FIELD OF THE INVENTION

This invention pertains to the field of antennas, and more particularly to planar antennas on a substrate that also provide a heating function.

BACKGROUND OF THE INVENTION

Mast or whip antennas mounted on the exterior of a vehicle such as an automobile have been used for receiving and transmitting electromagnetic signals (e.g., radio waves). It is also possible to place embedded wire antennas of quarter or half wavelength in laminated rear windows of vehicles. Such wires are easily visible and are therefore prohibited for use in the front windshield or side windows of an automobile.

The use of thin-film antennas has been gaining popularity in recent years. Thin-film antennas are generally formed by applying a thin layer of conductive material to sheets of plastic film such as polyester, and then patterning the resulting sheets to form the conductive surfaces of antennas. Alternatively, conductive material may also be deposited on plastic or other dielectric sheets in desired patterns to form the antennas with the use of well-known masking and deposition techniques.

One area where there has been increased interest in using such thin-film antennas is for window-mounted applications in motor vehicles, aircraft, and the like. Due to the increasing need for different modes of wire-less communication, thin-film window antennas represent a desirable alternative to populating a vehicle or aircraft structure with mast antennas, or other types of non-conformal type antennas, which can detract from the aerodynamic and aesthetic appearance of the surface.

Thin film antennas designed to be affixed to any window of the vehicle (e.g., the windshield) are known in the art. An example of such an antenna is described in U.S. Patent 5,083,135 to Nagy et al., entitled "Transparent film antenna for a vehicle window." Nagy et al. disclose using a transparent conductive film, such as indium-tin-oxide (ITO), for the antenna conductor. However, they acknowledge that there is a compromise between transparency, which requires a very' thin layer of ITO, and sufficient film conductivity to give good antenna performance, which requires a thick layer of ITO. Nagy et al. attempt to solve this problem by placing the antenna very high up on the windshield to inductively couple it to the car body. This substantially restricts design freedom.

There is a conflict between the optical transparency and the conductivity (or surface resistance) of thin-films utilized to make such antennas. For example, copper films having a surface resistance of about 0.25 milliohms/square are commercially available, but their transparency is well below the desired level of 70%. Other commercially available thin-films formed from conductive materials such as ITO or silver have acceptable transparencies (for example, AgHT™ silver type films have optical transparencies greater than 75%), but such films have surface resistances in the range of 4-8 ohms/square, which is several orders of magnitude greater than that of the above copper films, or conventional conductors used for antenna construction. When transparent thm- films having a higher surface resistance are used as the conductive surfaces for an antenna, the performance of the antenna is substantially diminished. Antenna efficiency is reduced due to ohmic loss in the higher resistance films, and as a result, antenna gain can be reduced by as much as 3-6 dB, depending upon the type of antenna.

The transparency of window-mounted thin-film antennas is an important consideration, but other factors are important to meet the requirement of invisibility. U.S. Patent 7,656,357 to Ishibashi et al., entitled "Transparent antenna for vehicle and vehicle glass with antenna," descnbes a transparent antenna to be installed on a glass surface of a vehicle. Ishibashi et al. achieve good antenna performance and light transmittance using a copper foil with a low- reflection treatment and photoetching to remove copper resulting in a sparse mesh pattern. To further reduce the visibility of the mesh, Ishibashi et al. require a gradation region of progressive wider openings and sparser lines in the mesh pattern at the outlines of each mesh. U.S. Patent 9,231,213 to Song et al., entitled "Methods for integrating and forming optically transparent devices on surfaces," describes coplanar waveguide antennas where the edges of the mesh are critical to the radiation emitted and need to be the highest conductivity region in the mesh and should not be compromised to reduce visibility.

In the past, attempts have been made to improve the efficiency of transparent thin-film antennas by increasing the conductivity of the surface. This is typically accomplished by increasing the thickness or type of conductive material applied, or by placing relatively thick sheets of non-transparent highly conductive material on the antenna. In doing so, the antennas become nontransparent.

U.S. Patent 8,941,095 to Song et al., entitled " Methods for integrating and forming optically transparent devices on surfaces," describes an ideal thin-film antenna as having regions of perfect electrical conductivity and regions of glass, which is an insulating dielectric. Song et al. propose using films of silver nanowire or graphene or other conductive materials such as ITO, that all give compromised performance. U.S. Patent 9,504,164 to Ramakrishnan et al., entitled "Manufacturing of high resolution conductive patterns using organometallic ink and banded anilox rolls," describes a method of making a touch sensor which includes flexographically printing a pattern of thin lines on a region of a substrate, and then plating the pattern to create a pattern of micro wires on the region of the substrate that exhibits high conductivity and high transparency. Areas that are not patterned and plated remain in an insulative state. The method described by Ramakrishnan et al. can be adapted to make a thin-film antenna, however the viewing conditions for a touch screen application is very different from that of a transparent antenna.

The touch screens of Ramakrishnan et al. are applied onto a digital display for applications that require touch input, such as cell phones and computers. In these applications, the touch screens have a very uniform pattern throughout the functional area; the touch screens are back lit (typically by LED displays); and the viewing conditions are normally in relatively low intensity indoor lighting environments.

In contrast, window mounted thin-film antennas are typically used in brightly lit viewing conditions (e.g., outdoor sunlight), the antenna pattern is ty pically much smaller than the entire glass surface to which it is affixed, the antenna can be viewed from both sides, with transmissive and reflective visibility requirements, and the conductivity requirement for the conductive regions is typically much higher than for a capacitive touch screen.

When a thin-film antenna is incorporated into surfaces such as automotive windows, such surfaces can suffer from being covered by fog, frost, snow or ice. Therefore, it can be desirable to provide a heating function in the region incorporating the antenna.

There remains a need for improved thin-film conducting antennas that can simultaneously provide a heating function.

SUMMARY OF THE INVENTION

The present invention represents a planar antenna providing a heating function, including: a planar antenna including: a substrate; a radiating element disposed over a surface of the substrate; and a ground element disposed over a surface of the substrate; wherein the radiating element and the ground element are conductive; wherein the ground element includes a conduction path between a first connection point and a second connection point; and wherein the ground element is adapted to be connected to a power source to provide a voltage between the first connection point and the second connection point, thereby producing heat by providing a current through the ground element along the conduction path.

This invention has the advantage that the ground element simultaneously functions as an antenna component and a heating element so that two different components. It has the further advantage that it enables heating of a window region incorporating the planar antenna to provide a defogging or defrosting function.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of a flexographic printing system for roll-to-roll printing on both sides of a substrate;

FIG. 2 is a schematic side view of a roll-to-roll electroless plating system;

FIG. 3 is a plan view of a planar antenna geometry;

FIG. 4A-4C illustrate different patterns appropriate for use in conductive and non-conductive regions in exemplary embodiments;

FIGS. 5A-5C illustrate the formation of a transparent antenna including a conductive antenna pattern and a complementary non-conductive fill pattern;

FIG. 6A-6C illustrate an alternate embodiment of a transparent antenna including a blurred outer edge in a transition region;

FIG. 7 illustrates transparent antennas incorporated into windows of an automobile;

FIG. 8 illustrates a transparent antenna incorporated into a building window;

FIG. 9 illustrates a transparent antenna incorporated into a helmet visor;

FIG. 10 is a plan view of a planar antenna providing a heating function according to an exemplary embodiment;

FIGS. 11 is a plan view of a planar antenna similar to that of FIG. 10 which incorporates a serpentine conduction path;

FIG. 12 is a plan view of a planar antenna providing a heating function according to an alternate embodiment;

FIG. 13 is a plan view of a planar antenna similar to that of

FIG. 12 which incorporates a serpentine conduction path and is disposed over the surface of a solar panel; and FIGS. 14A and 14B illustrate a stacked antenna configuration providing a heated function according to another embodiment.

It is to be understood that the attached drawings are for purposes of illustrating the concepts of the invention and may not be to scale. Identical reference numerals have been used, where possible, to designate identical features that are common to the figures.

DETAILED DESCRIPTION OF THE INVENTION

The present description will be directed in particular to elements forming part of, or cooperating more directly with, an apparatus in accordance with the present invention. It is to be understood that elements not specifically shown, labeled, or described can take various forms well known to those skilled in the art. In the following description and drawings, identical reference numerals have been used, where possible, to designate identical elements. It is to be understood that elements and components can be referred to in singular or plural form, as appropriate, without limiting the scope of the invention.

The invention is inclusive of combinations of the embodiments described herein. References to "a particular embodiment" and the like refer to features that are present in at least one embodiment of the invention. Separate references to "an embodiment" or "particular embodiments" or the like do not necessarily refer to the same embodiment or embodiments; however, such embodiments are not mutually exclusive, unless so indicated or as are readily apparent to one of skill in the art. It should be noted that, unless otherwise explicitly noted or required by context, the word "or" is used in this disclosure in a non-exclusive sense.

The example embodiments of the present invention are illustrated schematically and not to scale for the sake of clarity. One of ordinary skill in the art will be able to readily determine the specific size and interconnections of the elements of the example embodiments of the present invention.

References to upstream and downstream herein refer to direction of flow. Web media moves along a media path in a web advance direction from upstream to downstream. Similarly, fluids flow through a fluid line in a direction from upstream to downstream. In some instances, a fluid can flow in an opposite direction from the web advance direction. For clarification herein, upstream and downstream are meant to refer to the web motion unless otherwise noted.

FIG. 1 is a schematic side view of a flexographic printing system 100 that can be used in some embodiments of the invention for roll-to-roll printing of a catalytic ink on both sides of a substrate 150 for subsequent electroless plating. Substrate 150 is fed as a web from supply roll 102 to take-up roll 104 through flexographic printing system 100. Substrate 150 has a first side 151 and a second side 152.

The flexographic printing system 100 includes two print modules 120 and 140 that are configured to print on the first side 151 of substrate 150, as well as two print modules 110 and 130 that are configured to print on the second side 152 of substrate 150. The web of substrate 150 travels overall in roll-to-roll direction 105 (left to right in the example of FIG. 1). However, various rollers 106 and 107 are used to locally change the direction of the web of substrate as needed for adjusting web tension, providing a buffer, and reversing the substrate 150 for printing on an opposite side. In particular, note that in print module 120, roller 107 serves to reverse the local direction of the web of substrate 150 so that it is moving substantially in a right-to-left direction.

Each of the print modules 110, 120, 130, 140 includes some similar components including a respective plate cylinder 111, 121, 131, 141, on which is mounted a respective flexographic printing plate 112, 122, 132, 142, respectively. Each flexographic printing plate 112, 122, 132, 142 has raised features 113 defining an image pattern to be printed on the substrate 150. Each pnnt module 110, 120, 130, 140 also includes a respective impression cylinder 114, 124, 134, 144 that is configured to force a side of the substrate 150 into contact with the corresponding flexographic printing plate 112, 122, 132, 142. Impression cylinders 124 and 144 of print modules 120 and 140 (for printing on first side 151 of substrate 150) rotate counter-clockwise in the view shown in FIG. 1, while impression cylinders 114 and 134 of print modules 110 and 130 (for printing on second side 152 of substrate 150) rotate clockwise in this view. Each print module 110, 120, 130, 140 also includes a respective anilox roller 115, 125, 135, 145 for providing ink to the corresponding flexographic printing plate 112, 122, 132, 142. As is well known in the printing industry, an anilox roller is a hard cylinder, usually constructed of a steel or aluminum core, having an outer surface containing millions of very fine dimples, known as cells. Ink is provided to the anilox roller by a tray or chambered reservoir (not shown). In some embodiments, some or all of the print modules 110, 120, 130, 140 also include respective UV curing stations 116, 126, 136, 146 for curing the printed ink on substrate 150.

FIG. 2 is a schematic side view of a roll-to-roll electroless plating system 200 disclosed in commonly-assigned U.S. Patent Application Publication 2016/0168713 entitled “Roll-to-roll electroless plating system with liquid flow bearing,” by S. Reuter et al., which is incorporated herein by reference. The roll- to-roll electroless plating system 200 includes a tank 230 of plating solution 210. A web of substrate 150 is fed by a web advance system along a web-transport path in an in-track direction 205 from a supply roll 202 to a take-up roll 204. The web of substrate 150 is a substrate upon which electroless plating is to be performed. Drive roller 206 is positioned upstream of the plating solution 210 and drive roller 207 is positioned downstream of the plating solution 210. Drive rollers 206 and 207 advance the web of substrate 150 from the supply roll 202 through the tank of plating solution 210 to the take-up roll 204. Web-guiding rollers 208 are at least partially submerged in the plating solution 210 in the tank 230 and guide the web of substrate 150 along the web-transport path in the intrack direction 205.

As the web of substrate 150 is advanced through the plating solution 210 in the tank 230, a metallic plating substance such as copper, silver, gold, nickel or palladium is electrolessly plated from the plating solution 210 onto predetermined locations on one or both of a first surface 151 and a second surface 152 of the web of substrate 150. As a result, the concentration of the metal or other components in the plating solution 210 in the tank 230 decreases and the plating solution 210 needs to be refreshed. To refresh the plating solution 210, it is recirculated by pump 240, and replenished plating solution 215 from a reservoir 220 is added under the control of controller 242, which can include a valve (not shown). In the example shown in FIG. 2, plating solution 210 is moved from tank 230 to pump 240 through a dram pipe 232 and is returned from pump 240 to tank 230 through a return pipe 234. In order to remove particulates from plating solution 210, a filter 236 can be included, typically downstream of the pump 240.

FIG. 3 shows an exemplary thin-film antenna 300 that includes a non-opaque substrate 150 (i.e., a substrate that is at least partially transparent) overlaid with a conductive planar antenna pattern 320. Preferably, the substrate has an optical transparency that is at least 50% in a relevant wavelength range (e.g., the visible wavelength range). Examples of appropriate substrates would include plastic substrates (such polyester, polycarbonate or acrylic) or glasses (such as Coming® Willow® Glass). The thin-film antenna 300 can be configured to receive or transmit signals in the frequency band relevant for a particular application (e.g., RF frequencies, microwave frequencies or millimeter-wave frequencies). Methods for designing antenna patterns 320 appropriate for different applications are well-known in the art.

The exemplary thin-film antenna 300 illustrated in FIG. 3 shows a compound multi-frequency RF antenna pattern that includes features similar to those found in a slot antenna such as is shown in U.S. Patent 6,911,952 to E. Sievenpiper, entitled "Crossed-slot antenna for mobile satellite and terrestrial radio reception," and an aperture antenna such as is shown in U.S. 7,233,296 to H. Song et al., entitled "Transparent thin-film antenna." The antenna pattern 320 includes a center conductor signal strip (conductive region 365) and coplanar ground regions (conductive region 360), together with an inner non-conductive region 380 and outer non-conductive region 381. Preferably the conductive regions 360, 365 have a resistance of no more than 1 ohm/square.

In a preferred embodiment, the conductive regions 360, 365 of the thin-film antenna 300 are fabricated by using a printing press, such as the flexographic printing system 100 of FIG. 1, to print a pattern of catalytic ink, and then using a roll-to-roll electroless plating system 200 (FIG. 2) to plate a layer of metal over the catalytic ink. However, it will be clear to one skilled in the art that the pattern of conductive regions 360, 365 can be formed using a variety of methods known in the art. For example, a gravure printing press can be used instead of the flexographic printing system 100. In another embodiment, the thin- film antenna 300 can be formed using an imprint and fill technique such as that disclosed in commonly-assigned U.S. Patent 8,865,292 to D. Trauemicht et al., entitled "Micro-channel structure for micro-wires," which is incorporated herein by reference.

In an exemplary' configuration, the conductive regions 360, 365 consist of microwire meshes formed using the electroless plating method described previously relative to FIGS. 1-2 to deposit thin conductive micro wires with sufficient density to achieve the required conductivity and with sufficient spacing between the micro wires to achieve the required transparency. FIG. 4 A shows an exemplary microwire mesh pattern 410 that can be used in the conductive regions 360, 365. This mesh pattern 410 includes a pattern of interconnected microwires 412 and is preferred for isotropic electrical conductivity. The halftone patterns 430, 431 shown in FIG. 4B are not generally useful for electrical conductivity, but can be used to aid in masking the thin-film antenna 300 to make it more difficult to see. Similarly, FIG. 4C illustrates a halftone pattern 440 incorporating a density gradient.

In other configurations, the conductive regions 360, 365 can be microwire patterns formed using other methods such as direct printing of conductive inks (e.g., inks containing silver nanoparticles or other conductive particles), or etching of a uniform metal layer to create the microwire pattern. The conductive regions 360, 365 can also be formed as uniform conductive patterns rather than patterned microwires. Uniform conductive patterns can be formed from materials that are inherently transparent (e.g., ITO) or from nanoscale materials that form a conductive network (e.g., silver nanowires or carbon nanotubes). Uniform transparent conductive patterns can be formed by any means known in the art, including printing or substrative patterning.

In some embodiments, a protective layer of transparent material can be disposed over the conductive regions 360, 365 and the non-conductive regions 380, 381 on the surface of the substrate 150 to protect the thin-film antenna 300 from being damaged. For example, a layer of protective material can be laminated over the surface of the substrate.

Typically, the thin-film antenna 300 is formed on a flexible transparent substrate 150. In some configurations, the substrate with the thin-film antenna 300 can then be laminated onto the surface of a window (e.g., and automobile window, a building window or a helmet visor). The window can be made of a variety of materials such as glass, polycarbonate or acrylic. Preferably, the surface having the thin-film antenna 300 can face the window to protect it from physical damage. In some cases, the substrate with the thin-film antenna 300 can be laminated between two pieces of glass. In some arrangements, a portion of the thin-film antenna 300 that includes contact points can extend beyond the edges of the glass so that the thin-film antenna 300 can be connected to appropriate electrical circuitry.

Window mounted thin-film antennas are difficult to make completely invisible (while maintaining sufficient wire density) because they are often viewed in brightly lit viewing conditions (e.g., outdoor sunlight), the antenna pattern is typically much smaller than the entire glass surface to which it is affixed, and the antenna can be viewed from both sides, with both transmissive and reflective invisibility requirements. Thus, several methods for masking the visibility of the thin-film antennas (i .e., making them more difficult to detect visually) will be described.

The ink that is used in the flexographic printing system 100 shown in FIG. 1 remains on the substrate 150 even after electroless plating. The ink contains metal particles, such as silver nanoparticles, that act as nucleation sites for the electroless plating process. Preferably, the ink can also contain pigment particles that cause the printed ink patern to have a matte neutral color. The printed ink patern will still be visible when viewing the antenna from the first side 151 of the substrate 150 so that it will appear to have a mate neutral color. In some configurations, after plating the ink with a metal such as copper, the substrate 150 with the micro wires can be put through a second bath to apply a darkening agent. In an exemplary configuration, palladium is used as a darkening agent. This darkening agent covers the second side of the plated metal microwires as well as the edges of the microwires as they are also exposed to the bath with the darkening agent. Both the darkening agent and the ink with the pigment particles that cover the metal wires have the beneficial effect of creating a neutral color and reducing reflection and glint off the metallic surfaces of the microwires when they are viewed from the second side 152 of the substrate 150.

The flexographic printing system 100 (FIG. 1) has the capability to print a plurality of patterns on the substrate 150 in very good register. In an exemplary embodiment, one of the flexographic printing plates 112 is used to print the antenna pattern 320, and another of the flexographic printing plates 132 is used to print a complementary image 302 which includes an inverse pattern 385 as illustrated in FIGS. 5A-5C. The complementary image 302 is printed using a non-catalytic ink containing a pigment but no metallic nanoparticles. The non- catalytic ink is non-conductive and does not serve as a catalyst for the electroless plating process. In this way, the complementary image 302 is insulating so that it does not degrade the performance of the thin-film antenna. The required close alignment of the inverse pattern 385 with the antenna pattern 320 is enabled by the precision alignment capabilities of the flexographic printing system 100.

The inverse pattern 385 is an inverse of the antenna pattern 320 within a defined region of interest 315, and shares one or more common boundaries with the antenna pattern 320. Within the region of interest 315, a fill pattern 387 is printed in the areas of the complementary image 302 corresponding to the non-conductive regions 380, 381 of the antenna patter 320, and no fill pattern 387 is printed in the complementary image 302 in the areas corresponding to the conductive regions 360, 365 of the antenna pattern 320. The inverse pattern 385 can also be called a "complementary' pattern" or a "fill pattern" in the sense that it is complementary to the antenna pattern 320 and fills the open areas within and around the antenna pattern 320. In an exemplary' configuration, both the antenna pattern 320 and the inverse pattern 385 are printed on the same side of the substrate 150, however this is not a requirement.

In some configurations, the fill regions 387 of the inverse pattern 385 can be printed using a pattern of lines having a pattern geometry which matches the pattern of interconnected microwires in the conductive regions 360, 365 of the antenna pattern 320. For example, if the conductive regions 360, 365 are formed using the mesh pattern 410 of FIG. 4A, the fill regions 387 can be formed using a pattern of non-conductive lines arranged in the same mesh pattern 410. Within the context of the present disclosure the pattern geometry of the pattern of lines in the fill regions 387 is said to match the pattern of microwires in the conductive regions 360, 365 if they have the same line spacing and line angles. (They do not necessarily have the same line width.) In other configurations, the fill regions 387 can be printed using other types of patterns such as halftone patterns 430, 431 (FIG. 4C) or uniform density patterns (not shown).

The apparent density and color of the fill pattern 387 in the complementary image 302 is preferably chosen to closely match that of the metal- plated conductive regions 360, 365 (i.e., the radiative portions) in the thin-film antenna 300 so that when the images are overlaid with each other to form a composite antenna 304 the result is a visually uniform image appearance as shown in FIG. 5C so that the antenna is more difficult to detect and preferably visually undetectable. Within the context of the present disclosure, "visually undetectable" means that the structure of the thin-film antenna 300 is not readily detectable with the unaided eye for a typical human observer viewing the composite antenna 304 at a specified viewing distance. Said another way, the thin-film antenna 300 is substantially visually indistinguishable from the complementary image 302. The relevant viewing distance may be application dependent. For example, for cases where the thin-film antenna 300 is integrated into an automobile windshield, the relevant viewing distance would be the distance from the normal position of the dnver's head to the position of the thin- film antenna 300 on the windshield.

The density (or equivalently the average optical transparency) of the fill pattern 387 can be controlled by adjusting the linewidth or line spacing in the mesh pattern 410 or the halftone dot size of the halftone pattern 430, 431. The color of the fill pattern 387 can be controlled by the composition of the non- catalytic ink that is used to print the complementary image. Generally, it is desirable if the average optical transparency of the fill pattern 387 in the non- conductive regions 380, 381 differs from the average optical transparence of the conductive regions 360, 365 of the thin-film antenna 300 by no more than 10%. More preferably the average optical transparencies differ by 3% or less. Preferably, the average optical reflectance of the fill pattern 387 and the conductive regions 360, 365 are also controlled such that they differ by no more than 10%, and more preferably by nor more than 3%.

The color difference between the fill pattern 387 in the non- conductive regions 380, 381 and the conductive regions 360, 365 of the thin-film antenna 300 can be characterized using any metric known in the color *1* measurement art, such as the well-known CIE AE metric. Preferably the color difference should be no more than 10 AE , and more preferably is 3 AE or less.

In a preferred configuration, the resulting composite antenna 304 is substantially transparent so that it can be applied on a window (e.g., an automobile window) without significantly affecting the ability of an observer to look through the window. In many applications, it is desirable that the average optical transparency of both the fill pattern 387 in the non-conductive regions 380, 381 and the conductive regions 360, 365 of the thin-film antenna 300 be at least 50%, and more preferably at least 80%.

Depending on the average optical transparency of the fill pattern 387 in the non-conductive regions 380, 381 and the conductive regions 360, 365 of the thin-film antenna 300, the edges of the composite antenna 304 may be visually detectable even if the thm-film antenna 300 is visually indistinguishable from the fill pattern 387. FIGS. 6A-6C illustrate an alternate configuration where a composite antenna 308 is formed having a transition region 310 to reduce the visibility of the edges of the composite antenna 308. The composite antenna 308 is formed by combining the same antenna pattern 320 that was shown in FIG. 5A with a complementary image 306 including a complementary pattern 386 with a blurred outer edge in a transition region 310. The transition region 310 has an outer boundary 312 and an inner boundary corresponding to the other boundary of the region of interest 315. The transition region 310 provides a smooth transition between the average optical transparency of the fill pattern 387 and the higher optical transparency of the substrate 150. As is well-known to those skilled in the art, the human visual system is more sensitive to detecting sharp edges than it is to detecting gradual gradients. As a result, the use of a transition region 310 can substantially mask, or even eliminate, the visibility of the edges of the composite antenna 307. In some configurations, the transition region 310 can be formed using a gradient halftone pattern 440 such as that illustrated in FIG. 4D.

In some applications, the composite antenna 304 (FIG. 5C) can be placed in a portion of a window where a high level of optical transparency is not critical, such as in the top or bottom portion of an automobile windshield. These portions of the windshield are often tinted so that they have a transparency of less than 50%. In such cases, the optical transparency and color of the composite antenna 304 can be controlled to substantially match the transparency of the tinted region (e.g., to within 10%), or can actually serve to provide the tinting. In this case, even though the overall density of the composite antenna 304 may be visible to an observer, the antenna pattern 320 will be visually indistinguishable from the fill pattern 387 and the window tint so that the antenna pattern 320 will be visually undetectable.

FIG. 7 shows an automobile 500 where a shade band, shown as a tinted region 510, is provided at the top of the windshield 505. Two composite antennas 304, such as those described with respect to FIG. 5C, are provided in the tinted region 510. The average optical transparency and color of the composite antenna 304 (i.e., the average optical transparency and color of the metal-plated conductive regions 360, 365 in the thin-film antenna 300 and the fill pattern 387 in the complementary image 302 (see FIGS. 5A-5B)) are controlled to closely match each other and to match that of the tinted region 510 such that the composite antenna 304 is visually indistinguishable to an un-aided observer at a normal viewing distance. In some embodiments, the region of interest 315 for the composite antenna 304 can correspond to the entire area of the tinted region 510 such that the composite antenna 304 can be used to provide the tinting for the tinted region 510 without the need for additional tinting features. In this case, the average optical transparency and color of the composite antenna 304 can be selected to provide the desire density and color of the tinted region 510. In some applications, it is useful to provide a variety of antennas in the windows of the automobile 500 to serve various purposes (e.g., AM radio, FM radio, GPS, cell phone, WiFi, etc.). In the illustrated configuration, in addition to the composite antennas 304 provided in the tinted region 510 of the windshield 505, an additional composite antenna 308 is provided in a lower comer of the windshield 505, and two additional composite antennas 308 are provided in the rear window 515. In this case, the additional composite antennas 308 include transition regions 310 as shown in FIG. 6C to reduce the visibility of the edges of the antenna regions.

It will be obvious to one skilled in the art that the transparent composite antennas 304 of the present invention can be used for a wide variety of other applications. For example, they can be incorporated into other types of windows such as building windows and helmet visors (e.g., motorcycle helmets or military helmets), or into any other type of transparent or semi-transparent surface (e.g., tinted windows or visors). They can also be overlaid onto an opaque surface (e.g., a wall) such that they are substantially undetectable to an observer. FIG. 8 shows an example of a composite antenna 304 incorporated into a window 610 of a building 600, and FIG. 9 shows an example of a composite antenna 304 incorporated into a visor 630 of a helmet 620. In both of these cases, the window 610 or the visor 630 may include a tint, in which case the transparency and color of the composite antenna 304 is preferably controlled to match the tint or to produce the desired tint.

In some applications such as antennas in automotive window (FIG. 7) it is desirable to simultaneously incorporate features into the surface that provide a heating function, for example to defog or defrost the windshield. The heating function can also be used for other purposes such as reducing the buildup of snow or ice on a surface, or for regulating the temperature of a device in a cold environment. Conventionally, the heating function is provided by separate components such as wires that extend across the surface. In an exemplary embodiment, the antenna design can be modified so that the antenna provides both a signal detection/generation function together with a heating function. FIG. 10 illustrates an exemplary planar thin film antenna 700 that functions to detect and/or generate RF signals while simultaneously providing a heating function. This configuration has the advantage that heating can be provided without requiring a separate heater component. The thin-film antenna 700 includes a non-opaque substrate 150 (i.e., a substrate that is at least partially transparent) overlaid with a conductive planar antenna pattern 720. Preferably, the substrate has an optical transparency that is at least 50% in a relevant wavelength range (e.g., the visible wavelength range). The thin-film antenna 700 can be configured to receive or transmit signals in the frequency band relevant for a particular application (e.g., radio frequencies (RF), microwave frequencies or millimeter-wave frequencies). Methods for designing antenna patterns 720 appropriate for different applications are well-known in the art. The exemplary thin-film antenna 700 represents a compound multi -frequency RF antenna pattern based on the thin-film antenna 300 described previously relative to FIG. 3. The antenna pattern 720 includes a center conductive region 765 (which can also be referred to as a radiating element or a signal receiving/generating element) and coplanar conductive region 760 (which can also be referred to as a ground element), together with an inner non-conductive region 780 and outer non- conductive region 781. Preferably the conductive regions 760, 765 have a resistance of no more than 1 ohm/square.

In a preferred embodiment, the conductive regions 760, 765 of the thin-film antenna 700 are fabricated by using a printing press, such as the flexographic printing system 100 of FIG. 1, to print a pattern of catalytic ink, and then using a roll-to-roll electroless plating system 200 (FIG. 2) to plate a layer of metal over the catalytic ink. However, it will be clear to one skilled in the art that the pattern of conductive regions 760, 765 can be formed using a variety of methods known in the art. For example, a gravure printing press can be used instead of the flexographic printing system 100. In another embodiment, the thin- film antenna 700 can be formed using an imprint and fill technique such as that disclosed in commonly-assigned U.S. Patent 8,865,292 to D. Trauemicht et al., entitled "Micro-channel structure for micro-wires," which is incorporated herein by reference. In an exemplary' configuration, the conductive regions 760, 765 consist of micro wire meshes such as the exemplary microwire mesh pattern 410 (FIG. 4A) as discussed previously with respect to FIG. 3. This mesh pattern 410 includes a pattern of interconnected micro wires 412. In many applications, it is desirable that the average optical transparency in the conductive regions 760, 765 of the thin-film antenna 700 be at least 50%, and more preferably at least 80% such that the thin-film antenna 700 is substantially transparent and has a low visibility to a human observer.

A signal transmitter/receiver 795 connected to the conductive region 765 (i.e., the radiating element of the thin-film antenna 700) at signal connection point 774 is used to detect signals received by the thin-film antenna 700 and/or generate signals to be transmitted using the thin-film antenna 700. The signal transmitter/receiver 795 is also connected to the conductive region 760 (i.e., the ground element of the thin-film antenna 700) at the second connection point 772, which is connected to a ground 785. The design and function of the signal transmitter/receiver 795 is conventional and well-known in the art. In an exemplary embodiment, the connections made at the connection points 772, 774 are direct physical contacts. In other embodiments, capacitive couplings can be used. Capacitive couplings are well-known in the art (for example, see U.S. Patent 5,905,469).

The conductive region 760 (i.e., the ground element of the thin- film antenna 700) differs from the conductive region 360 of FIG. 3 in that a non- conductive region is introduced along the bottom edge so that it is no longer a closed loop surrounding the conductive region 765. To provide the heating function, the conductive region 760 includes a first connection point 770 and a second connection point 772 which are connected by a conduction path 776.

The conductive region 760 is adapted to be connected to power source 790 to provide a voltage between the first connection point 770 and the second connection point 774, thereby producing heat by providing a current through the conductive region 760 along the conduction path 776. In an exemplary embodiment, the power source 790 is a DC power source. In other embodiments, the power source 790 can be a pulse-width-modulated DC power source or a low-frequency AC power source. Within the context of this disclosure a low-frequency AC power source provides a periodic voltage variation having a frequency at least 3 orders of magnitude less than the signal being transmitted or received by the signal transmitter/receiver 795. Such power sources 790 are well- known to those skilled in the art. The DC (or low-frequency) current flowing through the conductive region 760 along the conduction path 776 provides heating without interfering with the ability of the antenna to detect or transmit radio frequency signals.

In an exemplary' embodiment, the connection between the power source 790 and the conductive region 760 at first and second connection points 770, 772 can be made with direct physical contacts. In other embodiments, an inductive connection can be used to pass the low frequency signal but block the high frequency signal. Such inductive connections are well-known in the art.

When the thin-film antenna 700 used for applications such as an antenna incorporated into the windshield 500 of an automobile 500 (FIG. 7), or an antenna incorporated into the visor 639 of a helmet 620 (FIG. 9), the heat produced by the current flowing through the conductive region 760 can be used to provide a defrosting or defogging function. In another exemplary embodiment, the thin-film antenna 700 is disposed over the surface of a solar panel. In this case, the produced heat can be used to reduce the buildup of snow' or ice on the solar panel. In other embodiments, the thin-film antenna 700 can be incorporated into a display device (e.g., an outdoor display device). In this case, the produced heat can be used to reduce the buildup of frost or snow or ice on the display device.

In some applications it can be desirable to increase the path length along the conduction path 776 in order to increase the resistance between the first and second connection points 772, 774 to control the amount of produced heat. FIG. 11 illustrates an alternate embodiment wherein a serpentine pattern 778 is provided in at least a portion of the conductive region 760, thereby increasing the length of the conduction path 776. It should be noted that for illustration purposes the gaps within the serpentine path are shown to have a larger width than would typically be used in practice. It is generally advantageous to keep the gaps small so that they are not visible to the human observer, and so that the conductive region 760 effectively functions as a uniform ground feature such that the gaps do not significantly affect the RF signals. The use of a serpentine pattern 778 is useful to be able to match sheet resistance of the conductive region 760 to the characteristics of power source 790.

One skilled in the art will recognize that the approach described with respect to FIGS. 5A-5C for reducing the visibility of the thin-film antenna 300 by introducing a non-conducting complementary image 302 to form a composite antenna 304 can also be applied to the thin-film antennas 700 of FIGS. 10-11. In this case, a pattern of non-conducting material having an optical transparency that substantially matches that of the conductive regions 760, 765 would be introduced in the non-conductive regions 780, 781.

The method of providing a heating function by providing a current along a conduction path 776 through the conductive region 760 can be applied to a wide variety of different thin-film antenna designs. For example, FIG. 12 illustrates an antenna design according to an alternate embodiment which utilizes an antenna pattern 720 with a T-shaped radiating element (conductive region 765) surrounded by a ground element (conductive region 760). The conductive regions 760, 765 are separated by a non-conductive region 780. The conduction path 776 between the first connection point 770 and the second connection point 772 circumvents the non-conducting region 780. The other features of the thin-film antenna 700 of FIG. 12 are analogous to those of those shown in FIG. 10-11.

FIG. 13 illustrates a thin-film antenna 700 similar to that shown in FIG. 12, except that the ground element (conductive region 760) is in the form of a serpentine pattern 778 so that the path length for the corresponding conduction path 776 is substantially longer. In this example, the thin-film antenna 700 is shown affixed to the surface of a solar panel 800. The serpentine ground element (conductive region 760) spans the surface of the solar panel 800 so that the produced heat can be used to keep the surface of the solar panel 800 clear by melting any snow or ice that may accumulate. In some applications, power generated by the solar panel 800 can be used for the power source 790, such that no external power is required. Power generated by the solar panel 800 can also be used to power the signal transmitter/receiver 795. One example application for this configuration would be for a self-powered WIFI repeater which could be located outside of a building where power is not conveniently available. The heating function of the exemplary thin-film antenna 700 is useful to melt any snow or ice that builds up the solar panel 800. Another exemplary application would be for a wireless traffic light with power supplied by a solar panel and a battery, where the antenna would enable a wireless connection of the traffic light to a control system.

The thin-film antenna designs shown in FIGS. 10-13 are all planar antennas wherein the radiating and ground elements (e.g., conductive regions 760, 765) are disposed on a surface of the substrate 150. In an exemplar}' embodiment, the conductive regions 760, 765 are disposed in a common layer on the same surface of the substrate 150 so that they are coplanar. Such antennas can be referred to as coplanar antennas.

In alternate embodiments, the conductive region 760 can be formed in a different layer than the conductive region 765. For example, they can be disposed on opposite sides of the substrate 150, or with an intervening dielectric layer. Such antennas would still be classified as planar antennas, although they would not be coplanar since the conductive regions 760 and 765 would be in different planes. In some such embodiments, the conductive region 760 may overlap with the conductive region 765 such to provide a stacked antenna design. An exemplary stacked thin-film antenna 701 of this type is illustrated in FIGS. 14A-14B. FIG. 14A shows a front view of the stacked thin- film antenna 701, and FIG. 14B shows a side view. The radiating element (conductive region 765) is disposed on a first side 151 of the substrate 150, and the ground element (conductive region 760) is disposed on a second side 152 of the substrate 150. In the front view of FIG. 14 A, the conductive region 765 overlaps with the conductive region 760, however they are in different planes separated by the substrate as can be seen in the side view of FIG. 14B. In this example, the conductive region 760 of the ground element is divided into dense mesh regions 760a (i.e., regions of lower sheet resistance) along the left and right edges of the conductive region 760 and a sparse mesh region 760b (i.e., a region of higher sheet resistance) which spans the intervening region. The first connection point 770 is located in one of the dense mesh regions 760a, while the second connection point 772 is located in the other of the dense mesh regions 760a. Since the sheet resistance of the dense mesh regions 760a will be lower than that of the sparse mesh region 760b, the voltage will be relatively constant within the dense mesh regions 760a such that the volage drop will mainly occur within the spare mesh region 760b. This will have the effect of distributing the current which flows along the conduction path 776 uniformly across the width of the conductive region 760. It should be understood by one skilled in the art that the sparse mesh regions are not required to be a mesh pattern, rather the requirement is that the pattern is optically transparent and electrically conductive. As noted above, these regions can be alternative patterns of microwires or uniform conductive patterns. Similarly, the dense mesh region is not required to be a dense mesh, and the phrase dense mesh should be understood to denote a region of lower sheet resistance. This region can be essentially opaque since it will typically be outside of the viewable area of the device after integration.

PARTS LIST flexographic printing system supply roll take-up roll roll-to-roll direction roller roller print module plate cylinder flexographic printing plate raised features impression cylinder anilox roller UV curing station print module plate cylinder flexographic printing plate impression cylinder anilox roller UV curing station print module plate cylinder flexographic printing plate impression cylinder anilox roller UV curing station print module plate cylinder flexographic printing plate impression cylinder anilox roller UV curing station substrate first side second side roll-to-roll electroless plating system supply roll take-up roll in-track direction drive roller drive roller web-guiding roller plating solution replenished plating solution reservoir tank drain pipe return pipe filter pump controller thin-film antenna complementary image composite antenna complementary image composite antenna transition region outer boundary region of interest antenna pattern conductive region conductive region non-conductive region non-conductive region inverse pattern complementary pattern fill pattern mesh pattern microwire halftone pattern halftone pattern halftone pattern automobile windshield tinted region rear window building window helmet visor thin-film antenna stacked thin-film antenna antenna patern conductive region a dense mesh region b sparse mesh region conductive region first connection point second connection point signal connection point conduction path serpentine patern non-conductive region non-conductive region ground power source signal transmiter/receiver solar panel