The invention relates to an antenna component suited for small-sized radio de¬ vices for forming a dielectric antenna.

In small-sized radio devices, such as mobile phones, the antenna must also be small. For reducing the size of the antenna, already for a long time, the whip of a monopole antenna has been replaced by a coil-like helix conductor or arranged in bends to form a meander pattern, for example. However, for comfort of use, the antenna is by choice placed inside the cover of the device. Internal antennas usu¬ ally have a planar structure, in which case they include a radiating plane and a ground plane at a certain distance therefrom. The space taken by the planar an¬ tenna depends on the size of the radiator and its distance from the ground plane. In order to reduce the size of the antenna, this distance can be made very small, but a harmful result of this is the deterioration of the electric characteristics of the antenna. The electric size of the radiator is determined by the operating frequency of the antenna. When the premise is an air-insulated antenna, favorable efficiency- wise, the physical size of the radiator and the size of the whole antenna as well can be reduced by a dielectric substrate. This means that there is a substantially lot of material with relatively high dielectricity between the radiator and the ground plane. The smaller size is achieved at the cost of increased losses of the antenna, but the increase can be kept reasonable by the choosing of materials.

In this description and the claims, an antenna which has a conductor radiator with a dielectric substrate as described above is called a "dielectric antenna". Numer¬ ous of dielectric antennas with somewhat different structures are known. An ex- ample of a dielectric antenna according to Fig. 1 is known from the publication EP 0766 340. It includes a circuit board 105 of a radio device, where a part of the up¬ per surface of the circuit board belongs to the conductive ground plane GND. On the circuit board there is a rectangular dielectric piece 121 , which functions as the substrate of the radiator. The radiator and its feed and short-circuit have been im- plemented by coating the substrate 121 with conductive material. The radiator 122 is a strip running across the upper surface of the substrate in its longitudinal direc¬ tion. The feed conductor of the radiator is formed of a first portion 110 on the sur¬ face of the circuit board 105, a second portion 123 on the end surface of the sub¬ strate and a third portion 124 on the upper surface of the substrate. The third por- tion joins to the radiator at a radiator intermediate point. The head end of the radia¬ tor 122 is connected to the ground GND through the short-circuit conductor 125 on

the above mentioned end surface of the substrate. At its tail end, the radiator can continue to the second end surface of the substrate, not visible in Fig. 2, and ex¬ tend on it close to the ground on the circuit board 105 for further reducing the size of the antenna. The substrate 121 with its conductive coating forms a unitary an- tenna component 120, which, as connected to the circuit board, together with it constitutes the whole antenna.

The impedance of the antenna according to Fig. 1 is matched by means of a short- circuit conductor 120 and by choosing the joining point of the feed conductor to the radiator. However, the matching can be unsatisfactory in a part of the operating band of the antenna, in which case it is necessary to use separate matching com¬ ponents, in addition, in the feed circuit of the antenna. An area 150 on the circuit board 105, on which matching components can be connected, is drawn with a dot¬ ted line in Fig. 1. Discrete matching components increase the production costs of the antenna. In addition, the reproducibility of the antenna unit is poor because of the tolerances of the component values. This results in a need to tune the an¬ tenna, which again has its own practical difficulties.

An object of the invention is to reduce the above mentioned drawbacks of the prior art. An antenna component according to the invention is characterized in what is set forth in the independent claim 1. Some preferred embodiments of the invention are set forth in the other claims.

The basic idea of the invention is the following: A small auxiliary circuit board is used for the matching of a dielectric antenna, in which case the matching is based on a conductor pattern on it. A substrate chip, on the surface of which the radiator is located, and the auxiliary board are fastened to each other, whereby the radiator is electrically connected to said conductor pattern. The radiator, its substrate and the auxiliary board form a unitary, solid antenna component, which is mounted on the circuit board of the radio device.

The invention has the advantage that almost the entire antenna with its feed and matching circuits can be designed and tested as a whole of its own. This results in good reproducibility and better performance of the antenna compared to the situa¬ tion that parts of the antenna structure would be on the circuit board of the radio device. In addition, the invention has the advantage that the design of the circuit board of the radio device is simplified, because the antenna matching need not be taken into account in it. What is required is only to reserve a space for the antenna component on the board and to provide contact surfaces on the board for connect-

ing the antenna component. Furthermore, the invention has the advantage that possible later changes in the antenna are relatively simple and cheap, because the main circuit board of the radio device need not be renewed. A further advan¬ tage of the invention is that the auxiliary circuit board of the antenna component can also function as an integration base for possible additional components having an effect on the operation of the antenna. In addition, the invention has the advan¬ tage that the antenna is small as compared e.g. to an air-insulated planar antenna operating in the same frequency range.

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 dielectric antenna,

Fig. 2 is a general, schematic drawing of an antenna component according to the invention,

Fig. 3a shows an example of an auxiliary board belonging to an antenna com- ponent according to the invention,

Fig. 3b presents an example of a radiating piece that fits the auxiliary board in Fig. 3a,

Fig. 4 shows another example of an auxiliary board belonging to an antenna component according to the invention, Fig. 5 presents another example of an antenna component according to the invention, and

Fig. 6 presents a third example of an antenna component according to the invention.

Fig. 2 is a schematic drawing of the principle of the antenna component according to the invention and of the circuit board of the radio device, on which circuit board the antenna component is intended to be mounted. The antenna component 200 is shown in the drawing above its mounting place. The antenna component has two main parts: an auxiliary board 210 and a radiation piece 220. The auxiliary board is a small circuit board, which is primarily for the matching of the antenna. The antenna conductors belonging to the auxiliary board form a conductor pattern, which is advantageous with regard to the matching. The antenna conductors can be on the surface of or inside the board. In the latter case, the auxiliary board is a multilayer board, which again can be based on ordinary circuit board material or it

can be a ceramic board manufactured by the LTCC (Low Temperature Co-fired Ceramic) technique. The radiation piece comprises a dielectric chip and a conduc¬ tor radiator on its surface. The dielectric chip, which in this drawing is elongated and rectangular, functions as a substrate for the radiator, increasing its electric size. The dielectric chip is made of some ceramic material, for example. The radia¬ tor is not shown in Fig. 2. The radiation piece 220 has been fastened to the auxil¬ iary board 210 from one long side by soldering, for example, and therefore they form a unitary, solid antenna component. For soldering, there are conductor pads aligned to each other on the surfaces facing each other. The fastening can be strengthened by some adhesive material, when required. Fastening can also be carried out by laminating, in which case the ceramic radiation piece is pressed against the auxiliary board at a high temperature, until they have become glued to each other.

On the upper surface of the circuit board PWB of the radio device, there is seen the signal ground GND, the edge of which is at a certain distance from the an¬ tenna component when it is mounted. As extension of the signal ground, there are two parallel conductor strips GC1 and GC2 in Fig. 2, between which strips there is a conductor strip FC belonging to the antenna feed conductor. These three con¬ ductor strips extend below the antenna component for connecting the antenna component to the radio device. The connecting can take place by soldering, for example, whereby the solder joints also serve to fasten the antenna component to the circuit board PWB. In addition, there can be conductor strips on the circuit board merely for fastening the antenna component, such as the conductor pads FP1 and FP2 in Fig. 2. In that case, there are similar conductor pads on the lower surface of the antenna component, of course.

Fig. 3a shows an example of an auxiliary board belonging to an antenna compo¬ nent according to the invention as seen from above. The auxiliary board 310 cor¬ responding to the auxiliary board 210 in Fig. 2 comprises a relatively thin rectangu- lar dielectric board 311 with two conductor pads and three parallel conductor strips on its upper surface. The conductor pads 318 and 319 are for soldering the radia¬ tion piece on. The middle one of the conductor strips is the antenna feed conduc¬ tor 312. On each side of it there is a ground conductor, the first ground conductor 313 and the second ground conductor 314. In the complete antenna, the feed conductor 312 is connected through the via of the auxiliary board to the extension FC of the feed conductor on the main circuit board PWB of the radio device, using the denotation of Fig. 2. Correspondingly, the first ground conductor 313 is con-

nected to the ground strip GC1 of the circuit board PWB, and the second ground conductor 314 to the second ground strip GC2.

Together with the board 311 , the strip conductors on the auxiliary board form the antenna feed line. The impedance of the feed line is determined by how the widths, mutual distances and the material of the board 311 have been chosen. The matching of the antenna again depends on the impedance of the feed line, and also on its length. In the example of Fig. 3a, the parallel conductors of the feed line start from one long side of the auxiliary board close to one end of the board, run in the direction of the long side, turn close to the opposite end of the board to the direction of that end and extend close to the opposite long side of the board. The whole conductor pattern has been designed to realize good impedance matching when the feed line is at its tail end connected to a radiator of a certain kind, shown in Fig. 3b. So the feed line functions as the antenna matching circuit, at the same time. In Fig. 3a, an area A, to which the radiation piece according to the invention is fastened at its bottom, is marked with a broken line on the board 311. The tail ends of the conductors of the feed line run across the area A at its one end, and they also serve the fastening of the radiation piece when it is sol¬ dered in place. The above mentioned conductor pads 318 and 319 are at the op- posite end of the area A.

The auxiliary board 311 of the example is a single layer board. When a multilayer board is used, one ground conductor can be placed above the feed conductor and one below it. In addition, there can be ground conductors on the level of the feed conductor. This increases the possibilities of finding a good matching and makes the feed line of the antenna better shielded against external interferences.

Fig. 3b shows an example of a radiation piece belonging to the antenna compo¬ nent according to the invention, suitable for the auxiliary board shown in Fig. 3a. The radiation piece 320 comprises a planar radiator 322 and its substrate 321. The substrate is a dielectric chip shaped like a rectangular prism, the length of which is I, height h and thickness t. Of these, the length dimension is clearly the highest in this example. The radiation piece is placed against the auxiliary board of the antenna component from its bottom, which is one of the sides with the length I and width t. In this example, the radiator 322 covers the most part of one of the sides of the substrate with the length I and width h. The plane of the radiator is thus vertical, when the bottom is horizontal. In addition, the radiator can reach to

some extent onto the upper surface or the end surface of the substrate in order to shape the radiation pattern.

The radiation piece 320 further comprises radiator connection strips. These in¬ clude a first 323 and a second 324 connection strip. The second connection strip 324 is at one end of the bottom of the radiation piece in the direction of the end and continues to the side where the radiator is located, joining the radiator proper at the upper part of the end of the side in question. The first connection strip 323 is beside the second connection strip in the direction of the end of the bottom of the radiation piece and continues to the side where the radiator is located, joining the radiator proper there. When the radiation piece is placed on the auxiliary board 310 according to Fig. 3a at the area A so that the radiator 322 comes to the oppo¬ site vertical surface of the piece as viewed from the feed line, the tail end of the feed conductor 312 of the feed line is connected to the first connection strip 323 and the first ground conductor 313 of the feed line is connected to the second connection strip 323. One end of the elongated radiator thus becomes connected to the ground, and the feed point of the radiator is close to that end. On the bottom of the radiation piece, at the opposite end as viewed from the connection strips 323 and 324, there are two conductor pads 328 and 329 for fastening the radiation piece. They are aligned at the conductor pads 318 and 319 of the auxiliary board, seen in Fig. 3a, when the radiation piece is set in place.

In this description and the claims, the "front surface" of the radiation piece means its surface on which the radiator is according to the above, i.e. the one of the verti¬ cal sides of the radiation piece that is furthest from the feed point of the antenna component. The qualifiers "upper" and "lower" refer to the position of the antenna component, in which the auxiliary board is horizontal.

Fig. 4 shows another example of an auxiliary board belonging to the antenna component according to the invention as seen from above. The auxiliary board 410 has a similar feed and matching arrangement as in the board 310 shown in Fig. 3a. The difference compared to Fig. 3 is that there is an additional component 417 and its wiring on the auxiliary board 410. This wiring comprises a strip 415 for controlling the additional component, a strip connecting the additional component to the second ground conductor 414 of the auxiliary board, and a conductor strip 416 extending from the additional component below the radiation piece in the complete antenna component. From the conductor strip 416, there is a galvanic or electromagnetic coupling to some point of the radiator. The additional component

can be a switch, for example, in which case changing its state shifts the operating band of the antenna, for example.

Fig. 5 shows another example of an antenna component according to the inven¬ tion. The radiator 522 is now on the upper surface of the radiation piece, and on the auxiliary board 510 of the antenna component there is under the radiation piece a conductor plane 519 connected to the signal ground. The feed conductor 523 and also to a conductor 524 connecting the radiator to the conductor plane 519 join the radiator the whole antenna thus being of the PIFA type. The radiator has been shaped so that the antenna has two bands. There is also a conductor pattern 518 on the auxiliary board, which improves the matching of the antenna.

Fig. 6 shows a third example of an antenna component according to the invention. On the auxiliary board 610 of the antenna component 600 there are now two ra¬ diation pieces, the first 620 and the second 630 radiation piece. These are located at the opposite ends of the auxiliary board. The antenna feed line is divided on the auxiliary board so that one branch leads to the first and another branch to the sec¬ ond radiation piece. The radiator 622 of the first radiation piece is largely on the front surface of the dielectric substrate, also extending to its outer side surface, as viewed from the centre of the auxiliary board, and to its upper surface. The radia¬ tor 632 of the second radiation piece is located symmetrically in respect of the first radiator 622.

In the above case, the resonance frequencies of the radiators are the same. When there are two or more radiation pieces, the radiators can also be tuned to different frequencies to widen the band or to form separate operating bands. In the latter case it helps if the dielectricities of the substrates of the radiators are selected suitably different.

An antenna component according to the invention has been described above. The details of its implementation can naturally differ from those presented. The shape of the conductor pattern of the radiator as well as the shape of the conductor pat¬ tern for the matching of the antenna can vary greatly. The inventive idea can be applied in different ways within the scope set by the independent claim 1.