Dual coupled vehicle glass mount antenna system

A dual coupled vehicle glass mount antenna system and method. The inventive system is adapted for operation through any suitable partition, such as an automobile windshield, and comprises an antenna mounted on a first side of the partition for receiving a signal and a first circuit connected to the antenna. The antenna and the first circuit are mounted on a first side of the partition. In accordance with the present teachings, an arrangement is provided for supplying power to the first circuit. The output of the first circuit is coupled through the partition to a second circuit mounted on a second side thereof by a first coupling arrangement. In the illustrative embodiment, the antenna is a radio frequency antenna, the partition is a vehicle windshield, the first circuit is an amplifier, and the arrangement for supplying power is a second coupling arrangement. In the illustrative embodiment, the first and second coupling arrangements are coils and power is supplied to the second coupling arrangement from a direct current source by a cable. In alternative embodiments, power is supplied to the first circuit by a battery or solar cell arrangement. In the illustrative embodiment, the second circuit includes an impedance matching circuit and a transmitter or receiver depending upon the application. The location of the amplifier on the antenna side of the windshield reduces the noise figure of the system and provides improved gained relative to the conventional design.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to antenna systems. More specifically, the
 present invention relates to antenna systems mounted on glass windshields
 of vehicles.
 2. Description of the Related Art
 Antennas are required for virtually every wireless communication
 application including radio, cellular, and global positioning system (GPS)
 applications. Many such applications involve the use of transmitters
 and/or receivers mounted in vehicles. For these applications, glass
 mounted antennas are often used. Typically, the antenna is electrically
 connected to a coupling mechanism which is secured to an outside surface
 of the windshield of the vehicle. On the opposite side of the windshield,
 a second coupling device couples radio frequency energy from the antenna
 to the transmitter or receiver via a cable.
 Unfortunately, a coupling loss is typically experienced with conventional
 glass mount antenna arrangements. At 800 MHz, the coupling loss may be as
 much as 3 decibels. At higher frequencies, the coupling loss increases
 substantially. Consequently, for certain high frequency applications, such
 as satellite radio (at 2.4 GHz), the coupling loss is expected to be
 unacceptably high (2-4 dB).
 As these losses would make reception difficult, a need exists in the art
 for a system or technique for reducing the losses associated with glass
 mounted vehicle antennas for high frequency wireless communication
 applications, particularly satellite radio applications.
 SUMMARY OF THE INVENTION
 The need in the art is addressed by the dual coupled vehicle glass mount
 antenna system and method of the present invention. The inventive system
 is adapted for operation through any suitable partition, such as an
 automobile windshield, and comprises an antenna mounted on a first side of
 the partition for receiving a signal and a first circuit connected to the
 antenna. The antenna and the first circuit are mounted on a first side of
 the partition. In accordance with the present teachings, an arrangement is
 provided for supplying power to the first circuit. The output of the first
 circuit is coupled through the partition to a second circuit mounted on a
 second side thereof by a first coupling arrangement.
 In the illustrative embodiment, the antenna is a radio frequency antenna,
 the partition is a vehicle windshield, the first circuit is an amplifier,
 and the arrangement for supplying power includes a second coupling
 arrangement. In the illustrative embodiment, the first and second coupling
 arrangements are coils and power is supplied to the second coupling
 arrangement from a direct current source by a cable. In alternative
 embodiments, power is supplied to the first circuit by a battery or solar
 cell arrangement. In the illustrative embodiment, the second circuit
 includes an impedance matching circuit and a transmitter or receiver
 depending upon the application.
 The location of the amplifier on the antenna side of the windshield reduces
 the noise figure of the system and provides improved gained.

DESCRIPTION OF THE INVENTION
 Illustrative embodiments and exemplary applications will now be described
 with reference to the accompanying drawings to disclose the advantageous
 teachings of the present invention.
 While the present invention is described herein with reference to
 illustrative embodiments for particular applications, it should be
 understood that the invention is not limited thereto. Those having
 ordinary skill in the art and access to the teachings provided herein will
 recognize additional modifications, applications, and embodiments within
 the scope thereof and additional fields in which the present invention
 would be of significant utility.
 Several methods of transferring radio frequency (RF) energy through a glass
 plate are known in the art. These methods are useful in that, they allow
 antennas to be mounted on vehicles without the need for drilling.
 FIG. 1 is a diagram which illustrates the mounting of an antenna 12' on a
 vehicle 10' in accordance with conventional teachings. In accordance with
 conventional teachings, RF energy is transferred though a glass plate,
 partition or windshield by various means, such as capacitive coupling,
 slot coupling, and aperture coupling.
 FIG. 2 is a block diagram of a conventional arrangement for coupling radio
 frequency energy received from an antenna through a windshield in
 accordance with conventional teachings. The arrangement 11' includes
 coupling elements 14' and 16' which transfer electromagnetic energy
 received from an antenna 12' through a windshield 18'. The coupling
 elements 14' and 16' may be implemented with capacitive plates, a slot, or
 an aperture. An impedance matching circuit 20' is typically electrically
 connected to the second coupling element 16' for optimum power transfer.
 The matching circuit 20' may include passive components or traces on a
 board. The matching circuit 20' is often implemented with one or two
 capacitors or a micro-strip line which acts as a transformer depending
 upon the frequency of operation or impedance desired. In typical
 application, the impedance matching circuit is designed to provide a 50
 ohm impedance.
 The output of the impedance matching circuit 20' is provided to a low noise
 amplifier (LNA) 26' by a cable or transmission line 22'. The output of the
 low noise amplifier 26' is input to a receiver 28'.
 An inherent drawback of conventional coupling arrangements is that the
 noise in the system is typically increased by losses in the RF coupling
 arrangement, the matching circuit, and the cable. The losses may be on the
 order of 2-3 decibels. As mentioned above in the Description of the
 Related Art, these losses limit the utility of conventional RF coupling
 arrangements for certain applications, such as satellite communication
 applications.
 The present invention addresses this problem by providing the an
 arrangement in which radio frequency energy is transferred across a
 partition such as a windshield without significant degradation of the
 system noise figure. As discussed in detail below, the inventive system
 includes an antenna mounted on a first side of the windshield along with a
 first circuit such as an amplifier. In accordance with the present
 teachings, an arrangement is provided for supplying power to the amplifier
 thereby allowing for its advantageous location relative to the antenna. In
 the illustrative embodiment, the arrangement for supplying power to the
 amplifier is a first coupling arrangement mounted on either side of the
 windshield. A second coupling arrangement facilitates the transfer of
 signals between the amplifier and a processing circuit located on the
 other side of the windshield relative to the amplifier. As discussed more
 fully below, the location of the amplifier on the antenna side of the
 windshield reduces the noise figure of the system and provides improved
 gained.
 FIG. 3 is a block diagram of an illustrative implementation of an RF
 coupling arrangement constructed in accordance with the teachings of the
 present invention. The system normal 11 employs a pair of modules 13 and
 15. The first module 13 is fixed on an exterior surface of the windshield
 18 and the second module 15 is fixed on the interior surface of the
 windshield 18 using a typical conventional attachment arrangement such as
 a bonding glue or an arrangement of nuts and bolts. The first module 13
 includes an antenna 12, a low-noise amplifier (LNA) 26, and the first RF
 coupling unit 14 as per the conventional arrangement of FIG. 2. In
 addition, in accordance with the present teachings, the first module 13
 includes a first low-frequency coupling coil 30 which supplies power to
 the low noise amplifier 26.
 The interior module 15 includes a second RF coupling unit 16, a matching
 circuit 20, and an RF cable or transmission line 22.
 In the illustrative embodiment, in accordance with present teachings, the
 interior module 15 further includes a second low-frequency coupling coil
 32. The low-frequency coupling coils 30 and 32 act as a power transformer
 with the windshield 18 providing a glass core therefor. The coils 30 and
 32 are commercially available and presently may be purchased from TDK and
 other manufacturers. Those skilled in the art will understand that the
 turns ratio of the coils will be determined at the time of manufacture
 based on a specification of an input and an output voltage for a given
 application.
 In the illustrative embodiment, the first coil 30 has tens of turns and the
 second coil 32 has 200 to 300 turns. (Those skilled in the art will
 appreciate that the present invention is not limited to the turns ratio of
 the coils 30 and 32.) The receiver 28 provides an AC voltage of 48 volts
 through the second and first coils 32 and 30, respectively. In the
 exterior module 13, the voltage is rectified to a DC voltage of 12 volts
 and then regulated to the voltage required by the low noise amplifier 26,
 i.e., 3 to 5 volts DC.
 In addition, the coil diameter is a matter of design choice. For example,
 in the illustrative embodiment, the coils were chosen to have a diameter
 on the order of 1/2 inch.
 In the illustrative embodiment, direct current (DC) power is transferred to
 the exterior module 13 through the low-frequency coils 30 and 32, while RF
 energy is transferred through coupling units 14 and 16. As per the
 conventional arrangement of FIG. 2, the RF coupling units 14 and 16 may be
 implemented as capacitive plates, slots, with an aperture or by any other
 suitable method. (RF coupling arrangements are known in the art, see for
 example U.S. Pat. No. 5,565,877 entitled Ultra-High Frequency Slot Coupled
 Low Cost Antenna System, the teachings of which are incorporated herein by
 reference.)
 Those skilled in the art will appreciate that the relocation of the low
 noise amplifier 26 from the interior side of the windshield 18 to the
 exterior side of the windshield 18, directly beneath the antenna 12,
 facilitates a substantial reduction in the noise figure of the system.
 Hence, those skilled in the art will appreciate that utilizing the present
 teachings, and with proper choice of LNA (i.e., keeping the noise figure
 of the LNA as small as possible, e.g., on the order of 0.5 to 1 decibel),
 losses due to the matching circuit, cable loss, and RF coupling should not
 have a significant impact on system performance and the noise figure
 should remain low.
 Those skilled in the art will appreciate that the teachings of the present
 invention may be utilized in connection with other arrangements for
 providing power. For example, the amplifier 26 may be powered by a battery
 or solar cell without departing from the scope the present teachings.
 In addition, the present invention is not limited to use of a low noise
 amplifier 26. Other electrical, electronic an electro-optical circuits
 and/or components may be used on either side of the windshield without
 departing from the scope the present teachings as well.
 Further, the invention is not limited to the coupling of power through a
 windshield. Those skilled in the art will appreciate that the present
 teachings may be utilized to couple power through other partitions as
 measured the required by a given application. In which case, the optimum
 coupling technology (conductive, capacitive, optical, etc.) and the
 coupling power will have to be determined by the designer on a
 case-by-case basis.
 Thus, the present invention has been described herein with reference to a
 particular embodiment for a particular application. Those having ordinary
 skill in the art and access to the present teachings will recognize
 additional modifications applications and embodiments within the scope
 thereof.
 It is therefore intended by the appended claims to cover any and all such
 applications, modifications and embodiments within the scope of the
 present invention.
 Accordingly,