WO1999035709A1

WO1999035709A1 - Antenna device mainly for use in a vehicle

Info

Publication number: WO1999035709A1
Application number: PCT/SE1998/002281
Authority: WO
Inventors: Tony BJÖRKMAN
Original assignee: Allgon Ab
Priority date: 1998-01-09
Filing date: 1998-12-10
Publication date: 1999-07-15
Also published as: DE29822825U1; SE9801248D0; SE511431C2; SE9801248L; AU2079999A

Abstract

The present invention relates to an antenna assembly, comprising an outer module (1) including at least one antenna radiator (16, 17) fixed to an electrically conductive base (15), comprising at least one base plate. This base constitutes a first part of a coupling capacitance transferring the RF-signal through a dielectric pane. A connection unit (20, 30) interacting with the base (15) is mounted on the inside of the pane directly opposite the base. A coaxial cable (6) from the vehicle's radio or communication apparatus is connected to this unit (20, 30), which comprises a box (14) of at least partially electrically conductive material, having at least two plates (10, 12) facing towards the pane, where a first plate (10) in series with a first connection conductor (9) is tuned for a first frequency band and a second plate (12) in series with a second connection conductor (11) is tuned for a second frequency band. The other end of the connection conductors are attached to the coaxial cable (6).

Description

ANTENNA DEVICE MAINLY FOR USE IN A VEHICLE

TECHNICAL FIELD

The present invention relates to an antenna assembly for transmitting and receiving high frequency RF-signals for communication apparatus in vehicles, where the assembly is mounted on a non-conductive surface such as a vehicle windshield.

BACKGROUND OF THE INVENTION

The recent introduction of cellular. telephones that may utilise services in dual frequency bands, e.g. 900 MHz/1800 MHz has increased the interest in efficient mobile antenna systems for those frequency bands.

Commonly used antennas for communication apparatus in vehicles comprise only a single frequency band. In U.S. Pat. No 5,457,468 such an antenna assembly for radio and communication apparatus is described. The antenna assembly can be mounted on a non-conductive surface, such as a window, and includes an antenna radiator fixed to an electrically conductive base. This base is a first part of a coupling capacitance, transferring the RF-signal through the window. A connection unit interacting with the base is placed on the inside of the window, directly opposite the base. A coaxial cable from the vehicle's radio or communication apparatus is connected to this unit, which comprises a box with a second part of said coupling capacitance and an impedance adjusting means, such as a matching circuit, including a ground plane.

Another assembly for a single frequency band antenna is described in U.S. Pat. No 4,764,773. The assembly includes two pair of conducting plates, one pair mounted on each side of a windshield, each pair opposite the other pair. A coaxial cable is coupled to the inside pair of plates and a matching circuit is connected across the outside pair of plates. An antenna is connected to the output of the matching circuit. The coaxial cable is thus coupled directly through the windshield, without an intervening matching network.

In prior attempts to achieve dual band antennas for a communication apparatus in vehicles, the antenna assembly comprises similar parts as described in U.S. Pat. No 5,457,468, except that the antenna radiator is tuned for dual frequencies and that the matching circuit on the j-nside of the window is adjusted to dual resonating frequencies. A good performance in both frequency bands has been difficult to achieve this way.

SUMMARY OF THE INVENTION

The object of the invention is to provide an antenna assembly of the type mentioned above in the first paragraph, operational with good performance in at least dual frequency bands.

In accordance with the invention this object is achieved by means of an antenna assembly, including at least one antenna radiator fixed to an electrically conductive base. This base is a first part of a coupling capacitance transferring the RF- signal through a dielectric pane. A connection unit interacting with the base is placed on the inside of the pane directly opposite the base. A coaxial cable from the vehicle's radio or communication apparatus is connected to this unit, which comprises a box of at least partially electrically conductive material, having at least two plates facing towards the pane, where a first plate connected in series with a first connection conductor is tuned for a first frequency band and a second plate connected in series with a second connection conductor is tuned for a second frequency band. The other end of the connection conductors are attached to the coaxial antenna conductor. The plates are interacting with at least said conductive base mounted on the outside of the pane, which can be of any kind of non-conductive material as long as the dielectric properties of the material allows transfer of signals with desired impedance for the coupling capacitance's that forms between the base and the plates.

An advantage with the present invention is that a single antenna assembly can be used for any communication apparatus operating in dual frequency bands, such as GSM 900/1800 MHz.

Another advantage is that the present invention allows an antenna to be mounted and dismounted without any damage to the vehicle .

Yet another advantage is that the present invention allows separate matching circuits for the different frequency bands, which in turn gives an increased performance of the antenna.

The foregoing and additional objects, features and advantages of the present invention will be more readily apparent from the detailed description of a preferred embodiment thereof, which proceeds with reference to the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 is an explanatory sketch of a suggested outer antenna radiator for dual frequency bands.

Fig. 2 is a schematic section of the connection unit mounted on the inside of the pane and the base mounted on the outside of the pane.

Fig. 3 is a schematic section of the connection unit with an alternative attachment of the coaxial cable to the connection conductors . Fig. 4 is a sectional view of the inside of the connection unit according to a preferred embodiment of the invention.

Fig. 5 and 6 are side views of alternative embodiments of the connection unit.

DESCRIPTION OF THE PREFERRED EMBODIMENT

An antenna assembly comprising an outer module 1 according to fig 1 including a radiator with a first radiating part 16 and a second radiating part 17, where said -first part 16 is tuned for a first frequency band and said first and second radiating part 16, 17 together are tuned for a second lower frequency band. The first and second part 16, 17 of the radiator is in electrical contact with each other and the radiator is in electrical contact with an electrical conductive base 15, which is mounted against a first side of a pane, e.g. the outside of a windshield utilising self adhesive tape. The impedance of the system is determined by the length and the design of the radiator in combination with matching circuits in a connection unit mounted to a second side, directly opposite to the first side, of the pane, e.g. the inside of said windshield.

The connection unit 20, 30 comprising a box 14 of at least partially electrically conductive material, including a ground plane 13, constitute, together with the base 15 on the outside of the plane, the connection for transmitting radio waves from and to the radiator 16, 17 to and from a communication radio in the vehicle via an antenna lead 6. The box has an open primary side facing towards the inside of the pane 18 and is situated directly opposite the base 15.

In fig 2 this primary side consist of a printed circuit board (not shown) incorporating controlling means for capacitances and/or inductances in the form of conductive plates 10, 12, and connection conductors 9, 11. A part of or the whole ground plane 13 may also be incorporated on the printed circuit board and connected to an outer conductor 7 of a coaxial cable 6. The primary side of the box 14 is covered at least partly with a adhesive material, for instance double-sided tape (not shown) , to attach the box to the inside of the pane 18. A housing 5 of the outer module 1 is attached in a similar way to the outside of the pane 18, where the base 15 comprises at least one base plate arranged directly opposite the conductive plates 10, 12 on the inside of the pane 18. The base 15 is directly connected to the first radiating part 16 of the outer module.

An alternative way (not shown) of implementing the invention is to provide the same number of base plates of the base 15 corresponding to the number of conductive plates 10, 12 on the inside of the pane 18.

A conductor 8 of the coaxial cable 6 is connected to a first connection conductor 9 in series with a first conductive plate 10, and a second connection conductor 11 in series with a second conductive plate 12. The purpose of the connection conductors 9, 11 is to match the conductive plates 10, 12 and the ground plane 13 in such a way that RF-signals in a first frequency band, e.g. 1800 MHz band, mainly is coupled through the pane via the first conductive plate 10 and the base 15, and RF-signals in a second frequency band, e.g. 900 MHz band, mainly is coupled through the pane via the second conductive plate 12 and the base 15. The critical dimensions are the size of the conductive plates 10, 12 and the base 15, and the length and the design of the connection conductors 9, 11 and the ground plane 13.

A first link via the first radiating part 16 and the base plate 15 of the outer module 1, the first conductive plate 10 and the first connection conductor 9 has a matched impedance corresponding to a first frequency band, e.g. 1800 Mhz to match the impedance of the coaxial cable 6. A second link via the first and second part 16, 17 and the base plate 15 of the outer module 1, the second conductive plate 12 and the second connection conductor 11 has a matched impedance corresponding to a second frequency band, e.g. 900 Mhz to match the impedance in said coaxial cable 6. The coaxial cable is an antenna lead connected to a radio or communication apparatus and used as a part of a system. The radiator connected to the base plate 15 may also be of a type that is constructed for a single frequency band, which results in an antenna assembly adjusted only to one frequency band.

Figure 3 shows an alternative embodiment of the matching circuit of a connection unit 30, where a first end of an inductance 19 connects to the second connection conductor 11 in series with the second conductive plate 12, a second end of said inductance 19 connects to the conductor 8 of the coaxial cable 6.

Figure 4 shows a main printed circuit board 40 and a second printed circuit board 41, with a sectioned ground plane, constituting an embodiment of the present invention, comprising a connection conductor 9 and a first plate 10, tuned for a first frequency, and an interconnection 11 and a second plate

12, where the connection conductor 9 in series with the printed board circuit 11 and the second plate 12 is tuned for a second lower frequency as described previously. The connection conductor 9 is a conductor 8 of a stripped part of a coaxial cable 6. Further, an outer conductor 7 of the coaxial cable 6 is connected to a ground plane 13, built into the second circuit board 41.

The design of the ground plane 13 is adjusted to match the lower frequency band, known in the prior art. The ground plane is adjusted to the lower frequency band, since the performance of the higher frequency band is working adequately. An adjustment to the higher frequency band would, on the other hand, not give an adequate performance in the lower band. Figure 5 and 6 shows two alternative ways of connection the plates 10, 12 to the coaxial cable 6. Instead of implementing the connection between plate 10 and 12 in a printed board circuit, the connection is made by a wire 11, as shown in figure 5, or by a wire 11 and an inductor 19, as shown in figure 6. These embodiments are more expensive to manufacture, but have the advantage of a better performance compared to the embodiment shown in figure 4.

It is important, in all previously described embodiments, for the performance of the antenna device where the connection conductors 9, 11, physically are attached to the conductive plates 10, 12. The best performance is obtained when the attachments are as close as possible to the center of respective conductive plates.

The base 15 in previously described embodiments of the present invention comprises at least one base plate facing the pane, where said base plate is connected to the first and second part 16, 17 of the radiator. The first and second conductive plate 11, 12 are capacity-coupled, through the pane 18, to the base plate of the base 15.

Claims

1. Antenna assembly mainly for communication apparatus in a vehicle, where the assembly is mounted against a pane (18) of the vehicle, said assembly comprising - an outer module (1) with at least one radiator (16, 17), adapted for at least a first and a second frequency band, coupled to an electrically conductive base (15) mounted on the outside of said pane (18) , a connection means (20, 30) interacting with said base and placed on the inside of said pane (18) directly opposite said base, there being a coaxial cable (6) from the communication apparatus connected to said connection means (20, 30) , which connection means comprises a box (14) including a ground means

(13) , characterised in that - a conductor (8) in said coaxial cable (6) is connected to two separate connection conductors (9, 11) , a first connection conductor (9) , in connection with a first conductive plate (10) and- said base (15), is mainly transferring signals in a first frequency band , - a second connection conductor (11) , in connection with a second conductive plate (12) and said base (15) , is mainly transferring signals in a second frequency band, said first connection conductor (9) is a single conductor that together with a coupling between said first plate (10) and said base (15) and said ground means (13) enables a transfer of signals via said radiator (16, 17) on the outside of said pane

(18) adjusted to said first frequency band, said second connection conductor (11) is a single conductor that together with a coupling between said second plate (12) and said base (15) and said ground plane (13) enables a transfer of signals via said radiator (16, 17) on the outside of said pane (18) adjusted to said second frequency band, and said connection means (20, 30) on the inside of the pane

(18) being adjusted in such a way that it together with said base (15) on the outside of the pane (18) provides a characteristic impedance for two separated frequency bands, including any stray capacitances, stray and leak inductances, resistors coupled in series and parallel, wherein said impedance is approximately the same as for said coaxial cable.

2. Antenna assembly according to claim 1, characteri sed in that said first and second conductive plate (11, 12) are capacity-coupled to a single base plate (5) in the base (15) , wherein sa_id base plate is facing the pane (18) .

3. Antenna assembly according to claim 1 or 2, characteri sed in that the design of said ground plane (13) is adjusted to the lower of said frequency bands.

4. Antenna assembly according to any of claims 1-3, characteri sed in that respective connection conductor (9, 11) is electrically connected approximately to the center of respective conductive plates (10, 12) .

5. Antenna assembly according to any of claims 1-4, characteri s ed in that at least one connection conductor (9, 11) is built into a main printed circuit board (40) .

6. Antenna assembly according to claim 5, characteri s ed in that said ground plane is built into a second printed circuit board (41) .

7. Antenna assembly mainly for communication apparatus in a vehicle, where the assembly, mounted against a pane of the vehicle, comprises a radiator (16, 17) adapted for at least a first and a second frequency band coupled to an electrically conductive base (15) , which is mounted on the outside of the pane, a connection means (20, 30) interacting with the base and placed on the inside of the pane directly opposite the base, there being a coaxial cable (6) from the communication apparatus connected to the connection means, - said connection means comprising a box (14) with a primary side facing toward the base, which connection means also includes a ground means (13) connected to an outer conductor (7) of the coaxial cable (6), said coaxial cable having a conductor (8) insulated from the box (14) , characteri sed in that said conductor (8) from the box (14) is connected via two matching circuits (9, 11, 19) to two independently arranged conductive plates facing the primary side of said box (14) , wherein said matching circuits (9, 11, 19) are adjusted to enable means for signal transfer in said first frequency band via the radiator (16, 17), the base (15), the first conductive plate (10) , the matching circuits (9, 11, 19) to the coaxial cable (6), and in said second frequency band via the radiator (16, 17), the base (15), the second conductive plate (12), the matching circuits (9, 11, 19) to the coaxial cable (6) .

8. Antenna assembly according to claim 7, characteri s ed in that said first and second conductive plate (11, 12) are capacity-coupled to a single base plate (5) in the base (15), wherein said base plate is facing the pane (18) .

9. Antenna assembly according to claim 7 or 8, characteri s ed in that the matching circuit comprises a first connection conductor (9) in series with a first conductive plate (10), which is tuned for a first frequency band and a second connection conductor (11) in series with a second conductive plate (12) , which is tuned for a second frequency band.

10. Antenna assembly according to claim 7 or 8, characteri s ed in that the matching circuit comprises a first connection conductor (9) in series with a first conductive plate (10) , which is tuned for a first frequency band and an inductor (19) in series with a second connection conductor (11) and a second conductive plate (12), which is tuned for a second frequency band.

11. Antenna assembly according to claims 9 or 10, characteri s ed in that said_ matching circuits (9, 11, 19) being adjusted in such a way that it together with said conductive plates (10, 12), said ground plane (13) and said base (15) provides a characteristic impedance for two separated frequency bands, where said impedance is approximately the same as for said coaxial cable (6) for each of said frequency bands.

12. Antenna assembly according to claim 11, characteri s ed in that said characteristic impedance, includes any stray capacitances, stray and leak inductances, resistors coupled in series and parallel.

13. Antenna assembly according to any of claims 7-12, characteri s ed in that the design of said ground plane (13) is adjusted to the lower of said frequency bands.

14. Antenna assembly according to any of claims 9-13, characteri s ed in that respective connection conductor (9, 11) is electrically connected approximately to the center of respective conductive plates (10, 12) .

15. Antenna assembly according to any of claims 7-14, characteri s ed in that at least one connection conductor (9, 11) is built into a main printed circuit board (40) .

16. Antenna assembly according to claim 15, characteri s ed in that said ground plane is built into a second printed circuit board (41) .