WO2006097567A1

WO2006097567A1 - Antenna component

Info

Publication number: WO2006097567A1
Application number: PCT/FI2005/050401
Authority: WO
Inventors: Juha Sorvala; Petteri Annamaa; Kimmo Koskiniemi
Original assignee: Pulse Finland Oy
Priority date: 2005-03-16
Filing date: 2005-11-08
Publication date: 2006-09-21
Also published as: EP1859507A1; EP1859507A4

Abstract

An antenna component (200) with a dielectric substrate and two radiating antenna elements. The elements are located on the upper surface of the substrate and there is a narrow slot (260) between them. The antenna feed conductor (241) is connected to the first antenna element (220), which is connected also to the ground by a short-circuit conductor (261). The second antenna element (230) is parasitic; it is galvanically connected only to the ground. The component is preferably manufactured by a semiconductor technique by growing a metal layer e.g. on a quartz substrate and removing a part of it so that the antenna elements remain. In this case the component further comprises supporting material (212) of the substrate chip. The antenna component is very small-sized because of the high dielectricity of the substrate to be used and mostly because the slot between the antenna elements is narrow. The efficiency of an antenna made by the component is high.

Description

Antenna component

The invention relates to a component, where conductive coatings of a dielectric substrate function as radiators of an antenna. The invention also relates to an antenna made by such a component.

In small-sized radio devices, such as mobile phones, the antenna or antennas are preferably placed inside the cover of the device, and naturally the intention is to make them as small as possible. An internal antenna has usually a planar structure so that it includes a radiating plane and a ground plane below it. There is also a variation of the monopole antenna, in which the ground plane is not below the radiating plane but farther on the side. In both cases, the size of the antenna can be reduced by manufacturing the radiating plane on the surface of a dielectric chip instead of making it air insulated. The higher the permittivity of the material, the smaller the physical size of an antenna element of a certain electric size. The antenna component becomes a chip to be mounted on a circuit board. However, such a reduction of the size of the antenna entails the increase of losses and thus a deterioration of efficiency.

Fig. 1 shows an antenna component and a whole antenna according to application Fl 20040892, known by the applicant. The antenna component 100 comprises an elongated and rectangular dielectric substrate 110 and two antenna elements on its surface. The first antenna element 120 comprises a portion 121 partly covering the upper surface of the substrate 110 and a head portion 122 covering one head of the substrate. The second antenna element 130 comprises symmetrically a portion 131 covering the upper surface of the substrate partly and a head portion 132 covering the opposite head. Each head portion 122 and 132 continues slightly on the side of the lower surface of the substrate, thus forming the contact surface of the element for its connection. In the middle of the upper surface between the elements there remains a slot 160, over which the elements have an electromagnetic coupling with each other. The slot 160 extends in the transverse direction perpendicularly from one lateral surface of the substrate to the other. The antenna component 100 is located on the circuit board PCB of a radio device its lower surface against the circuit board. The antenna feed conductor 140 is a strip conductor on the upper surface of the circuit board, and together with the ground plane, or the signal ground GND, and the circuit board material it forms a feed line having a certain impedance. The feed conductor 140 is galvanically coupled to the first antenna element 120 at a certain point of its contact surface. At another point of that contact surface, the first antenna element is galvanically coupled to the ground plane GND. At the opposite end of the substrate, the second antenna element 130 is galvanically coupled at its contact surface to the ground conductor 150, which is an extension of the wider ground plane GND.

At the operating frequency, both antenna elements together with the substrate, each other and the ground plane form a quarter-wave resonator. In compliance with the above described structure, the open ends of the resonators are facing each other, separated by the slot 160, and the electromagnetic coupling is clearly capacitive. The width d of the slot can be dimensioned so that the dielectric losses of the substrate are minimized. The optimum width is in that case e.g. 1.2 mm and a suitable range of variation 0.8-2.0 mm, for example. When a ceramic substrate is used, the structure provides a relatively small size. For example, the dimensions of a component of a Bluetooth antenna operating in the frequency range of 2.4 GHz can be 2x2x7 mm³.

The antenna is tuned by shaping the ground plane and by choosing the width of the slot between the antenna elements. The decreasing the width d of the slot lowers the natural frequency of the antenna. There is no ground plane under the antenna component 100, and on the side of the component the ground plane is at a certain distance s from it. The longer the distance, the lower the natural frequency. In turn, increasing the width d of the slot. The width and length of the ground conductor 150 affect directly the electric length of the second element and thus the natural frequency of the whole antenna, for which reason the ground conductor functions as a tuning element of the antenna. The distance s has an effect also on the antenna impedance, so that the antenna can be matched by finding the optimum distance of the ground plane from the long side of the antenna component.

The object of the invention is to implement an antenna component by a new and advantageous way in view of the prior art. An antenna component according to the invention is characterized in what is set forth in the independent claim 1. An antenna according to the invention is characterized in what is set forth in the independent claim 16. Some preferred embodiments of the invention are set forth in the other claims.

The basic idea of the invention is the following: The antenna component comprises a dielectric substrate and two radiating antenna elements. The elements are located on the upper surface of the substrate and there is a narrow slot between them. The antenna feed conductor is connected to the first antenna element, which is connected also to the ground by a short-circuit conductor. The second antenna element is parasitic; it is galvanically connected only to the ground. The component is preferably manufactured by a semiconductor technique by growing a metal layer e.g. on a quartz substrate and removing a part of it so that the antenna elements remain. In this case the component further comprises supporting material of the substrate chip.

The invention has the advantage that an antenna component according to it is very small-sized. This is due to that the slot between the antenna elements is narrow and that the high permittivity of the substrate to be used. In addition, the invention has the advantage that the efficiency of an antenna made by a component according to it is good in spite of the dielectric substrate. A further advantage of the invention is that both the tuning and the matching of an antenna can be carried out without discrete components just by shaping the conductor pattern of the circuit board near the antenna component.

In the following, the invention will be described in more detail. Reference will be made to the accompanying drawings, in which

Fig. 1 presents an example of a prior art antenna component and antenna,

Fig. 2 presents an example of an antenna component and antenna according to the invention,

Fig. 3 presents another example of an antenna component according to the invention,

Figs. 4a-c present examples of a shaping the slot between the antenna elements in the antenna component according to the invention, Fig. 4 presents a part of a circuit board belonging to the antenna of Fig. 2 from the reverse side,

Fig. 5 presents a third example of an antenna component according to the invention,

Fig. 6 presents an application of an antenna component according to the invention,

Fig. 7 presents a fourth example of an antenna component according to the invention, Fig. 8 shows examples of the matching of antennas according to the invention, and

Fig. 9 presents examples of the efficiency of antennas according to the invention.

Fig. 1 was already explained in connection with the description of the prior art.

Fig. 2 shows an example of an antenna component and an whole antenna according to the invention. A part of the circuit board 205 of a radio device and an antenna component 200 on its surface are seen enlarged in the drawing. The antenna component 200 comprises a dielectric substrate 211 and two antenna elements on its surface, one of which has been connected to the antenna feed conductor and the other is an electromagnetically fed parasitic element, like in the antenna component 100 in Fig. 1. The difference is that the antenna elements now are located totally on the upper surface of the substrate, where their connection points then also are located. In the component of Fig. 1 the elements extend via the head surfaces to the lower surface of the substrate, where their connection points then also are located. In addition, in the component according to the invention the slot 260 between the elements is considerably narrower than in the component of Fig. 1 and also generally in the next corresponding known antennas, so that the coupling between the elements is stronger.

In the example of Fig. 2 the substrate 211 is a thin chip with the thickness e.g. order of 100 μm. In this case its material is some basic material used in the semiconductor technique, such as quartz, gallium-arsenide or silicon. The antenna elements are preferably of gold, and their thickness is naturally even far smaller, for example 2 μm. The elements are formed by growing a metal layer on the surface of the substrate e.g. by the sputtering technique and removing the layer, among other things, at the place of the intended slot by the exposure and etching technique used in the manufacture of semiconductor components. This makes it possible to fabricate a slot having even 10 μm width. A very small component size can be achieved by means of the structure according to the invention, when using the semiconductor technique. The area of the substrate chip at the operating frequencies over 2 GHz is e.g. 2-3 mm². The slot width order of magnitude 50 μm or less and the dielectric substrate together result in that the electric size of the antenna elements is for example tenfold compared with the physical size. The substrate chip needs mechanical support, for which reason it has been attached on the upper surface of a dielectric support plate 212 belonging to the antenna component. The material of the support plate is stronger than the one of the substrate, and its thickness is e.g. 0.3 mm. The support plate again has been attached to the circuit board 205.

The antenna elements have in the example of Fig. 2 a shape of right-angled triangle so that the slot 260 between them travels diagonally from close a corner of the substrate close to the opposite farthest corner. The first antenna element 220 is the directly fed element and the second antenna element 230 is a parasitic element. The first antenna element is connected by the feed conductor 241 to a contact pad on the upper surface of the support plate 212 from the feed point, which is located at one end of the element side near the first end of the substrate. From the contact pad there is a via 242 to the circuit board 205, the lower end of which via is connected on the circuit board to a strip conductor 243 leading to the antenna port of the radio device. The whole feed conductor 240 of the exemplary antenna is then constituted from the strip conductor 243, via 242 and feed conductor 241. In addition, the first antenna element is connected by a short-circuit conductor 261 to a second contact pad on the upper surface of the support plate 212 from a short-circuit point, which is located at other, opposite end of the element side near the first end of the substrate. From this contact pad there is a via to the signal ground GND on the circuit board 205. The second antenna element 230 is connected by the second 251 and third 252 short-circuit conductors to the third and fourth contact pads on the upper surface of the support plate 212 from a short-circuit points, which are located at opposite ends of the element side near the second end of the substrate. From these contact pads there are vias to a ground conductor 255 on the circuit board 205. The feed conductor 241 and said three short-circuit conductors belong to the antenna component 200. They are most advantageously conductive wires made of gold and fastened by bonded joint at their ends.

Each antenna element forms with the substrate, ground and the other element a quarter wave resonator. The natural frequencies of these resonators are same or close to each other so that the antenna is one-band antenna.

The ground conductor 255 is an extension of the larger signal ground or ground plane GND, and it can be used for the tuning of the antenna by choosing its length and width suitably. The antenna tuning is affected by the shaping also other parts of the ground plane. There is no ground plane under the antenna component 200, and on the side of the component the ground plane is at a certain distance s from the antenna element. The longer the distance, the lower the natural frequency and location of the antenna operating band. In addition, the antenna matching can be improved by means of the area free of the ground plane. When the antenna component is placed in the inner area of the circuit board, the ground plane is removed from its both sides.

Fig. 3 shows another example of an antenna component according to the invention as a longitudinal section. The component comprises a ceramic substrate 310, on the upper surface of which there are the first 320 and second 330 antenna element. The feed conductor 341 belonging to the component is in this example a conductive via extending through the substrate from the first antenna element to a contact pad 345 on the lower surface of the substrate. The antenna component has been mounted on the circuit board 305 of a radio device, in which case the contact pad 345 makes contact with the counter contact on the circuit board and is through that contact further connected to the antenna port of the device. Also the short-circuit conductor of the first antenna element, which conductor is not seen in the drawing, and the short-circuit conductor 351 of the second antenna element 330 are implemented by the similar vias. The second antenna element can have also another short-circuit conductor.

Figs. 4a-c show examples of a shaping the slot between the antenna elements in the antenna component according to the invention. The antenna component is seen from above without a possible support plate in each of the three drawings. The substrate belonging to the component is rectangular seen from above, thus having parallel ends and parallel longer sides. In Fig. 4a the slot 460a between the antenna elements on the upper surface of the substrate 410a is straight and travels diagonally on the upper surface of the substrate in respect of the direction of its ends. In Fig. 4b the slot 460b between the antenna elements has turns. The turns are rectangular and the number of them is ten so that two finger-like strips 421 and 422 are formed in the first antenna element 420b, extending between the areas belonging to the second antenna element 430b. In addition, a third similar strip is formed at an outer edge of the area formed by the antenna elements. Symmetrically, two finger-like strips 431 and 432 are formed in the second antenna element, extending between the areas belonging to the first antenna element. In addition, a third similar strip is formed at another outer edge of the area formed by the antenna elements. In Fig. 4c the slot 460c between the antenna elements is straight and travels crosswise on the upper surface of the substrate in the direction of its ends. In addition, in the example of Fig. 4c the antenna elements have different sizes; the first element 420c is smaller than the second element 430c.

In Fig. 4b the slot between the antenna elements is considerably longer and also narrower than in Figs. 4a and 4c. For these reasons the operating band of an antenna corresponding to Fig. 4b lies in a clearly lower range than the operating band of an antenna corresponding to Fig. 4a and especially to Fig. 4c. By shaping the antenna elements again for example so that a diagonal slot like the slot 460a is replaced with a devious slot like the slot 460b, which is some narrower at the same time, the antenna operating band can be shifted e.g. from the range of 1.8 GHz to the range of 900 MHz without to change the structure otherwise. The number of the turns in the slot between the antenna elements can naturally vary as well as the lengths of the strips formed by the turns.

Fig. 5 shows a third example of an antenna component according to the invention, seen from above. On the upper surface of the substrate 510 there are now in addition to the antenna elements 520 and 530 an antenna filter 570 and the low noise pre-amplifier 580 (LNA) of a radio receiver. The filter 570 is for example of the FBAR type (Film Bulk Acoustic Resonator). The filter and the amplifier, as well as the inductive and capacitive parts required by the amplifier matching have been made on the surface of the substrate in the same process as also the antenna elements. In the example of Fig. 5 the antenna elements, filter and amplifier have been first processed as separate and then connected to each other by wiring. The connecting wiring could also be replaced by conductors processed on the surface of the substrate. Because the component at issue is a part of a receiver, the conductor 541 , connecting the first antenna element 520 to the filter input, is now not the feed conductor of the antenna, of course, but the receive conductor. In this description and the claims the term "feed conductor" covers for simplicity also such receive conductors. Naturally one and the same conductor is often for both the transmitting and the receiving.

In addition to the saving of space, the above described integrated structure has the advantage that there is no need to use a standard impedance level, such as 50Ω, at the antenna end of the receiver, but the impedance level can be chosen according to the optimum performance.

Fig. 6 shows an application of an antenna component according to the invention. Therein an antenna component 601 has been placed to the middle of one long side of the radio device circuit board 605, in the direction of the circuit board. The antenna component is now designed so that when it is fed, an oscillation is excited in the ground plane GND, the frequency of the oscillation being the same as the one of the feeding signal. In that case also the ground plane functions as a useful radiator. A certain area RA round the antenna component radiates to significant degree. The antenna structure can comprise also several antenna components, as the component 602 drawn with dashed line in the figure.

Fig. 7 shows a fourth example of an antenna component according to the invention as a longitudinal section. The antenna component 700 comprises now a plastic protective part 790, within the mass of which the substrate 710 with the antenna elements is entirely located. At the same time the protective part supports the substrate. On the lower surface of the protective and support part 790 there are a sufficient number of connection pads functioning as contacts, such as connection pad 745, to which a coupling conductor 741 of the antenna element has been connected within the component

Fig. 8 shows two examples of the matching of the antennas according to the invention. It presents a curve of the reflection coefficient S11 as a function of frequency. The curve 81 has been measured from an antenna made by a component according to Fig. 4a, the size of the substrate being 1.22 • 2.5 mm² and the slot width being 80 μm. The substrate is of Gallium-Arsenide. The operating band of the antenna lies in the range of the Bluetooth system. If the criterion for the boundary frequency is used the value -6 dB of the reflection coefficient, the bandwidth becomes about 100 MHz. In the center of the operating band the reflection coefficient is -7.4 dB. The curve 82 has been measured from an antenna made by a component according to Fig. 4b, the substrate being similar as before. The center frequency of the antenna is about 3.44 GHz and the bandwidth is about 440 MHz, if the criterion for the boundary frequency is used the value -6 dB of the reflection coefficient. In the center of the operating band the reflection coefficient is -26 dB.

Fig. 9 shows two examples of the efficiency of the antennas according to the invention. The efficiency curve 91 has been measured from the same antenna as the reflection coefficient curve 81 in Fig. 8, and the efficiency curve 92 has been measured from the same antenna as the reflection coefficient curve 82. In the operating bands of the antennas the efficiency is about 0.5 or a little better. The efficiency is considerably high taking into account that it is the case of an antenna using a dielectric substrate. In this description and the claims, the qualifiers "lower", "upper" and "from above" refer to the position of the antenna component shown in Figs. 2 and 3. The use position of the antenna can naturally be any.

Edella on kuvattu keksinnόn mukaista antennikomponenttia ja antennia. Niiden rakenneosat voivat yksityiskohdissaan poiketa esitetyista. Esimerkiksi antennielementtien muoto voi vaihdella suuresti. Ne voivat olla eri tavoin symmetrisia tai epasymmetrisia myόs muulla kuin kuvassa 4c esitetylla tavalla. Keksinnδllista ajatusta voidaan soveltaa eri tavoin itsenaisen patenttivaatimuksen 1 asettamissa rajoissa.

An antenna component and antenna according to the invention has been described above. Their structural parts can naturally differ from those presented in their details. For example, the shape of the antenna elements can vary largely. They can be symmetrical in a different way or asymmetric also in another way than what is presented in Fig. 4c. The inventive idea can be applied in different ways within the scope set by the independent claim 1.

Claims

1. An antenna component (200) for implementing an antenna of a radio device, which component comprises a dielectric substrate (210) and a first and a second antenna element on the substrate surface, which first antenna element (220) is to be fed by a feed conductor and to be short-circuited, and which second antenna element (230) is a parasitic element to be short-circuited, getting its feed electromagnetically over a slot (260) between the elements, characterized in that the first and second antenna elements are conductive areas on upper surface of the substrate, said feed conductor (241) connects the first antenna element (220) from its feed point to a contact pad at a level below the substrate (211), short- circuit of the first antenna element is implemented by a first short-circuit conductor (261), which connects the first antenna element from its short-circuit point to a second contact pad at the level below the substrate, short-circuit of the second antenna element (230) is implemented by a second short-circuit conductor (251), which connects the second antenna element from its short-circuit point to a third contact pad at the level below the substrate, and the width of said slot is at most 0.5 mm.

2. An antenna component according to Claim 1 , characterized in that it further comprises a dielectric support plate (212), on upper surface of which the substrate (211) with antenna elements is attached and said contact pads are located.

3. An antenna component according to Claim 2, characterized in that said feed and short-circuit conductors are conductive wires fastened by bonded joints.

4. An antenna component according to Claim 3, characterized in that the substrate is a basic material used in a semiconductor technique, and the antenna elements and the slot between them are formed by semiconductor technique.

5. An antenna component according to Claim 4, characterized in that said basic material is quartz, gallium-arsenide or silicon.

6. An antenna component according to Claim 1 , characterized in that said feed and short-circuit conductors (341 , 351) are conductive vias of the substrate (310), said contact pads (345) are located on lower surface of the substrate and make, after the mounting of the component, contact with counter contacts on the circuit board.

7. An antenna component according to Claim 6, characterized in that the dielectric substrate is of ceramic material.

8. An antenna component according to Claim 1 , characterized in that it further comprises a third short-circuit conductor (252), which connects the second antenna element (230) from its second short-circuit point to a fourth contact pad at the level below the substrate.

9. An antenna component according to Claim 1 , characterized in that it (700) further comprises a plastic protective and support part (790), within mass of which the substrate (710) and the antenna elements are entirely located, and said contact pads (745) are located on lower surface of the protective and support part.

10. An antenna component according to Claim 1 , characterized in that said slot (460c) is straight and travels crosswise on the upper surface of the substrate in the direction of its ends.

11. An antenna component according to Claim 1 , characterized in that said slot (260; 460a) is straight and travels diagonally on the upper surface of the substrate in respect of the direction of its ends

12. An antenna component according to Claim 1 , characterized in that said slot (460b) has at least two turns.

13. An antenna component according to Claim 12, characterized in that the turns of the slot form in one antenna element at least one finger-like extension

(421 , 422; 431 , 432), which extends between the areas belonging to the opposite antenna element.

14. An antenna component according to Claim 1 , characterized in that said antenna elements (420c, 430c) are asymmetric by shape.

15. An antenna component according to Claim 1 , characterized in that both the first and second antenna element forms at an operating frequency together with the substrate, the opposite antenna element and the ground plane a quarter-wave resonator, which resonators have a substantially same natural frequency.

16. An antenna of a radio device, the radio device comprising a circuit board (205), a conductive coating of which functions as a ground plane (GND) of the radio device, characterized in that it comprises at least one antenna component

(200; 601 , 602) according to claim 1 , which component is located on the circuit board with its lower surface against the circuit board, wherein the edge of the ground plane is at a certain distance (s) from the elements of the antenna component in the direction of the normal of the side of the component to tune the antenna and to improve its matching.

17. An antenna according to Claim 16, characterized in that the second antenna element is connected to the ground plane through a ground conductor (255), which is a tuning element of the antenna at the same time.

18. An antenna according to Claim 16, characterized in that the antenna component (601) is arranged to excite in the ground plane (GND) an oscillation with feed frequency, to utilize a radiation of the ground plane.