FR2896625A3 - Antenna system for a vehicle radio comprises a roof rack support arranged on a vehicle and containing a closed inner surface and an earth connection and an antenna element held by the inner surface of the roof rack support - Google Patents

Abstract

Antenna system comprises a roof rack support arranged on a vehicle and containing a closed inner surface and an earth connection (6) and an antenna element (1) held by the inner surface of the roof rack support and electrically coupled with the earth connection. Preferred Features: The inner surface is bent and the antenna element fitted to the bent surface. The antenna element is formed on a surface of a flexible substrate (2) which is fitted to the inner surface. The system has an active system with an amplifier unit for amplifying an electrical signal received from the antenna element.

Description

Antenna system for a motor vehicle.

  The present invention relates to an antenna system for a motor vehicle, more particularly to a miniature circuit board car radio antenna, preferably for reception of the AM / FM signal, where the antenna is placed on a carrier. roof luggage of a car. Conventional car antennas may suffer damage due to their length, when the car is in a carwash or at parking gates, so there is a need for a compact antenna solution to reduce the possibilities damage or theft.

  Some references related to this technical field are: [1]. HA Wheeler, Fundamental Limits of Small Antennas, Proceedings of the IRE (IEEE), December 1947, pages 1479 to 1484. [2] James S. McLean, "A Re-Examination of the Fundamental Limits on the Radiation of Electrically Small Antennas The present invention aims to overcome the positioning of a radio antenna in difficult physical conditions such as vibrations or humidity. This object is achieved according to the present invention by an antenna system of the type indicated at the beginning which comprises at least one roof rack configured to be installed on a motor vehicle, the roof rack comprising a surface internal enclosure and grounding for connecting an antenna element to the ground of the motor vehicle, and an antenna element supported by the enclosed internal surface of the roof rack and coupled to electrically to grounding.

  The invention therefore provides for the use of the AM / FM printed antenna in an electrical substrate or a robust dielectric support to ensure the proper position and viability of the different metal parts of the antenna. The active AM / FM radio system can be placed in a remote position with a specific ground connection of the car or the same physical antenna medium with connections to the car ground, also. roof rack must provide a water-resistant protection of the antenna card components and the active system, a fixing and a position of the antenna in the car. The antenna system is able to integrate other antenna services in the same space.

  According to advantageous embodiments, the invention may also comprise at least one of the following features: said internal surface is curved, and the antenna element is adapted to said curved surface; the antenna element is formed on one side of a flexible substrate adapted to said inner surface; the system comprises an active system comprising amplification means for amplifying an electrical signal received by said antenna element; the active module is housed in said roof rack; - the system includes a rear view camera supported by the roof rack; the antenna element is in the form of a solid curve; the antenna element has the shape of a Hilbert curve; the antenna element has the shape of a grid dimension curve; The curve has a box counting dimension or a gate size greater than 1.5; the curve has a box counting dimension or a grid dimension greater than 1.9; the antenna element is adapted for reception of the AM / FM bands; the antenna element is adapted for reception of DAB (digital broadcasting) / TV and GSM (global mobile communication system) tapes; - the antenna element is adapted for the reception of satellite signals: GPS bands (global positioning system) and SDARS (satellite radio); - The system comprises two roof rack, each being provided with an antenna element, and wherein the antenna system further comprises means for combining the received signals at said antenna elements.

  This antenna could be grouped to other antennas for wireless applications or could be part of a group of more than one antenna to improve signal reception. It is also possible to add a motion sensor with a rear view camera to avoid blind spot vision. Placing a miniature radio antenna in an external position of the car, such as the position of the roof rack, is advantageous for many reasons: to improve the aesthetics of the vehicle, to avoid interference from the electronics of the car. car, avoid the typical damage that the antenna of a conventional car undergoes, because of its length, when the car is in a washing machine or at the parking lot doors and finally a better antenna solution compact reducing the possibilities of flight. The invention will be better understood, and other objects, features, details and advantages thereof will appear more clearly in the following explanatory description made with reference to the accompanying schematic drawings given solely by way of example illustrating a Embodiment of the invention and in which: - Figure 1 is a side view of a roof rack plastic carrier for a motor vehicle. FIG. 2 is a schematic representation of the antenna system to be inserted into the roof rack. - Figure 3a is an example of location of the miniature FM / AM antenna at the roof of the car in the plastic rack of the roof rack, Figure 3b is a detail taken in Figure 3a. - Figure 4 is an example of the antenna installation at the plastic support of the roof rack and its point of grounding. FIG. 5a shows the position of two AM / FM fractal miniature combo antennas, FIG. 5b is a schematic representation of the combined antenna system. Figure 6 shows a block diagram of an antenna multiplexer unit. FIG. 7 is another block diagram of the multiplexer unit of an antenna. - Figure 8 shows examples of solid curves. Figure 9 shows one of the examples of a solid curve. - Figure 10 shows a solid curve in a first grid. Figure 11 shows a solid curve in a second grid. - Figure 12 shows a solid curve in a third grid. - Figure 13 shows a solid curve in a first box counting grid. Figure 14 shows a solid curve in a second box counting grid.

  FIG. 2 shows an antenna system according to the invention, in which an antenna element 1 in the form of a solid curve is formed on one face of a substrate 2, for example a printed circuit board. An active AM / FM module 3 is connected to the antenna element 1 by means of a wired connection 4. A coaxial output cable 5 and an earth connection 6, are also connected to the active module 3. The substrate 2 or the robust dielectric support 10 ensures the proper position and viability of different metal parts of the antenna. A solid or grid-sized curve is used as a concept for the design of the antenna element 1. The antenna geometry will include a Hilbert curve-based design as shown in Fig. 2, or minus a curve having a box counting dimension or a grid dimension greater than 1.5. In general, the higher the box count or grid count, the higher the antenna size compression. In some cases, an antenna comprising a curve having a dimension greater than 1.9 will be preferred. The solid or gate size curve is optimized for FM / AM reception. A coaxial or single cable is used for the cable antenna connection 4, to ensure the perfect electrical connection between the antenna element and its active module 3 when the active module is placed at a distance from the antenna element. Antenna 1. The active AM / FM module 3 consists of a PCB (printed circuit board) with surface mount components (SMD) of FM and AM amplifier stages. The board is implemented in a robust and inexpensive substrate amplifier at the same PCB of the solid curve geometry. There are other cases where these two elements are in the same PCB. The antenna system of the present invention may be installed in the plastic carrier of the luggage rack shown in Figure 1, which in turn may be mounted in a car in the positions shown in Figures 3, 4 and 5.

  The roof rack is provided with an inner surface, and the antenna element is preferably supported by said inner surface so that the antenna element is housed within the roof rack, so to protect the antenna element 1 from moisture or external damage. The miniature AM / FM antenna assembly of the present invention may be advantageously located at the roof of the car near the rear windshield 13, the grounding 6 being at the edge of the frame of the car. the rear of the car as shown in Figures 3 and 5. One of the advantages of the antenna in the roof rack is its integrated solution. The car designer does not bear any additional cost because the antenna comes from the supplier of the roof rack, for this the car manufacturer must only install the plastic support without drilling holes and other important operations necessary to install a mast in a roof. car. Another very important benefit is the aesthetic solution. With this solution, we avoid the image of a large cable that projects the shape of the car. This feature is very interesting for vehicles in the future. Another important benefit for this antenna design is to avoid the possibility of theft or breakage of the antenna in normal uses such as cleaning the car or in parking lots where the roof is sometimes not enough high. It has been established that for an electrically small antenna contained in a given volume, the antenna has an inherent minimal value of Q [2]. This places a limit on the impedance bandwidth that can be achieved by an electrically small antenna. For a miniature antenna of the FM band where At is larger than other wireless services, such as GSM900, GSM1800, it is expected that the GPS at the same volume will obtain a very poor impedance bandwidth, accordingly a way of solving this problem can be achieved by combining two miniature antennas with an adequate separation between them. Examples of this application with two combined miniature FM / AM antenna systems are shown in Figures 5 and 7. In the combined system are two miniature FM / AM antennas (9, 9 '). Two radiant elements as described in the previous sections include: a) a robust electrical substrate or dielectric support to ensure the proper position and viability of the different metal parts of the antenna. b) A solid or grid-sized curve as a concept of antenna design. The antenna geometry will include a Hilbert curve based design, or at least one curve having a box count dimension or a gate size greater than 1.5. In general, the higher the box count or grid count, the higher the antenna size compression. In some cases, an antenna 30 having a curvature greater than 1.9 will be preferred. The solid or gate size curve is optimized for FM / AM reception. The two miniature FM / AM antennas (9, 9 ') are respectively connected to two tuning units (10, 10') to ensure that the two miniature antennas work perfectly in the FM / AM bands. These units may include inductors or capacitors to optimize the entire system for FM / AM reception. This tuning unit must be made of an electrical substrate or a robust dielectric support to ensure the proper position and viability of the different components of the tuning antenna unit. Two coaxial radio frequency cables (11, 11 ') of lengths L1 and L2, respectively, connect the two tuning antenna units (10, 10') to the antenna multiplexer unit (12). These coaxials can be designed to operate at 50 Q or 75 Q depending on the input impedance of the radio. The antenna multiplexer unit (12) includes a perfect 50 ohm matching unit to ensure the correct addition of the two complex signals from the two antennas. There are different ways to implement this unit. One of them is to use a component designed by MiniCircuits el TCP-2-10 that includes a matching section (14) and a divider (15) as shown in Figure 6. If necessary at the level of the output of the combined antenna system, an active module (3 ') could be placed to amplify the signal levels. The active module (3) comprises a PCB (circuit board) with the SMD (surface mount) components of stages of an FM and AM amplifier, under the same conditions as those described in the previous sections. The PCB (printed circuit board) with SMD components of FM and AM amplifier stages. The card is implemented in a robust and inexpensive substrate amplifier at the same PCB as that of the antenna multiplexer unit. In the roof rack it is also possible to add a camera to increase visibility to the rear and to avoid blind spot vision. In a preferred embodiment of the invention, the antenna element (1) is a multiband antenna, and is adapted to transmit and / or receive signals for a plurality of communication services. By way of example, a multiband behavior can be obtained by an antenna element comprising the solid curve-shaped portions with a box count dimension or a different gate size as shown for example in the embodiment of FIG. Figure 2. The main communication services covered by the antenna system of the invention are: Broadcasting station radio reception in the AM band (kilometer wave: 150 kHz to 279 kHz and MF wave: 530 kHz to 1710 kHz ) Japanese and European FM (78 MHz to 108 MHz).

  Other services included in the device, can be for example: GSM900, GSM1800, GPS, DAB, TV, DVB, DTB, PCS1900, KPCS, CDMA, WCDMA, TDMA, UMTS, TACS, ETACS, SDARS, WiFi, WiMAX, UWB, Bluetooth, ZigBee, TV, DVB.

  Principles of solid curves Figure 8 shows examples of solid curves. The solid curves 1501 to 1504 are examples of solid curves of the prior art for antenna designs.

  Solid curves fill the surface or volume where they are effectively while maintaining the linear properties of their curvature condition. Among other possible definitions, a solid curve may be defined as a non-periodic curve composed of a number of connected straight segments smaller than a fraction of the operating free space wavelength, where the segments are arranged such that none of said adjacent and connected segments form another longer straight segment and wherein none of said segments intersect the others.

  Figures 9 to 11 show an example of how the grid size is calculated. The grid size of a curve (see Figure 10) can be calculated as follows. A first grid comprising square cells of length L1 is positioned on the geometry of the curve, so that the grid completely covers the curve. The number of cells (Ni) in the first grid that encompasses at least a portion of the curve are counted. Then, a second grid having square cells of length L2 is similarly positioned to completely cover the geometry of the curve, and the number of cells (N2) in the second grid that includes at least a portion of the curve are counted.

  In addition, the first and second grids must be positioned within a minimum rectangular area encompassing the curve, so that no entire row or column on the perimeter of one of the grids fails to encompass at least a portion of the curve .

  The first gate preferably comprises at least twenty-five cells, and the second gate preferably comprises four times the number of cells of the first gate. Thus, the length (L2) of each square cell in the second grid must be half the length (Ni) of each square cell in the first grid. The grid dimension (Dg) can then be calculated using the following equation: D = log (N2) log (N1) g log (L2) log (L1) In the interest of this application the term gate size curve is used to describe a curve geometry having a gate size that is greater than one (1). The larger the gate size, the greater the degree of miniaturization that can be achieved by the gate-size curve in terms of an antenna operating at a specific frequency or wavelength. In addition, a grid dimension curve may, in some cases, also satisfy the requirements of a solid curve, as defined above. Accordingly, in the interest of this application, a solid curve is a type of grid dimension curve. Figure 9 shows an example of a two-dimensional antenna 1600 forming a gate-size curve of approximately two (2). Figure 10 shows the antenna 1600 of Figure 9 enclosed in a first gate 1700 having thirty-two (32) square cells, each of a length L1. Figure 11 shows the same antenna 1600 enclosed in a second gate 1800 having one hundred and twenty-eight (128) square cells, each of a length L2. The length (L1) of each square cell in the first gate (1700) is twice the length (L2) of each square cell in the second gate 1800 (L2 = 2 x L1). An examination of Figure 11 and Figure 12 reveals that at least a portion of the antenna 1600 is encompassed in each square cell in each of the first and second grids 1700, 1800. Accordingly, the value of N1 in the Grid dimension equation (Dg) above is thirty-two (32) (ie, the total number of cells in the first grid 801), and the value of N2 is one hundred and twenty-eight (128) ( that is, the total number of cells in the second grid 802). Using the equation above, the gate size of the antenna 800 can be calculated as follows: D ù log (128) ù log (32) = 2 g log (2 × L1) ù log (L1)

  For a more accurate calculation of the grid size, the number of square cells can be increased to a maximum amount. The maximum number of cells in a grid depends on the resolution of the curve. As the number of cells approaches the maximum, the grid dimension calculation becomes more accurate. If a grid with more than the maximum number of cells is chosen, however, then the accuracy of the grid dimension calculation begins to decrease. Typically, the maximum number of cells in a grid is one thousand (1,000). By way of example, FIG. 12 shows the same antenna 1600 encompassed in a third grid 1900 with five hundred and twelve (512) square cells, each of length L3. The length (L3) of the cells in the third grid 1900 is half the length (L2) of the cells in the second gate 1800, shown in Fig. 8. As noted above, part of the antenna 1600 is encompassed in each square cell in the second grid 1800, so the value of N for the second grid 1800 is one hundred and twenty-eight (128). An examination of Figure 12, however, reveals that the antenna is encompassed in only five hundred and nine (509) of the five hundred and twelve (512) cells of the third grid 1900. As a result, the value of N for the third grid 1900 is five hundred and nine (509). Using Figure 11 and Figure 12, a more accurate value for the third dimension (D) of the antenna can be calculated as follows.

  Figures 13 and 14 show an alternative example of how the box count dimension is calculated. The antenna comprises a conductive pattern, at least a portion of which comprises a curve, and the curve comprises at least five segments, each of the at least five segments forming an angle with each adjacent segment log (509) -log (128), 1.9915 Dg = -log (2X L2) ûlog (L2) in the curve, at least three of the segments being shorter than one-tenth of the wavelength in the longest free space operation of the antenna. Each angle between the adjacent segments is less than 180 and at least two of the angles between the adjacent sections are less than 115, and in which at least two of the angles are not equal. The curve fits within a rectangular area, the longest side of the rectangular area being shorter than one fifth of the longest free space operating wavelength of the antenna . One aspect of the present invention is the box count dimension of the curve that forms at least a portion of the antenna. For a given geometry on a surface, the box count dimension is calculated as follows: first, a grid with L1 sized boxes is placed on the geometry, so that the grid completely covers the geometry , and the number of boxes N1 which comprise at least one point of the geometry is counted; then, a grid with boxes of size L2 (L2 being smaller than L1) is also placed on the geometry, so that the grid completely covers the geometry, and the number of boxes N2 which comprise at least one point of the geometry is counted again. The box counting dimension D is then calculated as: In terms of the present invention, the box counting dimension is calculated by placing the first and second grids within the minimum rectangular area encompassing the curve of the box. antenna and applying the algorithm above. D = ù log (N2) ù log (N1) log (L2) ù log (L1) The first grid should be chosen so that the rectangular area is meshed in an array of at least 5 x 5 boxes or cells, and the second gate is chosen so that L2 = 1/2 L and so that the second gate comprises at least 10 x 10 boxes. By minimum rectangular area, such area will be understood in which none of a row or an entire column on the perimeter of the grid contains a piece of the curve. Thus, some of the embodiments of the present invention will have a box counting dimension greater than 1.17, and in those applications where the required degree of miniaturization is higher, the designs will have a counting dimension of box ranging from 1.5 to 3, inclusive. For some embodiments, a curve having a box counting dimension of about 2 is preferred. For very small antennas, which fit, for example, in a rectangle of maximum size equal to one twentieth of the longest freewave operating wavelength of the antenna, the box counting dimension will necessarily be calculated with a finer grid. In these cases, the first grid will be taken as a mesh of 10 x 10 equal cells, while the second grid will be taken as a mesh of 20 x 20 equal cells, then D is calculated according to the equation above. In the case of small packages of flat designs, that is, designs in which the antenna is arranged in a single layer on a packaging substrate, it is preferred that the dimension of the curve included in the antenna geometry has a value close to D = 2. In general, for a given resonant frequency of an antenna, the larger the box counting dimension, the higher the degree of miniaturization that will be achieved by the antenna. One way of improving the miniaturization capabilities of the antenna according to the present invention is to arrange the plural segments of the antenna pattern curve so that the curve intersects at least one point of at least 14 boxes of the antenna pattern. the first grid having 5 x 5 boxes or cells including the curve. Likewise, in other embodiments where a high degree of miniaturization is required, the curve crosses at least one of the boxes twice in the 5x5 grid, i.e., the curve comprises two non-adjacent portions within. at least one of the cells or boxes of the grid.

Claims (15)

  An antenna system for a motor vehicle, characterized by comprising: at least one roof rack configured for installation on a motor vehicle, the roof rack comprising an enclosed internal surface and an earth ground for connecting an antenna element (1) to the ground of the motor vehicle, and an antenna element supported by said enclosed inner surface of the roof rack and electrically coupled to said grounding .   Antenna system according to claim 1, characterized in that said inner surface is curved, and that the antenna element is adapted to said curved surface.   3. Antenna system according to one of claims 1 or 2, characterized in that the antenna element is formed on one side of a flexible substrate adapted to said inner surface.   4. Antenna system according to one of the preceding claims, characterized in that the system comprises an active system comprising an amplification means for amplifying an electrical signal received by said antenna element.   Antenna system according to claim 4, characterized in that the active module (3) is housed in said roof rack.   Antenna system according to one of the preceding claims, characterized in that the system comprises a rear view camera supported by the roof rack.   Antenna system according to one of the preceding claims, characterized in that the antenna element is in the form of a solid curve.   8. Antenna system according to one of claims 1 or 7, characterized in that the antenna element has the shape of a Hilbert curve.   Antenna system according to one of claims 1 to 6, characterized in that the antenna element is in the form of a gate-size curve.   10. Antenna system according to one of claims 7 or 9, characterized in that the curve has a box count dimension or a gate size greater than 1.5.   11. Antenna system according to one of claims 7 or 9, characterized in that the curve has a box count dimension or a gate size greater than 1.9.   Antenna system according to one of the preceding claims, characterized in that the antenna element is adapted for reception of the AM / FM bands.   Antenna system according to one of the preceding claims, characterized in that the antenna element is adapted for reception of the DAB (digital broadcasting) / TV and GSM (global mobile communication system) bands.   14. Antenna system according to one of the preceding claims, characterized in that the antenna element is adapted for receiving satellite signals: GPS bands (global positioning system) and SDARS (satellite radio).   15. Antenna system according to one of the preceding claims, characterized in that it comprises two roof rack, each being provided with an antenna element, and wherein the antenna system further comprises means for combining the received signals at said antenna elements.