Multilayer substrate and antenna element

Abstract

This multilayer substrate comprises a first layer and a metal layer. The first layer is composed of an organic resin. The metal layer is exposed on a front surface of the first layer. The first layer has a black-based color tone, and the metal layer has any one of a gold-based, a yellow-based, a white-based, and a brown-based color tones.

Description

Multilayer substrate and antenna element

[0001] The disclosed embodiments relate to a multi-layer substrate and an antenna element.

[0002] Conventionally, an antenna element has been proposed that has a substrate in which a dielectric layer made of organic resin is laminated on a dielectric layer made of ceramic (see, for example, Patent Document 1).

[0003] Patent No. 6888674

[0004] The multilayer substrate of the present disclosure includes a first layer and a metal layer. The first layer is made of an organic resin. The metal layer is exposed on a front surface of the first layer. The first layer has a blackish color tone, and the metal layer has a goldish, yellowish, whiteish, or brownish color tone.

[0005] Fig. 1 is a perspective view showing an example of the configuration of a multilayer substrate according to an embodiment. Fig. 2 is a cross-sectional view taken along line A-A in Fig. 1. Fig. 3 is a plan view of an antenna device according to an embodiment. Fig. 4 is a bottom view of an antenna device according to an embodiment. Fig. 5 is a left side view of an antenna device according to an embodiment. Fig. 6 is a front view of an antenna device according to an embodiment.

[0006] Hereinafter, with reference to the accompanying drawings, embodiments of the multilayer substrate and antenna element disclosed herein will be described. Note that the present disclosure is not limited to the embodiments described below. Furthermore, each embodiment can be appropriately combined within the scope of not causing any contradiction in the processing content. Furthermore, the same components in each of the following embodiments will be given the same reference numerals, and duplicated explanations will be omitted.

[0007] Conventionally, an antenna element has been proposed that has a substrate in which a dielectric layer made of organic resin is laminated on a dielectric layer made of ceramic.

[0008] On the other hand, the above-mentioned conventional technology has a problem in that the visibility of the antenna element is significantly reduced as the antenna element becomes smaller, which means that when mounting the antenna element on a motherboard or the like using a mounting machine, it takes a long time to detect the antenna element, which may result in a longer mounting time for the antenna element.

[0009] Therefore, there is a need for a technology that can solve the above problems and improve the visibility of antenna elements.

[0010] <Multilayer Substrate and Antenna Element> First, the configuration of a multilayer substrate 1 according to an embodiment will be described with reference to Figures 1 and 2. Figure 1 is a perspective view showing an example of the configuration of a multilayer substrate 1 according to an embodiment, and Figure 2 is a cross-sectional view taken along line A-A in Figure 1.

[0011] As shown in Figure 1 and other figures, a multilayer substrate 1 according to an embodiment includes a first layer 2, a second layer 3, and a metal layer 4. The multilayer substrate 1 of the present disclosure is also an example of an antenna element. Therefore, in the following description, the multilayer substrate 1 will also be referred to as an "antenna element 1."

[0012] The first layer 2 is made of an organic resin. The organic resin constituting the first layer 2 may be, for example, an epoxy resin, an acrylic resin, a polycarbonate resin, a polyimide resin, an olefin resin, or a polyphenylene resin. The organic resin constituting the first layer 2 may also be, for example, polytetrafluoroethylene (PTFE) or other fluororesins, or polyphenylene ether resin.

[0013] The second layer 3 is located on the rear surface 2b side of the first layer 2 and is made of ceramic. The ceramic that makes up the second layer 3 may be, for example, an alumina-based or glass-ceramic-based ceramic, or may be a dielectric material such as cordierite, zirconia, barium titanate, strontium titanate, or calcium titanate, or aluminum titanate, lead zirconate titanate (PZT), etc. The second layer 3 may also include, for example, a plurality of ceramics.

[0014] The metal layer 4 is made of a metal and is exposed on the front surface 2a of the first layer 2. The metal layer 4 functions as a parasitic patch layer of the antenna element 1. The metal layer 4 may be made of, for example, tungsten (W), molybdenum (Mo), a W-Mo mixture, a W-Mo alloy, a W-Mo intermetallic compound, copper (Cu), silver (Ag), gold (Au), or nickel (Ni).

[0015] Furthermore, a metal film (e.g., a plating film) made of a metal different from the metal constituting the metal layer 4 may be formed on the exposed surface of the metal layer 4. In this case, in the present disclosure, such a metal film is also considered to be part of the metal layer 4.

[0016] In this embodiment, the first layer 2 may have a blackish color tone, and the metal layer 4 may have any of a goldish, yellowish, whiteish, and brownish color tone. In this way, by increasing the difference between the color tone of the metal layer 4 and the color tone of the first layer 2 located around the metal layer 4, the binarized visual image becomes clear when the multilayer board 1 is viewed with a camera of a mounting machine.

[0017] In the antenna element described in the above-mentioned prior art, the organic layer (corresponding to the first layer in the present disclosure) is made of polyimide, and therefore the organic layer has a yellowish color tone. Furthermore, in the antenna element described in the above-mentioned prior art, the radiating element (corresponding to the metal layer in the present disclosure) is made of copper, and therefore the radiating element also has a yellowish color tone. Therefore, when viewing the antenna element of the prior art with a camera of a mounting machine, the binarized visual image becomes unclear.

[0018] On the other hand, in the embodiment, the first layer 2 has a blackish color tone and the metal layer 4 has any of a gold, yellow, white, and brown color tone, thereby improving the visibility of the multilayer substrate 1.

[0019] Therefore, according to the embodiment, when mounting the multilayer substrate 1 (antenna element 1) on a motherboard or the like using a mounting machine, the speed of gripping and releasing operations can be increased.

[0020] In the present disclosure, the term "black" refers to a color that is in accordance with CIE 1976 (L ＊ a ＊ b ＊ ) Lightness L in color space ＊ In the present disclosure, the term "golden" refers to a color tone having a value of 10 or less. ＊ a ＊ b ＊ ) Lightness L in color space ＊ is 80-90, chromaticity a ＊ is -10 to 30, chromaticity b＊ This refers to a color tone whose value falls within the range of 40 to 90.

[0021] In addition, in the present disclosure, "yellow" refers to a color that is ＊ a ＊ b ＊ ) Lightness L in color space ＊ is 70-90, chromaticity a ＊ is -20 to 20, chromaticity b ＊ In the present disclosure, the term "white" refers to a color tone in which the CIE 1976 (L ＊ a ＊ b ＊ ) Lightness L in color space ＊ This refers to a color tone with a value of 90 or higher.

[0022] In addition, in the present disclosure, "brown" refers to a color according to CIE 1976 (L ＊ a ＊ b ＊ ) Lightness L in color space ＊ is 30 to 60, chromaticity a ＊ is 10 to 70, chromaticity b ＊ This refers to a color tone whose value falls within the range of 10 to 70.

[0023] In the embodiment, the lightness L ＊ and the lightness L of the metal layer 4 ＊ The difference between the lightness L of the metal layer 4 and the lightness L of the metal layer 4 may be 25 or more. ＊ and the lightness L of the first layer 2 located around the metal layer 4. ＊ By increasing the difference between the two, the binarized visual image becomes clear when the multilayer board 1 is visually recognized by a camera of a mounting machine.

[0024] That is, in the embodiment, the lightness L ＊ and the lightness L of the metal layer 4 ＊ The difference of 25 or more can improve the visibility of the multilayer board 1. Therefore, according to the embodiment, when mounting the multilayer board 1 (antenna element 1) on a motherboard or the like using a mounting machine, the speed of gripping and releasing can be increased.

[0025] 2, the thickness T1 of the first layer 2 may be greater than the thickness T2 of the second layer 3. By making the thickness T1 of the first layer 2 made of organic resin greater than the thickness T2 of the second layer 3 made of ceramic in this manner, the weight of the entire multilayer substrate 1 can be reduced.

[0026] Therefore, according to the embodiment, when mounting the multilayer substrate 1 (antenna element 1) on a motherboard or the like using a mounting machine, the speed of gripping and releasing operations can be further increased.

[0027] Furthermore, in the embodiment, by making the thickness T1 of the first layer 2 made of organic resin larger than the thickness T2 of the second layer 3 made of ceramic, it is possible to reduce the load on the second layer 3 when the first layer 2 is used as the location for gripping or suction in the mounting machine.

[0028] Therefore, according to the embodiment, when the multilayer substrate 1 (antenna element 1) is mounted using a mounting machine, damage to the ceramic second layer 3 can be reduced.

[0029] In addition, in the embodiment, the thickness T1 of the first layer 2 made of organic resin with a low dielectric constant is made larger than the thickness T2 of the second layer 3 made of ceramic, thereby making it possible to broaden the bandwidth of the transmission and reception performance of the antenna element 1.

[0030] In the embodiment, the first layer 2 made of organic resin may contain a carbon component. By including particles of a carbon component (carbon particles) having a specific gravity smaller than that of silica particles as an inorganic filler, the weight of the entire multilayer substrate 1 can be reduced.

[0031] Therefore, according to the embodiment, when mounting the multilayer substrate 1 (antenna element 1) on a motherboard or the like using a mounting machine, the speed of gripping and releasing operations can be further increased.

[0032] In addition, in the embodiment, the second layer 3 may have a greenish color tone. In this way, by increasing the difference between the color tone of the second layer 3 and the color tone of the first layer 2 located above the second layer 3, the binarized visual image becomes clear when the multilayer board 1 is visually observed from the side with a camera of a mounting machine.

[0033] That is, in the embodiment, the first layer 2 has a blackish color tone and the second layer 3 has a greenish color tone, thereby improving the visibility of the multilayer substrate 1 from the side.

[0034] Therefore, according to the embodiment, when mounting the multilayer substrate 1 (antenna element 1) on a motherboard or the like using a mounting machine, the speed of the work of grasping from the side can be increased.

[0035] In the present disclosure, the term "green" refers to a color according to CIE 1976 (L ＊ a ＊ b ＊ ) Lightness L in color space ＊ is 30 to 60, chromaticity a ＊ is -70 to -10, chromaticity b ＊ This refers to a color tone whose value falls within the range of 10 to 90.

[0036] In the embodiment, the lightness L ＊ and the lightness L of the second layer 3 ＊ The difference between the lightness L of the second layer 3 and the lightness L of the second layer 3 may be 25 or more. ＊ The lightness L of the first layer 2 located above the second layer 3 is ＊ By increasing the difference between the two, the binarized visual image becomes clear when the multilayer board 1 is visually recognized from the side by the camera of the mounting machine.

[0037] That is, in the embodiment, the lightness L ＊ and the lightness L of the second layer 3 ＊ When the difference between the above is 25 or more, the visibility of the multilayer board 1 from the side can be improved. Therefore, according to the embodiment, when the multilayer board 1 (antenna element 1) is mounted on a motherboard or the like using a mounting machine, the speed of the gripping operation from the side can be increased.

[0038] In the embodiment, the metal layer 4 may have a trapezoidal shape in cross section as shown in Fig. 2. Furthermore, in the embodiment, the surface 4a corresponding to the longer base of a pair of bases of the trapezoid may be exposed.

[0039] As a result, the corners 4b located on the periphery of the exposed surface 4a become sharp edges, and the light used in the binarization process is more likely to be reflected by the edges of the metal layer 4 (i.e., the corners 4b).

[0040] In other words, by exposing the surface 4a of the metal layer 4 corresponding to the long base edge, when the multilayer board 1 is viewed with the camera of the mounting machine, the binarized visual image becomes clearer, thereby further improving the visibility of the multilayer board 1.

[0041] Therefore, according to the embodiment, when mounting the multilayer substrate 1 (antenna element 1) on a motherboard or the like using a mounting machine, the speed of gripping and releasing operations can be further increased.

[0042] In the antenna element 1 according to the embodiment, the thermal expansion coefficient of the second layer 3 is 10×10 －６ ( / °C) or more. In this way, by increasing the thermal expansion coefficient of the second layer 3, even if the motherboard on which the antenna element 1 is mounted is an organic motherboard, the thermal expansion coefficient of the second layer 3 can be made closer to the thermal expansion coefficient of the motherboard.

[0043] Therefore, according to the embodiment, it is possible to reduce the amount of deformation and stress that occurs due to thermal changes in the motherboard on which the antenna element 1 is mounted.

[0044] In the antenna element 1 according to the embodiment, the thermal expansion coefficient of the first layer 2 is 30×10 －６ ( / °C) or less. By reducing the thermal expansion coefficient of the first layer 2 made of organic resin in this manner, it is possible to reduce the difference in thermal expansion coefficient between the first layer 2 made of organic resin and the second layer 3 made of ceramic.

[0045] Therefore, according to the embodiment, the thermal deformation of the antenna element 1 can be reduced when the antenna element 1 operates, and therefore the transmission and reception performance of the antenna element 1 can be stabilized.

[0046] Continuing with the description of other parts of the antenna element 1 (multilayer substrate 1), as shown in Fig. 2, the antenna element 1 according to the embodiment further includes a feed patch layer 5, a feed via 6, a feed layer 7, and a ground layer 8.

[0047] The power supply patch layer 5 is located inside the multilayer substrate 1 so as to overlap the metal layer 4 in a plan view. The power supply patch layer 5 is located, for example, at the interface between the first layer 2 and the second layer 3 (i.e., between the back surface 2 b of the first layer 2 and the front surface 3 a of the second layer 3).

[0048] The power supply via 6 electrically connects the power supply patch layer 5 and the power supply layer 7. The power supply via 6 is positioned, for example, so as to penetrate the second layer 3 in the stacking direction.

[0049] The power supply layer 7 is electrically connected to a control IC (not shown) and is located on the back surface 3 b of the second layer 3 , for example.

[0050] The control IC connected to the power feed layer 7 outputs, as an electrical signal corresponding to the radio waves to be transmitted, for example, a modulated electrical signal, to the power feed patch layer 5 via the power feed layer 7 and the power feed vias 6. The control IC also collects, from the power feed patch layer 5 via the power feed vias 6 and the power feed layer 7, the electrical signal corresponding to the radio waves received by the antenna element 1.

[0051] The ground layer 8 is connected to a ground potential (not shown) and is located, for example, on the rear surface 3 b of the second layer 3 at a position different from the power supply layer 7 .

[0052] <Antenna Device> Next, the configuration of an antenna device 10 equipped with an antenna element 1 according to the embodiment will be described with reference to Figs. 3 to 6. Fig. 3 is a plan view of the antenna device 10 according to the embodiment, and Fig. 4 is a bottom view of the antenna device 10 according to the embodiment. Fig. 5 is a left side view of the antenna device 10 according to the embodiment. Note that the right side view of the antenna device 10 is symmetrical to Fig. 5. Fig. 6 is a front view of the antenna device 10 according to the embodiment. Note that the rear view of the antenna device 10 is symmetrical to Fig. 6.

[0053] An antenna device 10 according to the embodiment includes an antenna element 1 and a feed circuit 20. As shown in Fig. 3 , in the antenna device 10 according to the embodiment, the antenna element 1 has a plurality of metal layers 4 arranged in a matrix (7 x 7 in the figure) on the front surface 2a of the first layer 2.

[0054] 5 and 6, the feed circuit 20 is located below the antenna element 1 so as to be stacked with the antenna element 1. The feed circuit 20 electrically connects the antenna device 10 to a control IC (not shown). A plurality of electrodes 21 are arranged in a matrix (7 × 7 in the figure) on the bottom surface 20a of the feed circuit 20.

[0055] If the antenna device 10 of the present disclosure is considered a design, it can be defined as follows: (Name of the design article): Antenna device (Description of the design article): This article is a chip-type antenna device that can be mounted on, for example, a motherboard. The organic resin layer that forms the upper surface of this article has a blackish color tone, and the multiple parasitic patch layers located on this upper surface have any of a gold, yellow, white, and brown color tone. This improves the visibility of the antenna device, thereby increasing the work speed of gripping and releasing when mounting it on a motherboard or the like using a mounting machine.

[0056] Examples of the present disclosure will be specifically described below, but the present disclosure is not limited to the following examples.

[0057] First, an uncured sheet of composite material was prepared by mixing silica powder and carbon powder with a thermosetting epoxy resin. The amount of silica powder added to the uncured sheet was 100 parts by mass per 100 parts by mass of epoxy resin. The amount of carbon powder added to the uncured sheet was 50 parts by mass per 100 parts by mass of epoxy resin.

[0058] Next, a copper foil pattern (later a parasitic patch layer) was transferred onto the uncured sheet to prepare a first patterned sheet. This copper foil pattern was formed by transferring a copper foil wiring pattern onto one surface of the uncured sheet.

[0059] The copper foil wiring pattern used in the transfer method was prepared by attaching a solid copper foil (thickness: 18 μm) to a PET film and then patterning the same by etching. Thus, a first patterned sheet was prepared.

[0060] Also, a green sheet containing 40% by mass of alumina particles in glass powder (borosilicate glass) was prepared. Next, the following second pattern sheet was fabricated from the prepared green sheet.

[0061] First, through holes were formed in the prepared green sheet, and a conductive paste was embedded and printed in the through holes to form raw via conductors that would become power supply vias. Next, a conductive pattern was formed on one surface of the green sheet on which the raw via conductors had been formed. This conductive pattern (later the power supply patch layer) was formed in a rectangular shape (square in this example) in the center of one surface of the green sheet.

[0062] Next, on the surface of the green sheet opposite to the surface on which the conductor pattern was formed, a conductor pad pattern (later a power supply layer) was formed by screen printing using the same conductor paste, and a GND pattern (later a ground layer) was also formed around the conductor pad pattern, spaced apart from the conductor pad pattern, at the same time. In this way, a second pattern sheet was produced.

[0063] Next, the second pattern sheet was fired to obtain a second substrate. The firing was performed in a nitrogen atmosphere at 950°C for 2 hours. After firing, the conductor pattern, via conductors, and conductor pad pattern were electrically connected.

[0064] Next, the prepared first pattern sheet was laminated on a second substrate, and a pressure and heat treatment was performed to prepare a laminate (multilayer substrate) in which the first pattern sheet was laminated on the second substrate. At this time, the first pattern sheet was laminated on the conductive pattern side of the second substrate. The pressure and heat treatment conditions were a temperature of 200 (°C), a pressure of 0.1 (MPa), and a heating time of 5 hours.

[0065] In this way, a multilayer substrate that would become an antenna element was obtained. The second base material (corresponding to the second layer of the present disclosure) had a thickness of 200 μm, and the first pattern sheet (corresponding to the first layer of the present disclosure) had a thickness of 350 μm.

[0066] The size (area) of the insulating layer as the antenna element was 5 (mm) x 5 (mm), the area of ​​the copper foil pattern (unpowered patch) formed on the first pattern sheet was 1 (mm) x 1 (mm), the area of ​​the conductor (powered patch) formed on the second substrate was 0.7 (mm) x 0.7 (mm), the diameter of the conductor pad pattern was 200 (μm), and the diameter of the via conductor (powered via) was 150 (μm).

[0067] In practice, a base laminate having 10×10 antenna elements of this size arranged lengthwise and widthwise was produced, and cut into individual pieces for use in evaluation.

[0068] The antenna element thus obtained had a second layer with a greenish color tone, a first layer with a blackish color tone, and a parasitic patch layer (corresponding to the metal layer of the present disclosure) with a brownish color tone. Furthermore, when a gold electroless plating film was formed on the surface of the parasitic patch layer, the parasitic patch layer had a golden color tone. Furthermore, when light was shone on the gold-plated sample, the parasitic patch layer had a whitish color tone.

[0069] Next, the lightness L of the first layer of the example sample was measured using a color analyzer manufactured by Satotec Co., Ltd. ＊ and the brightness of the parasitic patch layer L ＊ When the brightness of the first layer was measured, ＊ is 0, and the brightness L ＊ In other words, in the sample of the example, the lightness L of the first layer was 32. ＊ and the brightness of the parasitic patch layer L ＊ The difference between these was 32 (absolute value).

[0070] In addition, the antenna element prepared as a comparative example had a first layer with a greenish color tone and a parasitic patch layer with a brownish color tone. ＊ and the brightness of the parasitic patch layer L ＊ When the brightness of the first layer was measured, ＊ is 50, and the brightness L ＊ In other words, in the comparative sample, the lightness L of the first layer was 32. ＊ and the brightness of the parasitic patch layer L ＊ The difference between these was 18 (absolute value).

[0071] In the sample in which a gold electroless plating film was formed on the surface of the parasitic patch layer, the brightness L ＊ and the brightness of the parasitic patch layer L ＊ The difference between the gold-plated and the gold-plated sample is about 60 (absolute value). Furthermore, when light is irradiated onto the gold-plated sample, the lightness L ＊ and the brightness of the parasitic patch layer L ＊ The difference between these values ​​was approximately 90 (absolute value).

[0072] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present disclosure.

[0073] For example, in the above embodiment, an example in which the multilayer substrate 1 is used in an antenna element and an antenna device has been described, but the present disclosure is not limited to such an example. For example, the technology of the present disclosure may be applied to an insulating circuit board on which various elements (e.g., active elements, passive elements, etc.) are mounted on a circuit pattern.

[0074] This makes it possible to increase the difference in brightness between the insulating layer (corresponding to the first layer in the present disclosure) of the insulating circuit board and the circuit pattern (corresponding to the metal layer in the present disclosure), so that when the insulating circuit board is viewed with the camera of the mounting machine, the visual image of the binarized circuit pattern becomes clear.

[0075] Therefore, according to the embodiment, when various elements are mounted on an insulating circuit board using a mounting machine, the speed of gripping and releasing operations can be increased.

[0076] Further advantages and other aspects may readily occur to those skilled in the art. Therefore, the disclosure in its broader aspects is not limited to the specific details and representative embodiments shown and described above. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

[0077] The present technology can also be configured as follows: (1) A multilayer substrate comprising: a first layer made of organic resin; and a metal layer exposed on a front surface of the first layer, wherein the first layer has a black-based color tone, and the metal layer has one of a gold-based, yellow-based, white-based, and brown-based color tone. (2) A multilayer substrate comprising: a first layer made of organic resin; and a metal layer exposed on a front surface of the first layer, wherein the lightness L of the first layer is ＊ and the lightness L of the metal layer ＊ (3) The multilayer substrate according to (1) or (2), further comprising a second layer made of ceramic and located on a back surface opposite to the front surface of the first layer, wherein the thickness of the first layer is greater than the thickness of the second layer. (4) The multilayer substrate according to (3), wherein the second layer has a greenish color tone. (5) The multilayer substrate according to any one of (1) to (4), wherein the first layer contains a carbon component. (6) The multilayer substrate according to any one of (1) to (5), wherein the metal layer has a trapezoidal shape in cross section, and a surface corresponding to the longer of a pair of base sides is exposed. (7) An antenna element including the multilayer substrate according to any one of (1) to (6). (8) The multilayer substrate according to (1) or (2), further comprising a second layer made of ceramic and located on a back surface opposite to the front surface of the first layer, wherein the thermal expansion coefficient of the second layer is 10×10 －６ (9) The antenna element according to (7), wherein the coefficient of thermal expansion of the first layer is 30×10 ( / °C) or more. －６ ( / °C) or less.

[0078] 1 Multilayer substrate (an example of an antenna element) 2 First layer 2a Front surface 2b Back surface 3 Second layer 4 Metal layer 4a Surface T1, T2 Thickness

Claims

1. a first layer made of an organic resin; a metal layer exposed on the front surface of the first layer; Equipped with the first layer has a blackish color tone, The metal layer has a color tone of any of gold, yellow, white, and brown. Multilayer board.

2. a first layer made of an organic resin; a metal layer exposed on the front surface of the first layer; Equipped with The lightness L of the first layer ＊ and the lightness L of the metal layer ＊ The difference between Multilayer board.

3. a second layer made of ceramic and located on a back surface opposite to the front surface of the first layer; The thickness of the first layer is greater than the thickness of the second layer. The multilayer substrate according to claim 1 .

4. The second layer has a greenish color tone. The multilayer substrate according to claim 3 .

5. The first layer contains a carbon component. The multilayer substrate according to any one of claims 1 to 4.

6. The metal layer has a trapezoidal shape in cross section, and a surface corresponding to the longer of a pair of base sides is exposed. The multilayer substrate according to any one of claims 1 to 4.

7. A multilayer substrate according to any one of claims 1 to 4. Antenna element.

8. the multilayer substrate includes a second layer made of ceramic and located on a back surface opposite to the front surface of the first layer; The thermal expansion coefficient of the second layer is 10×10 －６ ( / ℃) or more 8. The antenna element of claim 7.

9. The thermal expansion coefficient of the first layer is 30×10 －６ ( / ℃) or less 8. The antenna element of claim 7.