DIRECTIONAL ANTENNA ASSEMBLY FOR VEHICULAR USE

Directional Antenna Assembly for Vehicular Use

Cross Reference to Related Applications

This application claims the benefit of priority pursuant to 35 USC §119(e)(1) from the provisional patent application filed pursuant to 35 USC §111(b): as Serial No. 60/062,247 on October 17, 1997.

Field of the Invention

This invention relates generally to antennas, and in particular to directional

antenna assemblies. The invention has particular utility in connection with dual band

or single band antennas for use in vehicular applications, and will be described in

connection with such utility, although other utilities are contemplated.

Background of the Invention

Wireless communication is well known for communicating over large

distances and also where the communicating devices require a high degree of

mobility. Known antenna devices for use in communication systems are capable of

resonating at two or more different frequencies. U.S. Patent 4,494,122 to Garay et

al. and U.S. Patent 5,406,296 to Egashira et al. are two representative examples of

multiple frequency antenna structures. Also known are antennas finding particular

applicability within the interior portions of vehicles. U.S. Patents 5,634,209 and

5,649,316 both to Prudhomme et al. disclose a radio antenna system that can be

positioned in a variety of locations within a vehicle interior. Summary of the Invention

This invention relates generally to an antenna assembly, and more

specifically to an antenna assembly for dual-band or single-band use in a vehicular

application. The antenna assembly is preferably a multiple-element directional

antenna having active, directive, and reflective elements.

In accordance with one embodiment of the invention, an antenna exhibiting

first and second predetermined resonant frequencies includes a pair of electrically

conductive driven elements having opposed ends. One end of each conductive

driven element is electrically coupled to a feed port. The antenna assembly further

includes a pair of LC trap members having opposed ends. The other end of each

conductive driven element is electrically coupled to one end of an LC trap. The

other end of each LC trap is electrically coupled to a conductive panel member such

that when a first radio frequency is applied to the feed port, the conductive element

and conductive panel member cooperate to resonate at a first resonant frequency.

The resonant circuit including the conductive elements, the LC traps, and the

conductive panel members operates such that when a second radio frequency is

applied to the feed port, the resonant circuit cooperates to resonate at a second

resonant frequency.

Several purposes and objects of the disclosed devices are described herein.

One object of the present disclosure is to provide an antenna assembly with

improved directionality and gain.

In one embodiment of the present invention, a directional antenna assembly

is provided for use in the cellular telephone and PCS device frequency ranges (800 - 900 MHz. and 1850 - 1990 MHz., respectively). The antenna assembly may be

adapted for in-vehicular use and may be housed within the rear view mirror, brake

light assembly, dashboard, rear deck, or other interior location which provides thru-

glass access. The improvements and benefits of the antenna assembly of the

present invention include:

* An increased signal strength, resulting in extended signal range and fewer dropped calls for a given power consumption rate;

* Reduced radio frequency radiation incident to a vehicle occupant's body, thereby reducing potential health risks;

* Reduction in the physical size of a directional antenna;

* Improved directionality and gain - reduced rearward radio radiation (front-to-back ratio of 1 - 10 nominal) and forward gain of 2.7 dBi; and

* Reduction in multipath interference, resulting from better call/data quality.

An antenna for cellular telephone and PCS device use has an antenna

housing which is secured within the vehicle. A coaxial cable operatively couples the

antenna assembly to the cellular telephone / PCS device. In a preferred form, the

cellular telephone / PCS device antenna assembly is positioned within an antenna

housing in the interior of a vehicle. Desirably, the antenna assembly provides a

disguised antenna which is hidden from view to make the antenna assembly less

visible and accessible to thieves and vandals and, therefore, minimizes antenna

theft. Since the antenna assembly is encased in a protective housing, it cannot

easily be bent, broke, or otherwise damaged. Advantageously, the in-vehicle antenna assembly is not contacted and adversely effected by external weather

conditions, e.g. ice, snow, sleet, or rain.

The antenna assembly is also less obstructive to the occupants of the vehicle

and provides a greater unimpaired range of vision for the driver. In another

embodiment, the antenna assembly may be positioned within an upper rear brake

light assembly of the vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

Yet other objects and advantages of the present invention may be seen from

the followed detailed description taken in conjunction with the accompanying

drawings wherein like numerals depict like parts throughout, and wherein

FIG. 1 illustrates a perspective view of an antenna assembly of the present

invention;

FIG. 2 illustrates a perspective view of a portion of the antenna assembly of FIG.

1 ;

FIG. 3 illustrates an elevational view of a portion of the antenna assembly of FIG.

1 ;

FIG. 4 illustrates a perspective view of a first embodiment of the present

invention; and

FIG. 5 illustrates a perspective view of a second embodiment of the present

invention;

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An antenna assembly 10 for a multiple-band radio frequency transceiver such

as a cellular telephone and PCS communication device. The antenna assembly 10 of the present invention may be mounted within the rear view mirror assembly 12 or

the rear upper brake light assembly 14 of an automobile. The invention provides a

directional antenna assembly 10 having an arranged dual-band driven element 16,

an optional one or more reflector elements 18 for some applications, and a director

element 20.

The inventive antenna assembly 10 shown in the figures and disclosed herein

is for in-vehicle use, particularly for an automobile. It is to be understood that the

inventive antenna assembly 10 can be used with other types of vehicles, such as:

vans, trucks, buses, motorcycles, construction equipment, or tractors and other

agricultural vehicles.

The cellular telephone / PCS device system has an antenna assembly 10

which is secured within a vehicle antenna housing. The antenna housing is

preferably entirely contained within the interior of the vehicle. Alternatively, the

antenna housing may be separate from the vehicle interior.

In preferred embodiments, the antenna assembly 10 is hidden from view and

is encased and positioned within and surrounded by the vehicle antenna housing.

The vehicle antenna housing can include: the rear view mirror assembly 12, a side

view mirror assembly (not shown), or a rear brake light assembly 14. In the

embodiment of FIG. 4, the vehicle antenna housing is an in-vehicle housing

comprising a rear view mirror assembly 12. The rear view mirror assembly 12 has a

housing portion 22 which is clipped, bonded, or otherwise secured to a front mirror

portion 24. The housing portion 22 is sized to entirely receive the antenna assembly

10. The rear view mirror assembly 12 is located at a position for viewing by the driver of the vehicle. The rear view mirror 24 may be made of glass and coated with

silver or other reflective coating. An electrically conductive coating on the mirror 24

or other interior surface 25 integral with the mirror assembly 10 may act as a

reflecting element for the antenna 10.

The in-vehicle dual-band antenna assembly 10 of the present invention

comprises a dual-band driven element 16 and parasitic reflector and director

elements 18, 20. Depending on the particular application, parasitic reflector element

18 may not be necessary for adequate antenna 10 performance. All elements 16,

18, 20 of the antenna assembly 10 are securely mounted within the interior of the

rear view mirror housing 22 behind the rear view mirror 24.

In one preferred embodiment according to the present invention, the antenna

assembly 10 is tuned to receive and transmit cellular telephone and PCS device

frequency signals. The antenna assembly 10 includes: a dual-band driven element

16, a parasitic reflector element 20 and a director element 18. A coaxial cable 28

operatively couples the antenna assembly 10 to a cellular telephone / PCS

communication device within the vehicle.

Referring now to FIGS. 1 and 2, the dual-band driven element 16 of the

antenna assembly 10 includes a pair of center conductor sections 30 disposed upon

a dielectric substrate 32, a pair of LC (inductor-capacitance) traps 34, and a pair of

conductive panel elements 36 each connected through an LC trap 34 to an

associated center conductor section 30. The purpose of the LC traps 34 is to block

their own resonant frequency, while passing lower frequencies. In the illustrated

embodiment, the LC traps 34 block the PCS frequency range (1850 - 1990 MHz.). The pair of conductor sections 36 are sized to create a second resonance over the

800 - 900 MHz. frequency range. The planar radiating conductive elements 30 are

fabricated of electrically conductive material, preferably a metal such as copper or

aluminum which can be deposited on the dielectric substrate 32 and configured with

the desired shape by photolithography and well known etching processes. The

dielectric substrate 32 may be fabricated of a ceramic, electrically-insulating material

such as alumina.

The center conductor sections 30 of the dual-band driven element 16 are a

pair of conductive elements attached to a surface of the dielectric substrate 32. The

dielectric constant of the substrate material 32 may be greater than unity, resulting in

a reduction in the length of the conductor/substrate combination as compared to a

unity dielectric constant substrate. The thickness, length, and width dimensions of

dielectric substrate 32 are approximately 0.2 inch, 3.4 inches, and 0.6 inch,

respectively. The dielectric substrate 32 has a dielectric constant of between 9.2

and 10, for these dimensions.

The width of the center conductors 30 is substantially equal to the width of the

underlying dielectric substrate 32. In the illustrated embodiments, the width of the

center conductors 30 is approximately 0.6 inch and the thickness is in the range of

approximately 0.001 — 0.062 inch. Each center conductor section 30 is

approximately 1.5 inches in length.

The LC traps 34 of the dual-band driven element 16 are configured as

inductive loops; an axis of the loops being substantially parallel with the direction of

maximum signal propogation 38. Each LC trap 34 is formed of a conductive wire having a thickness of 1/32 inch (nominal) and is shaped with loops having a 0.13

inch nominal inside diameter. Each LC trap 34 has approximately 3.5 turns and a

nominal overall length of 0.23 inch. One end of the LC trap 34 passes through an

aperture 40 in the dielectric substrate 32 and is connected to the center conductor

section 30. Referring to FIG. 2, the aperture 40 in the dielectric substrate 32 through

which one end of the LC trap 34 passes is positioned approximately 0.1 inch away

from the outer edge 42 of the dielectric substrate 32. The other end of the LC trap

34 is connected to one conductive panel member 36. Angled conductive panel

members 36 are illustrated as generally 'L' shaped, though alternatively, the panel

members 36 may be more complexly or simply formed. Angled panel members 36

include a first portion 44 which is generally perpendicularly aligned to the dielectric

substrate 32 and a second portion 46 which is generally parallelly aligned to the

dielectric substrate 32. Angled panel members 36 may be formed of a brass

material and have an area of 0.34 inches-squared and a thickness of 0.007 +/- 0.003

inch.

Dual-band reflector element 18 of the antenna assembly 10 is positioned

away from the dielectric substrate 32, in the direction substantially opposite the

direction of maximum propogation 38. Dual-band reflector element consists of a

center wire section 48, a pair of LC traps 50, and a pair of generally planar

conductive panel members 52. Center wire section 48 is formed with a 1/16 inch

nominal thickness and is approximately 3.5 inches in length, or approximately .57 λ

at 800 MHz. Center wire section 48 is maintained in a generally parallel relationship

with the dielectric substrate 32 by a support element (not shown). LC trap members 50 of the dual-band reflector element 18 are similarly configured to the LC trap

members 34 of the dual-band driven element 16. The conductive panel members 52

are substantially planar and include a first narrow section 54 and a second more

broad section 56. The LC trap members 50 are connected to the conductive panel

members 52 at the outermost edge 58 of the panel members 52. As illustrated in

FIG. 1 , the conductive panel members 52 are positioned at opposite ends of the

center wire section 48 and on either side of the center wire section 48. Referring to

FIG. 3, the center wire section 48 and rear-most edge 60 of the second broad

section 56 of the conductive panel members 52 are substantially aligned and

equidistant from the dual-band driven element 16. Referring again to FIG. 1 , the

spacing between the dual-band driven element 16 and the conductor elements 30 of

the dual-band reflector element 18, illustrated as the distance d2, is approximately

1.7 inches or approximately .115λ at 800 MHz.

The antenna assembly 10 also includes a parasitic director element 20,

formed as a wire member which is maintained a fixed distance, d1 , from the dual-

band driven element 16. Director wire 20 has a length of approximately 2.5 inches (

.48 λ at 1850 MHz.) with a nominal thickness of 1/16 inch. Director wire 20 is

secured to the antenna housing by a director wire support member (not shown)

which can assume a variety of shapes and configurations.

The coaxial cable 28 feed line for the antenna assembly 10 is illustrated in the

figures as extending in a direction substantially opposite to the direction of maximum

propogation 38. Referring to FIG. 4, the coaxial cable 28 includes a relatively

straight section 62 between the dual-band driven element 16 and the dual-band reflector element 18 and a curved section 64 which transitions to a second straight

section 66 as the cable 28 extends through the tubular mirror extension arm 26.

The antenna assembly 10 also includes a ferrite material shielding element

68 surrounding the coax cable 28 and suppressing radio frequency currents from the

outer shield of the coax cable 28. Shielding element 68 is illustrated in the figures

as ferrite beads which are positioned generally near center conductor section

feedpoints and dielectric substrate member. Alternatively, shielding element 68 may

be ferrite material configured in any manner to provide shielding.

A second reflector element 118 may be positioned between the first reflector

element 18 and the dual-band driven element 16 as illustrated in FIG. 5 to provide

additional directivity and gain of the transmitted signal in the PCS band. The second

reflector element 118 may be a wire element with a length of 3.0 inches and having

a nominal 1/16 inch thickness.

As illustrated in the figures, the dual-band driven element 16, dual-band

reflector element 18, and director element 20 are all subsantially elongate in form

and substantially aligned in a generally planar manner such that the elongate axes

of the elements 16, 18, 20 are substantially parallelly aligned. Alternative

geometries may also be practicable

Still now to FIG. 5, another embodiment of the antenna assembly 10 is

illustrated as housed within a rear brake light assembly 14 of an automobile.

Preferably, the housing is an upper brake light. Upper brake light assembly 14

includes a brake light 70 and a brake light reflector 72 and lens 74. Upper brake light assembly 14 may be positioned within the interior of the

automobile and generally proximate the rear window such that brake light 70 is

visible to others from behind the automobile. The antenna assembly 10 of FIG. 5 is

similar to that of FIGS. 1 — 4. One or more conductive interior surfaces of the brake

light assembly may act as a reflective element for the antenna assembly 10.

With knowledge of the present disclosure, other modifications will be apparent

to those persons skilled in the art. Such modifications may involve other features

which are already known in the design, manufacture and use of antennas and

component parts thereof and which may be used instead of or in addition to features

already described herein. Still other changes may be made without departing from

the spirit and scope of the present invention: