US20050195117A1

US20050195117A1 - Antenna

Info

Publication number: US20050195117A1
Application number: US11/120,216
Authority: US
Inventors: George Chadwick
Original assignee: Cocomo MB Communications Inc
Current assignee: Cocomo MB Communications Inc
Priority date: 2000-08-10
Filing date: 2005-05-02
Publication date: 2005-09-08
Also published as: US6600896B2; AU2003245376B2; AU2003245376A1; US20060187005A1; CN1819334A; WO2003103195A1; JP2005528848A; CA2525979A1; EP1512239A1; KR100623605B1; CN1656717A; KR20050008741A; US7392013B2; US20020142716A1; RU2307471C2; RU2004138297A

Abstract

An antenna system, particularly for vehicles. A discone-type antenna is preferably utilized for frequencies outside the vehicle. At various frequencies, either or both the antenna and the vehicle serve as exciters.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of U.S. patent application Ser. No. 635,402, entitled “In-Vehicle Exciter”, to Chadwick, filed on Nov. 27, 2000, and U.S. patent application Ser. No. 10/160,747, entitled “Exciter System and Excitation Methods for Communications Within and Very Near to Vehicles”, to Chadwick, et al., filed on May 30, 2002, and the specifications thereof are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention (Technical Field)
The present invention relates to an antenna and exciter systems for vehicles, such as automobiles, trucks, trains, buses, boats and aircraft.
2. Description of Related Art
Note that the following discussion refers to a number of publications by author(s) and year of publication, and that due to recent publication dates certain publications are not to be considered as prior art vis-a-vis the present invention. Discussion of such publications herein is given for more complete background and is not to be construed as an admission that such publications are prior art for patentability determination purposes.
The automobile manufacturing industry is undergoing an industry wide revolution to provide connectivity to automobiles. This field of endeavor has been coined as “telematics” by the automotive industry. Connectivity is required for AM/FM radio, cellular, GPS, internet and satellite linkage. The first phase of this revolution has already begun. All high-end model automobiles, such as those produced by Chrysler, Daimler-Benz and Cadillac, have already eliminated external antennas on the top side of their vehicles. These antennas have been moved to the front and rear windows of the automobile. Many automobiles will be so equipped in the next several years.
Now that automobile connectivity is required for emergency services, the survival of the antennas becomes a paramount issue. Unfortunately, one of the first things to be destroyed is the windows along with their antennas. In a severe accident, the automobile may often be upside down with the under-chassis pointed skyward. The telematics systems must be able to function even in this case.
The problem of providing a solution for a survivable antenna connectivity for vehicles has presented a major challenge to engineers and technicians in the automotive industry. The development of methods and apparatus that would supply a survivable antenna for vehicles would constitute a major technological advance, and would satisfy a long felt need within the automobile industry.
Several patents disclose an under-vehicle antenna. These include U.S. Pat. No. 2,111,398, entitled “Antenna Device” to Kippenberg; U.S. Pat. No. 2,073,336, entitled “Radio Ground Exciter” to Cook; and U.S. Pat. No. 4,968,984, entitled “Antenna Unit for a Vehicle” to Katoh, et al. None of these patents disclose the use of a discone-type of exciter.
Prior art discones do not have a coaxial cable extending through the cone portion. U.S. patent application Ser. No. 10/160,747, entitled “Exciter System and Excitation Methods for Communications Within and Very Near to Vehicles,” and U.S. patent application Ser. No. 635,402, entitled “In-Vehicle Exciter”, which are incorporated herein by reference, disclose a modified discone exciter, which is used for communications within a vehicle. The present invention is directed to a modified discone exciter, with a coaxial cable disposed in the cone, for communications outside the vehicle.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to discone-type of antenna. This antenna comprises a disc; a cone comprising an apex and a base comprising a diameter, the disc positioned at the apex of the cone; and a coaxial cable disposed in an interior of the cone from the apex through the cone and extending outwardly beyond the cone. The antenna further preferably comprises an insulator disposed between the disc and the cone. Preferably, a coaxial cable is disposed through a center of the diameter of the cone.
The antenna may be disposed on an exterior of the vehicle, and preferably disposed under the exterior of the vehicle. Alternatively, the antenna may be disposed in an interior of a vehicle, or in a structure. The antenna preferably operates at a frequency in the range of between approximately 500 KHz and between approximately 8 GHz.
The present invention is also directed to an exciter system for a vehicle. This system comprises an antenna disposed on or in a vehicle. The exciter system radiates exterior to the vehicle. The exciter system operates in at least three modes. These three modes comprise the following: (1) the antenna radiates at a higher frequency; (2) the vehicle radiates at a lower frequency; and (3) both the antenna and the vehicle radiate at a transition frequency between the lower frequency and the higher frequency.
The antenna preferably comprises a discone antenna. This discone antenna preferably comprises the discone antenna discussed above.
When the antenna is disposed under a vehicle, it is preferably disposed near a centerline of the vehicle, and most preferably disposed between approximately one and two feet of a front of a vehicle (e.g. the front bumper).
The lower frequency is determined by the size of the vehicle. The higher frequency is determined by the size of the discone. The cone angle is preferably between approximately 45 degrees and approximately 90 degrees. The cone height is preferably between approximately 0.4 inches and approximately 4 inches. The cable is preferably between approximately 0.08 inches and approximately 0.25 inches. The disk diameter is preferably at least 0.18 wavelengths in diameter at its lower operating frequency.
The present invention also relates to a method of excitation for sending and receiving various frequencies to and from a vehicle. This method comprises: disposing an antenna on or in a vehicle; exciting the antenna at higher frequencies that radiate outside of the vehicle; exciting the vehicle at lower frequencies that radiate outside the vehicle; and exciting both the antenna and the vehicle at transition frequencies that radiate outside the vehicle. A discone antenna, as discussed above, is preferably utilized.
The present invention provides methods and apparatuses for providing an antenna or exciter system for vehicles. In the preferred embodiment, the antenna is a modified discone exciter. In another embodiment of the invention, the invention comprises an exciter mounted on the underside of the vehicle which is separated from the vehicle frame by a dielectric separator. A signal is elicited from the exciter, and may be fed to a wide variety of radio or other frequency devices onboard the vehicle.
A primary object of the present invention is to provide an antenna that has a low profile in a vehicle.
It is another object of the present invention to provide an antenna that may be mounted under a vehicle.
Yet another object of the present invention is to provide an antenna that modifies a traditional discone-type of exciter.
A primary advantage of the present invention is that a low-cost, low-profile, effective antenna is provided.
Another advantage of the present invention is that the vehicle may be used as a direct radiator for the antenna.
Other objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The accompanying drawings, which are incorporated into and form a part of the specification, illustrate one or more embodiments of the present invention and, together with the description, serve to explain the principles of the invention. The drawings are only for the purpose of illustrating one or more preferred embodiments of the invention and are not to be construed as limiting the invention. In the drawings:
FIG. 1 is a side section view of the preferred embodiment of the present invention, showing a modified discone exciter;
FIG. 2 is a diagram of the evolution of the present invention;
FIG. 3A is a perspective cutaway view of an embodiment of the present invention intended for AM/FM radio applications;
FIG. 3B is a section view of the FIG. 3A embodiment;
FIG. 4 is a perspective cutaway view of another embodiment of the present invention;
FIG. 5 is a perspective cutaway view of a spiral embodiment of the present invention;
FIG. 6 is a graph of VSWR versus frequency for a PCS match;
FIGS. 7-11 show azimuth and elevation patterns at varying frequencies;
FIG. 12 is the measured return loss for various frequencies;
FIG. 13 is the measured VSWR for various frequencies;
FIGS. 14-20 show data comparison at various frequencies;
FIG. 21 shows a test range setup;
FIG. 22 shows patterns and absolute gain; and
FIGS. 23-25 show comparisons of the antenna location at various frequencies.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to antenna systems, particularly for use on vehicles, such as automobiles, trucks, trains, buses, boats, aircraft, and the like. The antenna operates at particular frequencies, such that at high frequencies, the antenna radiates and at lower frequencies, there is a transition so that the vehicle, itself, radiates. The preferred type of antenna, useful in the present invention, is a discone-type of antenna.
The terms “antenna” and “exciter” are used interchangeably throughout the specification and claims and are intended to mean a system for sending and receiving electromagnetic waves and to generate or produce an electric field. The term “discone” is intended to mean a particular type of antenna or exciter, having disc and cone components, and this term is also intended to cover “disc-cone” or other such exciters having this configuration. Although the invention is discussed as to a single antenna or exciter, multiple exciters may be utilized in or on a single vehicle.
The antenna of the present invention is particularly useful for vehicles. In vehicles, there are three modes of operation: the antenna serving as the exciter; the vehicle serving as the exciter; and a transition between the antenna and vehicle, both as exciters. At higher frequencies, when the size of the vehicle is large, the discone assembly is the major component that radiates. At lower frequencies, the vehicle itself radiates. Both the vehicle and antenna radiate at transition frequencies. Frequencies over all these ranges vary from between approximately 500 KHz to 8 GHz.
The frequencies in each of the ranges depend highly on the size of the vehicle. Three examples are given below, one for an automobile, one for a train and one for an airplane, using the following formula:
Wavelength=11.8/frequency.
Where f is in GHz, 11.8 is a constant for the speed of light, i.e. if f=1 GHz, then the above becomes 11.8″ wavelength.
Assume the car is 20 feet long. Its first resonance will occur where this dimension is ¼ (preferred) wavelength. Thus, the first resonant frequency, using the above formula, is 12.3 MHz (11.8/240 inches×1000×¼). This frequency sets the low end of the intermediate or transition band. If the car also has a quarter wavelength monopole operating at 1 GHz, the upper end of the band is 1 GHz. And, thus, the intermediate band extends from approximately 12.3 MHz to 1 GHz.
If there is a metal railroad car which is 50 feet long, then the first resonant frequency, using the above formula, is 4.9 MHz. The intermediate band is thus 4.9 MHz to 1 GHz.
For an airplane, 100 feet long, the first resonant frequency, using the above formula, is 2.46 MHz. The upper end is 1 GHz.
As can be seen by the above, the frequency ranges are highly dependent on the length of the vehicle. Structure and antenna size also affect the frequencies.
The upper range of frequencies is generally set at less than or equal to ⅛ wavelength, although a range of between approximately 1/16 and ¼ wavelength is useful in accordance with the present invention. The size of the discone or antenna also determines this range. For a discone, it is useful to have the top plate at approximately 0.7 diameter of the base diameter.
The lower range is set by the size of the vehicle.
The intermediate or transition range is between the upper and lower ranges.
The antenna principally serves as a transition from itself to the vehicle and the antenna then acts as a direct radiator working against the vehicle skin (as with a ground plane). The antenna preferably has a bandwidth of approximately 100 to 1 or up to approximately 200 to 1.
The antenna is preferably mounted outside the vehicle, and most preferably on the underside of the vehicle in order to minimize damage in the event of a crash. However, the antenna may be mounted at any place inside or outside the vehicle, preferably at a location that avoids interference with other functions of the vehicle or prevents interference with the antenna. For instance, it could be positioned on the back or front window ledges, near the bumper, etc. The antenna is capable of sending and receiving frequencies to and from outside the vehicle due to the particular frequencies.
The transition frequency from one mode to the other is a vehicle size and configuration variable. The lowest limit occurs where the size of the vehicle is approximately a quarter wavelength long and the match is good. Below the lower limit the match gradually degrades to a poorer and poorer value because the automobile is becoming smaller than the wavelengths. Above the lower limit region the loss is approximately 50% until the mode of operation where the antenna begins to act as a near independent radiator. The independent mode can be very match efficient.
In the low frequency region the match is poorest but the long wavelengths have less propagation loss and thus the match loss is generally acceptable. In the region above 60 MHz the 50% match loss can be reduced over limited bands by the use of diplexers and matching elements. In the upper region, the match is quite good (preferably from 800 MHz to 2 GHz).
The frequency zones are defined but radiation characteristics must be quantified. For frequencies about 60 MHz the radiation shape is that of a cardiod, being near omnidirectional in azimuth and similar to that of a monopole over a ground plane in elevation. As the frequency increases, the pattern is overall the same but with more fine structural detail as the frequency approaches 800 MHz. In the region from 800 MHz to 8.0 GHz the patterns are much like the low end except for automobile induced blockage effects.
The characteristics of the antenna, when applied to larger trucks and vans differ in details from those above described for an automobile. The characteristics referred to are those of match, patterns and gain. The performance from 800 MHz to 2.0 GHz (preferred range) is the same as in an automobile except for blockage detail. The intermediate range is now dependent on the size of the truck or van, but will generally be lower in frequency. The first resonance will generally be below 60 MHz because the truck is larger.
FIG. 1 is a depiction of the preferred discone antenna of the present invention. As shown therein, discone antenna comprises cone 10 (preferably a solid cone), disc 12, coaxial cable 14 which extends through cone to disc, cable connector 16, ground plane (e.g. undercarriage of automobile) 18, and preferably insulating spacer 20.
Coaxial cable 14 is connected to devices in the vehicle that receive or transmit various frequencies to or from outside the vehicle. These include AM/FM radio, GPS, cellular, internet, satellite linkage, garage door, gate and other outside devices, traffic control, roadside antenna, vehicle identification, video transfer, light and other electronics control, and the like. Wireless connections may also be utilized in accordance with the present invention.
The antenna of the present invention incorporates the vehicle (at low frequencies). This antenna is preferably located within one to two feet of the front bumper of the vehicle (e.g. automobile or truck) and near the centerline of the vehicle. The dimensions are selected to keep the match and pattern shapes acceptable. Cone angle 22 is preferably approximately 60 degrees but can vary between approximate 45 degrees and approximately 90 degrees. Cone height is preferably between approximately 0.5 inches and approximately 12 inches, preferably between approximately one and approximately four inches and most preferably between approximately two and approximately three inches (e.g. 2.84 inches). Coaxial cable 14 diameter is preferably between approximately 0.1 inches and approximately 0.2 inches (e.g. 0.141 inch diameter). Disc 13 diameter is at least 0.18 (e.g. 0.18 to 0.5 wavelengths) wavelengths in diameter at the lowest operating frequency (see FIG. 1).
When the discone is attached to the undersurface of the vehicle, disc 12 is positioned at the lowest level of cone 10. Ground plane 18 is intended to attach to the underside of the vehicle after validation is first obtained on the free space range.

INDUSTRIAL APPLICABILITY

The invention is further illustrated by the following non-limiting examples.

EXAMPLE 1

Initial data was first taken on a free space range and included the ground plane shown in FIG. 1. The match of the antenna is shown in FIG. 6. The VSWR is less than 2:1 from 600 MHz to 1800 MHz. The VSWR is less than 3:1 from 580 MHz to 2 GHz. The azimuth and elevation patterns are shown in FIGS. 7 through 11. The azimuth patterns are omnidirectional with 1 dB from 800 MHZ to 1.5 GHz and less than 2 dB to 1.9 GHz. The elevation patterns are typical cardiods over the entire band. The 0 degree reference was at the base of the ground plane. The results were considered adequate and the next phase was the testing of an automobile mounted antenna.

EXAMPLE 2

The FIG. 1 antenna was positioned 9″ from the centerline of the front bumper of an automobile. The measured return loss is shown in FIG. 14 and measured VSWR is shown in FIG. 13. The VSWR is less than 3 to 1 from approximately 620 MHz to 2 GHz. The effect of VSWR on the vehicle is quite small as shown in the comparison of FIG. 6.
Measured patterns are shown in FIGS. 14 through 16 for frequencies of 850 MHz, 1575 MHz and 1850 MHz and at elevation heights of 1, 3 and 5 feet (the transmitter was located approximately 10 feet away from the vehicle). The 850 MHz frequency generally provided the same response, however, the front lobe was typically 20 dB stronger than the rear lobe. The 1575 MHz frequency provided better coverage for heights of 1-3 feet above the ground and 10 feet away, but was reduced at an elevation of 5 feet. At 1575 MHz the front lobe was typically 20 dB stronger than the rear lobe. At 1850 MHz the front lobe was typically 20 dB stronger than the rear lobe and the pattern levels reduced slightly above 3 feet. The gain values are shown in FIG. 17 for all three frequencies. The absolute gains are measured in the forward 0 degree direction and are 5.4, 4.5, and −3.3 dBi. The gains were typically greater than a dipole in the forward direction, largely because the back lobe in all cases was approximately 20 dB lower. The gain data were obtained by the substitution method.

EXAMPLE 3

The relative gains of an analog cell phone stub antenna, GPS stub antenna and PCS stub antenna are shown in FIGS. 18 through 20 compared with the antenna of the present invention. The antenna of the present invention was stronger over most of the region except for the rearward direction. The stub antennas for each unit were located on the console between the driver and passenger seats. The stub antennas were mounted vertically to match the testing antenna polarization. The test range layout is shown in FIG. 21.

EXAMPLE 4

GPS test data were taken on the stub antenna of the present invention during actual driving conditions from Santa Clara to Lodi Calif., a 215 mile round trip. The average accuracy was 22 feet and compared well with the stub which provided accuracy from 20 to 26 feet at DRG. On average there were 6 to 10 satellites in view during the trip taken. The 22 foot accuracy was maintained through the foothill passes. The unit had readings as low as 16 feet and as high as 50 feet. The average duration of greater than 30 feet was 2 seconds. The most common accuracy was 18 feet. The satellites with the stronger signal strength were generally located overhead and forward, while those located to the rear and low horizon had the lower signal strength.
Both an analog and PCS phone were used to make connections. The measured signal strength on the phone indicators for both the antenna and the manufacturers' stub antennas were the same. The quality of the phone receptions appeared to be approximately the same.
The antenna of FIG. 1 was moved to the center of the automobile and was located under the passenger near center of the vehicle. FIG. 22 shows the patterns and the absolute gain at the three frequencies of 850, 1575 and 1850 MHz. The patterns are more symmetric than those located at the front of the vehicle. At 1850 MHz there was a significant notch at 30 degrees. FIGS. 23 through 25 show direction comparisons with the data taken when the antenna was at the front of the vehicle. The center mounted data was generally more uniform as expected. The relative gain of the center mounted antenna showed the increased interference of the vehicle undersurface.

EXAMPLE 5

The same structure used in FIG. 1 also served as an antenna for an intermediate range (50 to 800 MHz) in an automobile. In this case however, the major radiator transitioned from a body radiating device to 50 MHz to a partial body device as the frequency approached 800 MHz. The antenna design was the same except that the disk was approximately 6 inches in diameter for case 1. A 12 inch diameter disc produced far better results. The lower frequency resonance occurred in the region just below 60 MHz and had a mismatch that was generally less than 2:1 over a narrow bandwidth.

EXAMPLE 6

The VSWR and loss data when the antenna was mounted on an automobile is shown in FIG. 22. The reference point is the antenna terminal. The VSWR inflection point occurred at approximately 325 MHz for a 6 inch disk and at approximately 125 MHz for the 12 inch disk. The corresponding inflections for loss are shown in FIG. 22 for both the 6 and 12 inch disk. The improvement from 6 to 12 inches was dramatic. A 12 inch disk at 115 MHz had a 3 dB loss and at 230 MHz it had a 1 dB loss. A 6 inch disk had a 3 dB loss at 260 MHz and a 1 dB loss at 314 MHz. The approximate rule for selecting the disk diameter for a loss of 3 dB is 0.18 times the wavelength of the lowest operating frequency. The measured patterns in the azimuth plane at 1 foot elevation are shown in FIG. 23 for frequencies of 98 and 325 MHz. The pattern levels shown were relative. The patterns were taken with a disk diameter of 12 inches. The peak gain at 98 MHz was −4.8 dBi including match losses (4.3 dB) in the antenna. The peak gain at 325 MhZ was −6.0 dBi including match losses (1.5 dB) in the antenna. No pattern data was taken on the 6 inch disk. Absolute gains were obtained with a gain standard. The application of simple matching using a transformer and an inductor provided a maximum loss of 1.4 dB over the region from 86 MHz to 110 MHz using a 12 inch disk. This matching increased the gain from the earlier noted −4.8 dBi to −1.8 dBi. A 12 inch disk was used to receive FM signals over the full FM band. The results were compared with a standard automobile whip antenna. There was no discernable difference between the antenna with a 12 inch disk and the whip antenna.
Although the invention has been described in detail with particular reference to these preferred embodiments, other embodiments can achieve the same results. Variations and modifications of the present invention will be obvious to those skilled in the art and it is intended to cover in the appended claims all such modifications and equivalents. The entire disclosures of all references, applications, patents, and publications cited above are hereby incorporated by reference.

Claims

1. A discone-type of antenna comprising:

a disc;

a cone comprising an apex and a base comprising a diameter, said disc positioned at said apex of said cone; and

a coaxial cable disposed in an interior of said cone from said apex through said cone and extending outwardly beyond said cone.

2. The antenna of claim 2 further comprising an insulator disposed between said disc and said cone.

3. The antenna of claim 1 disposed on an exterior of a vehicle.

4. The antenna of claim 3 disposed under said exterior of the vehicle.

5. The antenna of claim 1 disposed in an interior of a vehicle.

6. The antenna of claim 1 disposed in a structure.

7. The antenna of claim 1 having a frequency in the range of between approximately 500 KHz and between approximately 8 GHz.

8. The antenna of claim 1, wherein said coaxial cable is disposed through a center of said diameter of said cone.

9-29. (canceled)

30. In a vehicle having transmitting and/or receiving communication equipment and a body that is in part metallic, an exciter system having broad bandwidth send/receive capability including

an antenna mounted on or in the vehicle radiating at high and intermediate frequencies and acting as a direct radiator on the vehicle body causing the body to radiate at lower and intermediate frequencies.

31. The exciter system of claim 30 wherein the lower frequency radiation limit is the vehicle body size defined by the one-quarter wavelength of the radiation.

32. The exciter system of claim 30 wherein the intermediate frequencies comprise a transition frequency range.

33. The exciter system of claim 32 wherein the transition frequency is defined by the vehicle size and configuration.

34. The exciter system of claim 30 wherein the high frequency range is between 800 MHz and 2 GHz.

35. The exciter system of claim 31 wherein the low frequency radiation limit is 60 MHz.

36. The exciter system of claim 35 wherein the low frequency radiation shape is a cadioid.

37. The exciter system of claim 36 wherein the low frequency radiation shape is omnidirectional in azimuth.

38. An exciter system comprising a discone antenna and an automobile metallic body acting as an antenna, the two antenna radiating over the frequency range of 600 KHz to 2 GHz.

39. The exciter system of claim 38 wherein said discone antenna is mounted beneath the automobile body.

40. The exciter system of claim 38 wherein the discone cone height is between 0.5 and 12 inches.

41. The exciter system of claim 40 wherein the disc diameter is between 0.18 and 0.5 wavelengths.