System with lossy material for reducing passive intermodulation

Abstract

A wireless communication system includes a transmitter, a plurality of passive substantially linear medium portions including one or more first portions and a second portion, one or more passive substantially nonlinear medium portions disposed proximate the substantially linear medium portions, and for each first portion, a dielectrically lossy or magnetically lossy first material disposed on the first portion. When the transmitter transmits first and second radio waves, the substantially linear and nonlinear medium portions receive the first and second radio waves and generate first and second signals propagating therein, where at least one intermodulation signal is generated in the one or more substantially nonlinear medium portions from the first and second signals, and the one or more first materials reduces the generation of the at least one intermodulation signal by at least 2 dB.

Description

[0001] SYSTEM WITH LOSSY MATERIAL FOR REDUCING PASSIVE INTERMODULATION

[0002] TECHNICAL FIELD

[0003] The present description relates generally to wireless communication systems.

[0004] BACKGROUND

[0005] As wireless communication networks evolve, signal quality (and, more specifically, signal-to- noise ratio, or SNR) becomes increasingly important. Higher orders of modulation are used to achieve very high data rates and require correspondingly higher levels of SNR. A common cause of SNR degradation is Passive Intermodulation (PIM) distortion, which can significantly reduce the performance and capacity of a network. PIM distortion is created when multiple frequencies encounter a non-linear material or feature, 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.

[0006] There are many mechanisms through which PIM can be created or propagated. Typically, the interactions and interconnections of electrically conductive mechanical components in a system can create a nonlinear element in the system. A nonlinearity may, in some cases, be caused by poor metal -to- metal contact at the location of an antenna mounting bracket, or if the bracket comprises a junction between dissimilar materials. Other causes of nonlinearities may be contamination, loose connections, nearby metal objects, or a variety of other causes.

[0007] SUMMARY

[0008] In some aspects, the present description provides a wireless communication system including a transmitter, a plurality of passive substantially linear medium portions including one or more first portions and at least one second portion, one or more passive substantially nonlinear medium portions disposed proximate the substantially linear medium portions, and for each first portion, a dielectrically lossy or magnetically lossy first material disposed on the first portion. When the transmitter transmits first and second radio waves, the substantially linear and nonlinear medium portions receive the first and second radio waves and generate first and second signals propagating therein, where at least one intermodulation signal is generated in the one or more substantially nonlinear medium portions from the first and second signals, and the one or more first materials reduces the generation of the at least one intermodulation signal by at least 2 dB.

[0009] In some aspects, the present description provides a wireless communication system including a transmitter, a plurality of electrically conductive passive substantially linear medium portions, and one or more electrically conductive passive substantially nonlinear medium portions disposed proximate the plurality of electrically conductive passive substantially linear medium portions. The transmitter is configured to transmit at least first and second radio waves having respective different frequencies F 1 and F2. The transmitter extends primarily along length and width directions and has a length LI and a width W1 along the respective length and width directions, where LI > Wl. The plurality of electrically conductive passive substantially linear medium portions includes one or more first portions and a second portion. Each first portion extends primarily along a first direction substantially orthogonal to the length and width directions. Each first portion has a maximum lateral dimension Dp less than each of 0.2 Wl and 0.1 LI . The second portion extends primarily along the length direction and has a width W2 along the width direction. W2 can be less than each of LI and Wl and greater than 2 Dp. Each first portion extends away from the transmitter along the first direction past the second portion for a length Lp, where Lp > 2 Dp. The one or more first portions and the second portion can be disposed on a same side of the transmitter. The wireless communication system includes, for each first portion, a dielectrically lossy or magnetically lossy first material substantially surrounding the first portion in each cross-section orthogonal to the first direction along greater than 50 percent of the length Lp of the first portion, such that when the transmitter transmits the first and second radio waves, the electrically conductive passive substantially linear and nonlinear medium portions receive the first and second radio waves and generate first and second signals propagating therein at the respective frequencies Fl and F2, where at least one intermodulation signal is generated in the one or more passive substantially nonlinear medium portions from the first and second signals, the at least one intermodulation signal has a frequency F3 equal to nFl+mF2 where m and n are positive or negative integers, and the one or more first materials reduces the generation of the at least one intermodulation signal by at least 2 dB.

[0010] In some aspects, the present description provides a wireless communication system including a transmitter, a plurality of electrically conductive passive substantially linear medium portions, and one or more electrically conductive passive substantially nonlinear medium portions disposed proximate the plurality of electrically conductive passive substantially linear medium portions. The transmitter is configured to transmit at least first and second radio waves having respective different frequencies F 1 and F2. The transmitter extends primarily along length and width directions and has a length LI and a width Wl along the respective length and width directions, where LI > Wl. The plurality of electrically conductive passive substantially linear medium portions includes one or more first portions and a second portion. Each first portion extends primarily along a first direction and has a length Lp along the first direction. Each first portion has a maximum lateral dimension Dp less than each of 0.2 Wl and 0.1 LI. Lp > 2 Dp. The second portion extends primarily along the length direction and has a width W2 along the width direction. W2 can be less than each of LI and W 1 and greater than 2 Dp. Each first portion is separated from the transmitter by a distance greater than LI . The wireless communication system includes, for each first portion, a dielectrically lossy or magnetically lossy first material substantially surrounding the first portion in each cross-section orthogonal to the first direction along greater than 50 percent of the length Lp of the first portion, such that when the transmitter transmits the first and second radio waves, the electrically conductive passive substantially linear and nonlinear medium portions receive the first and second radio waves and generate first and second signals propagating therein at the respective frequencies F 1 and F2, where at least one intermodulation signal is generated in the one or more passive substantially nonlinear medium portions from the first and second signals, the at least one intermodulation signal has a frequency F3 equal to nFl+mF2 where m and n are positive or negative integers, and the one or more first materials reduces the generation of the at least one intermodulation signal by at least 2 dB.

[0011] In some aspects, the present description provides a wireless communication system including a transmitter, a plurality of electrically conductive passive substantially linear medium portions, and one or more electrically conductive passive substantially nonlinear medium portions disposed proximate the plurality of electrically conductive passive substantially linear medium portions. The transmitter is configured to transmit at least first and second radio waves having respective different frequencies F 1 and F2. The transmitter extends primarily along length and width directions and has a length LI and a width W1 along the respective length and width directions, where LI > WL The plurality of electrically conductive passive substantially linear medium portions includes one or more first portions and a second portion. Each first portion extends primarily along a first direction and has a length Lp along the first direction. Each first portion has a maximum lateral dimension Dp less than each of 0.2 Wl and 0.1 LI. Lp > 2 Dp. The second portion extends primarily along the length direction and has a width W2 along the width direction. W2 can be less than each of LI and W 1 and greater than 2 Dp. Each first portion is separated from the transmitter by a distance greater than LI or is disposed on a same side of the transmitter as the second portion with the first direction of the first portion substantially orthogonal to the length and width directions. The wireless communication system includes, for each first portion, a dielectrically lossy or magnetically lossy first material substantially surrounding the first portion in each cross-section orthogonal to the first direction along greater than 50 percent of the length Lp of the first portion, such that when the transmitter transmits the first and second radio waves, the electrically conductive passive substantially linear and nonlinear medium portions receive the first and second radio waves and generate first and second signals propagating therein at the respective frequencies Fl and F2, where at least one intermodulation signal is generated in the one or more passive substantially nonlinear medium portions from the first and second signals, the at least one intermodulation signal has a frequency F3 equal to nFl+mF2 where m and n are positive or negative integers, and the one or more first materials reduces the generation of the at least one intermodulation signal by at least 2 dB.

[0012] These and other aspects will be apparent from the following detailed description. In no event, however, should this brief summary be construed to limit the claimable subject matter.

[0013] BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIGS. 1A-1B are schematic side views of wireless communication systems, according to some embodiments.

[0015] FIGS. 2A-2B are schematic perspective views of portions of a wireless communication, according to some embodiments.

[0016] FIGS. 3A-3D are schematic perspective views of dielectrically lossy or magnetically lossy materials configured to substantially surround at least one cross-section of an electrically conductive passive substantially linear medium portion, according to some embodiments. FIGS. 3E-3F are schematic cross-sectional views of dielectrically lossy or magnetically lossy materials 150 configured to substantially surround at least one cross-section of an electrically conductive passive substantially linear medium portion, according to various embodiments.

[0017] FIG. 4 is a schematic perspective view of a dielectrically lossy or magnetically lossy material including a plurality of discrete portions, according to some embodiments.

[0018] FIGS. 5A-5B are schematic perspective views of a dielectrically lossy or magnetically lossy material including a plurality of discrete portions arranged in a clamshell form factor, according to some embodiments.

[0019] FIGS. 6A-6B are schematic perspective views of dielectrically lossy or magnetically lossy material disposed in a slit-ring form factor, according to some embodiments.

[0020] FIG. 7 is a schematic cross-sectional view of a dielectrically lossy or magnetically lossy first material including a plurality of dielectrically lossy or magnetically lossy particles dispersed in a binder, according to some embodiments.

[0021] FIG. 8 is a schematic cross-sectional view of a weather resistant cover substantially covering a dielectrically lossy or magnetically lossy material that substantially surrounds at least one cross-section of an electrically conductive passive substantially linear medium portion, according to some embodiments.

[0022] DETAILED DESCRIPTION

[0023] In the following description, reference is made to the accompanying drawings that 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 present description. The following detailed description, therefore, is not to be taken in a limiting sense.

[0024] As wireless communication networks evolve, signal quality (and, more specifically, signal-to- noise ratio, or SNR) becomes increasingly important. Higher orders of modulation (64QAM, 256QAM, etc.) are used to achieve very high data rates and require correspondingly higher levels of SNR. A common cause of SNR degradation is Passive Intermodulation (PIM) distortion, which can significantly reduce the performance and capacity of a network. PIM distortion (“PIM” for short) is created when multiple frequencies encounter a non-linear material or feature, which then generate sum and difference combinations (products) of the fundamental frequencies and their harmonics. The resulting products, typically 3rd, 5th, and / or 7thorder products, often occur in uplink / receive frequency bands where the signal of interest is very weak, making coherent reception very difficult or impossible.

[0025] PIM is a form of electromagnetic interference that occurs in a wireless communication system when the system simultaneously transmits signals at multiple frequencies through passive devices, such as cables, connectors, antennas, mounting brackets, and other objects in or in proximity to the system's transmission path. PIM interference becomes particularly pronounced in nodes that transmit at high power, such as a cellular base station antenna. PIM is generated when two or more signals at different frequencies mix with each other due to nonlinearities in mechanical components of the system. Two signals may combine (through amplitude modulation) to produce sum and difference signals, including within the harmonic of the signals, within the operating bands of the wireless system, causing interference.

[0026] There are many mechanisms through which PIM can be created or propagated. Typically, the interactions and interconnections of electrically conductive mechanical components in a system can create a nonlinear element in the system. A nonlinearity may, in some cases, be caused by poor metal -to- metal contact at the location of an antenna mounting bracket, or if the bracket comprises a junction between dissimilar materials. For example, the fundamental frequencies (e.g., Fl and F2) of a cellular base station may be radiated by an antenna mounted on a galvanized steel mast. When signals (e.g., electric currents and / or electric voltages) are induced in the steel mast at these frequencies, those signals may encounter the mounting bracket (i.e., the nonlinearity), and be mixed within the nonlinearity to form a third signal (i.e., the intermodulation signal) at a new frequency, F3. The intermodulation signal may be radiated from the bracket as PIM, and / or conducted away from the bracket by a conductive linear portion, which may act as an antenna for the PIM and radiate the PIM out with even better efficiency than the nonlinear bracket. Electrically conductive shields are often applied to encapsulate the bracket, preventing the PIM from being radiated by the bracket, but intermodulation signal (e.g., current) may still travel from the bracket throughout the structure as well as to other antennas, eventually re-radiating and degrading the network.

[0027] Other causes of nonlinearities (and, therefore, PIM) may 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.

[0028] Magnetic film(s) have been used around the large vertical structure (e.g., the galvanized steel mast) supporting a wireless communication system (e.g., a system including an antenna and a cellular base station as components) as described in U.S. Pat. Appl. Pub. Nos. 2022 / 0052643 (Bruzzone et al.) and 2023 / 0327308 (Bruzzone er al.), for example.

[0029] According to some aspects of the present description, a wireless communication system includes a transmitter extending along length and width directions, and a plurality of electrically conductive, passive, substantially linear medium portions including one of more first portions extending primarily along a first direction (e.g., a direction orthogonal to the length and width directions) and a second portion extending primarily along the length direction, where each electrically conductive passive substantially linear medium portion may be capable of simultaneously propagating therealong electromagnetic first and second signals at different respective frequencies Fl and F2, where the wireless communication system further includes, for each first portion, a dielectrically lossy or magnetically lossy first material substantially surrounding the first portion in each cross-section (e.g., surrounding at least 70, 80, 90, 95 or 100 percent of the cross-section of the first portion) orthogonal to the first direction along greater than 50 percent of a length along the first direction of the first portion. It has been found, according to some embodiments of the present description, that including the dielectrically lossy or magnetically lossy first material along the first portion (e.g., an extended bolt) can substantially reduce PIM, while it has previously been believed that such portions do not significantly contribute to PIM due to their form factor (e.g., having a small cross-section and extending primarily orthogonally to the transmitter). The wireless communication system may further include a dielectrically lossy or magnetically lossy second material surrounding at least a portion of the second portion. Further, it has been found, according to some embodiments of the present description, that including the dielectrically lossy or magnetically lossy first material along a first portion substantially separated from the transmitter (e.g., by a distance greater than a maximum length of the transmitter) can substantially reduce PIM, while it has previously been believed that such portions do not significantly contribute to PIM due to their distance from the transmitter and / or due to their form factor.

[0030] An object may be described as extending primarily along a direction or directions when it extends along the direction or directions substantially more (e.g., by at least a factor of 2) than along any other direction.

[0031] In some embodiments, at least one of the first and second signals includes an electric current. In some embodiments, at least one of the first and second signals includes an electric voltage. In some embodiments, the first and second signals may be generated by two radio frequency (RF) signals being transmitted at similar but different frequencies (i.e., Fl and F2). In some embodiments, each of Fl and F2 is between about 100 MHz and about 10 GHz, or between about 200 MHz and about 5 GHz, or between about 300 MHz and about 3 GHz. In some such embodiments or in other embodiments, a difference between Fl and F2 is between about 5 MHz and about 1 GHz, or between about 10 MHz and about 900 MHz, or between about 10 MHz and about 800 MHz, or between about 10 MHz and about 700 MHz.

[0032] For example, in one embodiment, Fl may be 869 MHz and F2 may be 894 MHz, with an adjacent receive band for signals returned from external devices (e.g., a mobile device). For example, an adjacent receive band may be between 824 and 849 MHz. Another receive band may be adjacent at a frequency range above the transmit band (i.e., frequencies above the range of transmit band frequencies). These fundamental frequencies may mix to create products at new frequencies based on the formula nFl+mF2, where m and n may be positive or negative integers. Simple addition of the modulated signals (e.g., when both m and n are +1) in this example would produce a signal of 869 + 894 = 1763 MHz, and a difference (e.g., when n is +1 and m is -1) between the signals would be 894 - 869 = 25 MHz. Both 25 MHz and 1763 MHz are out of the receive bands of interest for a cellular system, and so these signals would not be of concern for that particular cellular system (although these frequencies may fall within the receive band or spectrum of interest of another, nearby system, and so may still cause PIM interference in those systems). However, when these signals combine to form third order (when the sum of the absolute values of m and n is 3) and sometimes higher order products, these can generate PIM signals within the receive bands of interest. For example, 2F1 - F2 (844 MHz) and 2F2 - Fl (919 MHz) produce 3rd order products within the receive portion of a cellular band that can lead to PIM distortion.

[0033] In some embodiments, the intermodulation signal may have a frequency F3 equal to nFl+mF2 which propagates along the first passive substantially nonlinear medium, where m and n may be 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 examples only, 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 equal to +2, such that F3 is equal to 2F2-F1. In some embodiments, n may be equal to +2 and m equal to -1, such that F3 is equal to 2F1-F2. In some embodiments, n may be equal to +1 and m equal to +1, such that F3 is equal to F1+F2. In some embodiments, n may be equal to +2 and m equal to +2, such that F3 is equal to 2F1+2F2. In some embodiments, Fl and F2 are both less than about 6 GHz. In some embodiments, both Fl and F2 are between about 600 MHz and 4 GHz. In some embodiments, both Fl and F2 are between about 600 MHz and 800 MHz. In some embodiments, Fl and F2 are frequencies which are less than about 100 MHz apart, or less than about 50 MHz apart.

[0034] In some embodiments, the electrically conductive passive medium includes at least one electrically conductive, passive substantially linear medium portion adjacent at least one electrically conductive, first passive substantially nonlinear medium portion. An intermodulation signal can be generated in the passive substantially nonlinear medium portion(s) from the first and second signals. The intermodulation signal may be generated based on a nonlinear interaction between the first and second signals (e.g., an indirect interaction arising from the first and second signals interacting with the passive substantially nonlinear medium portion(s)). For example, in some embodiments, the electrically conductive, passive substantially linear medium portion(s) may include the metallic mast (e.g., a galvanized steel mast) to which a cellular antenna (transmitter) is mounted and may further include bolts mounting the antenna to the mast, and the electrically conductive, first passive substantially nonlinear medium portion may be a mounting bracket of a dissimilar metal. This junction or meeting point of dissimilar materials may create a nonlinearity that acts similar to a diode which causes the first and second signals (at frequencies Fl and F2) to mix to create an intermodulation signal (PIM) at a new frequency. In some embodiments, the nonlinearity may be created by a junction between two dissimilar metals. In some embodiments, the nonlinearity may be created by a junction between a metal and a metal oxide (e.g., a metal oxide caused by oxidation effects). In some embodiments, the nonlinearity may be reacted by an area of corrosion or contamination (e.g., a region of rust, a contaminant such as dirt, poor metal -to-metal contact, etc.).

[0035] A medium portion is a portion of a medium. A medium portion can be a medium or a contact point or junction between adjacent materials, for example. A contact point or junction between adjacent materials can define a substantially nonlinear medium as the medium which includes the junction or contact point, and which has electrical properties significantly affected by the junction or contact point. For example, in some embodiments, for a nonlinearity created by a junction between two metals having different Fermi levels, a transfer of charge across the junction occurs to create a dipole which equalizes the Fermi levels and which significantly affects the electrical properties in a thin region (e.g., having a thickness which is small compared to overall dimensions of the metals, but which can be large compared to atomic lattice spacings of the metals) around the junction such that this region defines a substantially nonlinear medium. The first (resp., second, third, etc., where included) passive substantially linear medium portion may be a first (resp., second, third, etc.) passive substantially linear medium, since a portion of a medium can be considered to be a medium, and similarly, the first (resp., second, third, etc., where included) passive substantially nonlinear medium portion may be a first (resp., second, third, etc.) passive substantially nonlinear medium.

[0036] Substantially linear and substantially nonlinear media or media portions can be understood as follows. When first and second signals are induced in the media or media portion(s) and a modulation signal, or at least one intermodulation signal, is generated in the substantially nonlinear medium or medium portion from the first and second signals (e.g., based on a nonlinear interaction between the first and second signals) in the first passive substantially nonlinear medium or medium portion, any intermodulation signal generated in the substantially linear medium from the first and second signals (e.g., based on a nonlinear interaction between the first and second signals) has an amplitude A, and an amplitude of the intermodulation signal or at least one intermodulation signal generated in the passive substantially nonlinear medium is B, then B is greater than A by at least 2.5 dB. In some embodiments, a system includes an electrically conductive first passive substantially linear medium or medium portion and an electrically conductive first passive substantially nonlinear medium or medium portion. In some embodiments, any intermodulation signal generated in the first passive substantially linear medium or medium portion (e.g., based on a nonlinear interaction between the first and second signals) has an amplitude A, and an amplitude of the intermodulation signal or the at least one intermodulation signal generated in the first passive substantially nonlinear medium or medium portion is B, where B is greater than A by at least 3 dB, or at least 4 dB, or at least 5 dB, or at least 6 dB, or at least 8 dB, or at least 10 dB, or at least 15 dB, or at least 20 dB.

[0037] In some embodiments, the dielectrically lossy or magnetically lossy material can be or include a magnetic material which may be in the form of a magnetic film. A magnetic material may have a relative permeability having a real part greater than about 10 for at least one frequency in a range of about 100 MHz to about 10 GHz. A magnetic material may have a relative permeability having an imaginary part greater than about 1, 2, 3, 5, 10, 15, or 20 for at least one frequency (e.g., at least one of Fl, F2, F3) in a range of about 100 MHz to about 10 GHz. The imaginary part may be up to about 100, for example. The magnetic material may be electrically conductive or include an electrically conducive layer, or the magnetic film may be electrically nonconductive. An electrically nonconductive film may have an electrical resistivity of at least 100 Q m (evaluated at low frequencies (e.g., about 1 kHz or less) or evaluated statically (direct current)) along each direction (e.g., along orthogonal in-plane directions and along a thickness direction) and for each layer of the film in some embodiments where the film has more than one layer. An electrically nonconductive film may also be referred to as an electrically insulative film. Any suitable magnetic material may be used. Useful magnetic materials include magnetic ceramic materials such as ferrite, soft magnetic materials such as FeSiAl, and magnetic metal alloys such as Sendust. The magnetic material may be in the form of magnetic particles dispersed in a (e.g., polymeric) binder. In some embodiments, the magnetic material may be a magnetic absorber. Examples of magnetic absorbers are the 3M™ EMI Absorber AB7000E / HF and AB5000HF / SHF series of shielding fdms manufactured by 3M Company (St. Paul, MN). Other suitable magnetic absorbers include 3M™ Flux Field Direction Material (FFDM), such as 3M™ FFDM EM25TP, available from 3M Company. In some embodiments, the magnetic fdm includes an electrically conductive layer. In other embodiments, no electrically conductive layer is included (e.g., 3M™ Flux Field Direction Material (FFDM) EM25TP fdms are available without a conductive layer).

[0038] In some embodiments, the dielectrically lossy or magnetically lossy material can be or include a dielectrically lossy material. A dielectrically lossy material may have a tan delta (ratio of imaginary part of dielectric constant to real part of the dielectric constant) greater than about 0.4 for at least one frequency (e.g., at least one of Fl, F2, F3) in a range of about 100 MHz to about 10 GHz. The tan delta can be in a range of about 0.5 to about 2.5, for example. Any suitable dielectrically lossy material may be used. Useful dielectrically lossy materials include carbon black, lossy foam absorbers, and bubble absorbers that include a thin resistive (e.g., thin metallic) layer applied to the particles (e.g., glass microbubbles) for control of radio frequency absorption. Useful lossy foam absorbers include, for example, the conductive carbon loaded sheets available from MAST Technologies (San Diego, CA). Useful bubble absorbers include, for example, those described in U.S. Pat. No. 5,446,270 (Chamberlain et al.) and U.S. Pat. Appl. Pub. No. 2023 / 0119856 (Lu et al).

[0039] FIGS. 1A-1B are schematic side views of wireless communication systems, according to some embodiments. In some embodiments, a wireless communications system 200 includes one or more transmitters 50 (e.g., 50a, 50b) disposed on (e.g., mounted on and supported by) a structure 10 (e.g., a metallic antenna mast or mounting structure). The transmitters 50 may alternatively be referred to as antennas. In some embodiments, the structure 10 may include a plurality of electrically conductive passive substantially linear medium portions that includes one or more first portions 120, 120a (e.g., extended bolts) and a second portion 130 (e.g., mast), and may include one or more electrically conductive passive substantially nonlinear portion(s) 12, 12a (e.g., a mounting bracket, weld bead, or other connecting structure). In some embodiments, at least one electrically conductive passive substantially nonlinear portion 12b (see, e.g., FIG. IB) is spaced apart from the structure 10. In some embodiments, one or more dielectrically lossy or magnetically lossy materials 150, 150a, 11, I la, 1 lb is included to reduce PIM as described further elsewhere herein. The one or more dielectrically lossy or magnetically lossy materials typically includes at least, for each first portion 120, 120a, a dielectrically lossy or magnetically lossy first material 150, 150a substantially surrounding the first portion in each cross-section orthogonal to the first direction along greater than 50, 60, 70, 80, or 90 percent of a length Lp of the first portion. The one or more one or more dielectrically lossy or magnetically lossy materials 150, 150a, 11, 1 la, 1 lb may further include a dielectrically lossy or magnetically lossy second material 11 around portion 13, for example, of the plurality of electrically conductive passive substantially linear medium portions as generally described in U.S. Pat. Appl. Pub. Nos. 2022 / 0052643 (Bruzzone et al.) and 2023 / 0327308 (Bruzzone er al.), for example. The first material 150, 150a can be disposed only on the first potions 120, 120a and any other dielectrically lossy or magnetically lossy materials may be referred to as second, third, etc. materials.

[0040] The directions 350a and 350b of the main lobes of the respective antennas 50a and 50b are schematically illustrated in FIG. 1A. A nearfield region 357 behind the antennas 50a, 50b and not in the path of the main lobes is schematically indicated. The first portion(s), or at least some of the first portion(s), may be disposed in the nearfield region 357.

[0041] FIG. IB is a schematic side view of a wireless communication system 200 that includes first and second subsystems 200a and 200b, according to some embodiments. The first subsystem 200a may be a wireless communication system as schematically illustrated in FIG. 1A, for example. The direction 350 of the main lobes of the antenna 50 is schematically illustrated in FIG. IB. The second subsystem 200b can include portions of other structural elements (e.g., fence, light pole, etc.) in the vicinity of the first subsystem 200a. It has been found that such elements can generate PIM even though they may not be conventionally considered to be part of the wireless communication system. The first subsystem 200a includes the transmitter 50 and the second portion 130, while the second subsystem 200b includes at least one first portion 120 and first material 150 and can also include portion 131 which may be a third electrically conductive passive substantially linear medium portion or may be an electrically insulative portion, for example.

[0042] In some embodiments, the wireless communication system 200 includes one or more transceivers 60. In operation, in some embodiments, the transceiver(s) 60 of the wireless communication system 200 may generate two or more radio frequency (RF) signals, each at a unique frequency. The signals can propagate through a transmission line (e.g., a coaxial cable, or a fiber optic) to be broadcast / radiated from antenna(s) 50 as electromagnetic radiation 40. In some embodiments, electromagnetic radiation 40 may include electromagnetic first waves 40a, radiating at frequency Fl, and electromagnetic second waves 40b, radiating at frequency F2. In some embodiments, when electromagnetic first waves 40a and electromagnetic second waves 40b impinge upon the structure 10 (and / or upon subsystem 200b), first waves 40a and second waves 40b may induce first and second signals 20 and 21 within at least the nonlinear portion 12 (or 12b) at corresponding frequencies Fl and F2. In some embodiments, nonlinear portion 12 (or 12b) may act as a mixer, combining the first and second signals 20 and 21 to produce a third signal (i.e., an intermodulation signal) 22 at a third frequency F3. Third signal 22 may then propagate throughout the electrically conductive passive medium of the structure 10 possibly flowing back into transceiver 60, or into one or more antennas 50, or reradiating into space at new frequency F3 as second electromagnetic radiation 41, and thereby back to one or more antennas 50. In some embodiments, a second antenna 50b may re-transmit or receive RF signals originally generated at a first antenna 50a (with fundamental frequencies Fl and F2), including PIM signals at frequency F3 created within one or more nonlinearities 12 / 12a / 12b) or the third signal 22 may be generated in a structure (e.g., in subsystem 200b) separated from the one or more antennas 50 which reradiates the signal at the frequency F3 back to the one or more antennas 50 and / or to transceiver 60. These RF signals (and in particular the F3 signal) may be seen as increased noise at transceiver 60, greatly reducing the SNR of the intended signals. The transmitter 50 can be configured to transmit at least first and second radio waves (corresponding to the first and second signals and to radiation 40, 41) having respective different frequencies Fl and F2. A nonlinear medium portion 12, 12a, 12b can generate an intermodulation signal having a frequency F3 which can be equal to nFl+mF2, where m and n are positive or negative integers.

[0043] FIGS. 2A-2B are schematic perspective views of portions of a wireless communication 200, according to some embodiments. The transmitter 50 extends primarily along length and width directions (x- and y-direction) and having a length LI and a width W1 along the respective length and width directions, where LI > Wl, or LI > 2 Wl, or LI > 3W1, or LI > 4 WL In some embodiments, LI is no more than 30, 25, or 20 times WL The plurality of electrically conductive passive substantially linear medium portions 120, 130 can include one or more first portions 120, where each first portion extends primarily along a first direction (z-direction) substantially orthogonal (e.g., within 20, 15, 10, or 5 degrees of orthogonal) to the length and width directions. For each first portion 120, a dielectrically lossy or magnetically lossy first material 150 may substantially surround the first portion (not shown in FIG. 2A; see, e.g., FIG. 2B). In some embodiments, the one or more first portions 120 and the second portion 130 are disposed on a same side of the transmitter. The first portions 120 and first materials 150 may be disposed in the nearfield region 357 behind the antennas as schematically illustrated in FIG. 1A, or may be separated from the transmitter 50 by a distance D > LI as schematically illustrated in FIG. IB, or some first portions 120 and first materials 150 may be in the nearfield region 357 and some other first portions 120 and first materials 150 may be separated from the transmitter 50 by a distance D > LI.

[0044] In some embodiments, each first portion has a maximum lateral dimension Dp less than each of 0.2 Wl and 0.1 LI. In some such embodiments, or in other embodiments, Dp is less than 0.15, 0.1, 0.08, 0.07, 0.06, or 0.05 times WL In some such embodiments, or in other embodiments, Dp is less than 0.08, 0.06, 0.05, 0.04, 0.03, 0.02, or 0.01 times LI. In some embodiments, Dp is in a range of about 0.2 to 2 cm, or about 0.24 to 1.75 cm, or about 0.26 cm to 1.6 cm, or about 0.28 to 1.5 cm, or about 0.3 to 1.4 cm, for example. In some such embodiments, or in other embodiments, Wl is in a range of about 10 to 40 cm, or about 15 to 35 cm. In some such embodiments, or in other embodiments, LI is in a range of about 40 to 250 cm, or about 50 to 225 cm.

[0045] In some embodiments, the plurality of electrically conductive passive substantially linear medium portions 120, 130 includes a second portion 130 extending primarily along the length direction (x-direction) and having a width W2 along the width direction (y-direction), where W2 can be less than each of LI and Wl and greater than 2, 2.5, 3, 3.5, or 4 times Dp. In some such embodiments, or in other embodiments, W2 is in a range of about 2 to 15 cm, or about 3 to 13 cm, or about 4 to 11 cm. In some such embodiments, or in other embodiments, each first portion 120 extends away from the transmitter 50 along the first direction (z-direction) past the second portion for a length Lp, where Lp > 2, 4, 6, 8, 10, 12, 14, 16, 18, or 20 times Dp, In some such embodiments, or in other embodiments, Lp is in a range of about 2 to 25 cm, or about 2.5 to 22 cm, or about 2.6 to 21 cm. For example, a first portion 120 can be an extended bolt or a portion of an extended bolt extending past the second portion 130. In some embodiments, a wireless communication system 200 includes a transmitter 50 configured to transmit at least first and second radio waves having respective different frequencies Fl and F2; and a plurality of electrically conductive passive substantially linear medium portions 120, 130. The transmitter extends primarily along length and width directions (x- and y- directions) and has a length LI and a width W1 along the respective length and width directions, where LI can be greater than or equal to Wl. The plurality of electrically conductive passive substantially linear medium portions includes one or more first portions 120 and one or more electrically conductive passive substantially nonlinear medium portions disposed proximate the plurality of electrically conductive passive substantially linear medium portions. The one or more first portions 120 (or at least one of the one or more first portions 120) and the second portion 130 can be disposed on a same side of the transmitter 50. In some embodiments, each first portion 120 (e.g., 120a) extends primarily along a first direction (z-direction) substantially orthogonal to the length and width directions (e.g., first portion 120 can have a length along the first direction at least twice the largest dimension along the length and width directions), where each first portion 120 has a maximum lateral dimension Dp less than each of 0.2 Wl and 0.1 LI (or Dp can be in any range described elsewhere herein). In some embodiments, the second portion 130 extends primarily along the length direction and has a width W2 along the width direction. In some embodiments, W2 is less than each of LI and Wl and greater than 2 Dp (or W2 can be in any range described elsewhere herein). Each first portion 120 can extend away from the transmitter 50 along the first direction past the second portion for a length Lp, where Lp > 2 Dp (or Lp can be in any range described elsewhere herein). The one or more first portions 120 (or at least one of the one or more first portions 120) can be separated from the transmitter 50 by a distance D greater than LI (or the distance D can be in another range described elsewhere herein).

[0046] In some embodiments, for each first portion 120, a dielectrically lossy or magnetically lossy first material 150 substantially surrounds the first portion 120 in each cross-section orthogonal to the first direction along greater than 50 percent of the length Lp of the first portion, such that when the transmitter 50 transmits the first and second radio waves, the electrically conductive passive substantially linear and nonlinear medium portions 12, 12a receive the first and second radio waves and generate first and second signals 20 and 21 propagating therein at the respective frequencies Fl and F2, where at least one intermodulation signal 22 is generated in the one or more passive substantially nonlinear medium portions from the first and second signals 20 and 21 . The at least one intermodulation signal has a frequency F3 equal to nFl+mF2, where m and n are positive or negative integers. The one or more first materials 150 reduces the generation of the at least one intermodulation signal 22 by at least 2, 2.5, 3., 3.5, 4, 4.5, 5, 6, 7, 8, 9, or 10 dB. The one or more first materials 150 may reduce the generation of the at least one intermodulation signal 22 by up to 30, 25, 20, or 15 dB, for example.

[0047] In some embodiments, the wireless communication system 200 further includes at least one support structure 112 attaching the transmitter 50 to the second portion 130, where the at least one support structure 112 includes at least one of the one or more first portions 120. For example, the at least one support structure 112 can include a bracket and bolts and the one or more first portions 120 can include at least portions of the bolts extending away from the brackets. In some embodiments, the at least one support structure 112 includes each of the one or more first portions 120. In some embodiments, at least one of the one or more first portions 120 is separated from the at least one support structure.

[0048] In some embodiments, at least one first portion is separated from the transmitter by a distance D greater than LI . In some embodiments, each first portion is separated from the transmitter by a distance D greater than LI . In some embodiments, at least one first portion is disposed in nearfield region 357 and at least one first portion is separated from the transmitter by a distance D greater than LI . In some embodiments, each first portion is disposed in nearfield region 357. The distance D is the smallest distance between a first portion 120 and the transmitter 50. In some embodiments, the distance D is greater than 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, or 5 times LI. The distance D can be up to about 100, 50, 30, 20, 15, or 10 times LI, for example. The distance D may be at least 20, 30, 40, or 50 cm, for example. The distance D may be up to about 10, 8, 6, 5, or 4 m, for example.

[0049] FIGS. 3A-3F are schematic perspective views of dielectrically lossy or magnetically lossy materials 150 configured to substantially surround at least one cross-section of an electrically conductive passive substantially linear medium portion, according to various embodiments. The material 150 may be formed into a desired shape (see, e.g., FIGS. 3A-3C, 3E, 3F) via casting, molding, or extruding, for example, or may be in the form of a film wrapped into a desired shape (see, e.g., FIG. 3D), for example. A hole through, or partially through, the material along an axis of the material may be formed in an initial casting, molding, or extruding step, for example, or may be formed in a subsequent drilling or tapping step, for example. Other useful shapes (see, e.g., FIGS. 4-6B described elsewhere herein) may be made via casting, molding, or extruding, for example. When a film is used, the film may be wrapped directly around the portion 120 or may be wrapped around a hollow tube or around a cylindrical material that is subsequently drilled or tapped, for example.

[0050] In some embodiments, for at least one first portion, the first material 150 has an inner surface 171 facing the first portion that has a substantially right circular cylindrical shape (see, e.g., FIGS., 3A-3B and 3D). In some embodiments, for at least one first portion, the first material 150 has an outer surface 172 facing away from the first portion that has a substantially right circular cylindrical shape (see, e.g., FIG. 3A and 3D). In some embodiments, for at least one first portion, the first material 150 has an outer surface 173 facing away from the first portion that has a substantially right polygonal prism shape (see, e.g., FIGS. 3B-3C). In some such embodiments, or in other embodiments, for the at least one first portion, the first material 150 has an inner surface 171, 174 facing the first portion that has a substantially right circular cylindrical shape (see, e.g., FIG. 3B) or a substantially right polygonal prism shape (see, e.g., FIG. 3C). In some embodiments, for at least one first portion, the first material 150 includes a dielectrically lossy or magnetically lossy film 180 rolled into a substantially cylindrical shape (see, e.g., FIG. 3D). A material may be described as having substantially a specified shape when the material has that shape, or nominally has that shape, or has that shape up to variations small compared to the largest dimension of the material (e.g., deviations from the specified shape of less than about 10% of the largest dimension). FIGS. 3E-3F are schematic cross-sectional views of dielectrically lossy or magnetically lossy materials 150 configured to substantially surround at least one cross-section of an electrically conductive passive substantially linear medium portion, according to various embodiments. The inner surface 171, 174 (see, e.g., FIGS. 3A-3C) of the first material 150 may extend over a full length of the first portion so that each end 272, 273 of the first portion is open (see, e.g., FIG. 3E), or the inner surface may extend only over a portion of the full length so that one end 273 of the first portion is open and the opposite end 274 is closed (see, e.g., FIG. 3F). For example, the first material 150 may include a cylindrical portion covering the sides of a bolt and a cap portion covering an end of the bolt. In some embodiments, for at least one first portion, the first material has an outer surface 172, 173 facing away from the first portion and an inner surface 171, 174 facing the first portion, where the outer surface is coextensive with a length of the first material along the first direction and the inner surface extends along at least a portion of the length of the first material. In some embodiments, the inner surface extends along only a portion of the length of the first material. In some embodiments, the inner surface extends along the entire length of the first material.

[0051] FIG. 4 is a schematic perspective view of a dielectrically lossy or magnetically lossy material 150 including a plurality of discrete portions (e.g., 151, 152), according to some embodiments. FIGS. 5A-5B are schematic perspective views of a dielectrically lossy or magnetically lossy material 250 (e.g., corresponding to 150) including a plurality of discrete portions (e.g., 251, 252) arranged in a clamshell form factor, according to some embodiments.

[0052] In some embodiments, for at least one first portion, the first material 150, 250 includes at least two discrete portions (151, 152 or 251, 252) not integral with one another. In some embodiments, the at least two discrete portions are stacked on one another along a same axis 153, where each discrete portion is substantially centered on the axis 153. In some embodiments, each of the at least two discrete portions has opposing faces 253, 254 having a shape of an annular sector having a central angle Ac (see, e.g., FIG. 5 A) of at least 150 degrees. In some embodiments, the wireless communication system 200 of claim 10 further includes a shell 260 including a hinge 263 attaching first and second portions 261 and 262 of the shell, where the at least two discrete portions include first and second discrete portions 251 and 252 disposed in the respective first and second portions 261 and 262 of the shell 260. Related clam-shell designs including a shell and a hinge are known in the art for clamp choke cable clips, for example.

[0053] FIGS. 6A-6B are schematic perspective views of dielectrically lossy or magnetically lossy material disposed in a slit-ring form factor, according to some embodiments. In some embodiments, for at least one first portion 120, the first material 150 includes one or more discrete portions 355, 356 having a slit-ring geometry. Each discrete portion having a slit-ring geometry can have opposing faces 353, 354 having a shape of an annular sector having a central angle Ac in a range of 270 to 355 degrees.

[0054] FIG. 7 is a schematic cross-sectional view of a dielectrically lossy or magnetically lossy first material 150, according to some embodiments. In some embodiments, for at least one first portion 120, the first material 150 includes a plurality of dielectrically lossy or magnetically lossy particles 351 dispersed in a binder 352. The binder 352 can be a polymeric binder (e.g., epoxy), for example. The particles 351 can be particles of any of the dielectrically lossy or magnetically lossy materials described elsewhere herein.

[0055] FIG. 8 is a schematic cross-sectional view of a weather resistant cover 401 substantially covering a dielectrically lossy or magnetically lossy material 150 (e.g., covering at least 70, 80, 90, 95, or 100% by area of the material 150) that substantially surrounds at least one cross-section of an electrically conductive passive substantially linear medium portion 120, according to some embodiments. In some embodiments, the wireless communication system 200 further includes, for each first portion 120, a weather resistant cover 401 substantially covering the first material 150. Useful materials for the weather resistant cover 401 include vinyl, polyvinyl chloride (PVC), polytetrafluoroethylene (PTFE), acrylonitrile butadiene styrene (ABS), a blend of butyl rubber and polyisobutylene, or polyolefin, for example. In some embodiments, the weather resistant cover 401 is or includes one or more of butyl mastic tape, vinyl tape, or heat-shrink tubing.

[0056] EXAMPLES

[0057] Various experiments were conducted to determine the effectiveness of applying dielectric lossy or magnetically lossy materials around extend bolts of an antenna assembly. Experiments were conducted in anechoic chamber with a SBNH-1D6565B antenna (available from COMMSCOPE, Claremont, NC)) mounted on OD = 60 mm galvanized pole using standard galvanized steel brackets. A PIM analyzer, PIM Master MW82119 (available from Anritsu, Kanagawa, Japan), was used for reflected PIM measurement. The testing port of the analyzer was connected to one of the ports of antenna using a 3 meter long low PIM cable. The PIM analyzer was calibrated per manufacture guidelines.

[0058] A transmitter (antenna) was mounted to a metal antenna mast using an antenna mounting bracket attached to the antenna using four M8 nuts and attached to the mast with two extended M12 bolts and two M12 nuts. A PIM source (diode embedded in plastic washer) was placed in contact with one of the M8 nuts. EM25TP-015 (available from 3M Company, St. Paul, MN) was applied in a roll around the M8 nuts, the M12 bolts, and / or the M 12 nuts as indicated in the table below and PIM was measured for the frequency ranges indicated in the table below. Reported PIM results are median values based on multiple measurements. In this experiment, the PIM source and area treated with absorber (EM25TP) were in the nearfield region 357 depicted in FIG.1A. An antenna mounting bracket (corresponding to 12b of FIG. IB) was attached to a PVC pipe (corresponding to 131 of FIG. IB) using extended bolts (similar to those depicted in FIG. 2A, for example) and was placed in front of an antenna in the direction of the main lobe (see, e.g., FIG. IB). The separation between the antenna radome and the center of the PVC pipe was about 1 meter. A PIM source (diode embedded in plastic washer) was placed on the left bolt. EM25TP-015 (available from 3M Company, St. Paul, MN) was applied in a roll around one or both of the bolts as indicated in the table below and PIM was measured for the frequency ranges indicated in the table below.

[0059] A transmitter (antenna) was mounted to a metal antenna mast using two antenna mounting brackets, where each bracket was attached to the mast with two extended bolts (see, e.g., FIG. 2A). For each bolt, a nut was included adjacent the bracket. PIM was measured with 0, 1, 3, or 4 cylindrical rings of lossy material (see, e.g., FIGS. 2B and 4) applied over each bolt and / or nut. Each ring was die cut MF22-0009-01, which is a 1 inch (25.4 mm) thick lossy foam absorber sheet available from MAST Technologies (San Diego, CA), with a 51 mm outside diameter and a 21 or 22 mm inner diameter depending on whether the ring was intended to fit over the bolt or the nut. In this experiment, the PIM source and area treated with absorber (EM25TP) was in the back lobe of antenna. When three rings were included over the bolt, the rings spanned most of the length of the bolt past the nut. PIM was measured for the frequency ranges indicated in the table below. Terms such as “about” will be understood in the context in which they are used and described in the present description by one of ordinary skill in the art. If the use of “about” as applied to quantities expressing feature sizes, amounts, and physical properties is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, “about” will be understood to mean within 10 percent of the specified value. A quantity given as about a specified value can be precisely the specified value. For example, if it is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, a quantity having a value of about 1, means that the quantity has a value between 0.9 and 1. 1, and that the value could be 1.

[0060] Terms such as “substantially” will be understood in the context in which they are used and described in the present description by one of ordinary skill in the art. If the use of “substantially” with reference to a property or characteristic is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description and when it would be clear to one of ordinary skill in the art what is meant by an opposite of that property or characteristic, the term “substantially” will be understood to mean that the property or characteristic is exhibited to a greater extent than the opposite of that property or characteristic is exhibited.

[0061] All references, patents, and patent applications referenced in the foregoing are hereby incorporated herein by reference in their entirety in a consistent manner. In the event of inconsistencies or contradictions between portions of the incorporated references and this application, the information in the preceding description shall control.

[0062] Descriptions for elements in figures should be understood to apply equally to corresponding elements in other figures, unless indicated otherwise. Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and / or equivalent implementations can be substituted for the specific embodiments shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations, or variations, or combinations of the specific embodiments discussed herein. Therefore, it is intended that this disclosure be limited only by the claims and the equivalents thereof.

Claims

What is claimed is:

1. A wireless communication system comprising: a transmitter configured to transmit at least first and second radio waves having respective different frequencies Fl and F2, the transmitter extending primarily along length and width directions and having a length LI and a width W1 along the respective length and width directions, LI > Wl; a plurality of electrically conductive passive substantially linear medium portions, comprising: one or more first portions, each first portion extending primarily along a first direction substantially orthogonal to the length and width directions, each first portion having a maximum lateral dimension Dp less than each of 0.2 Wl and 0.1 LI; and a second portion extending primarily along the length direction and having a width W2 along the width direction, W2 less than each of LI and Wl and greater than 2 Dp, each first portion extending away from the transmitter along the first direction past the second portion for a length Lp, Lp > 2 Dp, the one or more first portions and the second portion disposed on a same side of the transmitter; one or more electrically conductive passive substantially nonlinear medium portions disposed proximate the plurality of electrically conductive passive substantially linear medium portions; and for each first portion, a dielectrically lossy or magnetically lossy first material substantially surrounding the first portion in each cross-section orthogonal to the first direction along greater than 50 percent of the length Lp of the first portion; such that when the transmitter transmits the first and second radio waves, the electrically conductive passive substantially linear and nonlinear medium portions receive the first and second radio waves and generate first and second signals propagating therein at the respective frequencies Fl and F2, at least one intermodulation signal being generated in the one or more passive substantially nonlinear medium portions from the first and second signals, the at least one intermodulation signal having a frequency F3 equal to nFl+mF2, m and n positive or negative integers, the one or more first materials reducing the generation of the at least one intermodulation signal by at least 2 dB.

2. A wireless communication system comprising: a transmitter configured to transmit at least first and second radio waves having respective different frequencies Fl and F2, the transmitter extending primarily along length and width directions and having a length LI and a width Wl along the respective length and width directions, LI > Wl; a plurality of electrically conductive passive substantially linear medium portions, comprising: one or more first portions, each first portion extending primarily along a first direction and having a length Lp along the first direction, each first portion having a maximum lateral dimension Dp less than each of 0.2 Wl and 0. 1 LI, Lp > 2 Dp, each first portion separated from the transmitter by a distance greater than LI; and a second portion extending primarily along the length direction and having a width W2 along the width direction, W2 less than each of LI and Wl and greater than 2 Dp;one or more electrically conductive passive substantially nonlinear medium portions disposed proximate the plurality of electrically conductive passive substantially linear medium portions; and for each first portion, a dielectrically lossy or magnetically lossy first material substantially surrounding the first portion in each cross-section orthogonal to the first direction along greater than 50 percent of the length Lp of the first portion; such that when the transmitter transmits the first and second radio waves, the electrically conductive passive substantially linear and nonlinear medium portions receive the first and second radio waves and generate first and second signals propagating therein at the respective frequencies Fl and F2, at least one intermodulation signal being generated in the one or more passive substantially nonlinear medium portions from the first and second signals, the at least one intermodulation signal having a frequency F3 equal to nFl+mF2, m and n positive or negative integers, the one or more first materials reducing the generation of the at least one intermodulation signal by at least 2 dB.

3. A wireless communication system comprising: a transmitter configured to transmit at least first and second radio waves having respective different frequencies Fl and F2, the transmitter extending primarily along length and width directions and having a length LI and a width W1 along the respective length and width directions, LI > Wl; a plurality of electrically conductive passive substantially linear medium portions, comprising: one or more first portions, each first portion extending primarily along a first direction and having a length Lp along the first direction, each first portion having a maximum lateral dimension Dp less than each of 0.2 Wl and 0.1 LI, Lp > 2 Dp; and a second portion extending primarily along the length direction and having a width W2 along the width direction, W2 less than each of LI and Wl and greater than 2 Dp, each first portion separated from the transmitter by a distance greater than LI or disposed on a same side of the transmitter as the second portion with the first direction of the first portion substantially orthogonal to the length and width directions; one or more electrically conductive passive substantially nonlinear medium portions disposed proximate the plurality of electrically conductive passive substantially linear medium portions; and for each first portion, a dielectrically lossy or magnetically lossy first material substantially surrounding the first portion in each cross-section orthogonal to the first direction along greater than 50 percent of the length Lp of the first portion; such that when the transmitter transmits the first and second radio waves, the electrically conductive passive substantially linear and nonlinear medium portions receive the first and second radio waves and generate first and second signals propagating therein at the respective frequencies Fl and F2, at least one intermodulation signal being generated in the one or more passive substantially nonlinear medium portions from the first and second signals, the at least one intermodulation signal having a frequency F3 equal to nFl+mF2, m and n positive or negative integers, the one or more first materials reducing the generation of the at least one intermodulation signal by at least 2 dB.

4. The wireless communication system of any one of claims 1 to 3, wherein for at least one first portion, the first material has an inner surface facing the first portion that has a substantially right circular cylindrical shape.

5. The wireless communication system of any one of claims 1 to 3, wherein for at least one first portion, the first material has an outer surface facing away from the first portion that has a substantially right circular cylindrical shape.

6. The wireless communication system of any one of claims 1 to 3, wherein for at least one first portion, the first material comprises a dielectrically lossy or magnetically lossy film rolled into a substantially cylindrical shape.

7. The wireless communication system of any one of claims 1 to 3, wherein for at least one first portion, the first material has an outer surface facing away from the first portion that has a substantially right polygonal prism shape.

8. The wireless communication system of any one of claims 1 to 3, wherein for at least one first portion, the first material has an outer surface facing away from the first portion and an inner surface facing the first portion, the outer surface coextensive with a length of the first material along the first direction, the inner surface extending along at least a portion of the length of the first material.

9. The wireless communication system of any one of claims 1 to 3, wherein for at least one first portion, the first material has an outer surface facing away from the first portion and an inner surface facing the first portion, the outer surface coextensive with a length of the first material along the first direction, the inner surface extending along only a portion of the length of the first material.

10. The wireless communication system of any one of claims 1 to 3 further comprising, for each first portion, a weather resistant cover substantially covering the first material.

11. The wireless communication system of claim 10, wherein the weather resistant cover comprises one or more of butyl mastic tape, vinyl tape, or heat-shrink tubing.

12. The wireless communication system of any one of claims 1 to 3, wherein for at least one first portion, the first material comprises at least two discrete portions not integral with one another.

13. The wireless communication system of claim 12, wherein each of the at least two discrete portions have opposing major surfaces having a shape of an annular sector having a central angle of at least 150 degrees.

14. The wireless communication system of claim 12 further comprising a shell comprising a hinge attaching first and second portions of the shell, the at least two discrete portions comprising first and second discrete portions disposed in the respective first and second portions of the shell.

15. The wireless communication system of claim 12, wherein the at least two discrete portions are stacked on one another along a same axis, each discrete portion substantially centered on the axis.

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