can 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 can equal -1 and m equal +2, such that F3 equals 2F2 - Fl. In some embodiments, n can equal +2 and m equal -1, such that F3 equals 2Fl - F2. In some embodiments, n can equal +1 and m equal +1, such that F3 equals Fl + F2. In some embodiments, n can equal +2 and m equal +2, such that F3 equals 2Fl + 2F2. In some embodiments, both Fl and F2 are less than about 6 GHz. In some embodiments, both Fl and F2 are between about 600 MHz and 4 GHz. In some embodiments, both Fl and F2 are between about 600 MHz and 800 MHz. In some embodiments, Fl and F2 are frequencies that are less than about 100 MHz apart, or less than about 50 MHz apart.

[0030] In some embodiments, the first magnetic film is disposed proximate to the electrically conductive outer surface of the first substantially linear medium portion, such that when the first signal and the second signal propagate along the first passive substantially linear medium portion toward the first passive substantially nonlinear medium portion, the magnetic film reduces the generation of intermodulation currents in the first passive substantially nonlinear medium by attenuating at least a portion of the first signal and the second signal (e.g., preventing propagation of the signals through the corresponding structure). In some embodiments, the magnetic film can reduce the strength of intermodulation radiation generated by and radiated from the first passive substantially nonlinear medium portion by at least 2 dB, or at least 3 dB, or at least 3.5 dB, or at least 4 dB, or at least 5 dB, or at least 6 dB (e.g., 2 dB to 100 dB or 3 dB to 50 dB).

[0031] The relative magnetic permeability of the magnetic film can have a real part greater than about 10 for at least one frequency in the range of about 100 MHz to about 10 GHz. The relative magnetic permeability of the magnetic film can have an imaginary part greater than about 5 or within any range described elsewhere herein for at least one frequency in the range of about 100 MHz to about 10 GHz. The magnetic film can be electrically conductive or include an electrically conductive layer, or the magnetic film can be electrically non-conductive. In some embodiments where the film has more than one layer, the electrically non-conductive film can have an electrical resistivity of at least 100 Ωm along each direction (e.g., along orthogonal in-plane directions and along the thickness direction) and for each layer of the film (evaluated at low frequency (e.g., about 1 kHz or lower) or statically (direct current)). The electrically non-conductive film can also be referred to as an electrically insulating film.

[0032] In some embodiments, the first magnetic film or other magnetic film can be a magnetic absorber. One example of a magnetic absorber is 3M™ TM EMI Shielding Absorber AB6000HF Series Shielding Films. Other suitable magnetic absorbers include 3M™ TM Flux Field Directional Material (FFDM), such as 3M™ TM FFDM EM25TP. In some embodiments, the magnetic film includes an electrically conductive layer (e.g., 3M™ TM EMI Shielding Absorber AB6000HF Film includes an electrically conductive shielding layer). In other embodiments, an electrically conductive layer is not included (e.g., 3M™ TM Flux Field Directional Material (FFDM) EM25TP Film is available without an electrically conductive layer).

[0033] In some embodiments, the magnetic film can attenuate the first signal and the second signal by absorbing at least a portion of the magnetic field generated by the first signal and the second signal. In some embodiments, the first magnetic film does not cover any portion of the first substantially nonlinear medium portion 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 passive substantially linear medium (e.g., along the first path) and no more than about 50% of the first passive substantially nonlinear medium or no more than about 50% of any electrically conductive passive substantially nonlinear medium. In some embodiments, the first magnetic film covers at least a first portion of the first passive substantially linear medium (e.g., along the first path) and no more than about 20% of the first passive substantially nonlinear medium or no more than about 20% of any electrically conductive passive substantially nonlinear medium. In some embodiments, the first magnetic film covers at least a first portion of the first passive substantially linear medium (e.g., along the first path) and no more than about 10% of the first passive substantially nonlinear medium or no more than about 10% of any electrically conductive passive substantially nonlinear medium. The X% (e.g., 50%, 20%, or 10%) of the electrically conductive passive substantially nonlinear medium refers to the X% of the entire contiguous nonlinear portion of the electrically conductive passive medium, and not just the X% of some portion of the nonlinear portion. For example, in embodiments where a rusted portion of the first mounting bracket is the substantially nonlinear medium, the X% of the electrically conductive passive substantially nonlinear medium refers to the X% of the entire rusted portion of the first mounting bracket. As another example, in embodiments where a contiguous first rusted portion of the first mounting bracket is the first substantially nonlinear medium and a contiguous second rusted portion of the first mounting bracket or the second mounting bracket is the second substantially nonlinear medium, where the first rusted portion and the second rusted portion are spaced apart from each other (i.e., the first rusted portion and the second rusted portion are not contiguous with each other), covering no more than about X% of any electrically conductive passive substantially nonlinear medium means covering no more than X% of the entire first rusted portion and no more than X% of the entire second rusted portion. Covering X% of the electrically conductive passive substantially nonlinear medium with a magnetic film can be understood to mean covering X% of the area of the substantially nonlinear medium facing the magnetic film. For example, in embodiments where the mounting bracket is the nonlinear medium, covering X% of the substantially nonlinear medium can be understood to mean covering X% of the area of the outer surface of the mounting bracket. As another example, in embodiments where the substantially nonlinear medium is defined by a junction, covering X% of the substantially nonlinear medium can be understood to mean covering X% of the area of the junction.

[0034] According to some aspects of the present specification, a wireless communication system includes an antenna (e.g., a cellular antenna), a conductive passive substantially linear medium portion, and a conductive passive substantially nonlinear medium portion electrically interconnected (e.g., a joint of two dissimilar materials such as a mounting bracket and an antenna mast), such that when the antenna radiates first and second waves of electromagnetic at different respective frequencies F1 and F2, the first and second waves induce respective first and second signals propagating through the first passive substantially nonlinear medium portion, which mixes the first and second signals to generate a third current (i.e., an intermodulation current, or PIM) having a frequency nF1 + mF2 and propagating along the passive substantially nonlinear medium portion and the passive substantially linear medium portion, where m and n are integers, which can be positive integers or negative integers. In some embodiments, a magnetic film can be disposed on the passive substantially linear medium portion instead of the substantially nonlinear medium portion and absorb at least a portion of the third current. For example, in some embodiments, the magnetic film can be a magnetic absorbing film wrapped around an antenna mast (substantially linear medium portion) in the vicinity of and in the propagation path prior to an attached antenna mounting bracket (substantially nonlinear medium portion). In some embodiments, placing a magnetic film on the substantially linear medium portion can impede the propagation of signals that can contribute to PIM interference (e.g., by attenuating the signals at least in part due to absorption of the magnetic fields generated by the signals). In some embodiments, a magnetic film can be disposed on both the passive substantially linear medium portion and a portion of the passive substantially nonlinear medium portion. Attenuating the signals in the passive substantially linear medium can result in a reduction of the intermodulation signals in the substantially nonlinear medium portion. The reduction of the intermodulation signals in the substantially nonlinear medium portion can be greater than the reduction of the signals in the substantially linear medium portion. For example, for a third order (|m| + |n| = 3) intermodulation signal, for every 1 dB reduction in power of the signals in the substantially linear medium portion, approximately 3 dB reduction in power of the intermodulation signals in the substantially nonlinear medium portion can occur. In some embodiments, a magnetic film is primarily disposed to attenuate at least a portion of the first and second signals propagating in the first passive substantially linear medium portion. A magnetic film that covers only a portion of the passive substantially linear medium portion, or a portion of the passive substantially linear medium portion and a portion of the substantially nonlinear medium portion, such that the attenuation of the intermodulation signals due to the attenuation of at least a portion of the first and second signals propagating in the passive substantially linear medium portion is greater than the attenuation of the intermodulation signals due to the attenuation of at least a portion of the signals propagating in the substantially nonlinear medium portion, can be described as being primarily disposed to attenuate at least a portion of the first and second signals propagating in the first passive substantially linear medium portion.

[0035] According to some aspects of the present specification, a wireless communication system (e.g., a cellular base station) can include one or more antennas; a plurality of spaced apart electrically conductive first segments (e.g., one or more mounting brackets, or irregular welds); a plurality of electrically conductive second segments (e.g., segments of an antenna mast) that interconnect the first segments such that when the one or more antennas radiate first and second electromagnetic waves at different respective frequencies Fl and F2, the first and second waves induce respective first and second signals at the respective Fl and F2 frequencies that can propagate through the first and second segments. In some embodiments, the first segments can cause mixing (e.g., combining by amplitude modulation) of the first and second signals to generate a third signal (e.g., an intermodulation signal) at a frequency F3 different from Fl and F2. In some embodiments, the generated third signal can propagate along the first and second segments, causing the first segments but not the second segments to generate an electrical signal at the new F3 frequency that can propagate along the second segments, which can then radiate electromagnetic energy at the frequency F3. In some embodiments, the second segments can also generate an electrical signal at the F3 frequency, which can contribute to the radiated electromagnetic energy. In some embodiments, this “mixing” of signals can be caused by non-linearity in the first segments. For example, corrosion on the mounting brackets, or loose connections, or any number of other causes can cause non-linearity in the first segments, causing the first segments to act as signal (e.g., current or voltage) mixers, producing 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) can be disposed on (e.g., wrapped around or placed on) an electrically conductive surface of each second segment to absorb at least a portion of the third signal propagating along the second segment.

[0036] According to some aspects of the present specification, a wireless communication system is provided that includes one or more antennas (e.g., a plurality of cellular antennas on a cellular base station); one or more transceivers (e.g., transceivers housed in a transceiver base station or BTS, for facilitating wireless communication between mobile devices and a cellular network), the one or more transceivers coupled to the one or more antennas; a plurality of electrically conductive passive substantially linear medium portions, the plurality of electrically conductive passive substantially linear medium portions interconnected with a plurality of electrically conductive passive non-substantially linear medium portions, and a magnetic film (e.g., a magnetic absorber) disposed on at least some of the substantially linear medium portions, but not on any of the non-substantially linear medium portions. In some embodiments, each of the substantially linear medium portions and the non-substantially linear medium portions can be capable of propagating electromagnetic first and second signals at different respective frequencies F1 and F2 simultaneously. In some embodiments, each of the passive non-substantially linear portions, but not the substantially linear portions, can be capable of mixing or otherwise combining the first and second signals to generate a third current having a frequency of nF1 + mF2, where m and n are positive or negative integers. In some embodiments, the third signal propagates along the passive non-substantially linear medium portions and / or along the passive substantially linear portions. In some embodiments, the magnetic absorber placed on the linear portions can impede the formation of signals in the substantially linear portions that would otherwise contribute to the generation of a third signal (e.g., a PIM signal) upon encountering the non-substantially linear portions. In some embodiments, the PIM signal can cause PIM emissions that will increase the overall noise level within a frequency band of interest (e.g., a cellular frequency band) used by the transceiver and cause communication signals to drop or distort.

[0037] A substantially linear and 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 is generated in a first passive substantially nonlinear medium or medium portion from the first signal and the second signal 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 generated in the substantially linear medium from the first signal and the second signal (e.g., based on a nonlinear interaction between the first signal and the second signal) has an amplitude A, and the amplitude of the intermodulation signal or at least one intermodulation signal generated in the passive substantially nonlinear medium is B, then B is at least 2.5 dB greater than A. In some embodiments, a system includes a conductive first passive substantially linear medium or medium portion and a conductive first passive substantially nonlinear medium or medium portion. In some embodiments, any intermodulation signal generated in the first passive substantially linear medium or medium portion (e.g., based on a nonlinear interaction between the first signal and the second signal) has an amplitude A, and the amplitude of the intermodulation signal or at least one intermodulation signal generated in the first passive substantially nonlinear medium or medium portion is B, where B is at least 3 dB, or at least 4 dB, or at least 5 dB, or at least 6 dB, or at least 8 dB, or at least 10 dB, or at least 15 dB, or at least 20 dB greater than A.

[0038] According to some aspects of the present specification, a wireless communication system is provided, the wireless communication system comprising: a transmitter configured to transmit at least a first radio wave and a second radio wave having respective different frequencies Fl and F2; a conductive first passive substantially linear medium; a conductive first passive substantially nonlinear medium disposed proximate to the first passive substantially linear medium; and a first magnetic film covering at least a first portion of the first passive substantially linear medium and no more than about 20% of any conductive passive substantially nonlinear medium; such that when the transmitter transmits the first radio wave and the second radio wave, the first passive substantially linear medium and the first passive substantially nonlinear medium receive the first radio wave and the second radio wave and generate first and second signals propagating therein at the respective frequencies Fl and F2. In some embodiments, at least one intermodulation signal is generated in the first passive substantially nonlinear medium from the first and second signals. The at least one intermodulation signal can be generated in the first passive substantially nonlinear medium based on a nonlinear interaction between the first and second signals. The nonlinear interaction can be a direct or indirect interaction. For example, the nonlinear interaction can be mediated by the first passive substantially nonlinear medium. In some embodiments, the first and second signals interact with the first passive substantially nonlinear medium to generate the at least one intermodulation signal. The at least one intermodulation signal has a frequency F3 equal to nFl + 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 an amount described elsewhere. In some embodiments, the at least one intermodulation signal propagates in the substantially nonlinear medium and / or in the substantially linear medium (e.g., the at least one intermodulation signal can be generated in the substantially nonlinear medium, propagate to the substantially linear medium in the substantially nonlinear medium, and then propagate in the substantially linear medium). In some embodiments, any intermodulation signal generated in the first passive substantially linear medium from the first and second signals has an amplitude A, and the at least one intermodulation signal generated in the first passive substantially nonlinear medium has an amplitude B, where B is at least 3 dB greater than A or an amount described elsewhere.

[0039] According to some aspects of the present specification, a wireless communication system is provided, the wireless communication system comprising: a transmitter configured to transmit at least a first radio wave and a second radio wave having respective different frequencies F1 and F2; an electrically conductive first passive substantially non-linear medium portion; and an electrically conductive first passive substantially linear medium portion disposed proximate to the first passive substantially non-linear medium portion, such that when the transmitter transmits the first and second radio waves, the first passive substantially linear medium portion receives the first and second radio waves and generates the first and second signals at the respective frequencies F1 and F2. The first and second signals propagate in the first passive substantially linear medium portion along a first path towards the electrically conductive first passive substantially non-linear medium portion. In some embodiments, an intermodulation signal (or at least one intermodulation signal or at least two intermodulation signals) is generated in the first passive substantially non-linear medium portion from the first and second signals. In some embodiments, an intermodulation signal is generated in the first passive substantially non-linear medium portion based on a non-linear interaction between the first and second signals. In some embodiments, the first and second signals interact with the first passive substantially non-linear medium portion (e.g., resulting in an indirect non-linear interaction between the first and second signals) to generate an 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 comprises a first magnetic film covering at least a first portion of the first passive substantially linear medium portion along the first path and disposed to attenuate the generated first and second signals propagating in the first passive substantially linear medium portion more than the generated intermodulation signal in the first passive substantially non-linear medium portion. For example, attenuating the signals propagating in the first passive substantially linear medium portion can result in a significant reduction of the intermodulation signal generated in the first passive substantially non-linear medium portion, even if little or substantially no intermodulation signal is attenuated (e.g., absorbed), as the reduction can occur due to a reduction in generation of the intermodulation signal rather than attenuation of the intermodulation signal that has already been generated. In some embodiments, the first magnetic film can also attenuate the intermodulation signal. For example, in some embodiments, the first magnetic film can also cover a portion of the first passive substantially non-linear medium portion, such that there is some attenuation of the intermodulation signal generated in the first passive substantially non-linear medium portion. In some embodiments, any intermodulation signal generated in the first passive substantially linear medium portion from the first and second signals has an amplitude A, and the intermodulation signal generated in the first passive substantially non-linear medium portion has an amplitude B, where B is at least 3 dB or elsewhere described amount greater than A.The conductive passive medium can include the conductive first passive substantially nonlinear medium portion and the conductive first passive substantially linear medium portion.

[0040] According to some aspects of the present specification, a system for reducing passive intermodulation is provided, the system comprising: a conductive first passive substantially linear medium configured to receive first and second radio waves having respective different frequencies Fl and F2 and to generate first and second signals at the respective frequencies Fl and F2, wherein the first and second signals propagate in the first passive substantially linear medium along a first path towards a conductive first passive substantially nonlinear medium. For example, the conductive first passive substantially linear medium can be configured to receive first and second radio waves and to generate first and second signals by being made of a material (e.g., steel or other metal) capable of generating signals from received radio waves. Suitable passive substantially linear media configured to receive first and second radio waves and to generate first and second signals include structural elements (e.g., antenna masts) for supporting emitters (e.g., metallic). In some embodiments, an intermodulation signal (or at least one intermodulation signal or at least two intermodulation signals) is produced in the first passive substantially nonlinear medium from the first and second signals. In some embodiments, the intermodulation signal is produced in the first passive substantially nonlinear medium based on a nonlinear interaction between the first and second signals. For example, in some embodiments, the first and second signals interact with the first passive substantially nonlinear medium to produce the intermodulation signal. The intermodulation signal has a frequency F3 equal to nFl + mF2, where m and n are positive or negative integers. The system comprises a first magnetic film covering at least a first portion of the first passive substantially linear medium along the first path. In some embodiments, the first magnetic film covers no more than about 20% of the first passive substantially nonlinear medium or no more than about 20% of any passive substantially nonlinear medium. In some embodiments, the first magnetic film covers a first portion of the first passive substantially linear medium along the first path, leaving a second portion of the first passive substantially linear medium exposed, wherein the first magnetic film faces the first passive substantially nonlinear medium and the second portion faces away from the first passive substantially nonlinear medium. In some embodiments, the first magnetic film reduces the intermodulation signal by at least 2 dB or an amount within the range described elsewhere. In some embodiments, any intermodulation signal produced in the first passive substantially linear medium from the first and second signals has an amplitude A, and the intermodulation signal produced in the first passive substantially nonlinear medium has an amplitude B, where B is at least 3 dB greater than A or an amount described elsewhere.

[0041] Turning now to the drawings, Figure 1A side view of a wireless communication system in accordance with some embodiments of the present specification. In some embodiments, the wireless communication system 200 includes one or more antennas 50 disposed on (e.g., mounted on and supported by) a conductive passive medium 10 (e.g., a metal antenna mast or mounting structure). In some embodiments, the conductive passive medium 10 can include two different portions: a conductive passive linear portion 11 (e.g., a main substantially homogeneous element of the mounting structure, such as a main shaft) and a conductive passive non-linear portion 12 (e.g., a mounting bracket, a welded bead, or other connection structure). It should be noted that the non-linear portion 12 can be formed by the presence of different materials and / or different conditions relative to the linear portion 11. That is, the non-linear element can be formed at the interface between two different metals (e.g., galvanized steel of an antenna mast and metal used in a mounting bracket attached to the mast) due to a loose or damaged connector point or cable, due to rust, corrosion, dirt, oxidation, etc., due to a nearby metallic object such as a roof flashing or a pipe, or due to any of a number of other reasons. The non-linear element 12 is shown in Figure 1 coincidence with a mounting bracket of an antenna for illustrative purposes, but can be any suitable non-linearity for any suitable reason or condition.

[0042] In some embodiments, the wireless communication system 200 can also include one or more transceivers 60 (e.g., transceivers housed in a transceiver base station of a cellular base station) coupled to the antennas 50. In some embodiments, the transceivers 60 can be used to facilitate wireless communication between external devices and a wireless network. In some embodiments, the transceivers 60 can be high-power transceivers (e.g., 20W or greater).

[0043] In operation, in some embodiments, the transceivers 60 of the wireless communication system 200 can 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) so as to be broadcast / radiated as electromagnetic radiation 40 from the antennas 50 (e.g., a first antenna 50a). In some embodiments, the electromagnetic radiation 40 can include an electromagnetic first wave 40a radiated at a frequency Fi and an electromagnetic second wave 40b radiated at a frequency F2. In some embodiments, when the electromagnetic first wave 40a and the electromagnetic second wave 40b impinge upon the structure including the linear portion 11 and the non-linear portion 12, respectively, the first wave 40a and the second wave 40b can induce a first signal 20 and a second signal 21 (the first signal 20 and the second signal 21 are shown in Figure 2(As shown in the diagram). In some embodiments, the nonlinear portion 12 may act as a mixer to combine 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 (along with the first signal 20 and the second signal 21) may then propagate through the conductive passive medium 10 (e.g., along the path of a metal antenna mast), possibly flowing back into the transceiver 60, or into one or more antennas 50, or being re-radiated into space as a second electromagnetic radiation 41 at a new frequency F3, thus returning to one or more antennas 50. In some embodiments, the second antenna 50b may retransmit or receive the RF signal (with fundamental frequencies F1 and F2) initially generated at the first antenna 50a, including the PIM signal at frequency F3 formed within one or more nonlinear portions 12 / 12a. These RF signals (especially the F3 signal) may be considered as added noise at the transceiver 60, thereby significantly reducing the SNR of the intended signal.

[0044] 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 dielectric portion 11. In some embodiments, the magnetic films 30 may reduce or prevent the generation of intermodulation signals 22 in the nonlinear portion 12. In some embodiments, the intermodulation signals 22 may be reduced by the magnetic films 30 in a variety of ways. In some embodiments, the magnetic films 30 may attenuate one or both of the first and second signals before they enter the nonlinear portion 12, such that the intermodulation signals 22 are not generated or are significantly reduced. In some embodiments, the magnetic films 30 may intercept signals or radiated energy from the nonlinear portion 12 as they leave the nonlinear portion 12 before entering the linear portions 11 / 11a / 11b. In some embodiments, additional magnetic films 30 (such as films 30a and / or 30b) may be disposed on or near additional linear portions 11 (such as portions 11a and / or 11b) to help attenuate signals induced in or passing through the structure. In some implementations, for example, a magnetic film 30 (e.g., a magnetic absorber) may be placed on either side of the nonlinear portion 12 on the linear portion 11, such that it attenuates and / or eliminates signals generated in or otherwise exiting the nonlinear portion 12.

[0045] Figure 2 for Figure 1 A side view of the conductive passive dielectric 10, showing additional details regarding the formation of the intermodulation signal. This signal is broadcast from a nearby antenna or generated by another conductive structure (such as...). Figure 1The electromagnetic radiation (RF signal) of the illustrated) radiation induces first signal 20 (corresponding to an RF signal having a base frequency Fi) and second signal 21 (corresponding to an RF signal having a base frequency F2) within the conductive passive medium 10 (e.g., the metal portion of an antenna mast). In some embodiments, the first signal 20 and the second signal 21 can be induced within the conductive passive linear portion 11 of the conductive passive medium 10 and then travel throughout other portions of the structure. In these embodiments, the first signal 20 and the second signal 21 can propagate through the conductive passive linear portion 11 until they encounter the conductive passive non-linear portion 12. As described elsewhere herein, the non-linear portion 12 can be formed in a variety of ways, including but not limited to a joint between different materials, a loose connection between mechanical components, a region of corrosion or damage, proximity to other conductive components (e.g., a pipe or a roof flashing), etc. As the first signal 20 and the second signal 21 enter the non-linear portion 12, the non-linearity can cause the first signal 20 and the second signal 21 to mix, generating a new signal having a new frequency. In some embodiments, at least a third signal 22 is generated having a frequency F3, which can represent, for example, a third order harmonic of Fi and F2, which can be calculated using the formula F3 = nFi + mF2, where n and m can be positive or negative integers. In other words, the third current can be an intermodulation signal having a frequency F3, which can cause the intermodulation signal to be received by the antenna 50 in a frequency region intended for receiving signals from external devices (e.g., mobile devices such as cellular telephones) when the intermodulation signal is radiated from the antenna or other structure, thereby increasing the noise level of the received signal and decreasing its fidelity. This in turn will decrease the rate at which information can be transferred from the mobile device to the antenna 50, or can cause a connection from the mobile device to the antenna to be lost (i.e., a "call drop"). In other embodiments, the first signal 20 and the second signal 21 can be induced directly in the non-linear portion 12 (rather than originating from the linear portion 11 and propagating into the non-linear portion 12). In these embodiments, each of the signals 20 and 21 and the intermodulation signal 22 can propagate out of and away from the non-linear portion 12 and into an adjacent linear portion 11.

[0046] In some embodiments, the magnetic film 30 can be disposed on (e.g., placed on the outer surface of or wrapped around) the linear portion 11 of the electrically conductive passive medium 10 adjacent to the non-linear portion 12. In some embodiments, the magnetic film 30 can be a magnetic absorber that at least partially attenuates the first signal 20 and the second signal 21 (by absorbing the magnetic fields they generate in the vicinity of the linear section), as well as at least a portion of any electromagnetic fields formed by the signals 20 and 21 before they enter the non-linear portion 12. By reducing or eliminating the first signal 20 and the second signal 21 before they enter the non-linear portion 12, the generation of the third (intermodulation) signal 22 can be prevented or significantly reduced. In some embodiments, the magnetic film 30 can limit or eliminate any signals (currents) that attempt to exit the non-linear portion 12, including the first signal 20, the second signal 21, and the third signal 22, when the first signal 20 and the second signal 21 are first generated within the non-linear portion 12.

[0047] In some embodiments, two or more magnetic films 30 can be disposed on multiple linear portions 11 (e.g., the shaft of an antenna mast that extends above and below a non-linear portion such as a mounting bracket) to prevent or reduce the propagation of PIM signals that can be generated within the non-linear portion 12 throughout other portions of the electrically conductive passive medium 10. Figure 3A side cross-sectional view of a conductive passive medium 10 having magnetic absorbing films according to embodiments of the present specification is provided. In the illustrated embodiment, the conductive passive medium 10 includes a conductive first passive linear medium portion 11 (or“first linear portion”) and a conductive second passive linear portion 11a (or“second linear portion”), both of which are adjacent to a conductive first passive nonlinear medium portion 12 (or“nonlinear portion”). That is, the first linear portion 11 and the second linear portion 11a are disposed on either side of the nonlinear portion 12. A first magnetic film 30 is disposed proximate to a conductive outer surface 13 of the first linear portion 11 (e.g., wrapped around the first linear portion 11), and a second magnetic film 30a is disposed proximate to a 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, a first induced signal 20 and a second induced signal 21 propagate along the first linear portion 11 and into the nonlinear portion 12. Once in the nonlinear portion 12, the first signal 20 and the second signal 21 can mix to form a third or intermodulation signal 22, which can 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 portion (i.e., disposed on the first linear portion 11 and the second linear portion 11a), the magnetic films 30 and 30a can absorb any electrical signals that attempt to enter the nonlinear portion 12 (where they can mix to form a new signal at a new frequency) or that attempt to exit the nonlinear portion 12. By absorbing these signals (including any PIM signals formed), and by additionally absorbing or preventing the formation of electromagnetic fields due to the signals, the magnetic films 30 and 30a can eliminate or significantly reduce PIM interference.

[0048] Figure 3 The illustrated exemplary nonlinear (i.e., nonlinear portion 12) can be formed by a mounting bracket or mounting hardware that is a material sufficiently different from, or loosely connected to, the conductive passive medium 10 such that the difference results in the creation of a nonlinear component. As another example, the nonlinearity can be a rusted bolt or other fastener that connects two portions of the conductive passive medium 10 or that is a material sufficiently different from the passive medium 10. Figure 4 Figure 5 Figure 6 A side cross-sectional view of similar embodiments of a wireless communication system according to the description herein is provided, in which various components and / or conditions form a nonlinearity, potentially resulting in the formation of PIM interference. Figure 4 Figure 5 Figure 6 each include elements similar to those of Figure 3 have similar functionality.​​​​Figure 3 Like numbered elements described can not be discussed again for Figure 4 , Figure 5 and Figure 6 are discussed unless needed.

[0049] In some embodiments, the magnetic film is non-conductive. In some such embodiments or in other embodiments, the magnetic film (e.g., first magnetic film 30) includes a first major surface (e.g., major surface 31) contacting a first portion of the first passive, substantially linear medium and an at least partially exposed opposing second major surface (e.g., major surface 32). For example, greater than 50% by area of the second major surface can be exposed (e.g., not covered by an additional layer such as a conductive layer).

[0050] Figure 4 is a side view of a conductive passive medium 10 in which a nonlinearity 12-1 is formed by a junction 14 between a first metal 11 and a second, different metal 15. For example, the area of surface contact between the first metal 11 and the second, different metal 15 can have different electrochemical potentials, resulting in a non-linear I / V curve (a non-linear junction). The use of one or more magnetic films 30 / 30a disposed on an outer surface 13 / 13a adjacent to the nonlinearity 12-1 can absorb / mitigate induced signals propagating to the non-linear junction and intermodulation signals propagating away from the non-linear junction, which can contribute to the formation of PIM effects.

[0051] Figure 5 is a side view of a conductive passive medium 10 in which a nonlinearity 12-2 is formed by a junction between a metal 11 and a metal oxide 17. For example, in some embodiments, an ionic chemical reaction can occur on the surface of an exposed metal when oxygen is present, causing electrons from the metal to move to oxygen molecules, resulting in negative oxygen ions that can form an oxide surface on the metal. The interface between the original metal and the formed metal oxide can be a source of PIM. As described herein, the disposition of one or more magnetic films 30 adjacent to the nonlinearity 12-2 can help mitigate the formation of PIM distortion.

[0052] Figure 6 is a side view of a conductive passive medium 10 in which a nonlinearity 12-3 is formed by a rusted area 18 on the conductive passive medium 10. Other conditions that can form a nonlinearity include, but are not limited to, contaminants (e.g., dirt joints), loose joints, irregular intermetallic contact (e.g., poor soldered beads), and uneven contact surfaces. As described herein, the disposition of one or more magnetic films 30 adjacent to the nonlinearity 12-3 can help mitigate the formation of PIM distortion.

[0053] Figure 7A graph to illustrate the frequencies of transmitted signals and intermodulation signals in a wireless communication system as described in the current description. The Y axis represents the relative amplitude (strength) of the signals, and the x axis illustrates the relative frequency band of the signals. In the center of the graph, the transmit or Tx band includes (in this example) two intended signals for transmission, which are labeled based on their corresponding frequencies Fl and F2, as described elsewhere herein. Moving away from the Tx band signals in either direction are odd-numbered passive intermodulation signals generated by mixing of the Tx band signals. Moving to the left of the page from the Fl signal are third-order intermodulation, fifth-order intermodulation, seventh-order intermodulation, etc. Moving to the right of the page from the F2 signal are alternative third-order intermodulation, fifth-order intermodulation, seventh-order intermodulation, etc. For example, the signal immediately to the left of the Fl signal is the third-order passive intermodulation radiation (PIM) resulting from the equation nFl + mF2 when n = +2 and m = -1 (i.e., 2Fl - F2). As seen, this third-order intermodulation falls into one of the intended receive bands or Rx bands being 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 intended legitimate signals by increasing the noise level and decreasing the signal-to-noise ratio (SNR) of the signals. Use of a magnetic absorber as described herein can help to mitigate the formation of these PIM distortion signals and improve the SNR of the intended wireless system signals. Figure 7 As seen, this third-order intermodulation falls into one of the intended receive bands or Rx bands being 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 intended legitimate signals by increasing the noise level and decreasing the signal-to-noise ratio (SNR) of the signals. Use of a magnetic absorber as described herein can help to mitigate the formation of these PIM distortion signals and improve the SNR of the intended wireless system signals.

[0054] Figures 8A-8F A schematic diagram of a wireless communication system according to some embodiments of the present description. The wireless communication system 500, 500', 500", 500"', 500"" includes a transmitter 150 (e.g., an antenna); a conductive first passive substantially linear medium 111 (which can also be referred to as a conductive first passive substantially linear medium portion); a conductive first passive substantially nonlinear medium 112 (which can also be referred to as a conductive first passive substantially nonlinear medium portion) disposed proximate to the first passive substantially linear medium 111; and a first magnetic film 130, 130', 130", 131, 130"', 130"", covering at least a first portion of the first passive substantially linear medium 111 and no more than about 20% of any conductive passive substantially nonlinear medium. The wireless communication system 500, 500', 500", 500"', 500"", or a system without a transmitter 150 can 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 the at least first portion of the first passive substantially linear medium (e.g., nominally conforms, or conforms to a variation in dimensions of no more than about three times the thickness of the magnetic film, or to a variation in dimensions of no more than about 20% or about 10% of the maximum dimension or diameter of the first portion). Figure 8A A schematic side view of the wireless communication system 500, andFigure 8B is a schematic back view of the wireless communication system 500. Figures 8C-8F are schematic back views of the wireless communication systems 500', 500", 500"', 500"", respectively, which correspond to the wireless communication system 500, except for the placement of the magnetic film. In some embodiments, the first passive substantially linear medium 111 is part of a support structure 122 for supporting the transmitter 150, and the first passive substantially nonlinear medium 112 is attached to the support structure 122. In the illustrated embodiment, the support structure 122 is or includes an antenna mast 121, such that the first passive substantially linear medium 111 is part of the antenna mast 121, and the first passive substantially nonlinear medium 112 is attached to the antenna mast 121. In other embodiments, the support structure can be other structures in a cellular base station, e.g., for supporting antennas. In the illustrated embodiment, the transmitter 150 is mounted to the antenna mast 121 by a first mounting bracket 141 and a second mounting bracket 142. In other embodiments, a single mounting bracket can be used, or more than two mounting brackets can be used. One or more of these mounting brackets can be a substantially nonlinear medium, or the joint between the mast 121 and one or more of these mounting brackets can be a substantially nonlinear medium, or the rust on one or more of these mounting brackets or on the antenna mast 121 adjacent to one or more of these antenna masts (schematically depicted in FIG. 1 1 1 on mounting bracket 141) can be the substantially nonlinear medium 112. Figure 8A

[0055] In some embodiments, the first magnetic film is at least partially wrapped around the first passive substantially linear medium. In Figures 8A-8B ​In embodiments, the first magnetic film 130 is wrapped only partially around the first passive substantially linear medium 111. In some embodiments, the electrically conductive first passive substantially linear medium 111 is configured to receive first and second radio waves (e.g., corresponding to radiations 40, 41) having respective different frequencies Fl and F2 and to generate first and second signals (e.g., corresponding to signals 20, 21) at the respective frequencies Fl and F2, the first and second signals propagating in the first passive substantially linear medium 111 along a first path 113 toward the electrically conductive first passive substantially nonlinear medium 112. In some embodiments, the first magnetic film 130 covers a first portion of the first passive substantially linear medium 111 along the first path 113 and leaves a second portion 116 of the first passive substantially linear medium 111 exposed, with the first magnetic film 130 facing the first passive substantially nonlinear medium 112 and the second portion 116 facing away from the first passive substantially nonlinear medium 112. In some embodiments, the first magnetic film 130 is wrapped only partially around the first passive substantially linear medium 111, leaving a portion 116 of the passive substantially linear medium exposed between opposite ends 117 and 119 of the first magnetic film 130, with the exposed portion 116 facing away from the first passive substantially nonlinear medium 112.

[0056] In Figure 8C In embodiments, the first magnetic film 130' is wrapped completely around the first passive substantially linear medium 111. In the illustrated embodiment, the ends of the magnetic film 130' overlap one another. In some embodiments, the system 500" includes a first magnetic film 130" and further includes a second magnetic film 131 covering at least a second portion of the first passive substantially linear medium 111 and no more than about 20% of any electrically conductive passive substantially nonlinear medium. In Figures 8E-8F In the illustrated embodiment, the first magnetic film 130", 130"" is wrapped helically around the first passive substantially linear medium. In some embodiments, the first magnetic film 130"' is wrapped helically and non-overlappingly around the first passive substantially linear medium. The magnetic film 130"' can be wrapped helically and non-overlappingly around the first passive substantially linear medium 111 with or without a gap between adjacent wraps. It has been found that having no gap between adjacent wraps facing the substantially nonlinear medium 112 results in improved reduction of intermodulation signals. In some embodiments, the first magnetic film 130"" is wrapped helically and overlappingly around the first passive substantially linear medium 111. In Figure 8EIn the illustrated embodiment, the first magnetic film 130”’ covers a portion of the mounting bracket 141, which can be a substantially non-linear medium. However, in some embodiments, the first magnetic film 130”’ covers no more than about 20% 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 passive substantially linear medium or medium portion along the first path 113 and is disposed to attenuate a generated first signal and a generated second signal propagating in the first passive substantially linear medium or medium portion more than a generated intermodulation signal in the first passive substantially non-linear medium or medium portion when the transmitter 150 transmits the first radio wave 240 and the second radio wave 241.

[0057] As further described elsewhere herein, the transmitter 150 is configured to transmit at least a first radio wave 240 and a second radio wave 241 having respective different frequencies Fl and F2 such that when the transmitter 150 transmits the first radio wave 240 and the second radio wave 241, the first passive substantially linear medium or medium portion and the first passive substantially non-linear medium or medium portion receive the first radio wave 240 and the second radio wave 241 and generate a first signal and a second signal (e.g., corresponding to signals 20, 21) propagating therein at respective frequencies Fl and F2. An intermodulation signal (e.g., corresponding to signal 22) or at least one intermodulation signal is generated in the first passive substantially non-linear medium or medium portion from the first signal and the second signal. The intermodulation signal or at least one intermodulation signal has a frequency F3 equal to nFl + mF2, where m and n are positive or negative integers. In some embodiments, the first magnetic film reduces generation of the intermodulation signal or at least one intermodulation signal by at least 2 dB, or at least 3 dB, or at least 3.5 dB, or at least 4 dB, or at least 5 dB, or at least 6 dB (e.g., 2 dB to 100 dB or 3 dB to 50 dB). In some embodiments, at least a first intermodulation signal and a second intermodulation signal are generated or produced in the first passive substantially non-linear medium or medium portion from the first signal and the second signal. The first intermodulation signal and the second intermodulation signal have respective different frequencies F3 and F3’. Each of F3 and F3’ is equal to nFl + mF2, where m and n are positive or negative integers. For example, the first intermodulation signal can correspond to Figure 7 one of the PIM signals (e.g., a signal having a frequency 2Fl - F2) and the second intermodulation signal can correspond to Figure 7a different one of the PIM signals indicated schematically (e.g., the signal with frequency 3F1-2F2 or the signal with 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, or at least 3 dB, or at least 3.5 dB, or at least 4 dB, or at least 5 dB, or at least 6 dB (e.g., 2 dB to 100 dB or 3 dB to 50 dB).

[0058] In some embodiments, the system 500, 500', 500", 500"', 500"" can include a receiver 160 such that when an intermodulation signal (e.g., corresponding to signal 22) or at least one intermodulation signal is generated or produced at the first passive substantially nonlinear medium 112, the intermodulation signal or at least one intermodulation signal radiates radio waves 242 at frequency F3, and the receiver 160 detects the radiated radio waves 242. In some embodiments, the 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 radio waves detected by the receiver by at least 2 dB. In some embodiments, the magnetic film reduces the radiated radio waves detected by the receiver by at least 3 dB, or at least 3.5 dB, or at least 4 dB, or at least 5 dB, or at least 6 dB (e.g., 3 dB to 100 dB or 3.5 dB to 50 dB).

[0059] Figures 9-10 is a plot of magnetic permeability versus frequency for various magnetic films. Figure 9 shows 3M TM Magnetic permeability of flux field direction material (FFDM) EM25TP-0100, which has a 100-micron thick composite magnetic FFDM layer. Figure 10The magnetic permeability of relevant magnetic films including a magnetic absorber layer with a magnetic filler in a carrier resin is shown. The real part (μ') and the imaginary part (μ") of the magnetic permeability are shown. In some embodiments, for at least one of F1 or F2, the relative magnetic permeability of the magnetic film has an imaginary part of at least about 5, or at least about 10, or at least about 15, or at least about 20. In some such embodiments or in other embodiments, for F3, the relative magnetic permeability of the magnetic film has an imaginary part of at least about 5, or at least about 10, or at least about 15, or at least about 20. In some embodiments, for each of F1, F2, and F3, the relative magnetic permeability has an imaginary part of at least about 5, or at least about 10, or at least about 15, or at least about 20. In some embodiments, the magnetic film includes a magnetic absorber layer having an average thickness in a range of about 25 microns to about 1 mm, or in a range of about 40 microns to about 500 microns. In some embodiments, when the absorber layer has a high μ" (e.g., at least about 10) and / or a magnetic loss tangent (e.g., μ" / μ' of at least about 2) at F1 and / or F2, a thinner absorber layer can be used, while when the μ" and / or magnetic loss tangent of the layer is lower, a thicker absorber layer can be used.

[0060] Example

[0061] A wireless communication system was set up in an anechoic chamber, including antennas (COMMSCOPE LNX-6513DS-A1M, available from CommScope, Inc., Hickory, NC) mounted to antenna masts (galvanized steel poles) with clamps at two mounting brackets (see, e.g., FIG. 1). The antennas were mounted to the masts using a mounting bracket (COMMSCOPE LNX-6513DS-A1M, available from CommScope, Inc., Hickory, NC) and a clamp (COMMSCOPE LNX-6513DS-A1M, available from CommScope, Inc., Hickory, NC). Figures 8A-8EThe antenna is approximately 4.5 feet tall, and the antenna mast has an outer diameter of approximately 2 inches. The antenna is positioned to radiate primarily away from the antenna mast. A PIM analyzer (SummiTek iQA850B, available from Kaelus Corporation, Spokane Valley, WA) is attached to the antenna port via a coaxial cable. Two 43dBm (20W) continuous wave (CW) carriers at 871MHz and 894MHz are input to a single port of the antenna, and the reflected PIM signal at 848MHz (2*871MHz-894MHz) is measured by the PIM analyzer through the same port. Without an external PIM source, the PIM analyzer reports a PIM signal of -126.9dBm, equivalent to -169.9dBc at an input power of 43dBm, indicating that the low noise floor stabilizes for at least 5 minutes. Experiments using magnetic films involve placing a PIM source (e.g., steel wool), applying the magnetic film, and then removing the magnetic film to re-establish a baseline in the absence of the magnetic film. This procedure ensures that the PIM source remains undisturbed during the experiment.

[0062] Steel wool is placed on top of the bottom mounting bracket to generate a PIM signal, and then a 13-inch wide magnetic film (dimensions parallel to the vertical direction of the antenna mast) is wrapped around the antenna mast near the bottom mounting bracket. For antennas with... Figures 9-10 For a magnetic film with the indicated permeability, changing the width of the magnetic film from 13 inches to 6.5 inches and / or moving the position of the film upwards (away from the bottom mounting bracket) about 4 inches along the mast will not significantly change the PIM signal.

[0063] Then, place the steel wool in each of the top and bottom supports. Place the magnetic film (6.5-inch wide 3M) in each position. TM The FFDM EM25TP-0150 strip, consisting of a multilayer magnetic film (including a backing, adhesive layer, and a 150μm thick magnetic absorption layer) with a total thickness of approximately 250μm, is wrapped around the antenna mast at the top or bottom of the top bracket and / or the top and bottom of the bottom bracket. Placing the magnetic film at the top of the top bracket has almost no effect on the PIM signal. Placing another magnetic film at the top of the bottom bracket reduces the PIM signal by approximately 10dB compared to the absence of the magnetic film. Removing these magnetic films, re-establishing the baseline for the absence of the magnetic film, and then placing the magnetic film at the bottom of the top bracket and the top of the bottom bracket reduces the PIM signal by approximately 14dB. Removing these magnetic films, re-establishing the baseline for the absence of the magnetic film, and then placing the magnetic film at the top and bottom of the top bracket and the top and bottom of the bottom bracket reduces the PIM signal by approximately 15dB.

[0064] In another experiment, steel wool was placed on top of each of the top and bottom mounts, and then a 3.5 inch wide, 2.5 inch wide, or 1 inch wide strip of magnetic film (3M TM FFDM EM25TP-0150) was wrapped around the antenna mast on top of the bottom mounting bracket. For the 3.5 inch width and 2.5 inch width, the PIM signal was reduced by 9 dB to 10 dB. For the 1 inch width, the PIM signal was reduced by about 8 dB.

[0065] In another experiment, steel wool was placed on top of the bottom mounting bracket, and then a 3.5 inch wide strip of 3M TM FFDM EM25TP-0150 was wrapped around the antenna mast on top of the bottom mounting bracket and various wrapping sections were tested. The magnetic film resulted in a 7 dB to 8 dB reduction in PIM signal at 100% wrapping. Similar results were found for 30%, 50%, and 90% wrapping when the magnetic film faced the steel wool and the uncovered portion of the mast faced away from the steel wool. A significant reduction in PIM signal was observed when the uncovered portion of the mast faced the steel wool, or when a spiral wrap was used with gaps between the wraps and the gaps between the spiral wraps faced the steel wool.

[0066] In another experiment, steel wool was placed on top of the bottom mounting bracket, and then a 3.5 inch wide strip of 3M TM FFDM EM25TP was wrapped around the antenna mast on top of the bottom mounting bracket (one full wrap) and various thicknesses of the magnetic absorbing layer were tested: EM25TP-0025 with a 25 pm thick magnetic absorbing layer, EM25TP-0050 with a 50 pm thick magnetic absorbing layer, EM25TP-0100 with a 100 pm thick magnetic absorbing layer, and EM25TP-0150 with a 150 pm thick magnetic absorbing layer. For the 25 pm and 50 pm thick magnetic absorbing layers, a 1 dB to 2 dB reduction in PIM signal was observed, while for the 100 pm and 150 pm thick magnetic absorbing layers, a 4 dB to 5 dB reduction in PIM signal was observed.

[0067] In another experiment, steel wool was placed on top of the bottom mounting bracket, and then a 3.5 inch wide strip of magnetic film was wrapped around the antenna mast on top of the bottom mounting bracket for two full wraps. 3M TM FFDM EM25TP-0150 and magnetic film with a 60 pm thick magnetic absorbing layer were tested, as well as Figure 10 magnetic permeability shown. The magnetic film with a 60 pm thick magnetic absorbing layer also included a 10 pm thick adhesive layer. For 3M TM FFDM EM25TP-0150, a 6 dB reduction in PIM signal was observed, while for the magnetic film with a Figure 10The magnetic films shown with magnetic permeability, a 2 dB drop in PIM signal was observed.

[0068] In another experiment, steel wool was placed on top of the bottom bracket and then a 3.5 inch wide strip of magnetic film was wrapped around the antenna mast two full turns on top of the bottom bracket. The magnetic film tested was 3M TM FFDM EM25TP-0150, the magnetic film included a 10 pm thick adhesive layer and a 60 pm thick magnetic absorbing layer with Figure 10 The magnetic films shown with magnetic permeability, a 2 dB drop in PIM signal was observed. Figure 10 Figure 10 The magnetic films shown with magnetic permeability, a 2 dB drop in PIM signal was observed. TM FFDM EM25TP-0150 film, a PIM signal drop of about 4 dB to 5 dB was observed, while a 2 dB to 3 dB drop was observed for the film with two 60 pm thick magnetic absorbing layers, and a 1 dB to 2 dB drop was observed for the magnetic film with a single 60 pm thick magnetic absorbing layer.

[0069] 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 in this specification. If the use of“about” to expressions of amounts of size, quantity, and physical properties that are unclear to those of ordinary skill in the art in the context in which they are used and described in this specification, then“about” will be understood to mean within 10% of the specified value. An amount given as about a specified value can be exactly the specified value. For example, if it is unclear to those of ordinary skill in the art in the context in which they are used and described in this specification, an amount having a value of about 1 means that the amount has a value between 0.9 and 1.1, and the value can be 1.

[0070] All cited references, patents and patent applications in the above disclosure in identically manner incorporated herein by reference. In the event that any inconsistency or conflict exists between a portion of the incorporated references and the application, the aforementioned description shall control.

[0071] Unless otherwise indicated, descriptions of elements in the figures should be understood to apply equally to corresponding elements in other figures. While specific embodiments have been illustrated and described, it will be appreciated that various alternate and / or equivalent implementations can be substituted for those illustrated and described herein without departing from the scope of the disclosure. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that the disclosure be limited only by the claims and the equivalents thereof.

Claims

1. A wireless communication system, the wireless communication system comprising: A transmitter configured to transmit at least a first radio wave and a second radio wave having correspondingly different frequencies F1 and F2; The first passive linear dielectric material with conductivity; A conductive first passive fundamental nonlinear medium, wherein the conductive first passive fundamental nonlinear medium is configured to be close to the first passive fundamental linear medium; as well as A first magnetic film, wherein the first magnetic film covers at least a first portion of the first passive essentially linear medium and no more than 20% of any conductive passive essentially nonlinear medium; When the transmitter transmits the first radio wave and the second radio wave, the first passive essentially linear medium and the first passive essentially nonlinear medium receive the first radio wave and the second radio wave and generate a first signal and a second signal propagating therein at corresponding frequencies F1 and F2. At least one intermodulation signal is generated in the first passive essentially nonlinear medium by the first signal and the second signal. 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 generation of the at least one intermodulation signal by at least 2 dB.

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

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

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

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

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

7. A wireless communication system, the wireless communication system comprising: A transmitter configured to transmit at least a first radio wave and a second radio wave having correspondingly different frequencies F1 and F2; The first passive fundamental nonlinear dielectric component; A conductive first passive fundamental linear dielectric portion is configured to be close to a first passive fundamental nonlinear dielectric portion, such that when the transmitter transmits the first radio wave and the second radio wave, the first passive fundamental linear dielectric portion receives the first radio wave and the second radio wave and generates a first signal and a second signal at corresponding frequencies F1 and F2. The first signal and the second signal propagate along a first path toward the conductive first passive fundamental nonlinear dielectric portion in the first passive fundamental linear dielectric portion. An intermodulation signal is generated in the first passive fundamental nonlinear dielectric portion from the first signal and the second signal. The intermodulation signal has a frequency F3 equal to nF1 + mF2, where m and n are positive or negative integers. as well as A first magnetic film covers at least a first portion of the first passive substantially linear medium portion along the first path and is configured such that the first and second signals generated propagating in the first passive substantially linear medium portion are attenuated more than the intermodulation signals generated in the first passive substantially nonlinear medium portion.

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

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 passive basic nonlinear medium portion, the first intermodulation signal and the second intermodulation signal having correspondingly different frequencies F3 and F3', each of F3 and F3' being equal to nF1 + mF2, where m and n are positive or negative integers, and the first magnetic film reduces each of the first intermodulation signal and the second intermodulation signal by at least 2 dB.

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

11. The wireless communication system according to any one of claims 1 to 9, wherein each of F1 and F2 is between 100 MHz and 10 GHz.

12. A system for reducing passive intermodulation, the system comprising: A conductive first passive fundamental linear medium is configured to receive a first radio wave and a second radio wave having correspondingly different frequencies F1 and F2 and generate a first signal and a second signal at corresponding frequencies F1 and F2. The first signal and the second signal propagate along a first path in the first passive fundamental linear medium toward the conductive first passive fundamental nonlinear medium. An intermodulation signal is generated in the first passive fundamental nonlinear medium by the first signal and the second signal. The intermodulation signal has a frequency F3 equal to nF1 + mF2, where m and n are positive or negative integers. as well as A first magnetic film, which covers at least a first portion of the first passive essentially linear medium and no more than 20% of the first passive essentially nonlinear medium along the first path.

13. A system for reducing passive intermodulation, the system comprising: A conductive first passive fundamental linear medium is configured to receive a first radio wave and a second radio wave having correspondingly different frequencies F1 and F2 and generate a first signal and a second signal at corresponding frequencies F1 and F2. The first signal and the second signal propagate along a first path in the first passive fundamental linear medium toward the conductive first passive fundamental nonlinear medium. An intermodulation signal is generated in the first passive fundamental nonlinear medium by the first signal and the second signal. The intermodulation signal has a frequency F3 equal to nF1 + mF2, where m and n are positive or negative integers. as well as A first magnetic film covers a first portion of the first passive substantially linear medium along the first path and leaves a second portion of the first passive substantially linear medium exposed, wherein the first magnetic film faces the first passive substantially nonlinear medium and the second portion faces away from the first passive substantially nonlinear medium, wherein the first magnetic film covers no more than 20% of the first passive substantially nonlinear medium.

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

15. The system of claim 12 or 13, further comprising a receiver such that when the intermodulation signal is generated, the intermodulation signal radiates radio waves at the frequency F3, and the receiver detects the radiated radio waves, wherein the first magnetic film reduces the radiated radio waves detected by the receiver by at least 2 dB.

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