WO2008065241A1

WO2008065241A1 - Dielectric antenna

Info

Publication number: WO2008065241A1
Application number: PCT/FI2007/050613
Authority: WO
Inventors: Mikko Junttila
Original assignee: Pulse Finland Oy
Priority date: 2006-11-28
Filing date: 2007-11-14
Publication date: 2008-06-05
Also published as: CN101589507A; FI20065751A; EP2097946A1; FI120120B; EP2097946A4; FI20065751A0

Abstract

A dualband dielectric antenna suitable for small radio devices. It has a chip substrate (720) with relatively high permittivity for reducing the size of the antenna. However, only a part (712, 713) of the radiating conductor is on the surface of the chip substrate the other part (711) being located adjacent to it so that the other part is surrounded by a material, the permittivity of which is substantially lower than that of the chip substrate. The surrounding material can be substantially of the material of a dielectric plate, onto which the chip substrate is fastened, or pure air. In the former case the whole substrate of the antenna then has two parts. The efficiency of the antenna improves compared to corresponding known antennas, because part of the radiating conductor travels on a substrate with lower permittivity, compared to the chip substrate. At the same time, the lower band which is in practice relatively narrow can be widened.

Description

Dielectric antenna

The invention relates to a dualband dielectric antenna suitable for small radio devices.

For the sake of convenience, the antenna of small radio devices' usually held in a pocket is preferably placed inside the casing of the device. Such internal antennas are generally of a planar structure so that they include a radiating plane parallel with the circuit board of the radio device and below the radiating plane a ground plane. The size of the antenna, i.e. the space it requires depends on the size of the radiator and the height of the antenna. The latter refers to the dimension of the structure in the direction of the normal of the circuit board of the device. For reducing a planar antenna its height can be arranged very small, but in this case the detrimental effect is the deterioration of the electrical characteristics of the antenna, due to the proximity of the ground plane. An internal antenna can also be of a monopole type, in which case its height can be made very small. The electrical size of an antenna radiator is determined by its use frequency, irrespective of the type of the antenna. When keeping as a basis an air-insulated antenna, which is advantageous from the point of view of efficiency, the physical size of the radiator and, at the same time, the size of the entire antenna can be reduced by means of a dielectric substrate. In this case, the radiator is a conductive coating of the substrate in question. However, in such an antenna, i.e. a dielectric antenna, the cost of the reduction of the antenna size is the increase of its losses.

In Fig. 1 there is an example of a known dielectric antenna. The antenna is of monopole type. A part of the circuit board PCB of a radio device is seen in the drawing. On the upper surface of the circuit board, near its one end, there is an antenna component 100, which consists of a dielectric substrate 120 and a radiating element 110. The substrate is an elongated piece so that it has an upper and lower surface, a first and second side surface, and a first and second head surface. The lower surface lies against the circuit board PCB. The feed point FP of the antenna is in the corner of the lower surface of the substrate defined by the first side surface and the first head surface. The radiating element 110 has been implemented by coating a part of the substrate 120 with a conductive material. It comprises three strip-like portions of the length or at least close to the length of the substrate positioned as continuations to each other. The first portion starts from the feed point FP and extends along the first side surface of the substrate to the second head surface. The second portion extends along the upper surface of the substrate on the side of the first side surface to the first end, near to the first head surface. The third portion is adjacent to the second portion on the upper surface on the side of the second side surface, and it extends to the second end near to the second head surface.

On the circuit board PCB there is the ground plane GND required also by the function of the antenna. The edge of the ground plane is at a certain distance from the antenna component in the direction perpendicular to the longitudinal direction of the component. The feed conductor FC of the antenna is a conductive strip on the circuit board PCB, extending to the feed point FP. For matching the antenna impedance, a matching component 150 has been connected between the feed conductor and the ground GND, which component is here an inductive chip component.

The antenna in Fig. 1 is a dualband antenna. The lower operating band is based on the resonance of the whole radiating element 110, and the upper operating band is based on the resonance of the slot between the first and second portion of the radiating element. Thus the antenna comprises a radiating slot in addition to the radiating (conductive) element.

As mentioned, a drawback with the antennas like the one described above is the considerable losses in the dielectric material of the substrate. This naturally affects the efficiency of the antenna in each operating band. In practice, the drawback is more serious in the lower operating band, because it is more difficult to make wide enough. Therefore the lowering of the efficiency caused by the use of a substrate with high permittivity means that the. usable band becomes even narrower.

The object of the invention is to reduce said drawback relating to the prior art. The antenna of the invention is characterised in what is presented in the independent claim 1. Some advantageous embodiments of the invention are disclosed in the other claims.

The basic idea of the invention is as follows: In a dielectric antenna, a chip substrate with relatively high permittivity is used for reducing the size of the antenna. However, only a part of the radiating conductor is on the surface of the chip substrate, the other part being located adjacent to the chip substrate so that it is surrounded by a material, the permittivity of which is substantially lower than that of the chip substrate. The surrounding material can be substantially of the material of the dielectric plate, onto which the chip substrate is attached, or mere air. In the former case, the whole substrate of the antenna then has two parts.

An advantage of the invention is that the efficiency of a dielectric antenna is improved compared to other corresponding known antennas. This is due to the fact that a part of the radiating conductor travels on a substrate with a lower permittivity, compared with the chip substrate. The improvement in the efficiency is achieved without the space required for the antenna in a radio device hardly increasing, compared to corresponding known dielectric antennas. Relating to the improvement in efficiency also in the lower operating band, an advantage of the invention is that the lower operating band, which is in practice relatively narrow, can be made broader. A further advantage of the invention is that the antenna components according to it are relatively cheap, and also the costs caused by their mounting in the production are low.

The invention will next be described in more detail referring to the enclosed drawings, in which

Fig. 1 shows an example of the dielectric antenna according to the prior art,

Fig. 2 shows an example of the dielectric antenna according to the invention,

Fig. 3 shows a second example of the dielectric antenna according to the invention,

Fig. 4 shows a third example of the dielectric antenna according to the invention,

Fig. 5 shows a fourth example of the dielectric antenna according to the invention,

Fig. 6 shows a fifth example of the dielectric antenna according to the invention,

Fig. 7 shows a sixth example of the dielectric antenna according to the invention,

Fig. 8 shows a seventh example of the dielectric antenna according to the invention,

Fig. 9 shows an eighth example of the dielectric antenna according to the invention,

Fig. 10 shows a ninth example of the dielectric antenna according to the invention, Figs. 11a,b show an example of the connection of the radiator wire according to Fig. 10 to the chip substrate of the antenna,

Figs. 12a,b show another example of the connection of the radiator wire according Fig. 10 to the chip substrate of the antenna, Fig. 13 shows examples of the band characteristics of the antennas according to the invention, and

Fig. 14 shows examples of the efficiency of the antennas according to the invention and two reference antennas.

Fig. 2 shows an example of the dielectric antenna according to the invention. A part of the circuit board PCB of a radio device is seen in the drawing, on the upper surface of the circuit board being an antenna component 200. This component consists of a dielectric chip substrate 220 and a radiating element, which is of conductive coating of the chip substrate, as in Fig. 1. The chip substrate is an elongated piece so that it has an upper and lower surface, a first and second side surface and a first and second head surface, the lower surface leaning against the circuit board PCB. Differing from the structure in Fig. 1 , the radiating element 212, 213 on the surface of the chip substrate does not form the entire radiating conductor 210 of the antenna, but only its second part. The first part 211 of the radiating conductor 210 is now a conductive strip on the circuit board PCB alongside the chip substrate. Thus the antenna comprises, in addition to the chip substrate 220, a second substrate 230, which in this example consists of a part of the dielectric base of the circuit board PCB below the chip substrate and especially below the first part of the radiating conductor.

The feed point FP of the antenna is on the circuit board PCB near the corner defined by the first head surface and the first side surface of the chip substrate

220. The first part 211 of the radiating conductor starts from the feed point, extends in the longitudinal direction of the chip substrate as far as the second head surface of the chip substrate, and then turns under the end of the chip substrate. On the lower surface of the chip substrate, in the corner defined by its first side surface and the second head surface, the first part of the radiating conductor connects to its second part. The second part of the radiating conductor comprises its first and second portion as continuations of each other. The first portion 212 of the second part starts from the above-mentioned connection point below the chip substrate, rises through the first side surface to the upper surface of the chip substrate and continues there on the side of the first side surface to the first end of the chip substrate near to the first head surface. The second portion 213 of the second part is adjacent to the first portion 212 on the upper surface on the side of the second side surface of the chip substrate and extends to the second end near to the second head surface and the starting end of the second portion.

On the circuit board PCB there is the ground plane GND required also by the antenna function. The edge of the ground plane is at a certain distance from the antenna component 200 in the direction perpendicular to its longitudinal direction. The feed conductor FC of the antenna is a conductive strip on the circuit board PCB extending to the feed point FP. The feed conductor does not belong to the radiating structure, because it is partly surrounded by the ground plane. For matching the antenna impedance, a matching component 250 has been connected between the feed conductor and the ground GND, which component is in this example an inductive chip component.

The antenna in Fig. 2 has two bands. The lower operating band is based on the resonance of the whole radiating conductor 210, and the upper operating band is based on the resonance of the slot between the first part 211 of the radiating conductor and the first portion 212 of the second part. Thus the antenna comprises a radiating slot in addition to the radiating conductor.

The substantial feature in the antenna structure illustrated above is that the permittivity of the second substrate 230 is substantially lower than that of the chip substrate 220. The second substrate is typically made of usual circuit board material FR4, the relative dielectric coefficient ε_r of which is about 4. The chip substrate again is e.g. ceramic, the coefficient ε_r of which is about 9. The lower permittivity means lower dielectric losses. Because the first part of the radiating conductor travels on the second substrate, the losses of the antenna are lower and the efficiency then better than of corresponding known antenna according to Fig. 1. The improvement of the efficiency concerns both operating bands. It concerns also the upper operating band, because the near field of the above- mentioned radiating slot is now in the air space to a greater extent than in the case of Fig. 1 , due to the geometry of the antenna.

The antenna component 200 is attached to the circuit board PCB for example by soldering. For the soldering, the starting end of the first portion of the second part of the radiating conductor on the lower surface of the chip substrate is made to have a suitable area, as also the tail end of the first part of the radiating conductor on the circuit board at said starting end. Also at the first end of the chip substrate, on its lower surface, can be formed conductive pad(s) for soldering the component. In this case, on the circuit board there are naturally conductive pad(s) at the respective point(s). When necessary, the fastening can be strengthened by adhesive material. The fastening can also be implemented by laminating, in which case the ceramic piece is pressed against the circuit board in a high temperature, until they have adhered to each other.

Fig. 3 shows a second example of the dielectric antenna according to the invention. It comprises a dielectric chip substrate 320 on the circuit board PCB of a radio device, the first part 311 of the radiating conductor 310 adjacent to the chip substrate, the second part 312 of the radiating conductor on the surface of the chip substrate and a matching component 350 like in Fig. 2. The dielectric part of the circuit board PCB functions as the second substrate 330 of the antenna like in Fig. 2. A difference to the structure shown in Fig. 2 is that the second part 312 of the radiating conductor does not make a turn on the upper surface of the chip substrate so that its tail end would be located beside the starting end, but it extends, substantially as wide as the upper surface of the chip substrate, from the second end of the chip substrate to the first end near to the first head surface. Another difference is that now the first part 311 of the radiating conductor branches in two at its starting end. Its first branch B1 is similar to the first part 211 of the radiating conductor in Fig. 2 connecting to the second part 312 of the radiating conductor from its tail end, and the second branch B2 is located between the first branch B1 and the chip substrate. As a result from such a shaping the slot between the first and second part of the radiating conductor, corresponding to the upper operating band, can be made bigger in electric size.

Fig. 4 shows a third example of the dielectric antenna according to the invention. The antenna comprises a chip substrate 420, a second substrate 430 and a radiating conductor 410, the first part of 411 of which is on the surface of the second substrate and the second part 412, 413 on the surface of the chip substrate, as in Fig. 2. In this example, the first portion 412 of the second part rises to the upper surface of the chip substrate through its second head surface. A more significant difference in respect of the structure in Fig. 2 is that the second substrate 430 now forms a separate small auxiliary plate, onto which the chip substrate is fastened. The chip substrate with its conductive coating and the second substrate with its conductive coating and possible discrete components form together an antenna component 400 to be mounted to some place in the radio device.

In Fig. 4, the antenna component 400 is presented both as a perspective drawing and seen from below. On the plate formed by the second substrate 430 there is a similar inductive discrete matching component 450 as in Fig. 2. One end of the matching component 450 is connected to the starting end of the first part 411 of the radiating conductor at the feed point FP of the antenna. From the feed point FP there extends a through hole to the lower surface of the second substrate to connect the radiator to the antenna port or switch of the radio device. From the other end of the matching component 450 there extends a through hole to the lower surface of the second substrate to connect the said other end to the signal ground GND in the radio device. In the drawing viewing the lower surface of the antenna component 400 the chip substrate 420 and the matching component 450, which are located on the reverse side, are marked by a dotted line.

Fig. 5 shows a fourth example of the dielectric antenna according to the invention. The structure of the antenna is similar to that in Fig. 4 with the difference that now the first portion 512 of the second part of the radiating conductor 510 is on the first side surface of the chip substrate 520 instead of the upper surface. The connection point of the first part 511 and the first portion 512 of the second part of the radiating conductor is under the chip substrate in the corner defined by its second head surface and first side surface, as in Figs. 3 and 4. The first portion 512 rises from the connection point directly to the first side surface. On the upper surface of the chip substrate there is only the second portion 513 of the second part of the radiating conductor. Correspondingly, the chip substrate is somewhat narrower than in Fig. 4.

Fig. 6 shows a fifth example of the dielectric antenna according to the invention. The antenna comprises a chip substrate 620, a second substrate 630 and a radiating conductor 610, the first part of 611 of which is on the surface of the second substrate and the second part 612 on the surface of the chip substrate, as in Figs. 2 to 5. The substantial difference to the structures presented in these figures is that now the feed of the radiating conductor takes place in its second part and not in the first part. The feed point FP is located on the second substrate 630 close to the second end of the chip substrate, and it connects under the second end of the chip substrate to the second part of the radiating conductor through a short conductor strip. The second part 612 rises to the upper surface of the chip substrate through its second head surface, extends on the upper surface, mostly as wide as it is, to the first end of the chip substrate and further to the lower surface of the chip substrate through the first head surface. In that place, below the first end of the chip substrate, there is the connection point of the second 612 and first 611 part of the radiating conductor. The first part of the radiating conductor starts from this connection point transversely, continues then in the longitudinal direction of the chip substrate adjacent to it, passes the second head surface of the chip substrate and makes finally a U-shaped turn towards the second head surface of the chip substrate. The first part is open at is tail end.

There is a matching component 650 between the feed point FP and the ground GND, as in the previous examples. The chip substrate with its conductive coating and the second substrate with its conductive coating and matching component form together an antenna component 600 to be mounted to some place in the radio device.

Fig. 7 shows a sixth example of the dielectric antenna according to the invention. The antenna structure is similar to the one in Fig. 6 with the substantial difference that now the second part of the radiating conductor 710 branches in two at the second end, or the end on the side of the feed point FP, of the chip substrate. The first branch 712 of the second part extends on the upper surface of the chip substrate to its first end and further to the lower surface of the chip substrate through the first head surface, where the connection point of the second part and first part 611 of the radiating conductor is located. The second branch 713 of the second part travels adjacent to the first branch 712 on the upper surface of the chip substrate and is open at its tail end. The aim of the second branch 713 is to implement an extra resonance in the upper operating band of the antenna for widening it.

The first part 711 of the radiating conductor in the example of Fig. 7. is shaped a little differently than in Fig. 6. The first part starts from the connection point below the first end of the chip substrate in the longitudinal direction of the chip substrate away from it, turns after that into the transverse direction and further into the longitudinal direction towards the second end of the chip substrate. Then the first part travels adjacent to the chip substrate and passes its second head surface and has finally a transverse portion.

Fig. 8 shows a sixth example of the dielectric antenna according to the invention.

The antenna comprises a chip substrate 820, a second substrate 830 and a radiating conductor 810, the first part of 811 of which is on the surface of the second substrate and the second part on the surface of the chip substrate, as in Figs. 2 to 7. The feed of the radiating conductor takes place in its second part as in Figs. 6 and 7. The substantial difference to the structures presented in Figs. 6 and 7 is that the second part of the radiating conductor is connected also to the ground GND from its certain point, for which reason the antenna is of IFA type (Inverted F- antenna). The second part of the radiating conductor rises from the feed point FP through the second head surface of the chip substrate to its upper surface, where the second part comprises three portions. The first portion 812 of the second part extends on the upper surface of the chip substrate to its first end and further to the lower surface of the chip substrate through the end of the first side surface, on which lower surface there is is the connection point of the second and first 811 part of the radiating conductor. The second portion 813 of the second part branches from the first portion 812 at the first end of the chip substrate and travels adjacent to it on the side of the second side surface back to the second end of the chip substrate, where said connection to the ground GND takes place. A slot remains between the first portion 812 and second portion 813, which slot is arranged to resonate in the upper operating band of the antenna.

The third portion 814 of the second part of the radiating conductor branches from the first portion 812 at the second end of the chip substrate and travels adjacent to the first portion on the side of the first side surface towards the first end of the chip substrate. The third portion 814 is open at its tail end. The first part 811 of the radiating conductor starts from its connection point at the first end of the chip substrate and travels beside the first side surface of the chip substrate extending near to the second head surface of the chip substrate. The first part 811 is open at its tail end. The slot between the first and second part of the radiating conductor resonates also in this example in the upper operating band of the antenna, in which case the upper operating band is based on the resonances of both this slot and the slot between the first portion 812 and second 813 portion of the second part of the radiating conductor. The shape of the slot between the first and second part is determined i.a. by the third portion 814 of the second part, by means of which the resonance frequency then can be tuned.

Fig. 9 shows an eighth example of the dielectric antenna according to the invention. The antenna structure comprises a chip substrate 920, a second substrate 930, and a radiating conductor 910, the first part 911 of which is on the surface of the second substrate and the second part on the surface of the chip substrate, as i.a. in Fig. 4. The difference compared to the structure presented in Fig. 4 is that now the chip substrate 920 is, seen from above, approximately square by shape, and the first part of the radiating conductor and the first portion 912 of the second part now follow two sides of the chip substrate. Thus, the first part 911 of the radiating conductor starting from the feed point FP near a corner of the chip substrate travels first next to one side of the chip substrate, turns then round the corner of the chip substrate to be parallel with the adjacent side, and finally turns under the opposite corner of the chip substrate, seen from the feed point. There the first part 911 joins the first portion 912 of the second part of the radiating conductor. This portion rises through the side surface to the upper surface of the chip substrate and continues along the upper surface close to above-mentioned sides of the chip substrate to the corner nearest to the feed point FP. From there the conductive coating of the chip substrate continues as the second portion 913 of the second part of the radiating conductor on the upper surface of the chip substrate close to its two other sides, turning finally to the middle area of the upper surface. The boundary between the first portion 912 and the second portion 913 of the second part is marked by a dotted line in Fig. 9.

The antenna component 900 is shown enlarged in Fig. 9, as in the previous figures. The sides of the chip substrate 920 are e.g. one centimetre long.

Fig. 10 shows a ninth example of the dielectric antenna according to the invention. The antenna comprises a chip substrate A20 mounted onto the circuit board PCB of a radio device, on the surface of which chip substrate there is the second part A12, A13 of the radiating conductor A10, as in Fig. 2. The significant difference compared to Fig. 2 is that now the first part A11 of the radiating conductor does not travel on the surface of the second substrate A30 implemented by the circuit board PCB. The first part A11 is instead a rigid conductor wire in the air above the circuit board and alongside the first side surface of the chip substrate. The starting end of the first part A11 bends against the first head surface of the chip substrate A20 and the tail end against the second head surface of the chip substrate A20. At the ends, the first part is mechanically attached to the chip substrate so that the chip substrate with its conductive coating and the first part of the radiating conductor form an integrated antenna component A00.

At the second end of the chip substrate the first part A11 of the radiating conductor is connected galvanically to the first portion A12 of the second part of the radiating conductor and at the first end to the conductive coating of the chip surface, the coating being further connected to the feed conductor FC of the antenna. A matching component A50 is connected between the feed conductor and the ground GND as in the previous examples.

In the structure according to Fig. 10 the first part of the radiating conductor, excluding of the starting and tail end, is surrounded only by air. This means further lowering in losses compared i.a. to the structure according to Fig. 2. The mechanical structure of the antenna component means that in the production components can be surface-mounted onto the circuit boards.

Figs. 11a and 11b show an example of the connection of the radiating wire according to Fig. 10 to the chip substrate. Fig. 11a shows the longitudinal vertical section of the first end of the antenna component, and Fig. 11 b shows the antenna component seen from the side of the first end. At the end of the chip substrate B20 there is a horizontal trough-like recess, to which the cylindrical starting end of the first part B11 of the radiating conductor is pressed when the first part is mounted. Thus its fastening becomes firmer than a fastening based on mere soldering. The starting end of the conductor B11 is soldered to the conductive coating B15 of the first head surface, which coating continues slightly to the side of the lower surface of the chip substrate. On the lower surface the conductor B15 is connected to the antenna feed conductor at the feed point FP. The conductor B15 is then functionally a part of the first part of the radiating conductor.

Figs. 12a and 12b show another example of the connection of the radiating wire according to Fig. 10 to the chip substrate. Fig. 12a shows the longitudinal vertical section of the first end of the antenna component, and Fig. 12b shows the antenna component seen from the side of the first end. In this example, there is a hole at the end of the chip substrate C20, being directed to the inside of the substrate, to which hole the starting end of the first part C11 of the radiating conductor is put when the first part is mounted. The cross-section of the hole has the same shape as the cross-section of the starting end of the conductor C11. Thus the fastening of the conductor becomes firmer than the fastening based on a mere soldering. The starting end of the conductor is soldered to the conductive coating C15 of the first head surface, which coating continues a little to the side of the lower surface of the chip substrate. On the lower surface, the conductor C15 is connected :to the antenna feed conductor at the feed point FP. The conductor C15 is then functionally a part of the first part of the radiating conductor. Figs. 11a to 12b present the first end of the antenna component. At the second end there is a similar joint as at the first one or the ways of joining the starting and tail ends of the.first part of the radiating conductor differ from each other.

Fig. 13 shows an example of the band characteristics of the antenna according to the invention. Curve D1 shows the variation of the reflection coefficient S11 as the function of frequency when the antenna is like the one in Fig. 3, curve D2 when the antenna is like the one in Fig. 7 and curve D3 when the antenna is like the one in Fig. 8. The smaller the reflection coefficient, the better the antenna has been matched and the better it functions as a radiator and receiver of the radiation. It is seen that each antenna has a lower and upper operating band. Regarding each antenna, the lower operating band is based on the resonance of the whole radiating conductor. From these resonances the resonance r11 , existing in the antenna according to Fig. 3, is marked in Fig. 13. Regarding each antenna, the upper operating band is based at least partly on the resonance of the slot between the first and second part of the radiating conductor. Curve D1 shows that the antenna according to Fig. 3 does not have other resonances in the upper operating band. Curve D2 again shows that the antenna according to Fig. 7 has two resonances in the upper operating band. The lower one of these, resonance r22, is the above-mentioned resonance of the slot between the parts of the radiating conductor and the upper one, resonance r23, is the resonance of the open branch 713 of the second part of the radiating conductor. In the example of Fig. 13, the resonances r22 and r23 are placed so that the antenna corresponding to them radiates relatively weakly in the mid range of the upper operating band. This can be improved by means of the design, true at the expence of the bandwidth. Curve D3 shows that also the antenna according to Fig. 8 has two resonances in the upper operating band. The lower one of these, resonance r32, is the above-mentioned resonance of the slot between the parts of the radiating conductor and the upper one, resonance r33, is the resonance of the slot between the middle portion 812 and the portion 813 connected to the ground of the second part of the radiating conductor.

Regarding each antenna, the width of the lower operating band in the range of 900 MHz is at least 80 MHz, which is enough to cover e.g. the frequency range 880- 960 MHz used by the European EGSM system (Extended GSM). The .antenna according to Fig. 7 has the widest lower operating band, almost 200 MHz. It is enough to cover both the frequency range 824-894 MHz used by the American GSM system and the frequency range used by the EGSM system. Regarding each antenna, the width of the upper operating band is at least 300 MHz, which is enough to cover both the frequency range 1710-1880 MHz used by the GSM1800 system and the frequency range 1850-1990 MHz used by the GSM1900 system or the frequency range 1920-2170 MHz used by the WCDMA system (Wideband Code Division Multiple Access), when the resonances are placed to the suitable points at the frequency scale, by means of the design.

Fig. 14 shows examples of the efficiency of the antennas according to the invention and the efficiency of two reference antennas. The curves show the efficiency as the function of frequency. Curve E1 concerns the antenna according to Figs. 2 and 4, curve E2 the antenna according to Fig. 3 and curve E3 the antenna according to Fig. 8. For comparison, also a curve E4 concerning a known antenna according to Fig. 1 and curve E5 concerning an air-insulated antenna, which has a main element of IFA type (Inverted F-Antenna) and a parasitic element, are shown in the figure. These elements are shaped so that the lower operating band of the antenna is based on the resonance of the parasitic element and the upper operating band on two separate resonances of the slots between the elements. The main and parasitic elements and the plastic frame supporting them form a component, the dimensions of which are 33 x 5.4 x 4 mm³. In the antennas corresponding to curves E1 and E2 the chip substrate is of ceramic and 25 x 3 x 1.5 mm³ by size. In the antennas corresponding to curves E1 , E2 and E3 the second substrate is made of the material FR4.

It can be seen that from the antennas according to the invention the antennas like the ones in Figs. 3 and 8 are best from the viewpoint of the efficiency. Their efficiency is on average about 0.67 in the range 1920-2170 MHz of the WCDMA system. The efficiency of the former antenna is about 0.52 and of the latter one about 0.65 in the lower operating band. The efficiency of the prototypes according to Figs. 2 and 4 is on average about 0.45 in the lower operating band and on average about 0.38 in the upper operating band. The efficiency of the corresponding known dielectric antenna (curve E4) is on average about 0.36 in the lower operating band and on average about 0.19 in the upper operating band. The efficiency of the air-insulated reference antenna is on average about 0.22 in the lower operating band and on average about 0.3 in the upper operating band. Thus the solution according to the invention improves distinctly the performance of the dielectric antenna. Also the air-insulated reference antenna remains clearly poorer in the lower operating band than the antennas according to the invention, corresponding to Figs. 2 and 4, although its volume corresponding to the dimensions mentioned above is over six-fold. Concerning the efficiency, an air- insulated antenna equalling the antenna according to the invention would then be even bigger.

In this description and claims, the 'end' of an object means its part which borders on its head surface and is relatively short compared to the length of the object.

The qualifiers "lower", "upper", "horizontal" and "vertical" and the epithets "under",

"below", "from below" and "on" refer in this description and claims to the position of an antenna component, in which the plate formed by the second substrate is horizontal and the chip substrate is located on its upper surface. Naturally, the use position of the antenna may be whichever.

The dielectric monopole antenna according to the invention has been described above. The details of the way it is implemented may naturally vary from the shown ones. For example, the shape of the conductive pattern of the radiator and the shape of the chip substrate may vary. The first portion of the radiating conductor can branch also in the other structures than the one according to Fig. 3. The air- insulated radiating conductor may also be, for example, a rigid strip conductor instead of the cylindrical wire shown in Figs. 10-12. The inventive idea may be applied in different ways within the limits set by the independent claim 1.

Claims

1. A dielectric antenna of a radio device, which antenna has a lower and upper operating band and comprises a chip substrate (220; 320; 420; 520; 620; 720; 820; 920; A20; B20; C20) with a first and second end, and a radiating element on a surface of the chip substrate, and a feed point (FP) to be connected to a feed conductor (FC) of the antenna, the ground plane (GND) of the antenna being at a certain distance from the chip substrate, characterised in that a radiating conductor (210; 310; 410; 510; 610; 710; 810; 910; A10) of the antenna comprises a first part (211 ; 311 ; 411 ; 511 ; 611 ; 711 ; 811 ; 911 ; A11 ; B11 ; C11) alongside the chip substrate, the permittivity of a material surrounding it being substantially lower than that of the chip substrate, in which case said radiating element (212, 213; 312; 412, 413; 512, 513; 612; 712, 713; 812, 813, 814; 912, 913; A12, A13) on the surface of the chip substrate is a second part of the radiating conductor.

2. An antenna according to claim 1 , characterised in that , said feed point (FP) is located at starting end of the first part (211 ; 311 ; 411 ; 511 ; 911 ; A11) of the radiating conductor on the side of the first end of the chip substrate (220; 320; 420; 520; 920; A20), and a tail end of the first part is connected to the second part of the radiating conductor on the chip substrate at its second end.

3. An antenna according to claim 1 , characterised in that , said feed point (FP) is connected to the second part (612; 712, 713; 812, 813, 814) of the radiating conductor at the second end of the chip substrate (620; 720; 820), and the second part of the radiating conductor is connected to the end of the first part of the radiating conductor on the chip substrate at its first end.

4. An antenna according to claim 1 , characterised in that it further comprises a second substrate (230; 330; 430; 530; 630; 730; 830; 930), the permittivity of which is substantially lower than that of the chip substrate, and onto which second substrate the chip substrate is fastened from its lower surface, the first part (211 ; 311 ; 411 ; 511 ; 611 ; 711 ; 811 ; 911 ) of the radiating conductor being located on a surface of the second substrate, in which case said material surrounding the first part of the radiating conductor is substantially of the material of the second substrate.

5. An antenna according to claim 4, characterised in that the second substrate (230; 330; 830) belongs to a dielectric body of a circuit board (PCB) of the radio device.

6. An antenna according to claim 4, characterised in that the second substrate (430; 530; 630; 730; 930) forms a separate small auxiliary plate, onto which the chip substrate (420; 520; 620; 720; 920) is fastened.

7. An antenna according to claim 1 , characterised in that the first part (A11 ; B11 ; C11) of the radiating conductor is a rigid conductor, a starting end of which is located against a head surface on the side of the first end of the chip substrate (A20; B20; C20) and the tail end against a head surface on the side of the second end of the chip substrate, and the portion between the starting end and the tail end is adjacent to a side surface of the chip substrate so that said material surrounding the first part of the radiating conductor is substantially air.

8. An antenna according to claim 7, characterised in that at least one of the starting and tail end of the first part (B11 ) of the radiating conductor is located in a trough formed by a head surface of the chip substrate (B20) to support the fastening of the first part of the radiating conductor.

9. An antenna according to claim 7, characterised in that at least one of the starting and tail end of the first part (C11) of the radiating conductor extends to a hole at an end of the chip substrate (C20), the cross-section of which hole has the same shape as the cross-section of an end of the first part of the radiating conductor to support the fastening of the first part.

10. An antenna according to claim 2, characterised in that its lower operating band is based on the resonance of the whole radiating conductor (210; 310; 410; 510; 910; A10), and at least a portion (212; 312; 412; 512; 912; A12) of the second part of the radiating conductor is a continuation of the first part (211 ; 311 ; 411 ; 511 ; 911 ; A11 ) of the radiating conductor adjacent to it so that the upper operating band is based on the resonance of a slot between these adjacent parts of the radiating conductor.

11. An antenna according to claim 10, in which the chip substrate (220; 420; 520; A20) is an elongated piece, characterised in that the second part of the radiating conductor comprises a first portion (212; 412; 512; A12) starting from a connection point of the first part (211 ; 411 ; 511 ; A11 ) of the radiating conductor and extending on the surface of the chip substrate to its first end and a second portion (213; 313; 513; A13) as a continuation of the first portion adjacent to it on an upper surface of the chip substrate extending to its second end, in which case said slot, on which the upper operating band is based, is a slot between the first part and the first portion (212; 412; 512; A12) of the second part of the radiating conductor.

12. An antenna according to claim 11 , characterised in that the first portion (212; 412; A12) of the second part of the radiating conductor is located at least almost entirely on the upper surface of the chip substrate (220; 420; A20).

13. An antenna according to claim 11 , characterised in that the first portion (512) of the second part of the radiating conductor is located at least almost entirely on one side surface of the chip substrate (520).

14. An antenna according to claim 10, in which the chip substrate (320) is an elongated piece, characterised in that the second part (312) of the radiating conductor starts from a connection point of the first part (311) of the radiating conductor and extends on an upper surface of the chip substrate to its first end, in which case said slot, on which the upper operating band is based, is a slot between the first (311 ) and second (312) part of the radiating conductor.

15. An antenna according to claim 10, characterised in that to increase the electric size of said slot corresponding to the upper operating band the first part (311) of the radiating conductor branches in two at its starting end so that a tail end of a first branch (B1) of the first part is said tail end of the first part connected to the second part (312) of the radiating conductor, and a second branch (B2) of the first part is located between the first branch and the chip substrate.

16. An antenna according to claim 3, characterised in that its lower operating band is based on the resonance of the whole radiating conductor (610; 710; 810), and at least a portion (612; 712; 812; 814) of the second part of the radiating conductor is located adjacent to the first part (611 ; 711 ; 811) so that a slot between these adjacent parts of the radiating conductor has a resonance, to which the upper operating band is based at least partly.

17. An antenna according to claim 16, characterised in that the second part (612) of the radiating conductor is a substantially united strip, in which case the upper operating band is wholly based on the resonance of said slot.

18. An antenna according to claim 16, characterised in that the second part of the radiating conductor comprises, seen from the feed point (FP), a first (712) and second (713) branch, which first branch is nearer the first part (711) of the radiating conductor and is connected to an end of the first part at the first end of the chip substrate (720), and the second branch (713) travels adjacent to the first branch and is arranged to resonate in the upper operating band, in which case the upper operating band is based on both the resonance of the slot between the first branch (712) and the first part (711) of the radiating conductor and the resonance of the second branch (713).

19. An antenna according to claim 16, characterised in that the second part of the radiating conductor comprises a first portion (812) which extends, starting from the feed point (FP), from the second to first end of the chip substrate (820) and is there connected to the first part (811) of the radiating conductor and a second portion (813), which travels adjacent to the first portion as its continuation extending from the first to second end of the chip substrate and is there connected to signal ground (GND), the antenna then being of IFA type, a slot between the first and second portion is arranged to resonate in the upper operating band, in which case the upper operating band is based both on the resonance of a slot between the first part (811) and the first portion (812) of the second part of the radiating conductor and the resonance of the slot between the first (812) and second (813) portion.

20. An antenna according to claim 19, characterised in that the second part of the radiating conductor further comprises a conductor strip (814), which branches from the first portion (812) at the second end of the chip substrate (820) and is located between the first portion and the first part of the radiating conductor, to increase the electric size of the slot between the first part (811) and the first portion (812) of the second part of the radiating conductor and to tune the resonance frequency of that slot.

21. An antenna according to claim 4, characterised in that the connection point of the first part (211 ; 311 ; 511 ; 811) and the second part (212, 213; 312; 512, 513; 812, 813, 814) of the radiating conductor is located on the lower surface of the chip substrate (220; 320; 520; 820), and the the second part rises from the connection point to an upper surface of the chip substrate through its side surface.

22. An antenna according to claim 4, characterised in that the connection point of the first part (411 ; 611 ; 711) and the second part (412, 413; 612; 712, 713) of the radiating conductor is located on the lower surface of the chip substrate (420; 620; 720), and the second part rises from the connection point to an upper surface of the chip substrate through its head surface.

23. An antenna according to claim 1 , characterised in that the chip substrate is ceramic.

24. An antenna according to claim 1 , characterised in that it further comprises a matching component (250; 350; 450; 550; 650; 750; 850; A50) connected between the feed point (FP) and the ground plane (GND).