Communications: radio wave antennas – Antennas – Slot type
Reexamination Certificate
2001-04-10
2003-11-11
Nguyen, Hoang (Department: 2821)
Communications: radio wave antennas
Antennas
Slot type
C343S713000
Reexamination Certificate
active
06646618
ABSTRACT:
TECHNICAL FIELD
This invention relates to an antenna that is capable of communicating with both a satellite system and a terrestrial system simultaneously. For example, the antenna may be conveniently used to receive signals broadcast by a direct broadcast satellite radio system or other high altitude broadcast system, in which radio or other signals signals are broadcast directly from one or more satellites to mobile vehicles on or near the ground and are also received by terrestrial repeaters, and then rebroadcast terrestrially to the mobile vehicles on or near the ground.
BACKGROUND OF THE INVENTION
Satellite-based direct broadcast systems are currently used to broadcast TV and radio signals to fixed ground stations which typically use a dish-shaped antenna to receive the signals. These systems have become very popular and soon this direct broadcast satellite technology is moving into the vehicular field. Vehicles pose a number of interesting challenges for this technology. First, in the case of terrestrial vehicles which can move on or near the surface of the earth, their movement means that the satellite signal will be occasionally blocked due to natural and man-made obstructions near which the vehicles travel. Since the satellite signals can be blocked by obstructions such as buildings and mountains, it has been proposed to transmit a second signal terrestrially which is locally provided by a repeater located to receive the satellite or high altitude broadcast signals without interference. See FIG.
1
. The direct broadcast satellite signals will arrive at the vehicle
1
with circular polarization from a location possibly high above the horizon due to the altitude of satellite
2
. In contrast, the repeated signals will arrive with vertical polarization from a repeater location
3
frequently near the horizon. Services which will be using such technology include possibly XM Radio and Sirius Radio. The entire frequency range allocated for XM Radio is 2.3325 to 2.345 GHz, and the entire frequency range allocated for Sirius Radio is 2.320 to 2.3325 GHz. This includes the satellite signal as well as the terrestrial signals from the repeaters. The total bandwidth required is much less than the bandwidth of the antenna disclosed herein.
Using conventional antenna technology, the antennas on a vehicle
1
to receive such signals would tend to be (i) numerous, (ii) unsightly and/or non-aerodynamic, (iii) possibly expensive, and (iv) would be difficult to point properly.
Similarly, as demand for existing wireless services grows and other new services continue to emerge, there will be an increasing need for still more 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, so to address a wide variety of communication systems, it is necessary to have numerous antennas positioned at various locations around the vehicle or to complicate the antenna design by making them multiband antennas. Furthermore, as data rates continue to increase, especially with 3G, Bluetooth, direct satellite radio broadcast, wireless Internet, and other such services, the need for antenna diversity will increase. This means that, if conventional antenna technology is followed, each individual vehicle would require multiple antennas each operating in different frequency bands, and/or with different polarizations and sensitive at different elevations relative to the horizon. Since vehicle design often dictated by styling, the presence of numerous protruding antennas will not be easily tolerated.
With the increasing number of wireless data access systems that will be incorporated into future vehicles, the number of antennas is also apt to increase. Many of these new data access systems will involve communication with a terrestrial network and also with a satellite or other high altitude transmitter. One such system is the previously mentioned direct broadcast satellite radio which will soon be operational. Transmitting systems aboard satellites typically broadcast in circular polarization so that the receiving mobile vehicle can be in any orientation with respect to the satellite, without the need to orient the vehicle's antenna. However, terrestrial broadcast systems typically use linear polarization for multi-path reasons, with vertical polarization being preferred for moving receiving stations for reasons well known in the art. Hence there is a need for antennas which can receive both circular polarization from the sky as well as vertical linear polarization near the horizon. These antennas exist, with the most common example being the helix antenna. One disadvantage of the helix antenna is that it protrudes one-quarter to one-half wavelength from the surface of the vehicle. Since current direct broadcast radio systems operate at 2.34 GHz, this results in an antenna that is several centimeters tall. The presence of an unsightly vertical antenna and/or a plurality of antennas, is often unacceptable from a vehicle styling point of view. Additionally, such antennas increase the aerodynamic drag of the automobile which is undesirable for energy-conservation reasons.
As a consequence, there is a need for an antenna that can perform as well as the vertical helix antenna, but has a low profile so that it can easily be adapted to conform to the roof over the passenger compartment of a vehicle, for example. The antenna should preferably be simple to manufacture using common materials. The antenna should be capable of receiving signals having circular polarization from orbiting satellites as well as signals having vertical linear polarization from terrestrial stations or repeaters.
In the design of antennas for low-angle radiation, one must consider each section of the radiating aperture and how it contributes to the overall radiation pattern. If one restricts the antenna design to one having a low-profile (for example, an antenna having a thickness much less than a quarter wavelength), there are only a few fundamental elements available. The most common low-profile antenna is the patch antenna, which is shown in FIG.
2
. The patch antenna consists of a metal shape
10
supported above a ground plane
12
and fed by a coaxial probe or other feed structure
14
. While the patch is a common low-profile antenna element, it is a poor choice for receiving (or transmitting) radiation at low angles. The reason for this is that the two edges
10
-
1
,
10
-
2
of the patch
10
both radiate and the interference between the two determines the overall radiation pattern of the antenna. In the direction normal to the ground plane
12
, the interference is constructive and the patch
10
provides significant gain in that direction. However, in a direction toward the horizon (e.g. in a direction parallel to the ground plane
12
), the interference is destructive, and the patch produces very little radiation in that direction. One way to avoid this problem is to bring the two edges
10
-
1
,
10
-
2
of the patch closer together. However the effective overall length must remain one-half wavelength, so this requires that the patch be loaded with a high dielectric material. Furthermore due to the difficulties of achieving very high dielectric materials, there is a limit to how small a patch can be. Moreover, as the patch size is reduced, its bandwidth is also reduced.
FEATURES OF THE PRESENT INVENTION
A unique feature of the preferred embodiments of antenna disclosed herein is that it can receive both circularly polarized signals from a satellite in the sky as well as vertical linearly polarized signals from a terrestrial repeater. For the purpose of this specification and the claims herein, the term “satellite” is defined to mean an object which is in orbit about a second object or which is at a sufficiently high altitude above the second object to be considered to be at least airborne and “terrestrial” or “earth” is defined to mean on or near the surface of the second object.
An advantage of the pre
HRL Laboratories LLC
Nguyen Hoang
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