The present invention relates to broadband antennas for vehicular communication. More specifically, the present invention relates to a broadband multi antenna module and a method of integrating this module into the exterior of a vehicle. The module contains multiple antennas operating in multiple frequency bands, which antennas, when excited appropriately, produce multiple beams and/or receive wireless signals in multiple bands for various wireless services. The present invention allows a single unit to be installed in the vehicle in one operation, which unit can contain all of the antennas necessary for the communication needs of an occupant of the vehicle.
Furthermore, the disclosed antenna module is thin enough to fit between a metallic ground plane that may be part of the vehicle frame. A second surface consisting of dielectric that acts as a radome may also form a part of the module. The module itself preferably combines a ground plane, a feed network, several antennas covering multiple bands and producing multiple beams and preferably also employs techniques for isolating these antennas from their neighbors. This invention reduces or eliminates antenna radiation from entering the interior of the vehicle, while maintaining a thin form factor. Other methods exist for creating low-profile, broadband antennas; however, many of them require removal of a portion of the metallic exterior of the vehicle, thus allowing antenna radiation into the vehicle interior.
As demand for existing wireless services grows and new services continue to emerge, there will be an increasing need for antennas on vehicles. Existing antenna technology usually involves monopole or whip antennas that protrude from the surface of the vehicle. These antennas are typically narrow band. Thus, to address a wide variety of communication systems, it is necessary to have numerous such antennas positioned at various locations on the vehicle. Furthermore, as data rates continue to increase, especially with 3G, Bluetooth, direct satellite radio broadcast, and wireless Internet services, the need for antenna diversity will increase. This means that each individual vehicle will require multiple antennas each operating in different frequency bands, and/or with different polarizations and/or at different elevations relative to the horizon. Since vehicle design is often dictated by styling, the presence of numerous protruding antennas will not be easily tolerated. Furthermore, the installation of multiple antennas is costly.
The most basic prior art antenna is the simple whip monopole that is used for FM radio reception and cellular phones. The antenna has a nearly omnidirectional radiation pattern, producing a null only towards the sky. The primary disadvantage of the monopole antenna is that it protrudes from the exterior of the vehicle as an unsightly vertical wire with a height of roughly one quarter wavelength. The monopole is also typically narrowband with a bandwidth of roughly 10%. In order to access multiple wireless services operating on multiple frequencies, multiple monopole antenna would thus be required. Furthermore, if antenna diversity is used to provide directional sensitivity, the number of required antennas is even greater. A logical alternative might be to use a single broadband antenna that could cover all frequency bands of interest. Examples of broadband antennas include spiral antennas, flared notch antennas and log periodic antennas. However, with all of these types of antennas and with broadband antennas in general, the presence of the metallic ground plane is not tolerated. However, if a part of the metal vehicle body is removed and replaced with a dielectric, such a broadband antenna could be integrated into this dielectric and would function over a broad bandwidth. This concept is shown in FIG. 1. A significant drawback of this approach is that it allows the interior of the vehicle to receive just as much antenna radiation as the exterior. With increasing questions over the effects of electromagnetic radiation, this design may be undesirable.
Antennas exist which can function well in the presence of the metallic ground plane, such as patch antennas and various types of traveling wave antennas. These antenna all tend to excite surface currents in a surrounding ground plane. Such surface currents can tend to cause interaction between the individual antennas and can also cause radiation to occur at discontinuities or at edges of the ground plane. This problem is shown in FIG. 2.
Thin antennas exist, such as patch antennas; however, they typically exhibit a narrow bandwidth and do not provide flexibility in the shape of the radiation pattern and/or their sensitivity pattern. Conversely, broadband antennas exist, but they generally are not thin and/or they cannot tolerate the presence of a nearby metal ground plane. One possible solution is to eliminate the metallic ground plane by removing a portion of the vehicle frame or body and replacing it with a sheet of dielectric. A thin broadband antenna can then be mounted on the dielectric sheet to provide access to many wireless services. The problem with this solution is that the elimination of the ground plane allows radiation inside the vehicle interior. Furthermore, with many services sharing the same antenna, interference between devices within the vehicle is increased.
The prior art includes the following:
1) D. Sievenpiper and E. Yablonovitch, xe2x80x9cCircuit and Method for Eliminating Surface Currents on Metalsxe2x80x9d U. S. provisional patent application, Ser. No. 60/079,953, filed on Mar. 30, 1998 by UCLA and corresponding PCT application PCT/US99/06884, published as WO99/50929 on Oct. 7, 1999, the disclosures of which are hereby incorporated herein by reference.These applications disclose a Hi-Z surface.
2) U.S. Pat. No. 4,821,040 entitled xe2x80x9cCircular Microstrip Vehicular RF Antennaxe2x80x9d, assigned to Ball Corporation of Muncie, Ind. This patent describes an antenna consisting of a circular slot radiator that may be mounted within the roof of a vehicle.
3) U.S. Pat. No. 6,091,367 entitled xe2x80x9cLight-weight Flat Antenna Device Tolerant of Temperature Variationxe2x80x9d, by Kabashima, Shigenori; Ozaki, Tsuyoshi; Takahashi, Toru; Konishi, Yoshihiko; and Ohtsuka, Masataka. This patent describes an array of multiple conventional patch antennas.
4) U.S. Pat. No. 6,037,912 entitled xe2x80x9cLow Profile Bi-Directional Antennaxe2x80x9d, by DeMarre, Allen G. This patent describes a low-profile antenna system for mounting on the exterior of a vehicle.
5) U.S. Pat. No. 5,850,198 entitled xe2x80x9cFlat Antenna with Low Overall Heightxe2x80x9d, by Lindenmeier, Heinz; Hopf, Jochen; and Reiter, Leopold. This patent describes an antenna for accessing multiple frequency bands for multiple RF services by providing multiple resonant regions that act as separate antennas.
6) U.S. Pat. No. 5,818,394 entitled xe2x80x9cFlat antennaxe2x80x9d, by Aminzadeh, Mehran; Burkert, Manfred; Daginnus, Michael; and Chen, Shun-Ping. This patent describes an antenna mounted below the windshield of a vehicle, resulting in a low-profile design which is hidden from view.
7) U.S. Pat. No. 5,682,168 entitled xe2x80x9cHidden Vehicle Antennasxe2x80x9d, by James, Jesse C.; and Blackmon, Jr., James B. This patent describes a way of mounting antennas in motor vehicles.
8) U.S. Pat. No. 5,177,493 entitled xe2x80x9cAntenna Device For Movable Bodyxe2x80x9d, by Kawamura, Katsuaki. This patent describes a method of mounting an antenna on a vehicle.
9) U.S. Pat. No. 4,760,402 entitled xe2x80x9cAntenna System Incorporated in the Air Spoiler of an Automobilexe2x80x9d, by Mizuno, Hiroshi; Sakurai, Takashi ; and Shibata, Yoshihisa. This patent describes a way of hiding an antenna in the air spoiler of a vehicle.
Still there is a need for a single antenna unit that combines antennas for various services, and can be installed in a vehicle simply, preferably in one operation. This antenna unit should be thin and should contain a ground plane that can be integrated with or made to cooperate with the metal exterior of the vehicle so as to avoid vehicle interior radiation. Furthermore, this antenna unit should allow access to multiple wireless services which means it should operate in multiple frequency bands. For the reasons described above, it should contain several separate antennas with each antenna operating at a single band. These individual antennas should be isolated from one another and should also not allow radiation to leak into the interior of the vehicle, such as through surface currents. In order to cooperate to vehicle styling considerations, this antenna unit should also be covered by a smooth surface that can be painted to match the color of the vehicle on which it is installed. To enable low-cost installation, it should have a single connector that supplies DC power and provides an RF interface to each antenna.
Related art includes the following patent applications which are assigned to assignee of the present invention:
1) D. F. Sievenpiper, J. H. Schaffner, xe2x80x9cA Textured Surface Having High Electromagnetic Impedance in Multiple Frequency Bandsxe2x80x9d, U.S. patent application Ser. No. 09/713,119 filed Nov. 14, 2000, the disclosure of which is hereby incorporated herein by reference. A Hi-Z surface with multiple band capability is disclosed by this US Patent Application.
2) D. F. Sievenpiper; J. H. Schaffner; H. P. Shu; G. Tangonan, xe2x80x9cA Method of Providing Increased Low-Angle Radiation in an Antennaxe2x80x9d U.S. patent application Ser. No. 09/905,796 filed on the same date as this application the disclosure of which is hereby incorporated herein by reference. A crossed slot antenna able to receive vertically and circularly polarized RF signals is disclosed by this application.
3) D. F. Sievenpiper; J. Pilulski; J. H. Schaffner; T. Y. Hsu xe2x80x9cMolded High Impedance Surface and A Method of Making Samexe2x80x9d U.S. patent application Ser. No. 09/905,794 filed on the same date as this application the disclosure of which is hereby incorporated herein by reference. An inexpensive and flexible Hi-Z surface is disclosed by this application.
4) D. Sievenpiper, H. P. Hsu, G. Tangonan, xe2x80x9cPlanar Antenna with Switched Beam Diversity for Interference Reduction in Mobile Environmentxe2x80x9d, U.S. patent application Ser. No. 09/525,831 filed Mar. 15, 2000, the disclosure of which is hereby incorporated herein by reference.
5) D. Sievenpiper; A. Schmitz; J. Schaffner; G. Tangonan; T. Y. Hsu; R. Y. Loo; R. S. Miles, xe2x80x9cA Low-Cost HDMI-D Packaging Technique for Integrating an Efficient Reconfigurable Antenna Array with RF MEMS Switches and a High Impedance Surfacexe2x80x9d U.S. patent application Ser. No. 09/906,035 filed on the same date as this application the disclosure of which is hereby incorporated herein by reference.
In one aspect, the present invention provides a method of integrating a thin antenna module into a vehicle, the thin antenna module comprising a high impedance surface with at least one antenna element disposed thereon, the antenna having a thickness which is less than one tenth of a wavelength of the frequencies which the antenna is responsive. The method comprises the steps of inserting the thin antenna module between a conductive layer and a dielectric layer located above a passenger compartment of the vehicle, and connecting at least one antenna element disposed on the high impedance surface to a receiver in the vehicle.
In another aspect, the present invention provides an antenna which may be conveniently mounted in a vehicle, the antenna comprising: (a) a ground plane formed by a structural portion of the vehicle; (b) a high impedance surface mounted on the ground plane formed by a structural portion of the vehicle, and (c) at least one antenna element disposed on the high impedance surface. The high impedance surface comprises (1) at least one layer of a dielectric material; (2) a plurality of conductive elements arranged in an array and disposed adjacent one surface of the at least one layer of a dielectric material; and (3) a ground plane layer disposed adjacent another surface of the at least one layer of a dielectric material. The least one antenna element is disposed on the high impedance surface adjacent the plurality of conductive elements arranged in an array, the antenna element having at least one major axis which is parallel to the array when the at least one antenna element is disposed on the high impedance surface adjacent the plurality of conductive elements.
In yet another aspect, the present invention provides an antenna for mounting in a vehicle, the antenna comprising: a sheet of dielectric material forming a portion of the vehicle; a ground plane sheet disposed adjacent a headliner in the vehicle, the headliner being disposed in the vehicle in a confronting relationship with the sheet of dielectric material; and a high impedance surface which comprises: (1) at least one layer of a dielectric material; (2) a plurality of conductive elements arranged in an array and disposed adjacent one surface of the at least one layer of dielectric material; and (3) a ground plane layer disposed adjacent another surface of the at least one layer of dielectric material. The antenna further comprises at least one antenna element disposed on the high impedance surface adjacent the plurality of conductive elements. The high impedance surface is disposed between the ground plane sheet and the sheet of dielectric material such that the plurality of conductive elements of the high impedance surface and the at least one antenna element disposed thereon confront the sheet of dielectric material forming a portion of the vehicle.
In yet another aspect, the present invention provides an antenna for mounting on a vehicle, the antenna comprising: a high impedance surface adapted to be mounted on a ground plane formed by a structural portion of the vehicle, the high impedance surface comprising: (1) at least one layer of a dielectric material; (2) a plurality of conductive elements arranged in an array and disposed adjacent one surface of the at least one layer of a dielectric material; and (3) a ground plane layer disposed adjacent another surface of the at least one layer of a dielectric material. At least one antenna element is disposed on the high impedance surface adjacent the plurality of conductive elements arranged in an array, the antenna element having at least one major axis which is parallel to the array when the at least one antenna element is disposed on the high impedance surface adjacent the plurality of conductive elements. A connector is provided for coupling a source of DC to active components associated with the antenna and for coupling RF from the antenna.
The present invention provides a new way of integrating antennas into vehicles which solves several problems that exist with current vehicular antennas. The primary problem with current vehicle antennas is that they typically extend a large distance from the surface the vehicle, resulting in an unsightly protrusion that is unacceptable given current vehicle styling trends. One technique that has been proposed to avoid this problem is to replace a portion of the vehicle""s exterior, such as the roof, with an area of dielectric. This eliminates the presence of a metallic ground plane and allows an antenna to lie within the plane of the vehicle exterior and to not protrude from the surface. The problem with this solution is that the removal of the metallic ground plane allows antenna radiation to reach into the vehicle. The present invention allows the metallic ground plane to be retained and instead to uses low-profile antennas which are preferably covered by a dielectric radome or color surface. The use of small low-profile antennas permits several radiating apertures to share the same ground plane. The separate apertures are then separated using a passivation material, which may be either a Hi-Z surface or a lossy material.