EP0795926A2 - Flat, three-dimensional antenna - Google Patents

Abstract

The antenna is built up in three planes with a baseplate (1) defining one plane as the wall of a metal box or the metallisation on a circuit board. The slot distributor in another plane is a U-shaped metallic strip with a quarter wavelength centre portion (2) and two limbs (3,4), each of one-eighth of a wavelength long and short circuited (5,6) to the baseplate. The resonant structure in the third plane comprises two symmetrical plates (9,10) separated by a gap (11). The feeder is a strip line (7) joined by a leg (8) to a coaxial connection under the baseplate, or to a microstrip line on a circuit board.

Description

State of the art

In wireless communication in local area networks (LAN), new requirements are added to the usual requirements (such as adapted input impedance, good radiation characteristics, efficiency). So it is z. B. desirable that the antenna or a diversity antenna system has space on a PCMCIA card. In the case of communication-capable laptop computers, horizontal insertion slots are provided for such cards. An antenna system integrated on a PCMCIA card should therefore radiate approximately equally well in all directions in the horizontal plane. In order for an antenna to be integrated on a card of this type, it must not exceed the standard permitted height. It is therefore not possible in many frequency ranges to use a simple monopole antenna for the communication described.

Presentation of the invention

The object of the invention is to provide a flat, compact three-dimensional antenna which is suitable for the wireless transmission of digital data in local networks. The antenna should have as omnidirectional radiation characteristics as possible and little dependence of the adaptation on neighboring external objects.

The solution according to the invention is defined by the features of claim 1. As a result, the antenna is constructed in three levels. A base plate is located in a first level, a U-shaped slot divider is arranged in a second, and a resonance structure is arranged in a third. The slot divider is angled in a U-shape in the second plane, so that a central part and two lateral legs are formed.

horizontal"). Durch die Resonanzstruktur erhält die Antenne eine äusserst grosse Bandbreite (z.B. 20% bis 30%). Dadurch kann der Einfluss von benachbarten Umgebungsgegenständen klein gehalten werden. Die Existenz einer leitenden Grundplatte unterstützt diesen Vorteil zusätzlich.This antenna is extremely compact and radiates primarily in the spatial directions defined by the base plate (ie

horizontal "). The resonance structure gives the antenna an extremely wide bandwidth (eg 20% to 30%). This allows the influence of neighboring objects to be kept small. The existence of a conductive base plate additionally supports this advantage.

The antenna is preferably fed by a strip conductor which is guided in the second plane between the two legs and contacts the slot divider on the middle part. The antenna's input impedance can be adjusted by varying the width and length of the stripline. The stripline can e.g. B. completely fill the area between the legs. The length of the stripline is preferably less than the length of the leg, so that the feed does not take up more space than is already used by the antenna. However, it is also possible to make the stripline longer (that is to say to lead it out of the antenna on the second level and to reduce the width, for example). Depending on the embodiment, the antenna can be fed via a microstrip line or a coaxial line (led through the base plate).

The middle part of the slot divider has z. B. the length λ / 4 (λ = wavelength at the resonance frequency). The two bars are each λ / 8 long. The slot divider is connected to the base plate at the ends of the legs. The length of the middle part can also be a little longer or shorter. Accordingly, the antenna becomes more or less elongated.

The resonance structure is supported by (electrically conductive) flank elements on the legs of the slot divider. If the antenna is embedded in a dielectric medium, the mechanical support function is in principle performed by the dielectric medium. The flank elements can then be suitably attached metallizations for connecting the resonance structure to the slot divider. In the event that the antenna or at least the resonance structure is to be in air, the entire antenna can in principle be made by bending a plate with a suitable cutting pattern. The resonance structure can e.g. B. have a gap in the middle so that it is formed by two plate-shaped mirror-symmetrical elements. From an electrical point of view, the gap is of no importance, since there is a current node in the middle of the resonance structure anyway.

A first antenna slot formed between the base plate and slot divider is preferably larger than a second antenna slot formed between the slot divider and the resonance element. The length of the second antenna slot can be varied, the bandwidth of the antenna changing accordingly. In extreme cases, it is possible to construct an antenna with two separate resonances (dual frequency mode). Conversely, the resonances can also be brought very close to one another, which leads to a narrow bandwidth.

The antenna according to the invention can be constructed in different ways. It is conceivable, for. B. that the antenna is formed from a stamped or etched sheet and soldered onto a base plate (z. B. a metallized circuit board). A dielectric can be present between the first and second levels of the antenna. So z. B. the slot divider as a printed circuit structure on the upper side of a suitably thick printed circuit board, the base plate by a Metallization is formed on the back of the substrate. The resonance structure in the third level can then e.g. B. like a flat inverted U-profile (plate with two opposite flanks) (the flanks are soldered to the conductor structures).

According to a particularly preferred embodiment, the antenna is formed on a ceramic block. The resonance structure is then a metallization on a first (upper) main surface of the ceramic block. The slot divider in the second level is e.g. B. represented by a metallization on the narrow side surfaces of the ceramic block. The base plate can be formed by a metallization on the second (lower) main surface of the ceramic block or by a metal surface to which the ceramic block is soldered. A metallized slot in the ceramic block can be provided between the two main surfaces, in which the strip conductor for feeding the antenna is arranged. Such an antenna is not only extremely compact (due to the relative dielectric constant ε _r > 1), but also very robust. It can be handled and soldered on like any other electronic component (SMD = Surface Mounted Device). Due to the small size of the antenna, the risk of damage is also avoided (no antenna protruding from the housing).

To adjust the antenna is u. U. provide an inductance. This is preferably integrated in or in front of the stripline.

The antenna according to the invention is also well suited for diversity reception. This applies to both spatial and angular diversity, sometimes called pattern diversity.

Remarkably, by juxtapositioning, sectoral angular diversity is achieved. This means that each of the two antennas is particularly sensitive in one direction in which the other has only an extremely low sensitivity. Switching or combining the two antenna feeds can increase the performance of a receiver (diversity gain). It will e.g. B. switched from one antenna to the other when the signal of the former becomes too weak. If the antenna signals are additionally phase-shifted from each other, the sensitivity pattern can be rotated in space.

To achieve spatial diversity, several antennas can be placed next to each other at a certain distance (e.g. λ / 3 to λ / 2). With the antenna element described below, for. For example, a 3-way spatial diversity antenna system can be set up, which is packed in a volume of 54x28x5.2 mm3 (which corresponds to an extension of a PCMCIA card).

The antenna according to the invention is particularly suitable for HIPERLAN applications and handheld radio telephones (including cordless telephones). The frequency ranges provided for such applications are typically over 1 GHz (e.g. at 5.2 GHz in the European Telecommunication Standard-HIPERLAN).

The antenna is also suitable for use in an antenna array, since the large bandwidth also allows adaptation in the vicinity of the neighboring antennas.

Further advantageous embodiments and combinations of features result from the following detailed description and the entirety of the claims.

Brief description of the drawings

Fig. 1

Eine schematische perspektivische Darstellung einer erfindungsgemässen Antenne in Luft;

Fig. 2

eine schematische perspektivische Darstellung einer erfindungsgemässen Antenne auf einem Keramikblock;

Fig. 3

eine schematische perspektivische Darstellung der Ausführungsform gemäss Fig. 2 von hinten gesehen;

Fig. 4

eine schematische Darstellung eines Antennensystems zur Erzielung eines Diversity-Empfangs.

The drawings used to explain the exemplary embodiments show:

Fig. 1

A schematic perspective view of an antenna according to the invention in air;

Fig. 2

is a schematic perspective view of an antenna according to the invention on a ceramic block;

Fig. 3

is a schematic perspective view of the embodiment of FIG 2 seen from behind.

Fig. 4

is a schematic representation of an antenna system to achieve diversity reception.

In principle, the same parts are provided with the same reference symbols in the figures.

Ways of Carrying Out the Invention

1 shows an antenna according to the invention in air. It is structured in three levels or layers. The first level is defined by a base plate 1. It can be a wall of a metal box or a metallization on a printed circuit board.

The slot divider is on the second level. In principle, it is a U-shaped metal strip with a middle part 2 and two legs 3, 4. The length of the middle part 2 is preferably λ / 4, that of the legs 3, 4 is λ / 8. The slot divider is short-circuited to the base plate 1 at both ends of the legs 3, 4 via two legs 5, 6.

There is a resonance structure on a third level. In the present example, this is formed by two symmetrical plates 9, 10. These are supported by vertical side surfaces 12, 13 on the outer sides of the angled legs 3, 4 of the slot divider. The two plates 9, 10 are separated by a gap 11. From an electrical point of view, this is of no importance since it is located in a power node. 1, on the other hand, it enables the antenna to be formed from a flat, suitably cut sheet metal shape.

For feeding the antenna, for. B. a strip conductor 7 is provided, which is connected via a leg 8 to a coaxial connection below the base plate 1. If the base plate is designed as a printed circuit board, a further microstrip line can also take the place of the coaxial connection. The strip conductor completely fills the area formed between the two legs 3, 4 in accordance with the required impedance matching (wherein it is separated from the legs 3, 4 only by two gaps 14, 15).

The following should be said about the dimensioning:
The two plates 9, 10 essentially cover the area spanned by the U-shaped slot divider. The distance between the resonance structure and the slot divider is preferably smaller than the distance between the slot divider and the base plate 1. B. the second level at a height of 2.6 mm (λ / 8) and the third level at a height of 4.2 mm (λ / 20) above the base plate (center frequency f ₀ = 6.4 GHz, λ ≅ 4.7 cm).

Between the resonance structure and the slot divider there is an antenna slot, which is limited in length by the side surfaces 12, 13. The length of this slot can be varied to determine the bandwidth. Are the side surfaces 12, 13 z. B. the same length as the legs 3, 4, then the antenna slot is the same length as the middle part 2. In principle, the vertical side surfaces 12, 13 can even be around the corner on the middle part 2. Conversely, they can also only claim a small part of the legs 3, 4 and be placed close to the ends or legs 5, 6. Accordingly, the upper antenna slot would then be approximately the same size as the lower antenna slot between the slot divider and the base plate 1.

In principle, the antenna according to the invention is two stacked and angled λ / 2 slots with different slot lengths.

The impedance is adjusted via the dimensioning of the strip conductor 7. In the numerical example started above, it has a width of z. B. 11 mm (0.24 λ) and a depth of z. B. 5.5 mm (0.12 λ). The two legs 3, 4 each a width of e.g. B. 0.75 mm (0.015 λ). The gap 11 is z. B. 1 mm (λ / 50) wide. The entire antenna has a width of z. B. 0.28 λ and a depth of z. B. 0.14 λ.

The stripline 7 can u. U. may also be less wide and / or run out of the area spanned by the two legs 3, 4. It is particularly suitable for feeding via microstrip lines.

The antenna structure shown in FIG. 1 can be partially or completely embedded in a dielectric medium (of course, by adapting the dimensions due to the higher relative dielectric constant ε _r > 1). So z. B. the slot divider (legs 3, 4, middle part 2) and the strip conductor 7 are applied as a conductor track structure on a dielectric substrate (printed circuit board). The base plate 1 can be provided as a metallization on the back of the substrate, the legs 5, 6, 8 (in the form of pins) being passed through the substrate.

In this case, the resonance structure can be a continuous rectangular plate, which in turn is electrically connected to the legs 3, 4 via side surfaces 12, 13 and at the same time is supported on the substrate. The simplest way is to cut a piece of sheet metal which is able to cover a surface spanned by the legs 3, 4 and is equipped with lateral tabs for forming the side surfaces 12, 13 (by right-angled bending). The gap 11 is neither necessary nor desirable in this embodiment (mechanical stability).

A dielectric can also be provided between the second and the third level. This can e.g. B. can be achieved by selective lamination of a dielectric material in the desired layer thickness. The side surfaces 12, 13 can be applied to corresponding boundary surfaces of the laminated layer. The plate-shaped resonance structure can be printed on the surface of the laminated layer.

A particularly preferred embodiment will be explained with reference to FIGS. 2 and 3. A ceramic block 16 is shown schematically in FIG. He has an upper one and a lower major surface 17 and 18 respectively. A metallization is provided as a resonance structure over the entire main upper surface 17. The lower main surface 18 can also be metallized (in order to form the base plate 1 or to be able to simply solder the ceramic block onto a base plate or a metal box).

The ceramic block 16 has two short and two long side surfaces 19, 20 and 21, 22. The slot divider is formed in that a continuous strip-like metallization is provided on the side surfaces 19, 21, 20 to form a U-shaped circumferential conductor track. Said conductor track is formed by a strip-shaped region 25, 26 approximately in the middle between the two main surfaces 17, 18. At the rear end (according to the illustration chosen in FIG. 2) of the side surface 19, a metallization 24 is led down to the main surface 18. The electrical connection between the resonance structure and the slot divider is also established by a metallization 27 attached to the side surface 19. The side surface 20 is selectively metallized in mirror symmetry to the side surface 19. It is obvious that the metallization 24 corresponds to the leg 6, the metallization 25 to the leg 4, the metallization 26 to the middle part 2 and the full-area metallization of the main surface 17 to the two plates 9, 10 in FIG. 1.

What is still missing is a metallization corresponding to the strip line 7. For this purpose, however, a flat, continuous slot 23 is provided. This extends from the side surface 21 to the side surface 22 and is, for. B. fully metallized. Then only one metallization 32 (see FIG. 3) led from the slot 23 on the side surface 22 is to be provided for the supply. The slot mentioned can be made in the mold before hardening or can be produced by drilling. However, it is also conceivable for two thin ceramic blocks to be joined to form a thick one, the strip conductor and possibly also the slot divider being formed between them in a flat design.

To bring the input resistance up to 50 Ω, it may be necessary to provide an inductance (e.g. 1 - 2 nH). Such can be elegantly integrated. A possible variant will be explained with reference to FIG. 3. This figure shows in exaggerated perspective view of the ceramic block 16 from behind. The slot 23 has a rectangular cross section and thus four inner surfaces 28, 29, 30, 31, which are all metallized. The (already mentioned) selective metallization 32 is now provided for the supply on the side surface 22. It contacts the inner region of the slot 23. The inductance is now generated in that the current is first passed in a loop along the slot edge 34, 35, 36 before it can flow in the passage direction of the slot 23. In order to achieve this, a non-conductive line-shaped area 33 is provided which separates the rear end of the slot metallization. A variant is shown in FIG. 3, in which the non-conductive region 33 separates approximately half the width of the inner surface 28, the entire width of the inner surface 29 and approximately half the width of the inner surface 30 from the metallization in the slot. The current must therefore flow around half the circumference of the slot, which creates a corresponding inductance. The size of the inductance can be varied simply by suitably choosing the length of the non-conductive region 33.

In principle, the inductance can also be forced by a corresponding loop of the current on the side surface 22. This means that the current must first flow a certain amount around the slot before it is fed into it.

bekannt.In the dielectric, the antenna becomes smaller at the same frequency. In order to optimize the bandwidth that is simultaneously becoming smaller within the physical limits, z. B. to increase the length of the upper slot (between the second and third levels). However, there is sufficient bandwidth reserve for the preferred applications in the dielectric as well. It should also be noted that the losses caused by the dielectric should not be too great. The antenna according to the invention has a very high efficiency of over 90% in air. There are also ceramic materials with very cheap ones $\text{tanδ values}$

known.

In general, the antenna is characterized by a large bandwidth (in air, for example, 20% to 30%) and by a radiation with less or negligibly smaller Power perpendicular to base plate 1. A good omnidirectional characteristic is given in the direction of the base plate.

An important application of the antenna according to the invention is in the area of wireless LANs (e.g. HIPERLAN). For this application, the antenna can be mounted on a PCMCIA card. It is particularly advantageous to position two or more antennas of the type described. In this way, diversity reception can be realized.

To achieve spatial diversity, several antenna elements are placed next to each other at a certain distance (λ / 3 to λ / 2). (A spatial diversity effect occurs even when the antennas touch.) An exemplary arrangement of three antennas at a distance of 0.4λ shows that the antennas influence each other relatively little, i. H. that each antenna largely maintains its omnidirectional behavior. The signals received by the different antennas are relatively independent of one another. In the exemplary arrangement mentioned, the antenna system could be packed in a volume of 54x28x5.2 mm3 (which corresponds to an extension of a PCMCIA card).

4 shows an example of a U-shaped arrangement of three antenna elements 37, 38, 39 on an extension of a PCMCIA card 40. The adjacent antenna elements 37 and 38 or 38 and 39 are each placed at right angles to one another. For reasons of space, the antenna elements 37, 38, 39 (which are each designed, for example, as shown in FIG. 1) are arranged as close as possible to the corresponding edge of the PCMCIA card 40.

To achieve angular diversity, two antennas with the narrow sides (i.e. the angled legs) can be set up directly next to one another.

In this arrangement, the two antennas have an angular selectivity that they do not have (or not in a pronounced form) as a single antenna. Depending on the direction from which a strong signal arrives, the receiver can select the appropriate one Antenna can be switched. The antenna signals can also be advantageously combined. By changing the phase of the signal from one antenna to that of the other antenna, the angle selectivity can also be rotated as required.

The antenna is also suitable as an element for so-called antenna arrays. In this case, several individual antennas are isolated or expediently arranged in the network in order to achieve a desired radiation / reception characteristic by combining their signals.

However, the invention is also suitable for hand-held radio telephones (cordless telephones, GSM cell phones, etc.). In the ceramic block variant in particular, the antenna can be placed on top of the cell phone as a compact component in order to show the desired radiation characteristics. It is even conceivable that the antenna according to the invention can be designed for the reception of two adjacent frequencies (dual frequency mode).

The antenna described has a large number of advantages. In summary, the following should be mentioned: Large bandwidth, variability of the bandwidth, good options for impedance-based adaptation, small space requirements, omnidirectional radiation pattern in one plane and no radiation perpendicular to the plane, compatibility with a PCMCIA card (especially as a system consisting of several antenna elements) and Suitability for diversity reception. Reference list 1 Base plate 2nd Middle section 3, 4 leg 5, 6 leg 7 Stripline 8th leg 9, 10 plate 11 gap 12, 13 Side surface 14, 15 gap 16 Ceramic block 17, 18 Main area 19, 20, 21, 22 Side surface 23 slot 24, 25, 26, 27 Metallization 28, 29, 30, 31 Inner surface 32 Metallization 33 non-conductive area 34, 35, 36 Slot edge 37, 38, 39 Antenna element 40 PCMCIA card

Claims (14)

Flat three-dimensional antenna, in which in a first plane a base plate (1), in a second plane a U-shaped and thus forming a middle part (2) and two legs (3, 4) forming slot dividers and in a third plane above the slot divider a resonance structure (9, 10) is arranged. Antenna according to claim 1, characterized in that the slot divider is fed by a strip conductor (7) which is guided in the second plane between the two legs (3, 4) in order to contact the middle part (2). Antenna according to claim 1 or 2, characterized in that the resonance structure (9, 10) is short-circuited by flank elements (12, 13) to the legs (3, 4) of the slot divider and thus delimits an antenna slot. Antenna according to claim 3, characterized in that the resonance structure (9, 10) is severed (11) in the middle. Antenna according to one of claims 1 to 4, characterized in that a first antenna slot formed between base plate (1) and slot divider (2, 3, 4) is larger than one between slot divider (2, 3, 4) and resonance structure (9, 10) second antenna slot formed. Antenna according to one of claims 1 to 5, characterized in that a dielectric substrate is present between the first and second levels. Antenna according to claim 6, characterized in that the slot divider is applied as a conductor track layer on the substrate, that the base plate (1) is formed by a metallization on a back of the substrate and that the resonance structure is built up on the conductor track layer. Antenna according to claim 6, characterized in that it is formed on a ceramic block (16), the slot divider being formed by conductor tracks (24, 25, 26) on side surfaces (19, 20, 21) such that the resonance structure on a main surface ( 17) and that a slot (23) is provided for the feed in the second level. Antenna according to claim 8, characterized in that an inductance is integrated in the feed. Antenna according to one of claims 1 to 9, characterized in that it can be adapted in terms of impedance by varying a width and a length of the stripline (7). Antenna according to one of claims 5 to 10, characterized in that a bandwidth of the antenna can be changed by varying the second-mentioned antenna slot. Antenna array with several antennas according to one of claims 1 to 11. PCMCIA card with preferably at least two antennas according to one of claims 1 to 11 for digital communication using spatial and / or angular diversity reception. Hand-held radio telephone with at least one antenna according to one of Claims 1 to 11, the antenna being designed in particular according to Claim 8.

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