Patent Application
20080129635
1. Field of the Invention
The subject invention relates to a method of operating a patch antenna.
2. Description of the Related Art
Satellite Digital Audio Radio Service (SDARS) providers use satellites to broadcast RF signals, particularly circularly polarized RF signals, back to receiving antennas on Earth. The elevation angle between a satellite and an antenna is variable depending on the location of the satellite and the location of the antenna. Within the continental United States, this elevation angle may be as low as 20° from the horizon. Accordingly, specifications of the SDARS providers require a relatively high gain at elevation angles as low as 20° from the horizon.
SDARS reception is primarily desired in vehicles. SDARS compliant antennas are frequently bulky, obtuse-looking devices mounted on a roof of a vehicle. SDARS compliant patch antennas typically have a square-shaped radiating element with sides about equal to ½ of the effective wavelength of the SDARS RF signal. These patch antennas typically also include a square-shaped ground plane that has a surface area larger than that of the radiating element. When the patch antenna is disposed on a window of the vehicle, the large “footprint” defined by the radiating element and ground plane often obstructs the view of the driver. Therefore, these patch antennas are not typically disposed on the windows of the vehicle.
Various methods of operating patch antennas to receive RF signals are well known in the art. Examples of such methods are disclosed in the U.S. Pat. No. 4,887,089 (the '089 patent) to Shibata et al. and U.S. Pat. No. 6,252,553 (the '553 patent) to Soloman.
The '089 patent discloses a method of operating a patch antenna having a radiating element. The method includes the step of feeding a signal to the radiating element at either a first port or a second port, utilizing a switching mechanism. The method also includes the step of generating a horizontally polarized (i.e., linearly polarized) radiation beam in a higher order mode. The patch antenna of the '089 patent does not generate a circularly polarized radiation beam and therefore is of little value in the reception of circularly polarized RF signals broadcast from satellites.
The '553 patent also discloses a method of operating a patch antenna having a radiating element. The method includes the step of shifting the phase of a base signal to produce at least one phase-shifted electromagnetic signal. The method continues by feeding the base signal and the phase-shifted signal to side feed ports of the radiating element and feeding the base signal to a central feed port of the radiating element. The method also includes the step of generating a circularly-polarized radiation beam in a fundamental mode and a higher order mode. The patch antenna of the '553 patent does not generate the circularly polarized radiation beam solely in a higher order mode. As a result, the surface area defined by the radiation element is significantly large.
There remains an opportunity to introduce a method of operating a patch antenna that aids in the reception of a circularly polarized RF signal from a satellite at a low elevation, especially when the patch antenna is disposed on an angled pane of glass, such as the window of a vehicle. There also remains an opportunity to introduce a method of operating a patch antenna which significantly reduces the required “footprint” of the antenna's radiating element when compared to other prior art patch antennas.
The invention provides a method of operating a patch antenna at a desired frequency. The patch antenna includes a radiating element formed of a conductive material. The method includes generating a circularly polarized radiation beam solely in a higher order mode at the desired frequency by exciting the radiating element.
By generating the circularly polarized radiation beam solely in a higher order mode the maximum gain of the radiation beam is tilted away from an axis perpendicular to the radiating element. This tilting-effect is very beneficial when attempting to receive the circularly polarized RF signals from a satellite at a low elevation angle. Furthermore, by generating the circularly polarized radiation beam solely in a higher order mode, the dimensions of the radiating element are much smaller than many prior art radiating elements. This is very desirable to automotive manufacturers and suppliers who wish to mount the radiating element on a window of a vehicle and still maintain good visibility for a driver through the glass.
Other advantages of the present invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:
Referring to the Figures, wherein like numerals indicate corresponding parts throughout the several views, a patch antenna 20 and associated method of operation are provided.
The method of operation of the antenna 20 is described herein with reference to a preferred structural embodiment for the antenna 20. Those skilled in the art realize that the method may be practiced with other antennas of alternative embodiments that differ in design and construction from that of the preferred embodiment. Therefore, the structure of the antenna 20 recited herein should not be read as limiting.
In the preferred embodiment, the antenna 20 is utilized to receive a circularly polarized radio frequency (RF) signal from a satellite. Specifically, the antenna 20 may be utilized to receive a left-hand circularly polarized (LHCP) RF signal like those produced by a Satellite Digital Audio Radio Service (SDARS) provider, such as XM® Satellite Radio or SIRIUS® Satellite Radio. However, those skilled in the art understand that the antenna 20 may also receive a right-hand circularly polarized (RHCP) RF signal. Furthermore, in addition to receiving the LCHP and/or RHCP RF signals, the antenna 20 may also be used to transmit the circularly polarized RF signal. The antenna 20 will be described hereafter mainly in terms of receiving the LHCP RF signal, but this should not be read as limiting in any way.
Referring to
The window 22 preferably includes at least one pane of glass 28. The pane of glass 28 is preferably automotive glass and more preferably soda-lime-silica glass, which is well known for use in panes of glass of vehicles 24. The pane of glass 28 functions as a radome to the antenna 20. That is, the pane of glass 28 protects the other components of the antenna 20, as described in detail below, from moisture, wind, dust, etc. that are present outside the vehicle 24. The pane of glass 28 defines a thickness between 1.5 and 5.0 mm, preferably 3.1 mm. The pane of glass 28 also has a relative permittivity between 5 and 9, preferably 7. Of course, the window 22 may include more than one pane of glass 28. Those skilled in the art realize that automotive windows 22, particularly windshields, include two panes of glass sandwiching a layer of polyvinyl butyral (PVB).
Referring now to
The antenna 20 also includes a ground plane 32 formed of an electrically conductive material such as, but not limited to, copper. The ground plane 32 is disposed substantially parallel to and spaced from the radiating element 30. It is preferred that the ground plane 32 also defines a generally rectangular shape, specifically a square shape. In the preferred embodiment, the ground plane 32 measures about 60 mm×60 mm. However, the ground plane 32 may be implemented with various shapes and sizes.
At least one dielectric layer 34 is disposed between the radiating element 30 and the ground plane 32. Said another way, the at least one dielectric layer 34 is sandwiched between the radiating element 30 and the ground plane 32. The preferred embodiment of the at least one dielectric layer 34 is described in greater detail below.
In the preferred embodiment, as shown in
Referring now to
In the preferred embodiment, the antenna 20 is implemented with four feed lines 36, 38, 40, 42 electrically connected to the radiating element 30 at four feed ports 44, 46, 48, 50. Specifically, a first feed line 36 is electrically connected to the radiating element 30 at a first feed port 44, a second feed line 38 is electrically connected to the radiating element 30 at a second feed port 46, a third feed line 40 is electrically connected to the radiating element 30 at a third feed port 48, and a fourth feed line 42 is electrically connected to the radiating element 30 at a fourth feed port 50.
The feed ports 44, 46, 48, 50 of the preferred embodiment are disposed with relationship to one another such that the feed ports 44, 46, 48, 50 define corners of a square shape. Of course, the square shape is merely a hypothetical construct for easily showing the physical relationship between the feed ports 44, 46, 48, 50. Those skilled in the art realize that the feed ports 44, 46, 48, 50 of the preferred embodiment also define a circle shape with each feed port 44, 46, 48, 50 about equidistant along a periphery of the circle shape from adjacent feed ports 44, 46, 48, 50 and a diameter equal to the diagonals of the square shape. For ease in labeling, the feed ports 44, 46, 48, 50 are assigned sequentially counter-clockwise around the square or circle. For example, if the feed port 43 in the upper, left-hand corner of the square is the first feed port 44, then the second feed port 46 is in the lower, left-hand corner, the third feed port 48 is in the lower, right-hand corner, and the fourth feed port 50 is in the upper, right-hand corner.
The antenna 20 of the preferred embodiment also includes at least one phase shift circuit 51 for shifting the phase of a base signal. In the preferred embodiment, the base signal is provided to a low noise amplifier 25 and/or a receiver 26 from the antenna 20. Of course, in other embodiments, in which the antenna 20 is used to transmit, the base signal is provided by a transmitter (not shown). The base signal, since it is not phase shifted, may be referred to as being offset by zero degrees (0°).
In the preferred embodiment, as shown in
As stated above, the subject invention provides a method of operating the patch antenna 20. This method includes the step of generating a circularly polarized radiation beam solely in a higher order mode at the desired frequency by exciting the radiating element 30. Said another way, the circularly polarized radiation beam is not generated in a fundamental mode, but only in a higher order mode. That is, the operating mode of the antenna 20 consists of a higher order mode. Preferably, the higher order mode is a transverse magnetic mode. More preferably, the higher order mode is a TM22 mode. However, those skilled in the art realize that the other higher order modes besides the TM22 mode may achieve acceptable results. Furthermore, in other embodiments, the radiation beam may also be generated in both the higher order and fundamental modes.
Generating the circularly polarized radiation beam solely in a higher order mode is accomplished due to the application of the base signal and the phase-shifted signals to the radiating element 30 along with the spacing of the feed ports 44, 46, 48, 50 with respect to one another. In the preferred embodiment, each side of the square defined by the feed ports 44, 46, 48, 50 measures about ⅙ of the effective wavelength of the resulting radiation beam. Said another way, each feed port 44, 46, 48, 50 is separated from two other adjacent feed ports 44, 46, 48, 50 by about ⅙ of the effective wavelength. The spacing between the feed ports 44, 46, 48, 50 is dependent on the desired operating frequency of the antenna 20, which, in the preferred embodiment, is about 2.338 GHz. Within the teaching of the present invention, the dimensions may be modified by one skilled in the art for alternative operating frequencies. Furthermore, the effective wavelength depends on the window 22 and the dielectric layers 34. As such, the permittivity and thickness of these elements has an effect on the size of the patch as is appreciated by those skilled in the art.
By generating the circularly polarized radiation beam solely in a higher order mode, a null is established in the LHCP radiation beam at an axis perpendicular to the radiating element 30. Said another way, the pattern of the radiation beam shows a null in the broadside direction, as is shown in
The method of operating the patch antenna 20 also includes the step of shifting the phase of a base signal to produce at least one phase-shifted signal. This may be accomplished, as described above, with one or more phase shift circuits 51. In the preferred embodiment, this step includes shifting the phase of the base signal by 90 degrees to produce a first phase-shifted signal.
The method of operating the patch antenna 20 may also include the step of feeding the base signal to the radiating element 30 through at least one of the plurality of feed ports 44, 46, 48, 50 and feeding the at least one phase-shifted signal to the radiating element 30 through at least one of the other feed ports 44, 46, 48, 50. In the first implementation, the step includes feeding the base signal through the first and third feed ports 44, 48 and feeding the first phase-shifted signal through the second and fourth feed ports 46, 50. In the second implementation, the step includes feeding the base signal through the first feed port 44, feeding the first phase-shifted signal through the second feed port 46, feeding the second phase-shifted signal through the third feed port 48, and feeding the third phase-shifted signal through the fourth feed port 50.
Referring again to
The patch antenna 20 preferably includes a feed line network 58 formed of conductive strips 59 as shown in
In the preferred embodiment, where the feed lines 36, 38, 40, 42 are electromagnetically coupled to the radiating element 30, the feed line network 58 is sandwiched between the first and second dielectric layers 60, 62. The conductive strips 59 of the feed line network 58 are disposed either on the first dielectric layer 60 or the second dielectric layer 62 at the junction of the dielectric layers 34. The conductive strips 59 may be etched on one of the dielectric layers 34 by processes known to those skilled in the art.
In both the preferred and alternative embodiments, the feed line network 58 is also utilized to shift the phase of a signal applied to the feed lines 36, 38, 40, 42, thus, acting as the phase shift circuits 51 described above. This phase shifting is accomplished due to the inductive and capacitive properties of the conductive strips 59 of the feed line network 58. The inductive and capacitive properties of the conductive strips 59 are determined by the impedance and length of each conductive strip 59. The impedance of each conductive strip 59 is determined by the frequency of operation, the width of each conductive strip 59, the dielectric constant of the first dielectric layer 60, and the distance between the conductive strips 59 and the ground plane 32. In the described embodiments, a conductive strip 59 width of about 1/60 of the effective wavelength yields an impedance of about 70.71 ohms and a width of about 1/35 of the effective wavelength yields an impedance of about 50 ohms.
The feed line network 58 shown in
Those skilled in the art realize that many of the Figures are not drawn to scale. This is particularly evident in the cross-sectional representations of the various embodiments of the antenna 10 in
The present invention has been described herein in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. Obviously, many modifications and variations of the invention are possible in light of the above teachings. The invention may be practiced otherwise than as specifically described within the scope of the appended claims.
This application claims the benefit of U.S. Provisional Application No. 60/868,436, filed Dec. 4, 2006.
| Number | Date | Country | |
|---|---|---|---|
| 60868436 | Dec 2006 | US |
