>42 by being co-located upon substrate 14 over a portion 40b of region 20b providing ground plane 40, and over a portion 42a of region 20a providing main radiator 42. This is illustrated by the dashed outline of region 18a in FIG. 1B showing where region 18a of first layer 18 lies on the opposite surface 15 with respect to surface 16 of substrate 14. By co-locating feeding circuit over parts of ground plane 40 and main radiator 42 enables antenna 10 operation by RF signals to be capacitively conveyed and received, via substrate 14, between the feeding circuit 19 and main radiator 42, or between the feeding circuit 19 and ground plane 40.

Each of regions 18a, 20a, and 20b provides a different radiating structure as each are shaped to provide a length of conductive material along substrate 14 for excitation or resonance as a quarter-wave monopole over one of three different ranges of frequencies, thereby enabling RF signals to be wirelessly sent and received over such three different ranges of frequencies. The length of conductive material of each region 18a, 20a, 20b being approximately one quarter of the wavelength of the RF waves about the lowest in each range associated with that region. In the embodiment shown in the figures, region 20a (main radiator 42) has a large conical shape to resonate at a range of frequencies in a low band, such as in the VHF band, region 20b (ground plane 40) resonates at a range of frequencies in a first high band, such as in the UHF band, and region 18a (feeding circuit 19) resonates in a range of frequencies at a second high band, higher than the first high band, such as in cellular band(s). These different bands will be described further below in connection with FIG. 7 where it was found that antenna 10 extends beyond their designed frequency ranges to provide wideband performance over the entire first and second high bands and frequencies therebetween. Other patterning of conductive material of layers 18 and 20 along substrate 14 may be used to obtain different RF characteristics of antenna 10 so long as first layer 18 is co-located upon substrate 14 over a portion of second layer 20 that provides the ground plane 40 and over a portion of second layer 20 that provides main radiator 42. By configuring the body 12 of antenna 10 to form the shape and size of a typical window mountable sunshade provides the additional benefit of providing a larger volume along surfaces 15 and 16 of substrate 14 for extending monopole radiating structures of regions 18a, 20a, and 20b of conductive material than is generally available in typical interior mounted covert antennas for vehicles.

The body 12 of antenna 10 is preferably planar, where layers 18 and 20, and substrate 14 each extend along planes parallel to each other. Optionally, substrate 14 has curvature as illustrated for example in FIG. 1E that may approximate the surface curvature of a window along which the antenna will be mounted, in which layers 18 and 20 when each formed integral with such substrate 14 will follow its curvature along back surface 15 and front surface 16, respectively, thereof. Where the body 12 has height and width dimensions, the curvature shown in FIG. 1E is along such height of body 12, but may be along one or more of the height and width dimensions as desired depending on the surface curvature of the window.

As best shown in FIGS. 1A-D and 2, connector 24 is mounted onto or upon the back 11a of body 12 of antenna 10, so that a central pin or conductor member 25a of connector 24 extends through hole 22, and four ground pins or conductor members 25b of connector 24 each extend through one of four holes 23 through body 12, where holes 23 are spaced about hole 22. Once members 25a and 25b are received in their respective holes 22 and 23, end 21b of transmission line 21 is soldered to member 25a, and ground members 25b are soldered to second layer 20 that extends along the perimeter of holes 23 thereby electrically connecting members 25b to the portion of second layer 20 providing the ground plane 40 of the antenna 10. To assist in preventing connector member 25a from contacting the second layer 20 when solder is applied thereto to make electrically connection to end 21b of transmission line 21, hole 22 along second layer 20 is made larger than the diameter of member 25a, as best shown in FIGS. 3, 4A and 4B. A cover 25c, such as of plastic material, is applied upon body 12 along front 11b, opposite connector 24, over holes 22 and 23 and ends of connector members 25a and 25b. Cover 25c may be retained to body 12 by having central opening sized to frictionally engage the end of connector member 25a, but other or additional means such as adhesive may be used to retain cover 25c to body 12. A threaded end 25d (FIGS. 1C, 1D, and 2) of connector 24, extending perpendicular to the plane of body 10, faces away from back 11a to enable engagement with a mating connector 26a of a cable 26 (FIG. 2), such as a 50-ohm coaxial cable, for conveying and receiving RF signals via connector member 25a to and from transmission line 21, and a ground line to ground plane 40 of antenna 10 via connector members 25b, as typical in connecting monopole antennas to RF transmitting and/or receiving equipment (not shown).

A plurality of holes 28 perforating body 12 are distributed substantially along an entirety of body 12 over a central or first area 27 along each of the back 11a and front 11b of body 12 to enable a majority of body 12, along the front 11b and back 11a thereof, to appear semitransparent where holes 28 are present. Such holes 28 are each of the same diameter and together operate as a sunshade (or blind) for screening sunlight when antenna 10 is mounted along a window, as shown for example in FIGS. 6A, 6B, and 9. Holes 28 extend through first layer 18 where such first layer covers substrate 14, through substrate 14, and through second layer 20 where such second layer covers substrate 14. An edge 13 defines the outer perimeter of body 12, and along each of the back 11a and front 11b of body 12, between first area 27 and edge 13 is a second or frame area 29 surrounding area 27 and preferably without holes 28. When lower portion 12a of body 12 is present, area 29 extends to lower portion 12a of body 12. Area 29 enhances the appearance of antenna 10 as a frame of a typical sunshade when attached to a vehicle window as will be described later below. Transmission line 21 extends along area 29 along back 11a adjacent a portion of edge 13, and holes 22 and 23 extend through body 12 along area 29 between back 11a and front 11b of body 12 of antenna 10.

The holes 28 are distributed along two-orthogonal dimensions of an array along area 27 having adjacent ones of holes 28 in such proximity to each other to configure body 12 to appear semitransparent along area 27 to a viewer, thereby enabling antenna 10 to not only mimic a sunshade, but operate as one as well. In the preferred embodiment, holes 28 are (or at least approximately) disposed in an array at a 45-degree orientation from the horizontal and vertical dimension of body 12 in order to mimic a screen of a sunshade. Thus, when viewed from back 11a and front 11b of body 12 of antenna 10, holes 28 are distributed in the array in area 27 along two-dimensional rows and columns tilted 45 degrees from the horizontal and vertical defined by the width and height, respectively, of body 12 so that rows and columns of holes 28 appear to extend in grid or grid-like positions along such two-orthogonal diagonal dimensions. The holes 28 along different rows and columns of the array may differ in number. The size, number, and orientation of holes 28 in the figures are illustrative, and other size, number, and/or array orientation (e.g., at zero or other angular degree orientations than shown) may be used. As shown in FIGS. 1A and 1i, holes 28 extend through substrate 14 and depending on their position along body 12 different ones of holes 28 extend through none of layers 18 and 20, and other ones of holes 28 either extend entirely or partially through only one of layer 18 or 20 where such layers are not co-located about substrate 14, or extend entirely or partially through both layers 18 and 20 where such layers are co-located about substrate 14.

To enable mounting of antenna 10 along a window, two holes 30 adjacent edge 13 along two opposite top corners of antenna 10 extend through body 12 along area 29 between back 11a and front 11b of body 12, and two fixtures in the form of suction cups 32 have their rearwardly extending threaded shaft 34 (FIG. 2) extend from front 11b through a different one of holes 30 into a threaded hole 35a of a nut 35 along back 11a, and then tightening nuts 35 retains suction cups 32 to body 12. For example, suction cups 32 may each have a diameter of 25.4 mm or less and can be installed or mounted directly on flat/smooth surface of a window or other smooth surface. While two suction cups 32 are shown, additional ones of suction cups 32 may similarly provided along area 29 of the antenna. Alternatively, suction cups 32 used to mount antenna 10 may be reversed with respect to back 11a and front 11b of body 12, such that back 11a faces window 37, and connector 24 is instead mounted to front 11b using holes 22 and 23. Other fixtures for mounting or installing antenna 10 to a window may alternatively be used than suction cups 32 as will be described later below.

Substrate 14 may be composed of a board of glass-reinforced epoxy laminate material grade FR4, or polyimide, or other dielectric material, cut or formed to a profile of body 12 defined by the shape of its outer perimeter along edge 13. For example, substrate 14 may represent a double-sided circuit board. To form body 12 of antenna 10, the first layer 18 and second layer 20 are formed along substrate 14 using conventional circuit board fabrication. A layer of metallization, such as copper, is deposited along back surface 15, a mask defining the desired pattern of first layer 18 is applied over such metalized back surface 15, and then an etching solution applied to etch away leaving the pattern forming first layer 18. The pattern of second layer 20 is similarly formed with respect to front surface 16 of substrate 14. Alternatively, the first layer 18 and second layer 20 may be printed/deposited by an inkjet printer using conductive material on substrate's back surface 15 and front surface 16, respectively, of substrate 14. Transmission line 21 is formed on substrate 14 when first layer 18 is formed.

Once the layers 18 and 20 are formed along substrate 14, each of holes 22, 23, 28, and 30 are then made. For example, each of holes 22, 23, 28, and 30 are drilled with a desired diameter bit under control of a programmed CNC machine at desired positions along body 12, and at diameter depths in the case of hole 22 in second layer 20. A thin coating layer 50 of a liquid epoxy material of a black color is then applied to the formed body 12. The epoxy material for example may be a black non-conductive solder resist liquid or solution applied to all exposed surfaces on back 11a and front 11b of body 12, the outer surface of body 12 along its edge 13, and along the interior surfaces of holes 28 and 30. Application of coating layer 50 to body 12 may be by dipping, spraying, or by otherwise coating body 12. To avoid epoxy material when applied from entering holes 22 and 23, adhesive tape, such as masking tape, may be applied to cover holes 22 and 23 along both surface 15 and 16, and then peeled off after the body 12 is coated. Once the liquid epoxy material sets, with application of heat if needed, body 12 is complete, such that body 12 of antenna 10 is of a uniform black color similar to a typical sunshade that may be present in a vehicle. While the manufactured antenna 10 with coating layer 50 provides a black colored body 12 as illustrated in the front antenna view of FIG. 6A and the back antenna view of FIGS. 6B and 9, for purposes of illustration FIGS. 1A, 1B, 1C, 2, 3, 4A, 4B, 5, 8A, and 8B show antenna body 12 without layer 50 to distinguish patterning of the conductive material forming layers 18 and 20 with respect to substrate 14.

Next, connector 24 is mounted to or upon body 12 such that its members 25a and 25b are received in their respective holes 22 and 23, end 21b of transmission line 21 is soldered to member 25a, and ground members 25b are soldered to second layer 20 that extends along the perimeter of holes 23. Cover 25c is then applied to body 12 as described earlier. Fixtures in the form of suction cups 32 are used for mounting antenna 10 to window 37 as shown for example in FIGS. 6A, 6B and 9, where such suction cups 32 are mounted to body 12, via holes 30, using nuts 35 as described earlier.

While black is the preferred color of body 12 of antenna 10 to provide a covert antenna that has the appearance of a sunshade, a different color of coating layer 50 or no coating may be applied to body 12 where a disguised antenna 10 appearance is not desired when applied to a window or other surface. Less preferably, body 12 of antenna 10 may be provided with or without holes 28, and printed and/or painted images, stickers or displays on the antenna 10 are provided along the back 11a and/or front 11b of body 12 of antenna 10 to disguise the patterning of layers 18 and/or 20 of body 12.

Body 12 of antenna 10 may be sized smaller than (as shown in FIGS. 6A, 6B and 9), or equal to, the size of physical material of the window it would be mounted to. For example, body 12 of antenna 10 may be about 14.2 inches in length, about 11.5 inches in height, and have a maximum thickness of about 0.068 inches (where layers 18 and 20 are present along surfaces 15 and 16, respectively, of substrate 14, with coating layer 50), where substrate 14 is 0.062 inches thick, coating layer 50 is 0.0016 inches thick, and first and second layers 18 and 20 are each 0.0028 inches thick. When present, extending lower portion 12a for example may be about 10.3 inches in length, and extends downward about 0.6 inches from the upper portion 12b of body 12. However other dimensions may be used as desired. In the preferred embodiment, body 12 of antenna 10 has a very low profile, e.g., maximum thickness of about 7.6 millimeters or less.

As shown in FIGS. 6A and 6B, to mount or install antenna 10 in a vehicle 36, body 12 is positioned along the glass, or other transparent composite material, of a desired window 37 of vehicle 36 such that front 11b of antenna body 12 faces the interior surface 38 of window 37 with lower portion 12a of antenna body 12 inserted into a window slot 39 of door 49, such that lower portion 12a is substantially or entirely hidden from view (as depicted by dashed lines) and the width of the frame provided by area 29 (such width being the distance between outer edge 13 and area 27 occupied by holes 28) appears even along the top and bottom of body 12 when viewed along window 37. Due to the thinness of body 12, lower portion 12a can easily be located between surface 38 of window 37 and along any weatherstripping that may extend along slot 39 about the window's frame in door 49. Then, by manually applying pressure from the back 11a of body 12 towards window 37, suction cups 32 are forced against surface 38 of window 37 thereby mounting antenna 10 to attach by suction to window 37 where lower portion 12a of antenna 10 is retained in slot 39. One end of cable 26 having connector 26a is then coupled to engage connector 24 of antenna 10 and the other end of cable 26 to an antenna port of RF equipment (not shown) in the vehicle. As cable 26 extends from connector 24 along area 29 of back 11a of antenna body 12, it is hidden to the causal viewer from outside the vehicle to maintain the disguised appearance of antenna 10 as a sunshade. The lower portion 12a of body 12 when positioned in slot 39 results in partial contact of antenna 10 with a lower part of the window's interior surface 38 near or along slot 39. The antenna 10 may lie all or partly against the window, or spaced by an air gap from the window.

To release antenna 10 from window 37, body 12 of antenna 10 is manually pulled away from window 37 and upwards from slot 39 after the suction force by cups 32 against window 37 is released by placing one's fingernail or gently sliding a flat head screwdriver head between each of suction cups 32 and window 37 to release their applied suction to the window's interior surface 38. Thus, antenna 10 is portable and readily attachable and removable by being detachably mountable for placement upon different windows in the same vehicle or upon windows of another vehicle as needed.

Once attached to the material, physical window 37, such as of glass or other transparent composites, in a vehicle (or upon another window for locating antenna 10 such as along an interior surface of a window of a building or other structure), the presence of holes 28 provides semitransparency about area 27 along back 11a and front 11b, which with body 12 being preferably planar and generally square or other rectangular shape with optional rounded corners and optional lower portion 12a, enables the antenna 10 to appear like a typical sunshade or blind as may be typically mounted on a window, thereby disguising antenna 10 and providing a covert antenna. Further, in the case of antenna 10 with lower portion 12a inserted in door window slot 39, by making the frame area 29 appear even along the top and bottom of body 12 promotes the appearance of antenna 10 as a typical sunshade or blind in a vehicle.

As the black coating layer 50 covers exposed portions of surfaces 15 and 16 of substrate 14 and the conductive material of layers 18 and 20, layers 18 and 20 of antenna 10 are not readily discernable to human eyes at a distance, such as 5 feet, away from antenna 10 when viewed through window 37. When protruded lower portion 12a of antenna 10 is inserted into a door window slot 39 (FIGS. 6A and 6B), the ground of the vehicle is utilized in antenna 10 operation. However, when antenna 10 is mounted elevated along the window 37, spaced a distance above door window slot 39 as shown in FIG. 9 for the embodiment of antenna 10 of FIGS. 8A and 8B without lower portion 12a, the antenna 10 is disposed above the vehicle ground and operates independent of the ground the vehicle may provide. Unlike other covert antennas when mounted in a vehicle, antenna 10 thus need not be directly mounted to or adjacent the metal body of the vehicle, hence antenna 10 can be used in a vehicle even when its body is made of aluminum or fiberglass. In addition to the mounting surfaces for antenna 10 being windows, other mounting surfaces or structures for antenna 10 may include tiles and/or apertures surrounded by metallic framing.

In operation, with connector 24 of antenna 10 coupled by cable 26 to RF transmitting and/or receiving equipment (not shown), the first layer 18, electrically connected to connector 24 via transmission line 21, provides feeding circuit 19 for antenna 10 by capacitively feeding and receiving RF signals to and from second layer 20 through the dielectric material of substrate 14, since as described earlier portions of first layer 18 and portions 40b and 42a (FIG. 1B) of the second layer 20 providing ground plane 40 and main radiator 42, respectively, of antenna 10 are co-located over each other separated by the dielectric material of substrate 14. The dielectric constant of substrate 14 is selected to enable capacitive feeding and receiving RF signals, similar to that of typical planar patch antennas.

Main radiator 42, provided by region 20a of the conductive material of second layer 20, is shaped to provide a conical shape quarter-wave monopole with a directional pattern. The region 20b of the conductive material of second layer 20 outside main radiator 42 provides ground plane 40 of antenna 10. The impedance along gap 41 between ground plane 40 and main radiator 42 along front surface 16 of substrate 14 is preferably set to match the impedance of cable 26. The shape of ground plane 40 along front surface 16 of substrate 14 from the bottom of body 12 (including lower portion 12a when present) to along the top of body 12 to region 40a enables a defected ground plane structure increasing its electrical length, which can excite higher order modes in main radiator 42. To increase the electrical length of main radiator 42 as a monopole, a slot 43 of exposed dielectric material of substrate 14 is provided along front surface 16 extending within region 20a of second layer 20 to gap 41.

Wideband performance of antenna 10 is enabled by gap 41 between ground plane 40 and main radiator 42, along the front surface 16 of substrate 14, providing a resonant slot which generates higher order modes in main radiator 42. In other words, main radiator 42 by being in proximity to the ground plane 40 on the front surface 16 of the dielectric substrate 14 can excite higher order modes in antenna 10. The wideband performance provided antenna 10, as shown for example in FIG. 7, may be considered remarkably wide which make antenna 10 especially versatile. It is believed that the bandwidth and reduced return loss performance of antenna 10 may be due in part to the structure provided by the window 37 upon which the antenna 10 is mounted providing a dielectric load.

Referring to FIG. 7, a VSWR plot of the operation of antenna 10 when mounted to a window 37, such as depicted in FIGS. 6A and 6B, is shown illustrating performance of antenna 10 in wirelessly sending and receiving RF signals. In exemplary embodiments, the antenna may be configured to be operable with a voltage standing wave ratio (VSWR) of less than 2:1 (i.e., SWR along the vertical axis between 2 and 1) within a first frequency range 44, a second frequency range 45 and a third frequency range 46, where each is primarily associated with monopole resonating structures provided by regions 20a, 20b, and 18a, respectively, described earlier for main radiator 42, ground plane 40, and feeding circuit 19, respectively. The first frequency range 44 (low band) may be from about 134 MHz (or 150 MHz) to about 174 MHz within the VHF band, the second frequency range 45 (first high band) may be from about 400 MHz to about 512 MHz within the UHF band, and the third frequency range 46 (second high band) may be from about 600 MHz to about 900 MHz within cellular bands. Thus antenna 10 provides a tri-band antenna, which further includes a wide fourth band 47 which extends from about 400 MHz to about 900 MHz by the SWR being less than 2:1, inclusive of second and third frequency ranges 45 and 46, and frequencies between those ranges. As described earlier, one or more of first and second layers 18 and 20 are patterned along substrate 14 to excite higher order modes, such enables antenna 10 to further operate over frequencies between two successive ones of the second and third frequency ranges 45 and 46 along the RF spectrum, and thereby promotes antenna 10 wideband performance over fourth band 47 inclusive of second and third frequency ranges 45 and 46 and frequencies therebetween. Triangle shaped markers numbered 1 through 10 are noted on the plot at legend 48. A different frequency performance can be achieved using different patterns of conductive material for region 18a (feeding circuit 19) of first layer 18, and region 20a (main radiator 42) and region 20b (ground plane 40) of second layer 20, as desired for the particular application of antenna 10.

Referring to FIGS. 8A and 8B, another embodiment of antenna 10 is shown which is the same as antenna 10 described above, except lower portion 12a of body 12 is not provided. In this embodiment, two additional ones of holes 30 are placed adjacent edge 13 along the bottom two corners of body 12 in area 29, and two additional ones of suction cups 32 with threaded shafts 34 via such holes tighten into additional nuts 35, thereby providing four suction cups 32 for use in releasably attaching antenna 10 to window 37 as shown in the FIG. 9 example installation of antenna 10 of this embodiment to window 37 of vehicle 36. The operational performance of the antenna 10 without lower portion 12a is same or similar to that described in connection with FIG. 7. The position of the antenna 10 with respect to window 37 may be different than shown or may be differently oriented (e.g., rotated 180 degrees or any angle therebetween) as desired so long as suction cups 32 mount to releasably attach antenna 10 to interior surface 38 of window 37. The forming of body 12 of antenna 10 of this embodiment is the same as described earlier, except that substrate 14 has a shape, such as a square or rectangle with optional rounded corners, that will provide the desired overall profile along outer perimeter of edge 13 without protruding lower portion 12a. For example, antenna 10 of this embodiment may be about 14.2 inches in length, about 10.8 inches in height, with a maximum thickness of about 0.068 inches, representing upper portion 12b of antenna 10 of FIGS. 1A-D without lower portion 12a, but other dimensions may be used. One benefit of this embodiment is that frame area 29 along back 11a and front 11b of body 12 of antenna 10 appears even along outer perimeter of edge 13 about area 27 occupied by holes 28 (from left to right and top to bottom perspectives) like a typical sunshade for a vehicle, and enables versatility in installation positions (i.e., either elevated or not elevated above window slot 39) along any side or rear vehicle window, fixed or movable, sufficient in size for mounting the antenna.