Magnetic absorbers for passive intermodulation mitigation

Abstract

1. A wireless communication system comprising: a conductive passive medium, the conductive passive medium including a conductive first passive linear medium portion adjacent to a conductive first passive nonlinear medium portion, the conductive first passive linear medium portion capable of simultaneously propagating first and second electromagnetic currents of different frequencies F1 and F2 along the conductive passive medium, the first passive nonlinear medium portion capable of generating an intermodulation current based on a nonlinear interaction between the first and second currents, 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 the magnetic film attenuates at least a portion of the first and second currents when the first and second currents propagate along the first passive linear medium portion toward the first passive nonlinear medium portion, thereby reducing or preventing generation of the intermodulation current in the first passive nonlinear medium portion.

Description

Summary of the Invention

[0001] In some aspects herein, a wireless communication system is provided that includes: a conductive passive medium, the first electromagnetic current and the second electromagnetic current of different respective frequencies F1 and F2 can propagate simultaneously 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 can generate an intermodulation current based on a nonlinear interaction between the first current and the second current, the intermodulation current having a frequency Fi 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 reduces generation of the intermodulation current in the first passive nonlinear medium portion by attenuating at least a portion of the first current and the second current.

[0002] In some aspects herein, a wireless communication system is provided that includes 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 of 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, 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 that includes 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 of different respective frequencies F1 and F2, the first and second electromagnetic waves induce first and second currents of respective frequencies F1 and F2 propagating through the first and second sections, the first sections mixing the first and second currents to generate a third current of a frequency Fi different from F1 and F2, the third current propagating along the first and second sections, causing the first sections to radiate electromagnetic waves of the frequency Fi but not the second sections; and a magnetic film disposed on a 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 that includes 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, the linear medium portions and the nonlinear medium portions each capable of simultaneously propagating a first electromagnetic current and a second electromagnetic current of different respective frequencies F1 and F2 along the linear medium portions and the nonlinear medium portions, 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, m and n being 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, and correspondingly higher levels of SNR are required. 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 signals of interest are 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 in a system can create nonlinear elements in the system. In some cases, nonlinearities can occur due to poor metal-to-metal contact at the location of the antenna mounting bracket, or when 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 sources. [Brief description of the drawings]

[0008] [Figure 1] 1 is a side view of a wireless communication system according to an embodiment of the present disclosure. [Diagram 2] 1 illustrates a side view of a conductive passive medium capable of propagating electrical current in a wireless communication system according to an embodiment herein. [Diagram 3] FIG. 2 is a side view of a conductive passive medium having a magnetically absorbing film according to an embodiment herein. [Figure 4]FIG. 2 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. [Diagram 5] FIG. 13 is a side view of a conductive passive medium showing a bond between a metal and a metal oxide according to an alternative embodiment herein. [Figure 6] FIG. 13 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 PREFERRED EMBODIMENTS

[0009] In the following description, reference is made to the accompanying drawings which form a part hereof, and in which various embodiments are shown by way of illustration. 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 (64QAM, 256QAM, etc.) is used, and correspondingly higher levels of SNR are required. 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 signals of interest are 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 transmission path of the system. PIM interference is particularly noticeable in nodes that transmit at high power, such as cellular base station antennas. PIM occurs when two or more signals of different frequencies mix with each other due to nonlinearities in the mechanical components of the system. Two signals can be combined (by amplitude modulation) to produce sum and difference signals within the operating band of the wireless system, including within the harmonics of the signals, causing interference.

[0012] There are many mechanisms that can create or propagate PIM. Typically, the interaction and interconnection of conductive mechanical components in a system can create nonlinear elements in 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 in the nonlinearity to form a third current (i.e., the intermodulation current) at a new frequency Fi. The intermodulation current can be radiated from the bracket as PIM and / or conducted away from the bracket by a to a conductive linear part that acts as an antenna for the PIM and can radiate the 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 as well as 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., a 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 in 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 based on 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) would generate a signal of 869+894=1763 MHz, and the difference between the 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 intended reception band of the cellular system, and therefore these signals are not of concern for that particular cellular system (but these frequencies may be within the intended reception band or reception spectrum of another nearby system, and therefore may cause PIM interference in those systems). However, when these signals are combined to form third order products (when the sum of the absolute values ​​of m and n is 3), and sometimes higher order products, they can generate PIM signals within the intended reception band. For example, 2F1-F2 (844 MHz) and 2F2-F1 (919 MHz) generate third order products within the reception portion of the cellular band that can lead to PIM distortion.

[0016] In some embodiments, the conductive passive medium includes a conductive first passive linear medium portion adjacent to a conductive first passive nonlinear medium portion, the first passive nonlinear medium portion being capable of generating an intermodulation current based on a nonlinear interaction between a first current and a second current. For example, in some embodiments, the conductive first passive linear medium portion can be a metal mast (e.g., a galvanized steel mast) on which a cellular antenna is mounted, and the conductive first 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 current and the second current (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 nonlinear portion 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 conductive second passive linear medium portion adjacent to the conductive first passive nonlinear medium portion on the opposite side of the first passive linear medium portion (e.g., the nonlinear portion may be "sandwiched" between the first and second linear portions). In some embodiments, the second magnetic film may be disposed proximate to a conductive outer surface of the second linear medium portion such that when the first and second currents propagate along the first linear portion toward the nonlinear portion, the first magnetic film reduces the generation of intermodulation currents in the first nonlinear portion by absorbing at least a portion of the first and second currents. In some embodiments, at least a portion of the remaining portion of the first and second currents mix in the first nonlinear portion to generate an intermodulation current that propagates through the first nonlinear portion and the second linear portion, and the intermodulation current is at least partially absorbed by the second magnetic film.

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

[0019] In some embodiments, the intermodulation current may have a frequency Fi equal to nF1+mF2 propagating along the first passive nonlinear medium portion, 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 Fi is equal to 2F2-F1. In some embodiments, n may be equal to +2 and m may be equal to -1, and thus Fi is equal to 2F1-F2. In some embodiments, n may be equal to +1 and m may be equal to +1, and thus Fi is equal to F1+F2. In some embodiments, n may be equal to +2 and m may be equal to +2, so that Fi is equal to 2F1+2F2. In some embodiments, F1 and F2 are both less than about 6 GHz. In some embodiments, F1 and F2 are both between about 600 MHz and 4 GHz. In some embodiments, F1 and F2 are both between about 600 MHz and 800 MHz. In some embodiments, F1 and F2 are frequencies that are less than about 100 MHz apart, or less than about 50 MHz apart.

[0020] In some embodiments, the first magnetic film is disposed proximate to a 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 may reduce the intensity of intermodulation radiation 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 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 field 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 of 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, where 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 propagating 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 to absorb at least a portion of the third current. For example, in some embodiments, the magnetic film may be a magnetic absorbing film that is wrapped around the antenna mast (linear medium portion) adjacent to and in 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) interconnecting with the first sections such that when the one or more antennas radiate first and second electromagnetic waves of 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 of respective frequencies F1 and F2. In some embodiments, the first sections may generate a third current (e.g., an intermodulation current) of a frequency Fi 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 the Fi frequency in the first section that may propagate along the second section, but not in the second section, which may then radiate electromagnetic energy at the frequency Fi. In some embodiments, the second section may also generate a current at the Fi frequency 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., a plurality of 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 a mobile device and a cellular network) 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, 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 a first electromagnetic current and a second electromagnetic current of different respective frequencies F1 and F2. In some embodiments, each passive nonlinear portion may mix or otherwise combine 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 the passive linear portions do not generate the third current, and m and n are positive or negative integers. In some embodiments, the 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, the PIM currents may cause PIM emissions that increase the overall noise level in the frequency band (e.g., the cellular band) that the transceiver is intended to use, leading to degradation or distortion of the communication signal.

[0025] Referring now to the figures, FIG. 1 is a side view of a wireless communication system according to the present disclosure. 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 metallic antenna mast or mounting structure). In some embodiments, the 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 connection structure). It should be noted that the nonlinear portion 12 may be created by the presence of different materials and / or different conditions for the linear portion 11. That is, nonlinear elements may be created at the interface between two dissimilar metals (e.g., between the galvanized steel of an antenna mast and the metal used in a mounting bracket attached to the mast), by loose or broken connector points or cables, by rust, corrosion, dirt, oxidation, etc., by nearby metal objects such as roof flashing or pipes, or by any of a number of other causes. For illustrative purposes, Figure 1 shows a nonlinear element 12 that coincides 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, the wireless communication system 200 may also include one or more transceivers 60 (e.g., a transceiver housed in a base transceiver station for a cellular base station) coupled to the antenna 50. In some embodiments, the transceiver 60 may be used to facilitate wireless communication between an external device and a wireless network. In some embodiments, the 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 a linear portion 11 and a nonlinear portion 12, respectively, the first electromagnetic wave 40a and the second electromagnetic wave 40b may induce a first 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 act as a mixer that combines the first current 20 and the second current 21 to generate a third current (i.e., an intermodulation current) 22 at a third frequency Fi. The third current 22 (as well as the first current 20 and the second current 21) may then propagate (e.g., flow through a path in a metallic antenna mast) throughout the conductive passive medium 10, possibly flowing back to the transceiver 60 or to one or more antennas 50, or returning to one or more antennas 50 by being re-radiated into space as a second electromagnetic radiation 41 at a new frequency Fi. In some embodiments, the second antenna 50b may retransmit or receive the RF signals (having fundamental frequencies F1 and F2) originally generated in the first antenna 50a, including the PIM signals at frequency Fi generated in the one or more nonlinear sections 12 / 12a. These RF signals (and especially the Fi signals) may be seen as an increase in 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 media 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, such that the intermodulation currents 22 do not occur or are significantly reduced. In some embodiments, the magnetic film 30 may block the 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 the 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 the linear portions 11 on either side of the nonlinear portions 12, for example, to attenuate and / or eliminate currents generated in or exiting the nonlinear portions 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 signal) broadcast by a nearby antenna or emitted 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) in 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, the nonlinear portion 12 may be created by a number of things, including, but not limited to, joints between dissimilar materials, loose connections between machine parts, corroded or damaged areas, the proximity of other conductive components (e.g., pipes or roof flashing), etc. When the first current 20 and the second current 21 enter the nonlinear portion 12, the nonlinearity may cause the first current 20 and the 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, which has a frequency Fi that may represent the third harmonic of F1 and F2, which may be calculated, for example, using the formula Fi=nF1+mF2, where n and m may be positive or negative integers. Stated another way, 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 may then result in a reduction in 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 propagate away from nonlinear section 12 and into the 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 outer 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 entering 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 entering the nonlinear portion 12, the generation of the third (intermodulation) current 22 may be prevented or significantly reduced. In some embodiments, when the first current 20 and the second current 21 first occur within the nonlinear portion 12, the magnetic film 30 may limit or eliminate any currents, including the first current 20, the second current 21, and the third current 22, that attempt to exit 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 herein. 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 either side 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 portion (i.e., on the first linear portion 11 and the second linear portion 11a), the magnetic films 30 and 30a can absorb either any currents attempting to enter the nonlinear portion 12 (which may combine to generate new currents at new frequencies) or any currents attempting to exit the nonlinear portion 12. By absorbing these currents (including any PIM currents that are generated), 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 the conductive passive medium 10 or loosely connected to the conductive passive medium 10, whereby the difference results in a nonlinear component. In another example, the nonlinearity may be a rusted bolt or other fastener connecting two portions of the conductive passive medium 10 or connecting two portions of a material sufficiently different from the passive medium 10. FIGS. 4, 5, and 6 provide side cutaway views of similar embodiments of wireless communication systems, where various components and / or conditions may 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 in common with FIG. 3 and perform similar functions. Similar numbered elements already discussed with respect to FIG. 3 may not be discussed again with respect to FIGS. 4, 5, and 6, unless 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 to the nonlinear junction and intermodulation currents propagating away from the nonlinear junction that may contribute to the creation of PIM effects.

[0034] FIG. 5 is a side cutaway view of the conductive passive medium 10 in which the nonlinearity 12-2 is created by the junction between the metal 11 and the metal oxide 17. For example, in some embodiments, when oxygen is present, an ionic chemical reaction can occur on the surface of the exposed metal, 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 the nonlinearity 12-2 can help mitigate the creation of PIM distortion, as described herein.

[0035] 6 is a side view of the conductive passive medium 10 in which a nonlinearity 12-3 is created by a rust area 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 contacts (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, Figure 7 is a graph showing frequencies of transmitted and intermodulation 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 may arise from mixing of the Tx band signals. Moving from the F1 signal to the left of the page, there is a third order intermodulation, a fifth order intermodulation, a seventh order intermodulation, etc. Moving from the F2 signal to the right of the page, there is another third order intermodulation, a fifth order intermodulation, a seventh order intermodulation, etc. For example, the signal immediately to the left of the F1 signal is a third order passive intermodulation emission (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 into 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 raising the noise level and reducing the signal-to-noise ratio (SNR) of the signal. The use of magnetic absorbers as described herein can help to 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 skill in the art in the context in which they are used and described herein. If the use of "about" as applied to quantities describing feature sizes, quantities, and physical characteristics is not clear to those of 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, if it is not clear to those of 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 the value may be 1.

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

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

[0040] Descriptions of elements in a figure should be understood to apply equally to corresponding elements in other figures unless otherwise indicated. Although specific embodiments have been illustrated and described herein, those skilled in the art will appreciate 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, it is intended that the present disclosure be limited only by the claims and the equivalents thereof.

Claims

1. a conductive passive medium capable of simultaneously propagating a first current and a second 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 Fi equal to nF1+mF2 and propagating along the first passive nonlinear medium portion, m and n being positive or negative integers; a first magnetic film disposed proximate to a conductive outer surface of the first passive linear medium portion such that the magnetic film attenuates at least a portion of the first current and the second current as they 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. 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. 2. 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. 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 an opposite side from the first passive linear medium portion; a second magnetic film disposed proximate to a conductive outer surface of the second passive linear media portion such that when the first current and the second current propagate along the first passive linear media portion toward the first passive nonlinear media 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 media portion, at least a portion of a remaining portion of the first current and the second current mixes in the first passive nonlinear media portion to generate the intermodulation current, which propagates through the first passive nonlinear media portion and the second passive linear media portion, and the second magnetic film absorbs at least a portion of the intermodulation current propagating through the second passive linear media portion; The wireless communication system of claim 1 , further comprising:

9. The 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 of 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, the first passive nonlinear medium portion mixing 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 passive 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 of different respective frequencies F1 and F2, the first and second electromagnetic waves induce first and second currents of the respective frequencies F1 and F2 propagating through the first and second sections, the first sections mixing the first and second currents to generate a third current of 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 of the frequency Fi, but not the second sections; a magnetic film disposed on a conductive surface of each second section for absorbing at least a portion of the third current propagating along the second section; A wireless communication system comprising:

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