Patent Application
20070229359
The present invention relates to the field of antenna technology, and relates in particular to a broadband patch antenna that includes a planar patch plate with a rectangular rim that is at a predetermined first height above and parallel to a planar base surface of an electrically conductive reflector, and an RF signal feed apparatus for feeding an RF signal into the patch plate.
The applications of wire-free communication techniques have actually been increasing almost exponentially in the last two decades. This has now led to both speech services and data services being transmitted in frequency bands including, the 400, 800, 900, 1800 and 1900 MHz bands, which are available worldwide for mobile speech transmission. This frequency range has been extended to 2170 MHz with the introduction of UMTS Standard (Universal Mobile Telecommunication System). As an alternative to landline telephony, the frequency range between 3400 and 3600 MHz, keyword WLL (Wireless Local Loop), has been released in various European countries in previous years. In addition, transmission of high data rates can now be done without the use of wires, using the WLAN frequencies (Wireless Local Area Network). The frequencies released for these applications are in the 2.4 and 5.5 GHz range.
In order to supply all of these services efficiently to an in-house area, such as commercial buildings, airports, railroad stations, underground garages and hotels, an entire forest of antennas would be necessary if individual antennas were to operate exclusively in each relevant frequency band. However, a forest of antennas such as this is highly complex in terms of the space required, installation and operation. Thus, it is desirable to minimize this forest of antennas as far as possible by the use of particularly broadband antennas. One shape which is particularly suitable by virtue of its simplicity is the patch antenna, in which a patch plate, which is arranged above a conductive base surface, is used as an antenna element. In contrast to a monopole antenna, this concentrates the emitted energy in a smaller spatial angle.
Patch antennas have been described in numerous documents and articles (see, for example, the “Microstrip Antenna Design Handbook”, Artech House, Boston London, 2001, pages 8-9 and 16-17). Patch antennas are distinguished by their flat design, which can be produced at low cost. Various basic shapes of patch antennas can also be found in U.S. Pat. No. B1 6,317,084. One important disadvantage of patch antennas in comparison to other antenna shapes is, however, that their bandwidth is relatively narrow. A patch antenna typically results in bandwidth ratios of 1:1.2 for a VSWR (Voltage Standing Wave Ratio) of <2. Extensive efforts have therefore already been made in the past to widen the bandwidth of patch antennas. Some of the solutions proposed for this purpose are quoted and discussed in the introductory part (columns 1-3) of U.S. Pat. No. B1 6,317,084, but lead to comparatively complex antenna structures, without being able to comply completely with the broad bandwidth requirements.
The object of the invention is therefore to develop a simple patch antenna which as far as possible covers the frequency range from 800 to 6000 MHz and is suitable for use in the in-house field.
In accordance with one embodiment of the present invention, the patch plate is provided in the form of a cross, and the conductor of the feed apparatus is provided in the form of an inner conductor of a coaxial conductor between the base surface of the reflector and the patch plate. The specific cruciform shape of the patch plate interacts with the geometry of the coaxial feed to achieve an extremely broad bandwidth, so that the antenna covers a bandwidth ratio of 1:3 with a VSWR (Voltage Standing Wave Ratio) of <2, and at the same time can be produced very easily.
In a preferred embodiment of the broadband patch antenna according to the present invention: (1) the patch plate originates from a rectangular basic shape with a rectangular cutout at each of the four corners of the rectangle, (2) the patch plate is mirror-image symmetrical with respect to a center line, (3) the feed point is located on the center line, and (4) the rectangular cutouts have the same width transversely with respect to the center line.
It has been found to be particularly advantageous for the rectangular basic shape of the patch plate to have a width of 0.58λu and a length of 0.465λu, when the rectangular cutouts each have a width (W2, W3) of 0.165λu and a length of 0.11λu or 0.055λu, and the predetermined first height (H) is 0.08λu where λu is the wavelength of the lower operating frequency of the antenna.
In another embodiment of the broadband patch antenna according to the present invention, the size of the base surface of the reflector is chosen such that the vertical projection of the patch plate onto the base surface is located entirely within the base surface. In this embodiment, it is also preferred that the base surface is square the base surface of the reflector has an edge length of 0.66λu, where λu is the wavelength of the lower operating frequency of the antenna, the reflector has side walls, which are at right angles to the base surface and surround the patch plate at the sides, and the height of the side walls are equal to the predetermined first height of the patch plate above the base surface of the reflector.
The reflector and the patch plate are preferably composed of an electrically highly conductive metal sheet, in particular composed of copper, aluminum or brass, and the metal sheet has a thickness which is substantially greater than the penetration depth of the skin effect at the intended operating frequency.
In one embodiment, electrically insulating spacers, which are arranged in a distributed manner, are provided in order to maintain the predetermined first height of the patch plate above the base surface of the reflector.
In another embodiment, instead of the spacers, an intermediate layer composed of a dielectric, for example a plastic foam, is provided to maintain the predetermined first height of the patch plate above the base surface of the reflector.
Another aspect of the present invention is that the patch plate can be conductively shorted to the reflector at one or more points by means of electrically conductive connection elements without any adverse effect on the antenna characteristics.
In another embodiment of the present invention, the inner conductor of the coaxial conductor is surrounded by an electrically conductive hollow cylinder, starting from the base surface of the reflector, to a predetermined second height, which is less than the predetermined first height. In this embodiment, the external diameter of the hollow cylinder is 0.052λu and the predetermined second height is 0.052λu, where λu is the wavelength of the lower operating frequency of the antenna.
Further embodiments are specified in the dependent claims.
The invention will be explained in more detail in the following text with reference to exemplary embodiments and in conjunction with the drawing, in which:
The electrically conductive reflector 11 has a rectangular, planar base surface 11a with a width, Wg, and a length, Lg. In the illustrated exemplary embodiment, the base surface 11a is square (Lg=Wg). At the sides, the base surface merges into vertical side walls 11b, which have a uniform height, Hg. The planar patch plate 12 is arranged parallel to the base surface 11a, at a height H above the base surface 11a and parallel to it. The base surface 11a of the reflector 11 is larger than the surface of the patch plate 12, so that the vertical projection of the patch plate 12 is located entirely within the base surface 11a, and the patch plate 12 is at an adequate distance from the surrounding side walls 11b.
The patch plate 12 is in the form of a cross with a rectangular edge contour. The cruciform shape is produced by rectangular cutouts 20a, . . . , d in the corners of the rectangle—starting from a rectangular base shape with the external dimensions (W1+W2+W3)×(L1+L2+L3), and whose sides run parallel to the sides of the base surface 11a. The patch plate 12 with its cutouts 20a, . . . , d is preferably mirror-image symmetrical with respect to a center line 21 on which the feed point 16 is arranged, and can be moved for adaptation of the antenna characteristics (double-headed arrow in
The patch plate 12 is fed via a (coaxial) RF connector 15, which is positioned on the lower face of the reflector base surface 11a, whose central conductor is passed as the inner conductor 14 through the base surface 11a to the feed point 16 on the patch plate 12. Starting from the base surface 11a, the inner conductor 14 is coaxially surrounded up to a height Hk by an electrically conductive hollow cylinder 13 whose external diameter is Dk, so that, together with the hollow cylinder 13, it forms a coaxial line.
All of the materials (reflector 11, patch plate 12, etc.) must be electrically highly conductive. Copper, aluminum or brass are preferably used. In order to keep the electrical losses as low as possible, the thicknesses of the parts used should be substantially greater than the penetration depth of the skin effect at the operating frequency. Since the reflector 11 has to ensure the mechanical robustness of the antenna, it is preferably produced from sheet aluminum.
As shown in
In another embodiment, the patch plate 12 can be conductively shorted to the reflector 11 at one or more points by means of a connection element 17 in the form of a metallic bolt, without adversely affecting the electrical operation of the antenna.
The following dimensions are advantageous for matching of the broadband patch antenna to a 50 ohm impedance system, for the wavelength λu at the lower operating frequency (λu=c/f, c=speed of light, f=frequency):
The input impedance of the antenna can be matched to values of <50 ohm or >50 ohm by movement of the feed point 16 in the direction of the center point or toward the edge of the patch plate 12.
b shows a protective shroud 19, which provides external protection for the antenna elements 11 and 12. This ensures that (1) the electromagnetic radiation can emerge with as little impediment as possible from the antenna, (2) people cannot directly touch live metal surfaces and, (3) the antenna is protected against weather influences and environmental influences. The protective shroud is generally made of plastic, and is placed over the antenna.
Based on the fundamental broadband design illustrated in FIGS. 1 to 3, it is, of course, additionally possible to make use of all the methods known from the prior art in order to further widen the bandwidth.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1060/04 | Jun 2004 | CH | national |
This application is a continuation of International Application No. PCT/CH2005/000319, having an international filing date of Jun. 7, 2005, and claims the benefit under 35 USC §119(a)-(d) of Swiss Application No. 1060/04, filed Jun. 23, 2004, the entireties of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/CH05/00319 | Jun 2005 | US |
| Child | 11566265 | Dec 2006 | US |
