WO2000074172A1

WO2000074172A1 - Patch antenna and a communication device including such an antenna

Info

Publication number: WO2000074172A1
Application number: PCT/SE2000/001086
Authority: WO
Inventors: Olov Edvardsson
Original assignee: Allgon Ab
Priority date: 1999-05-31
Filing date: 2000-05-26
Publication date: 2000-12-07
Also published as: AU5263400A; SE9902003D0; EP1186073A1; SE516482C2; CN1353877A; KR20020010917A; SE9902003L

Abstract

The present invention relates to an antenna (20; 80) comprising a patch element (21; 83), a conductive base plate (22; 82) essentially parallel with said patch element, where said patch element is provided with at least one feed means (26; 89) to provide circular polarisation, wherein said patch element has a first opening arranged essentially in the centre of said patch element (21; 83), said conductive base plate has a corresponding second opening arranged opposite to said first opening, and said antenna further comprises a conductive connection (25; 85) connected between said first and second openings periphery, thus creating a hole (24; 84) through said antenna, where said hole (24; 84) is adapted to be used for at least one function not being an antenna function. A capacitive load may also be provided between the edge (21') of said patch element (21; 83) and said conductive base plate (22', 22; 82). The invention also relates to a communication device (30; 62) comprising such an antenna (35; 61).

Description

PATCH ANTENNA AND A COMMUNICATION DEVICE INCLUDING SUCH AN ANTENNA

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a patch antenna according to the preamble of claim 1. The invention further relates to a communication device including such an antenna. A patch antenna according to the invention will have substantial advantages for integration in various products, especially when used as a ceramic GPS-antenna in a mobile telephone.

BACKGROUND OF THE INVENTION

The use of navigation system GPS and other related systems (Glonass etc.) has strongly increased during the last decade and has found a very wide range of applications. Among the antennas the ceramic patch antennas are very popular due to their small size and inherent filtering function necessary to protect the GPS receiver.

The GPS patch antenna may be installed in many ways and a typical handheld GPS receiver has a flat upper side with a display (for map etc.), a keyboard and a patch antenna, which during typical use is directed upward or slightly against the face of the user. A typical size of the flat side of a handheld GPS may be 60x150 mm and a typical patch size is 25x25 mm with a connection from below.

One inherent problem with patch antenna is that they require a "ground plane", i.e. an essentially flat conductive surface.

Ideally it should be big, and a smaller surface will gradually decrease its performance. As an example a conductive base plate of 50x50 mm will give around 2dB lower gain for the GPS ceramic patch than a good ground plane (big conductive base plate) and a smaller surface of the conductive base plate will degrade it further.

Typically for the GPS system, as well as for any other satellite communication/receiving system, is that the power margin is just a few dB so more than a very limited loss w ll be disastrous for the function. As a remark, another type of GPS antenna, the quadrifilar helix, does not need a conductive base plate but has a less handy geometry to maintain its function.

The bandwidth of such a patch is usually small but m US

5,861,848, by Iwasaki , an improved patch antenna is described which can be tuned for two frequencies for satellite communications. An annular patch antenna is one of the elements and as prior art is cited an annular patch antenna grounded by a circular grid of wires. The use cited is purely as an antenna element alone and m an array antenna. No considerations of the installation on a very small unit, like a mobile phone, are discussed.

In JP 10247815 an antenna configuration is disclosed, which has a patch antenna arranged on a dielectric substrate and a ground conductor arranged on the opposite side of the substrate. A vertical hole is formed through the central portion of the patch antenna and the ground conductor and the patch antenna is short-circuited by a cylindrical conductor. A monopole antenna is installed through the hole and thereby eliminating interference between communication signals generated by the patch and the monopole antennas, respectively. SUMMARY OF THE INVENTION

The object of the invention is to provide a patch antenna having a shape that will simplify the integration with a communication device, e.g. m a mobile phone, where said patch antenna is provided with a hole, where a device, such as a loudspeaker, a microphone or a GPS amplifier, is locatable.

In accordance with the invention this object is achieved by the features the characterising portion of claim 1.

This object is also achieved by the features m the characterising portion of claim 9.

An advantage with the present invention is that a patch antenna may be combined with a device to incorporate a function that is different from the antenna. In a small unit like a mobile phone there are few possibilities to combine at least a small conductive base plate for the patch with a design wise acceptable integration with the devices necessary for the basic functions of the phone.

In the following, the invention will be disclosed m greater detail by way of example with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. la shows a perspective view of a patch antenna according to the invention.

Fig. lb is a diagonal cross section along line A-A Fig. la

Fig. 2 is a cross section of an alternative embodiment of a patch antenna. Fig. 3a and 3b shows a mobile cellular phone with a patch antenna according to present invention.

Fig. 4 shows a roof mounted antenna for mobile phones including a GPS antenna according to the invention.

Fig. 5 shows a diagram for a ceramic filled patch antenna with patch size versus hole diameter for a specific frequency.

Fig. 6 shows a mobile phone with an integrated GPS antenna according to the invention.

Fig. 7a and 7b shows a GPS antenna according to the invention having a low noise amplifier arranged in the hole.

Fig. 8 shows an alternative embodiment according to the invention of the embodiment described in connection with Fig. 2.

DETAILED DESCRIPTION OF EMBODIMENTS

Fig. la shows a perspective view of a typical patch antenna 10 according to the present invention having a patch element 11 with an approximately square surface, where the side is λ/2. This gives a square surface of 95x95 mm at 1575.42 MHz (GPS frequency for C/A-code only) . A conductive base plate 12, functioning as a ground plane, essentially parallel to said patch element is provided, which is necessary for the function. Printed circuit boards, screening covers, car roofs, etc. may be used as conductive base plates when they have the function of a ground plane in connection with a patch antenna.

A conductive base plate will degrade the antenna gain, which is a typical trade off on this type of antennas on small equipment. The space 13 between the patch element 11 and the conductive base plate 12 may be filled by a ceramic (e.g. ε=10 or ε=36) or plastic filling, which in the ceramic case will shrink the size to 25x25 mm or 19x19 mm, respectively, with a thickness of a few mm. The shrunk physical size of the patch due to the ceramic filling will severely degrade the bandwidth, but the bandwidth may be reduced to 2 MHz (plus allowance for frequency stability due to temperature etc.) for maintaining the function of the simplest GPS (using C/A-code only) .

The patch element 11 has a feeding 16, where the antenna is made with the plate 12 as ground. Typically a coaxial line is connected with the centre of the feeding 16 and the outer conductor to the plane 12. The thickness of the feeding wire may be different from the thickness of the centre conductor of the coaxial line, or can have a modified shape to improve matching. The feeding is located very near the diagonal of the nearly square patch 11 at a distance from the center hole 14 which will give a suitable match (50 ohm etc.) . The nearly square patch can be understood conceptually as two linearly polarized patches tuned to slightly different frequencies determined by the length of each side. The order of magnitude of this difference in side length of each side is one percent or differently expressed one impedance bandwidth of the patch. By this difference the current in each conceptual patch has approximately ±45° phase creating a circularly polarized radiation. This is a common solution for circular polarization which can be called "self -polarizing" but which is usable for very narrow bandwidths only. The impedance bandwidth may be bigger but the polarization bandwidth is small. The typical ceramic patch antenna is made of metallised ceramic, where the patch is slightly smaller than the ceramic. In that case the metallic layer obviously is very thin compared to the illustrated patch in the figures. The hole and the conductive tube does not interfere with the half-wave function, as long as the size of the hole is kept below approximately 1/3 of the size of the patch. To illustrate this the size of the patch as a function of the diameter of the hole has been calculated in the case of Al₃0₂ as a dielectric .

The inventive patch antenna 10 has a hole 14 in the middle of the antenna, within which hole 14 a conductive tube 15 is arranged to shorten the patch element 11 to the conductive base plate 12, i.e. said conductive tube is in electric contact with the patch element and the conductive base plate. The conductive tube 15 may be created by metallisation of the hole 14 if the antenna is made with solid material as filling. The conductive tube 15 may also be made of a metal tube which is inserted in said hole and connected to said patch element

11 and said conductive base plate 12. In the latter case there is no need for a solid material as filling, so the space 13 may have no filling, i.e. air between the patch element 11 and the conductive base plate 12, shown in figure 5, for a specific frequency. As can be seen a small hole has a small influence on the resonance frequency, which easily can be compensated for by increasing the side length slightly.

Obviously a wide range of holes may be used still keeping the overall size by adjusting the side length of the patch, but if a 20% increase of the side length is thought as the practical upper limit then the hole should be kept below 10-11 mm for a 25x25 mm patch. The centre hole can thus take a wide range of diameters for instance within 0-40 % of the side of the nearly square patch. In the limiting case just a wire can pass through a small hole, but the obvious advantage of the invention is that it is possible to use a fairly big hole too install a device, such as a loudspeaker or a microphone or use the hole as an acoustic channel. Due to the metallisation of the hole, the interference between the device and the antenna is small .

Another important feature of the present invention is that the feeding 16 is arranged for circular polarisation, which is needed when communicating with orbiting satellites in the GPS system. This is obtained by arranging the patch element 11, the conductive tube 15 or the feeding 16 to be slightly asymmetric in order to give a circular polarisation with one feeding point only. The inventive antenna will work with linear polarisation too, but that is of less practical use.

The function of the inventive patch antenna will be similar to that of a normal patch antenna for circular polarisation but benefits of the geometry that the hole may be used for various purposes as described below.

Fig. lb shows a diagonal cross section along line A-A in Fig. la.

The ceramic filling is a preferred embodiment but in other embodiments a low ε material can be used and still preserve the size necessary for the installation in a communication device such as a modern cellular phone. The extra capacitances created by the high ε can be replaced by various types of lumped capacitances, close to the edge of the patch, of which one possibility is shown in figure 2 discussed below.

An alternative embodiment of the present invention is shown in Fig. 2, where the patch antenna 20 comprises a patch element 21, having down folded edges 21' around the periphery, and a conductive base plate 22, having ridges 22' to capacitively load said down folded edges 21' to said conductive base plate in a region 27. The antenna 20 further comprises a hollow metal tube 25 shorting said patch element 21 to said conductive base plate 22 essentially in the centre of said patch element 21, thus creating a hole 24 through said patch antenna 20. A feeding means 26, isolated from said conductive base plate 22, is provided to said patch element 21 through said conductive base plate 22. The feeding is normally in the form of a coax cable, where the outer conductor of the coax is connected to the conductive base plate 12.

In this embodiment there is no need to introduce high ε dielectric material in the space 23 between said patch element 21 and the conductive base plate 22, since the capacitive coupling in the region 27 reduces the required size of the patch element 21. One obvious advantage is that a considerable weight of the ceramic material is avoided. This lumped capacitance, close to the circumference, can be achieved in many ways. The isolation material can be air or a low ε material (e.g. plastic) supporting corresponding metal coating.

Yet another embodiment of a patch antenna 80, which is developed from the embodiment in figure 2, is shown in figure 8. A plastic body 81 is used to support conductive surfaces

82, 83, 87 created by metallisation. The plastic body 81 has a hole 84 and a conductive tube 85 essentially in the centre of the body 81 and is fitted with a grove 86 near the edge and the grove has also an internal metallisation. The outer edge 88 of the grove 86 is not covered with metal, thereby separating the conductive base plate 82 from the patch element

83. A conductive pattern 87 makes it possible to connect an amplifier to a feeding point 89, as described in connection with Fig. 7. The corresponding shape as in figure 2 is created with the exception that the grove will, due to currents in parallel to the to the tube, create an extra length making the small patch easier to tune in spite of its small size.

The antenna 80 is preferably fastened to a large conductive surface 90, by e.g. an adhesive, to improve the ground plane of the antenna. This patch antenna will be able to have the same size as a ceramic patch antenna and has a good mechanical stability. Obviously it can be combined with the mounting inside a phone, as shown in Fig. 6, as well as with an integrated amplifier, as shown in Fig. 7.

Fig. 3a and 3b shows a communication device 30, such as a mobile cellular phone, having a first antenna for GPS according to the present invention and a second conventional antenna for receiving and transmitting signals in a frequency band different from the GPS frequency.

Fig. 3a shows the mobile phone 30 in a first position for receiving and transmitting radio signals in a cellular telephone system, e.g. GSM, AMPS, PCS, etc. The radio signals are received/transmitted via a second antenna 31 (e.g. a patch antenna for a GSM frequency, a monopole antenna, a helix antenna, etc) . The mobile phone 30 comprises a casing 32, a microphone 33, a loudspeaker 34 and a patch antenna 35 for GPS frequency. The loudspeaker 34 is located in the hole 36 of the patch antenna 35, thus making the integrated GPS/GSM communication device compact but still maintaining a usable ground plane around the GPS patch. A display 37 is also provided to present information during phone operation.

Fig. 3b shows the communication device in a second position for receiving GPS signals by the patch antenna for GPS 35. The communication device also has a display 37 for presenting information (maps, etc) in this second position. As said above the hole 36 in the patch antenna 35 may be used to locate the loudspeaker 34 or an acoustic channel transporting the sound from a loudspeaker, since most phones have a flat, or slightly bent, surface there to acoustically connect to the ear. The loudspeaker 34 is preferably fed from the back and does not necessarily need to be integrated with the patch antenna 35. Instead of locating the loudspeaker in the hole a microphone or an acoustic channel transporting sound to a microphone may be located there, where the microphone preferably is fed from the back and does not necessarily need to be integrated with the patch antenna.

The existence of a rather big hole can be used to various applications to simplify integration of various parts. One of this is to get a neatly sized roof antenna for cars where both size and symmetry are utilized to create a practical solution.

Fig. 4 shows a car antenna application 40 having a first antenna 41 for GPS communications and a second antenna 42 operating in a frequency band for mobile cellular communication (e.g. GSM, PCS, etc) . The hole 43 may be used to feed a phone antenna (whip, stub, helix, etc) for said cellular phone system, by which symmetry will not disturb the GPS function. On the other hand, the patch antenna 41 will not disturb the phone antenna 42 due to the very different operating frequencies and due to the different type of symmetry. The geometry of this antenna including a GPS antenna will be very similar to a conventional antenna without the GPS antenna. The conductive base 44 of the antenna 41 is normally not in direct contact a grounded part 45 of the car, such as the roof. Magnetic coupling of the antenna 41 to the roof is widely used to secure the antenna to a vehicle. A low noise amplifier will in many cases be installed close to the GPS antenna. Yet another use of the hole is to locate the low noise amplifier 71, with its associated circuits, in the hole 72 of the patch antenna 70, as described in figure 7a and 7b. The patch element 73 has in this example a smaller surface area than the ceramic filling 74, which is common when arranging the patch element 73 on a ceramic filling. The conductive base plate 75 may be any suitable size.

The low noise amplifier 71, having a cover preferably made of metal, is preferably squeezed into the metallised hole 72 for grounding purposes, and has cables 76, for feeding said amplifier, arranged trough the hole 72. A coaxial cable may be used instead of the illustrated cables 76. The amplifier also has a contact, isolated from the cover, which is connected to the feeding point 77 via a conductive pattern 78 on the topside of the patch element 73. The conductive pattern 78 is isolated from the patch element 73. The feeding point 77 is also connected to the conductive base plate via a grounding wire 79. It is of no importance if the feeding is connected from the top 77 or from the bottom 75, but in this case the top feeding is preferred.

In all examples a flat essentially square patch has been discussed. As all skilled in the art understand slight modifications of the shape can be accommodated for by suitable changes of size and thickness. Many patch antennas have dents or short slots on the sides or have one or more corners cut. For the antenna function to create circular polarisation etc. the real importance is that two linear and orthogonal resonating frequencies can be found at suitable spaced frequencies to create ± 45° phase shift of the two currents in the orthogonal directions. Most shapes between slightly rectangular and elliptic shape including , super-elliptical shape, can be used to fit the exterior design.

For integration on a mobile phone the surface can for instance be slightly bent to fit the design of the phone and the corners can be cut within rather big limits assuming other measures are changed to maintain resonance frequency. This is exemplified in figure 6, where a bent patch antenna 61 is mounted in a phone 62. A loudspeaker 63 in mounted in a hole in the centre of the patch antenna 61. Obviously the ceramic material can be manufactured in virtually any shape by conventional shaping or by using a mixture ceramic/plastic to injection mould it.

The term communication device used in the text and the claims is understood to mean any device that can receive and/or transmit radio signals, such as a GPS-receiver, a mobile telephone, and a pager.

Claims

1 . An antenna comprising

a patch element (21; 83), a conductive base plate (22; 82) essentially in parallel with said patch element, said patch element being provided with at least one feed means (26; 89) to provide circular polarisation, said patch element (21; 83) has a first opening arranged essentially in the centre of said patch element, - said conductive base plate (22; 82) has a corresponding second opening arranged opposite to said first opening, and said antenna further comprises a conductive connection (25; 85) between said first and second opening, thus creating a hole (24; 84) through said antenna,

characterised in that said hole is adapted to be used for at least one function not being an antenna function.

2. The antenna according to claim 1, wherein said at least one function is related to

locating a loudspeaker (34; 63) or a microphone (33) within said hole, or using the hole as an acoustic channel transporting sound to a microphone (33) or from a loudspeaker (34) , or locating an amplifier or other electronic circuitry.

3. The antenna according to claim 1 or 2 , wherein a capacitive load is provided between the edge (21') of said patch element (21; 83) and said conductive base plate (22', 22; 82) .

4. Antenna according to claim 3 , wherein said patch element (83) is provided on a support (81) having a groove (86) , which groove (86) is metallised to create said capacitive load.

5. Antenna according to claim 4, wherein said support (81) is made from a plastic material .

6. Antenna according to any of claims 1-5, wherein said conductive connection is a conductive tube (25; 85) .

7. Antenna according to any of the preceding claims, wherein said hole (24; 84)) has a diameter being at least 10% of the diameter of the patch element (21; 83) .

8. Antenna according to any of the preceding claims, wherein said antenna is used for receiving GPS signals.

9. A communication device (30; 62) characterised in that said device (30; 62) comprises a first antenna (35; 61) according to any of claims 1-8.

10. Communication device according to claim 9, wherein

a loudspeaker (34; 63) or a microphone (33) is located within said hole, or the hole is used as an acoustic channel transporting sound to a microphone (33) or from a loudspeaker (34) , or an amplifier or other electronic circuitry is located within said hole.

11. Communication device according to any of claims 9-10, wherein said communication device is a mobile telephone (30; 62) .

12. Communication device according to any of claim 9-11, wherein said first antenna (61) is slightly bent to fit the design of said communication device (62) .