Magnetic absorbers for passive intermodulation mitigation

Abstract

To provide a wireless communication system and method for reducing the generation of an intermodulation current occurring in an electrically conductive passive medium.SOLUTION: In a wireless communication system including one or more antennas and transceivers disposed on an electrically conductive passive medium, the electrically conductive passive medium 10 has an electrically conductive passive linear portion 11, an electrically conductive passive nonlinear portion 12, and a first magnetic film 30. The magnetic film 30 is disposed proximately to an electrically conductive external surface of the first linear medium portion 11 such that, when a first current 20 and a second current 21 propagate along the first passive linear medium portion 11 toward the first passive nonlinear medium portion 12, the magnetic film reduces or prevents the generation of an intermodulation current in the first passive nonlinear medium portion 12 by attenuating at least portions of the first and second currents.SELECTED DRAWING: Figure 2

Description

Summary of the Invention

[0001] In some aspects herein, a wireless communication system is provided, including: a conductive passive medium capable of simultaneously propagating a first electromagnetic current and a second electromagnetic current having different frequencies F1 and F2 along the conductive passive medium, the conductive passive medium including a conductive first passive linear medium portion adjacent to the conductive first passive nonlinear medium portion, the first passive nonlinear medium portion capable of generating an intermodulation current based on a nonlinear interaction between the first current and the second current, the intermodulation current having a frequency F equal to nF1 + mF2 and propagating along the first passive nonlinear medium portion, where m and n are positive or negative integers; and a first magnetic film disposed proximate to a conductive outer surface of the first linear medium portion such that when the first current and the second current propagate along the first passive linear medium portion toward the first passive nonlinear medium portion, the magnetic film attenuates at least a portion of the first current and the second current, thereby reducing generation of the intermodulation current in the first passive nonlinear medium portion.

[0002] In some aspects herein, a wireless communication system is provided, including: an antenna; a conductive passive linear medium portion electrically interconnected with the conductive passive nonlinear medium portion such that when the antenna radiates first and second electromagnetic waves having different frequencies F1 and F2, the first and second electromagnetic waves induce respective first and second currents propagating through the first passive nonlinear medium portion, wherein the first passive nonlinear medium portion mixes the first and second currents to generate a third current having a frequency nF1+mF2 and propagating along the passive nonlinear medium portion and the passive linear medium portion, where m and n are positive or negative integers; and a magnetic film disposed on the passive linear medium portion but not on the nonlinear medium portion, and absorbing at least a portion of the third current.

[0003] In some aspects herein, a wireless communication system is provided, including one or more antennas; a plurality of spaced-apart conductive first sections; a plurality of conductive second sections interconnected with the first sections such that when the one or more antennas radiate first and second electromagnetic waves at different respective frequencies F1 and F2, the first and second electromagnetic waves induce first and second currents at the respective frequencies F1 and F2 propagating through the first and second sections, and the first sections mix the first and second currents to generate a third current at a frequency F1 different from F1 and F2, which third current propagates along the first and second sections, causing the first sections to radiate electromagnetic waves at the frequency F1 but not the second sections; and a magnetic film disposed on the conductive surface of each second section to absorb at least a portion of the third current propagating along the second sections.

[0004] In some aspects herein, a wireless communication system is provided, including: one or more antennas; one or more transceivers coupled to the one or more antennas; a plurality of conductive passive linear medium portions interconnected with a plurality of conductive passive nonlinear medium portions, wherein the linear medium portions and the nonlinear medium portions are each capable of simultaneously propagating a first electromagnetic current and a second electromagnetic current of different frequencies F1 and F2 along the linear medium portion and the nonlinear medium portion, and each passive nonlinear portion is capable of mixing the first current and the second current to generate a third current having a frequency nF1+mF2 and propagating along the passive nonlinear medium portion, but each passive linear portion does not generate the third current, and m and n are positive or negative integers; and a magnetic film disposed on at least some of the linear medium portions but not on the nonlinear medium portions. [Technical Field]

[0005] The present invention relates to wireless communication systems, and more particularly to a system and method for mitigating the effects of passive intermodulation distortion in wireless communication systems. [Background technology]

[0006] As wireless communication networks evolve, signal quality (more specifically, signal-to-noise ratio, or SNR) becomes increasingly important. To achieve very high data rates, higher-order modulation is used, requiring correspondingly higher levels of SNR. A common cause of SNR degradation is passive intermodulation (PIM) distortion, which can significantly reduce network performance and capacity. PIM distortion is generated when multiple frequencies encounter nonlinear materials or features, which then generate sum and difference combinations (products) of the fundamental frequencies and their harmonics. The resulting products often occur in uplink / receive frequency bands where the signal of interest is very weak, making coherent reception very difficult or impossible.

[0007] There are many mechanisms that can create or propagate PIM. Typically, the interaction and interconnection of conductive mechanical components within a system can create nonlinear elements within the system. In some cases, nonlinearities can occur due to poor metal-to-metal contact at the location of the antenna mounting bracket, or if the bracket contains a joint between dissimilar materials. Other sources of nonlinearities can be contamination, loose connections, nearby metal objects, or a variety of other causes. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a side view of a wireless communication system according to an embodiment of the present disclosure; [Figure 2] 1 is a side view of a conductive passive medium capable of carrying electrical current in a wireless communication system according to an embodiment herein; [Figure 3] FIG. 1 is a side view of a conductive passive medium having a magnetically absorbing film according to an embodiment herein. [Figure 4]FIG. 1 is a side view of a conductive passive medium showing a junction between a first conductive portion and a second conductive portion according to an embodiment herein. [Figure 5] FIG. 10 is a side view of a conductive passive medium showing a junction between a metal and a metal oxide according to an alternative embodiment herein. [Figure 6] FIG. 10 is a side view of a conductive passive medium showing metal corrosion according to an alternative embodiment herein. [Figure 7] 1 is a graph illustrating transmission frequencies and intermodulation frequencies of a wireless communication system, according to an embodiment herein; DETAILED DESCRIPTION OF THE INVENTION

[0009] In the following description, reference is made to the accompanying drawings which form a part hereof, and in which are shown by way of illustration various embodiments. The drawings are not necessarily to scale. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the specification. Accordingly, the following detailed description is not to be taken in a limiting sense.

[0010] As wireless communication networks evolve, signal quality (more specifically, signal-to-noise ratio, or SNR) becomes increasingly important. To achieve very high data rates, higher-order modulation (e.g., 64QAM, 256QAM) is used, requiring correspondingly higher levels of SNR. A common cause of SNR degradation is passive intermodulation (PIM) distortion, which can significantly reduce network performance and capacity. PIM distortion (abbreviated as "PIM") is generated when multiple frequencies encounter nonlinear materials or features, which then generate sum and difference combinations (products) of fundamental frequencies and their harmonics. The resulting products, especially third-order products, often occur in uplink / receive frequency bands where the signal of interest is very weak, making coherent reception very difficult or impossible.

[0011] PIM is a form of electromagnetic interference that occurs in wireless communication systems when the system simultaneously transmits signals at multiple frequencies through passive devices such as cables, connectors, antennas, mounting brackets, and other objects in or near the system's transmission path. PIM interference is particularly noticeable in nodes transmitting at high power, such as cellular base station antennas. PIM occurs when two or more signals at different frequencies mix with each other due to nonlinearities in the system's mechanical components. Two signals can be combined (through amplitude modulation) to produce sum and difference signals within the operating band of the wireless system, including within the signal's harmonics, causing interference.

[0012] There are many mechanisms that can create or propagate PIM. Typically, the interaction and interconnection of conductive mechanical components within a system can create nonlinear elements within the system. In some cases, nonlinearities can occur due to poor metal-to-metal contact at the location of the antenna mounting bracket or if the bracket contains a joint between dissimilar materials. For example, the fundamental frequencies (e.g., F1 and F2) of a cellular base station can be radiated by an antenna mounted on a galvanized steel mast. When currents are induced in the steel mast at these frequencies, they encounter the mounting bracket (i.e., the nonlinearity) and can mix within the nonlinearity to form a third current (i.e., intermodulation current) at a new frequency, F1. The intermodulation current can radiate from the bracket as PIM and / or be conducted away from the bracket to a conductive linear portion, which can act as an antenna for PIM and radiate PIM with even better efficiency than the nonlinear bracket. Although a magnetic absorber can be applied to encapsulate the bracket and prevent it from radiating PIM, intermodulation currents can still travel from the bracket, throughout the structure, and to other antennas, and ultimately be re-radiated, degrading the network.

[0013] Other causes of nonlinearity (and therefore PIM) can be contamination (e.g., rust, corrosion, dirt, oxidation, etc.), loose connections, nearby metal objects (e.g., guy wires, anchors, roof flashing, pipes, etc.), or a variety of other causes.

[0014] According to some aspects herein, a wireless communication system (e.g., a system including a cellular base station as a component) includes a conductive passive medium (e.g., the metallic structure of an antenna mast) along which first and second electromagnetic currents of different respective frequencies F1 and F2 can propagate simultaneously. In some embodiments, the first and second currents can be generated by two radio frequency (RF) signals transmitted at similar but different frequencies (i.e., F1 and F2).

[0015] For example, in one embodiment, F1 may be 869 MHz and F2 may be 894 MHz, with an adjacent receive band for signals returned from an external device (e.g., a mobile device). For example, the adjacent receive band may be 824-849 MHz. Another receive band may be adjacent to a frequency range above the transmit band (i.e., frequencies above the range of transmit band frequencies). These fundamental frequencies may be mixed to generate new frequency products according to the formula nF1 + mF2, where m and n are positive or negative integers. Simple addition of the modulated signals in this example (e.g., when both m and n are +1) produces a signal of 869 + 894 = 1763 MHz, and the difference between the signals (e.g., when n is +1 and m is -1) is 894 - 869 = 25 MHz. Both 25 MHz and 1763 MHz are outside the intended receive band of a cellular system, so these signals are not a concern for that particular cellular system (but these frequencies may be within the intended receive band or receive spectrum of another nearby system and therefore may cause PIM interference in that system). However, when these signals combine to form third-order products (when the sum of the absolute values ​​of m and n equals 3), and sometimes higher-order products, they can generate PIM signals within the intended receive band. For example, 2F1-F2 (844 MHz) and 2F2-F1 (919 MHz) generate third-order products within the receive portion of the cellular band that can lead to PIM distortion.

[0016] In some embodiments, the electrically conductive passive medium includes a first electrically conductive passive linear medium portion adjacent to a first electrically conductive passive nonlinear medium portion, which can generate an intermodulation current based on a nonlinear interaction between a first current and a second current. For example, in some embodiments, the first electrically conductive passive linear medium portion can be a metal mast (e.g., a galvanized steel mast) to which a cellular antenna is attached, and the first electrically conductive passive nonlinear medium portion can be a mounting bracket made of dissimilar metals. This junction or confluence of dissimilar materials can create a nonlinearity that acts similar to a diode, mixing the first and second currents (at frequencies F1 and F2) to generate an intermodulation current (PIM) at a new frequency. In some embodiments, the nonlinearity can be created by a junction between two dissimilar metals. In some embodiments, the nonlinearity can be created by a junction between a metal and a metal oxide (e.g., a metal oxide resulting from oxidation effects). In some embodiments, the nonlinearity may respond to areas of corrosion or contamination (eg, areas of rust, contaminants such as dirt, poor metal-to-metal contact, etc.).

[0017] In some embodiments, the wireless communication system may further include a second conductive passive linear medium portion adjacent to the first conductive passive nonlinear medium portion on the opposite side from the first passive linear medium portion (e.g., the nonlinear portion may be "sandwiched" between the first linear portion and the second linear portion). In some embodiments, a second magnetic film may be disposed proximate to a conductive outer surface of the second linear medium portion such that when the first current and the second current propagate along the first linear portion toward the nonlinear portion, the first magnetic film absorbs at least a portion of the first current and the second current, thereby reducing the generation of intermodulation currents in the first nonlinear portion. In some embodiments, at least a portion of the remaining portions of the first current and the second current mix in the first nonlinear portion to generate intermodulation currents that propagate through the first nonlinear portion and the second linear portion, and the intermodulation currents are at least partially absorbed by the second magnetic film.

[0018] In some embodiments, the first and second currents may be induced by electromagnetic radiation transmitted from an antenna coupled to the conductive passive linear medium. In some embodiments, the first and second currents may be induced by electromagnetic radiation radiated from a second passive nonlinear medium coupled to the first passive linear medium section. That is, PIM distortion may be generated in and radiated from a second nonlinear section coupled to the linear section, inducing a current in the linear section.

[0019] In some embodiments, the intermodulation current propagating along the first passive nonlinear medium portion may have a frequency F equal to nF1 + mF2, where m and n are positive or negative integers. For example, as discussed elsewhere herein, n may be 2 and m may be −1, or n may be −1 and m may be 2. These values ​​are merely examples, and other values ​​of n and m are possible. In some embodiments, one of m and n is a negative integer and the other of m and n is a positive integer. In some embodiments, n may be equal to −1 and m may be equal to +2, and thus F1 is equal to 2F2 − F1. In some embodiments, n may be equal to +2 and m may be equal to −1, and thus F1 is equal to 2F1 − F2. In some embodiments, n may be equal to +1 and m may be equal to +1, and thus F1 is equal to F1 + F2. In some embodiments, n may be equal to +2 and m may be equal to +2, such that F i is equal to 2F i + 2F i. In some embodiments, F i and F i are both less than about 6 GHz. In some embodiments, F i and F i are both between about 600 MHz and 4 GHz. In some embodiments, F i and F i are both between about 600 MHz and 800 MHz. In some embodiments, F i and F i are frequencies that are less than about 100 MHz apart, or less than about 50 MHz apart.

[0020] In some embodiments, the first magnetic film is disposed proximate to the conductive outer surface of the first linear medium portion such that when the first and second currents propagate along the first passive linear medium portion toward the first passive nonlinear medium portion, the magnetic film attenuates at least a portion of the first and second currents, thereby reducing the generation of intermodulation currents in the first passive nonlinear medium portion (e.g., preventing the currents from propagating through the corresponding structure). In some embodiments, the magnetic film can reduce the intensity of intermodulation emissions generated by and radiated from the first passive nonlinear medium portion by at least 3 dB.

[0021] In some embodiments, the first magnetic film can be a magnetic absorber. One example of a magnetic absorber is the 3M™ EMI Shielding Absorber AB6000HF series shielding film manufactured by 3M Corporation. In some embodiments, the magnetic film can attenuate the first current and the second current by absorbing at least a portion of the magnetic fields generated by the first current and the second current. In some embodiments, the first magnetic film does not cover any portion of the nonlinear portion.

[0022] According to some aspects herein, a wireless communication system includes an antenna (e.g., a cellular antenna) and a conductive passive linear medium portion (e.g., a junction of two dissimilar materials, such as a mounting bracket and an antenna mast) electrically interconnected with the conductive passive nonlinear medium portion such that when the antenna radiates first and second electromagnetic waves at different respective frequencies F1 and F2, the first and second electromagnetic waves induce respective first and second currents that propagate through the first passive nonlinear medium portion, wherein the first passive nonlinear medium portion mixes the first and second currents to generate a third current (i.e., an intermodulation current, or PIM) having a frequency nF1+mF2 and that propagates along the passive nonlinear medium portion and the passive linear medium portion, where m and n are integers that can be either positive or negative. In some embodiments, a magnetic film is disposed on the passive linear medium portion but not on the nonlinear medium portion and absorbs at least a portion of the third current. For example, in some embodiments, the magnetic film may be a magnetically absorbing film wrapped around the antenna mast (linear medium portion) adjacent to and within the propagation path, before the attached antenna mounting bracket (nonlinear medium portion). In some embodiments, disposing the magnetic film on the linear medium portion may impede the propagation of currents that may contribute to PIM interference. In some embodiments, the magnetic film may be disposed on both the passive linear medium portion and the passive nonlinear medium portion.

[0023] According to some aspects herein, a wireless communication system (e.g., a cellular base station) may include one or more antennas, a plurality of spaced-apart conductive first sections (e.g., one or more mounting brackets or irregular welds), and a plurality of conductive second sections (e.g., sections of an antenna mast) interconnected with the first sections such that when the one or more antennas radiate first and second electromagnetic waves at different respective frequencies F1 and F2, the first and second electromagnetic waves may propagate through the first and second sections, inducing first and second currents at the respective frequencies F1 and F2. In some embodiments, the first sections may generate a third current (e.g., an intermodulation current) at a frequency F1 different from F1 and F2 by mixing (e.g., combining by amplitude modulation) the first and second currents. In some embodiments, the generated third current may propagate along the first section and the second section, generating a new current at frequency F i in the first section that may propagate along the second section but not in the second section, which may then radiate electromagnetic energy at frequency F i. In some embodiments, the second section may also generate a current at frequency F i that may contribute to the radiated electromagnetic energy. In some embodiments, this "mixing" of currents may be caused by nonlinearities in the first section. For example, corrosion of a mounting bracket, a loose connection, or any number of other causes may cause nonlinearities in the first section, causing the first section to act as a current mixer and generate a third (intermodulation) current based on the first and second currents and their respective frequencies. In some embodiments, a magnetic film (e.g., a magnetic absorber) may be disposed on the conductive surface of each second section (e.g., wrapped around or disposed on the outer surface of the second section) to absorb at least a portion of the third current propagating along the second section.

[0024] According to some aspects of the present disclosure, a wireless communication system is provided that includes one or more antennas (e.g., multiple cellular antennas on a cellular base station), one or more transceivers (e.g., transceivers housed in a base transceiver station or BTS used to facilitate wireless communication between mobile devices and a cellular network) coupled to the one or more antennas, multiple conductive passive linear medium portions interconnected with multiple conductive passive nonlinear medium portions, and a magnetic film (e.g., a magnetic absorber) disposed on at least some of the linear medium portions but not on the nonlinear medium portions. In some embodiments, the linear medium portions and the nonlinear medium portions may each be capable of simultaneously propagating first and second electromagnetic currents of different respective frequencies F and F. In some embodiments, each passive nonlinear portion may mix or otherwise combine the first and second currents to generate a third current having a frequency n+m and propagating along the passive nonlinear medium portion, but the passive linear portion does not generate the third current, and m and n are positive or negative integers. In some embodiments, a magnetic absorber disposed on the linear portion may prevent the formation of currents in the linear portion that may otherwise contribute to the generation of third currents (e.g., PIM currents) when a nonlinear portion is encountered. In some embodiments, PIM currents may cause PIM emissions that increase the overall noise level within a frequency band (e.g., a cellular band) of interest for use by the transceiver, leading to degradation or distortion of communication signals.

[0025] Referring now to the figures, FIG. 1 is a side view of a wireless communication system in accordance with the present disclosure. In some embodiments, wireless communication system 200 includes one or more antennas 50 disposed on (e.g., mounted on, supported by) a conductive passive medium 10 (e.g., a metallic antenna mast or mounting structure). In some embodiments, conductive passive medium 10 may include two distinct portions: a conductive passive linear portion 11 (e.g., a major substantially dissimilar element of the mounting structure, such as a main shaft) and a conductive passive nonlinear portion 12 (e.g., a mounting bracket, weld bead, or other connecting structure). Note that nonlinear portion 12 may be created by the presence of different materials and / or different conditions for linear portion 11. That is, nonlinear elements may be created at the interface between two dissimilar metals (e.g., between the galvanized steel of an antenna mast and the metal used in a mounting bracket attached to the mast), by loose or broken connector points or cables, by rust, corrosion, dirt, oxidation, etc., by nearby metal objects such as roof flashing or pipes, or by any of a number of other causes. For illustrative purposes, Figure 1 shows nonlinear element 12 coinciding with the antenna's mounting bracket, but in fact it could be any suitable nonlinearity of any suitable cause or condition.

[0026] In some embodiments, wireless communication system 200 may also include one or more transceivers 60 (e.g., transceivers housed in a base transceiver station for a cellular base station) coupled to antenna 50. In some embodiments, transceiver 60 may be used to facilitate wireless communication between external devices and a wireless network. In some embodiments, transceiver 60 may be a high-power transceiver (e.g., 20 W or greater).

[0027] In operation, in some embodiments, the transceiver 60 of the wireless communication system 200 may generate two or more radio frequency (RF) signals, each at a unique frequency. These signals propagate through a transmission line (e.g., a coaxial cable or an optical fiber) and are broadcast / radiated as electromagnetic radiation 40 from an antenna 50 (e.g., a first antenna 50a). In some embodiments, the electromagnetic radiation 40 may include a first electromagnetic wave 40a radiating at a frequency F1 and a second electromagnetic wave 40b radiating at a frequency F2. In some embodiments, when the first electromagnetic wave 40a and the second electromagnetic wave 40b impinge on a structure comprising the linear portion 11 and the nonlinear portion 12, respectively, the first electromagnetic wave 40a and the second electromagnetic wave 40b may induce a first current 20 and a second current 21, respectively, in the nonlinear portion 12 at corresponding frequencies F1 and F2 (the first current 20 and the second current 21 are shown in FIG. 2 ). In some embodiments, the nonlinear section 12 may function as a mixer, combining the first current 20 and the second current 21 to generate a third current (i.e., an intermodulation current) 22 at a third frequency F i. The third current 22 (as well as the first current 20 and the second current 21) may then propagate throughout the conductive passive medium 10 (e.g., following the path of a metal antenna mast) and, in some cases, return to the transceiver 60 or to one or more antennas 50, or to one or more antennas 50 by being re-radiated into space as second electromagnetic radiation 41 at a new frequency F i. In some embodiments, the second antenna 50b may retransmit or receive the RF signals (having fundamental frequencies F i and F i ) originally generated at the first antenna 50a, including PIM signals at frequency F i generated within one or more nonlinear sections 12 / 12a. These RF signals (and particularly the F i signals) may be seen as increased noise in the transceiver 60, significantly reducing the SNR of the signal of interest.

[0028] To mitigate the effects of PIM, one or more magnetic films 30 (including 30a and 30b in some embodiments) may be disposed on or near the conductive outer surface 13 of the linear medium portion 11. In some embodiments, the magnetic film 30 may reduce or prevent the generation of intermodulation currents 22 in the nonlinear portion 12. In some embodiments, the intermodulation currents 22 may be reduced by the magnetic film 30 in several ways. In some embodiments, the magnetic film 30 may attenuate one or both of the first current and the second current before they enter the nonlinear portion 12, thereby preventing or significantly reducing the generation of intermodulation currents 22. In some embodiments, the magnetic film 30 may block current or radiated energy from the nonlinear portion 12 before it exits the nonlinear portion 12 and enters the linear portion 11 / 11a / 11b. In some embodiments, additional magnetic films 30 (such as films 30a and / or 30b) may be disposed on or adjacent to additional linear portions 11 (such as portions 11a and / or 11b) to help attenuate currents induced in or passing through the structure. In some embodiments, magnetic films 30 (e.g., magnetic absorbers) may be disposed on linear portions 11 on either side of nonlinear portion 12, for example, to attenuate and / or eliminate currents generated in or exiting nonlinear portion 12.

[0029] FIG. 2 is a side view of the conductive passive medium 10 of FIG. 1 , showing further details regarding the generation of intermodulation currents. Electromagnetic radiation (RF signals) broadcast by a nearby antenna or radiated by another conductive structure (as shown in FIG. 1 ) induces a first current 20 (corresponding to an RF signal having a fundamental frequency F1) and a second current 21 (corresponding to an RF signal having a fundamental frequency F2) within the conductive passive medium 10 (e.g., a metallic portion of an antenna mast). In some embodiments, the first current 20 and the second current 21 may be induced in the conductive passive linear portion 11 of the conductive passive medium 10 and then travel through other portions of the structure. In these embodiments, the first current 20 and the second current 21 may propagate through the conductive passive linear portion 11 until they encounter the conductive passive nonlinear portion 12. As described elsewhere herein, nonlinear portion 12 can be created by several things, including, but not limited to, joints between dissimilar materials, loose connections between mechanical parts, corroded or damaged areas, the proximity of other conductive components (e.g., pipes or roof flashing), etc. When first current 20 and second current 21 enter nonlinear portion 12, the nonlinearity can cause first current 20 and second current 21 to mix and generate a new current having a new frequency. In some embodiments, at least a third current 22 is generated, having a frequency Fi that can represent a third harmonic of Fi and F2, which can be calculated, for example, using the formula Fi = nF1 + mF2, where n and m can be positive or negative integers. In other words, the third current may be an intermodulation current having a frequency Fi that, when radiated from an antenna or other structure, may cause the antenna 50 to receive an intermodulation signal in a frequency range intended to receive signals from an external device (e.g., a mobile device such as a cellular telephone), thereby increasing the noise level and reducing the fidelity of the received signal. This, in turn, may reduce the rate at which information can be transferred from the mobile device to the antenna 50, or may result in a loss of connection from the mobile device to the antenna (i.e., a "dropped call").In other embodiments, first current 20 and second current 21 may be induced directly in nonlinear section 12 (rather than originating in linear section 11 and propagating to nonlinear section 12). In these embodiments, each of currents 20 and 21, as well as intermodulation current 22, may exit nonlinear section 12 and propagate away to adjacent linear section 11.

[0030] In some embodiments, the magnetic film 30 may be disposed on the linear portion 11 of the conductive passive medium 10 adjacent to the nonlinear portion 12 (e.g., disposed on the exterior surface or wrapped around the linear portion 11). In some embodiments, the magnetic film 30 may be a magnetic absorber that at least partially attenuates the first current 20 and the second current 21, and at least a portion of any electromagnetic fields generated by the currents 20 and 21, before they enter the nonlinear portion 12 (through absorption of the magnetic fields generated by the currents 20 and 21 adjacent to the linear section). By reducing or eliminating the first current 20 and the second current 21 before they enter the nonlinear portion 12, the generation of the third (intermodulation) current 22 can be prevented or significantly reduced. In some embodiments, when the first current 20 and the second current 21 initially occur within the nonlinear portion 12, the magnetic film 30 can limit or eliminate any currents, including the first current 20, the second current 21, and the third current 22, from exiting the nonlinear portion 12.

[0031] In some embodiments, two or more magnetic films 30 may be disposed on multiple linear portions 11 (e.g., on the shaft of an antenna mast that extends both above and below a nonlinear portion, such as a mounting bracket) to prevent or reduce PIM currents that may occur in the nonlinear portion 12 from propagating throughout other portions of the conductive passive medium 10. FIG. 3 is a side cutaway view of a conductive passive medium 10 having a magnetic absorbing film, according to one embodiment of the present disclosure. In the illustrated embodiment, the conductive passive medium 10 includes a conductive first 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 the 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 opposite sides of the nonlinear portion 12. The first magnetic film 30 is disposed proximate to the conductive outer surface 13 of the first linear portion 11 (e.g., wrapped around the first linear portion 11), and the second magnetic film 30a is disposed proximate to the conductive outer surface 13a of the second linear portion 11a. In some embodiments, the first induced current 20 and the second induced current 21 propagate along the first linear portion 11 and enter the nonlinear portion 12. Upon entering the nonlinear portion 12, the first current 20 and the second current 21 mix to generate a third or intermodulation current 22, which may then propagate out of the nonlinear portion 12 as a surface wave. By placing the first magnetic film 30 and the second magnetic film 30a on either side of the nonlinear section (i.e., on the first linear section 11 and the second linear section 11a), the magnetic films 30 and 30a can absorb any currents either attempting to enter the nonlinear section 12 (which may combine to generate new currents at new frequencies) or attempting to exit the nonlinear section 12. By absorbing these currents (including any generated PIM currents), as well as absorbing the electromagnetic fields resulting from the currents or preventing the formation of electromagnetic fields, the magnetic films 30 and 30a can eliminate or significantly reduce PIM interference.

[0032] The exemplary nonlinearity shown in FIG. 3 (i.e., nonlinearity 12) may be created by a mounting bracket or mounting hardware made of a material sufficiently different from, or loosely connected to, the conductive passive medium 10, thereby resulting in a nonlinear component. In another example, the nonlinearity may be a rusted bolt or other fastener connecting two portions of the conductive passive medium 10 or connecting two portions of a material sufficiently different from the passive medium 10. FIGS. 4, 5, and 6 provide side cutaway views of similar embodiments of wireless communication systems, in which various components and / or conditions create nonlinearities and potentially lead to the generation of PIM interference as described herein. Each of FIGS. 4, 5, and 6 includes similarly numbered elements that are common to FIG. 3 and perform similar functions. Similar numbered elements already described with respect to FIG. 3 may not be discussed again with respect to FIGS. 4, 5, and 6, except where necessary.

[0033] 4 is a side cutaway view of a conductive passive medium 10 in which a nonlinearity 12-1 is created by a junction between a first metal 11 and a second, dissimilar metal 15. For example, the surface contact area between the first metal 11 and the second, dissimilar metal 15 may have different electrochemical potentials, creating a nonlinear I / V curve (nonlinear junction). The use of one or more magnetic films 30 / 30a disposed on the outer surface 13 / 13a adjacent to the nonlinearity 12-1 can absorb / mitigate induced currents propagating toward the nonlinear junction and intermodulation currents propagating away from the nonlinear junction, which may contribute to the generation of PIM effects.

[0034] FIG. 5 is a side cutaway view of conductive passive medium 10, in which nonlinearity 12-2 is created by the junction between metal 11 and metal oxide 17. For example, in some embodiments, in the presence of oxygen, an ionic chemical reaction can occur on the exposed metal surface, transferring electrons from the metal to oxygen molecules and creating negative oxygen ions that can create an oxide surface on the metal. The interface between the original metal and the created metal oxide can be a PIM source. Placing one or more magnetic films 30 adjacent to nonlinearity 12-2 can help mitigate the creation of PIM distortion, as described herein.

[0035] 6 is a side view of a conductive passive medium 10 in which a nonlinearity 12-3 is created by a rust region 18 on the conductive passive medium 10. Other conditions that can create nonlinearities include, but are not limited to, contaminants (e.g., dirty connections), loose connections, irregular metal-to-metal contact (e.g., poor weld beads), and uneven contact surfaces. Placing one or more magnetic films 30 adjacent to the nonlinearity 12-3 can help mitigate the creation of PIM distortion, as described herein.

[0036] Finally, FIG. 7 is a graph illustrating the frequencies of transmitted and intermodulated signals in a wireless communication system as described herein. The y-axis shows the relative amplitude (strength) of the signals, and the x-axis shows the relative frequency bands of the signals. In the center of the graph, the transmit band, or Tx band (in this example), includes two signals for intended transmission, labeled based on their corresponding frequencies F1 and F2, as described elsewhere herein. Moving in either direction from the Tx band signals, there are an odd number of passive intermodulation signals that can arise from mixing of the Tx band signals. Moving from the F1 signal to the left side of the page, there are third-order intermodulations, fifth-order intermodulations, seventh-order intermodulations, etc. Moving from the F2 signal to the right side of the page, there are another third-order intermodulation, fifth-order intermodulation, seventh-order intermodulation, etc. For example, the signal immediately to the left of the F1 signal is third-order passive intermodulation emissions (PIM) generated by the equation nF1 + mF2 when n = +2 and m = -1 (i.e., 2F1 - F2). As can be seen in Figure 7, this third-order intermodulation falls within one of the intended receive bands, or Rx bands, used by the wireless communication system, and the amplitude of the signal is still relatively high. These types of PIM signals can interfere with the reception of legitimate intended signals by increasing the noise level and reducing the signal-to-noise ratio (SNR) of the signal. The use of a magnetic absorber as described herein can help mitigate the generation of these PIM distortion signals and improve the SNR of the intended wireless system signals.

[0037] Terms such as "about" will be understood by those of ordinary skill in the art in the context in which they are used and described herein. Where the use of "about" as applied to quantities expressing feature sizes, amounts, and physical characteristics is not clear to those of ordinary skill in the art in the context in which they are used and described herein, "about" will be understood to mean within 10 percent of a particular value. A quantity given as about a particular value may be exactly that particular value. For example, where it is not clear to those of ordinary skill in the art in the context in which they are used and described herein, an amount having a value of about 1 means that the amount has a value between 0.9 and 1.1, and means that the value may be 1.

[0038] Terms such as "substantially" will be understood by those skilled in the art in the context in which they are used and described herein. If the use of "substantially equal" is not clear to those skilled in the art in the context in which it is used and described herein, "substantially equal" means approximately equal, with approximately being as described above. If the use of "substantially parallel" is not clear to those skilled in the art in the context in which it is used and described herein, "substantially parallel" means within 30 degrees of parallel. Directions or surfaces described as substantially parallel to each other may, in some embodiments, be within 20 degrees or within 10 degrees of parallel, or may be parallel or nominally parallel. If the use of "substantially aligned" is not clear to those skilled in the art in the context in which it is used and described herein, "substantially aligned" means aligned within 20% of the width of the objects to be aligned. Objects described as being substantially aligned may, in some embodiments, be aligned within 10% or within 5% of the width of the objects to be aligned.

[0039] All of the above-referenced references, patents, or patent applications are hereby incorporated by reference in their entirety. In the event of any inconsistency or contradiction between the incorporated reference portions and this application, the information in the foregoing description shall prevail.

[0040] Descriptions of elements in a figure should be understood to apply equally to corresponding elements in other figures unless otherwise indicated. While specific embodiments have been illustrated and described herein, those skilled in the art will recognize that the specific embodiments illustrated and described may be replaced by various alternative and / or equivalent embodiments without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Accordingly, the present disclosure is intended to be limited only by the claims and equivalents thereof.

Claims

1. a conductive passive medium capable of simultaneously propagating a first electromagnetic current and a second electromagnetic current of different respective frequencies F1 and F2 along the conductive passive medium, the conductive passive medium comprising a conductive first passive linear medium portion adjacent to a conductive first passive nonlinear medium portion, the first passive nonlinear medium portion capable of generating an intermodulation current based on a nonlinear interaction between the first current and the second current, the intermodulation current having a frequency F i equal to nF1 + mF2 and propagating along the first passive nonlinear medium portion, where m and n are positive or negative integers; a first magnetic film disposed proximate to a conductive outer surface of the first linear medium portion such that the magnetic film attenuates at least a portion of the first current and the second current when the first current and the second current propagate along the first passive linear medium portion toward the first passive nonlinear medium portion, thereby reducing or preventing the generation of the intermodulation current in the first passive nonlinear medium portion; A wireless communication system comprising:

2. 10. The wireless communication system of claim 1, wherein the first passive nonlinear medium portion comprises a junction between dissimilar first and second metals.

3. 10. The wireless communication system of claim 1, wherein the first passive nonlinear medium portion comprises a junction between a metal and a metal oxide.

4. 10. The wireless communication system of claim 1, wherein the first passive nonlinear medium portion comprises a rusted region of the conductive passive medium.

5. 2. The wireless communication system of claim 1, wherein the first current and the second current propagating along the first passive linear medium portion toward the first passive nonlinear medium portion are induced by electromagnetic radiation radiated from an antenna coupled to the first passive linear medium portion.

6. 2. The wireless communication system of claim 1, wherein the first current and the second current propagating along the first passive linear medium portion toward the first passive nonlinear medium portion are induced by electromagnetic radiation radiated from a second passive nonlinear medium coupled to the first passive linear medium portion.

7. 2. The wireless communication system of claim 1, wherein the first magnetic film does not cover any portion of the first passive nonlinear medium portion.

8. a second electrically conductive passive linear medium portion adjacent to the first electrically conductive passive nonlinear medium portion on the opposite side from the first electrically conductive passive linear medium portion; a second magnetic film disposed proximate to a conductive outer surface of the second linear medium portion such that when the first current and the second current propagate along the first passive linear medium portion toward the first passive nonlinear medium portion, the first magnetic film absorbs a portion of the first current and the second current, thereby reducing the generation of the intermodulation current in the first passive nonlinear medium portion, and at least a portion of the remaining portion of the first current and the second current mixes in the first passive nonlinear medium portion to generate the intermodulation current, which propagates through the first passive nonlinear medium portion and the second passive linear medium portion, and the second magnetic film absorbs at least a portion of the intermodulation current propagating through the second passive linear medium portion; The wireless communication system of claim 1 further comprising:

9. The antenna and a conductive passive linear medium portion electrically interconnected with the conductive passive nonlinear medium portion such that when the antenna radiates first and second electromagnetic waves having different respective frequencies F1 and F2, the first and second electromagnetic waves induce respective first and second currents propagating through the first passive nonlinear medium portion, wherein the first passive nonlinear medium portion mixes the first and second currents to generate a third current having a frequency nF1+mF2 and propagating along the passive nonlinear medium portion and the passive linear medium portion, m and n being positive or negative integers; a magnetic film disposed on the passive linear medium portion but not on the nonlinear medium portion, the magnetic film absorbing at least a portion of the third current; A wireless communication system comprising:

10. one or more antennas; a plurality of spaced apart conductive first sections; a plurality of conductive second sections interconnected with the first sections such that, when the one or more antennas radiate first and second electromagnetic waves at different respective frequencies F1 and F2, the first and second electromagnetic waves induce first and second currents at the respective frequencies F1 and F2 that propagate through the first and second sections, the first sections mixing the first and second currents to generate a third current at a frequency Fi different from F1 and F2, the third current propagating along the first and second sections and causing the first sections to radiate electromagnetic waves at the frequency Fi but not the second sections; a magnetic film disposed on the conductive surface of each second section to absorb at least a portion of the third current propagating along the second section; A wireless communication system comprising:

Images