EP1204160B1 - Multiband microwave antenna - Google Patents

Description

The invention relates to a microwave antenna with a substrate having at least one resonant conductor track structure, in particular for mobile dual or multi-band telecommunication devices such as mobile and cordless telephones, as well as for devices that communicate according to the Bluetooth standard. The invention further relates to a circuit board with such an antenna and a telecommunication device with such an antenna.

In mobile telecommunications, microwave electromagnetic waves are used to transmit information. In the field of cellular systems, only the GSM mobile phone standard is used in Europe exclusively and worldwide. Within this GSM standard there are several frequency bands in which the communication can take place: On the one hand from 880-960 MHz (so-called GSM900) as well as from 1710-1880 MHz (so-called GSM1800 or DCS). A third band, which is used predominantly in the USA, uses the frequencies from 1850 to 1990 MHz (GSM1900 or PCS).

Usually, a network operator offers its services in only one of these frequency bands. However, in order to ensure a high degree of accessibility and to be able to use the mobile phones universally at any location, regardless of the prevailing conditions and the networks operated there, mobile phones are increasingly being designed so that they can work in several frequency bands. These mobile phones are also referred to as dual or multi-band mobile phones. However, this presupposes that the antenna of such a mobile phone is capable of correspondingly transmitting and receiving electromagnetic waves in both or more frequency bands.

As another standard, the so-called Bluetooth standard (BT) has emerged recently, for which the frequency range of 2.4 to 2.48 GHz is provided and which serves to data between, for example, mobile phones and other electronic devices such as Computers, other mobile phones, etc. to exchange.

Furthermore, a strong trend towards miniaturization of the devices can be seen on the market. This results in the desire to downsize the components for mobile communication, that is, the electronic components as well. However, the types of antennas currently used in mobile phones, which are mostly wire antennas, have significant disadvantages in this respect since they are relatively large. They protrude from the cell phones, can break easily, may result in unwanted eye contact with the user, and are also an aesthetic design in the way. Increasingly, an undesirable microwave irradiation of the user of mobile phones is discussed in the public. With wire antennas protruding from the mobile phone, much of the radiated power emitted can be absorbed in the user's head.

In general, in the technical realization of modern digital electronic devices, surface mounting (SMD), that is, the flat soldering of electronic components to a printed circuit board (PCB), has been implemented by means of a wave soldering bath or a reflow process. However, the antennas used so far elude this assembly technique, since they can often be attached only by means of special brackets on the board of the mobile phone and the supply of electromagnetic power is only possible via special Zuführungshalterungen such as pens or the like. This causes unwanted assembly steps, quality problems and additional costs in production.

It is attempted to take into account these very different requirements and problems with the best possible antenna design. It should be noted that in particular the structure of the antenna is more than any other RF components of the desired frequency range and the application of the relevant electronic device is dependent, since the antenna is a resonant component, which on the respective Operating frequency range must be tuned. In general, ordinary wire antennas are used to send and receive the desired information. In order to obtain good radiation and reception conditions for this type of antenna, certain physical lengths are absolutely necessary. So-called λ / 2-Dipolantennen (λ = wavelength of the signal in free space) have proven to be particularly advantageous in this context, in which the antenna consists of two each λ / 4 long wires, which are rotated by 180 degrees from each other. However, since these dipole antennas are too large for many applications, in particular for mobile telecommunications (for example, for the GSM900 range, the wavelength is about 32 cm), alternative antenna structures are used. A widely used antenna, in particular for the field of mobile telecommunications, is the so-called λ / 4 monopole, which consists of a wire with the length λ / 4. The radiation behavior of this antenna is acceptable with a reasonable physical length (about 8 cm for GSM900). This type of antenna is also characterized by a high impedance and radiation bandwidth, so that it also applies to systems that require a relatively large bandwidth, such as mobile radio systems. To achieve optimum 50 ohm power matching, this type of antenna uses passive electrical matching (as with most λ / 2 dipoles). This usually consists of a combination of at least one coil and a capacitor which, with suitable dimensioning, adapts the input impedance, which is different from 50 Ohm, to the upstream 50 Ohm components.

A further possibility is to bring about miniaturization of this antenna by using a medium having a dielectric constant ε _r > 1, since the wavelength in such a medium becomes smaller by a factor of 1 / ⊆ε _r .

An antenna of this type comprises a solid block (substrate) of dielectric material. On this block a metallic trace is printed. This trace can emit energy in the form of electromagnetic waves upon reaching an electromagnetic resonance. The values of the resonance frequencies depend on the dimensions of the printed circuit traces and the value of the dielectric constant of the block. The values of the individual resonant frequencies decrease with increasing conductor length and with increasing values of the dielectric constant. Consequently, in order to achieve a high degree of miniaturization of the antenna, one will select a material with a high dielectric constant and select the mode with the lowest frequency from the resonance spectrum. This mode is referred to as the fundamental mode, the next highest mode in terms of resonance frequency as the first harmonic. Such an antenna is also referred to as a printed wire antenna. The bandwidth of such a known antenna is sufficient only at resonant frequencies within the range of the GSM standard to achieve full coverage of one of the frequency bands of the GSM standard. The aforementioned dual or multi-band applications are therefore not possible.

A multi-band application with an antenna suitable for surface mounting (SMD technology) is described in EP 1 146 590 A2. This antenna has both elements that are connected to an electromagnetic power supply and elements that are not supplied with electromagnetic power. Both elements are spaced apart from each other on a surface of the antenna and each consist of branched individual elements. The elements not connected to the feeder form two electrodes. Another electrode is formed by the elements connected to the feeder. Due to the three electrodes, the antenna can be adapted to several frequency bands. Furthermore, the resonance wave of the three electrodes can be independently controlled.

In WO 99/03168 a microstrip antenna is described. This antenna is incorporated in a mobile communication device to receive and transmit radio frequency signal in one or more frequency bands. The antenna consists of a flat, rectangular material with feeding means for electromagnetic Power and N radiating elements, where N is an integer greater than zero. Furthermore, the antenna has on its surface a first, conductive surface. The first, conductive surface is connected to the supply means, so that a high-frequency signal is conducted to the radiating elements. One of the N radiating elements is formed as a second, conductive surface, which is inductively coupled to the first conductive surface.

An object of the invention is therefore to provide a suitable for said dual or multi-band applications microwave antenna having the smallest possible dimensions.

Furthermore, a microwave antenna is to be created, which can be applied for surface mounting (SMD technique) by flat soldering and contacting with the tracks - possibly together with other components of the circuit board - without additional supports (Sifte) for supplying the electromagnetic power required are.

The invention is also based on the object of providing a microwave antenna whose resonant frequencies can be adjusted individually and without a change to the basic antenna design such that they can be tuned to a specific installation situation.

Finally, a microwave antenna is also to be created in which the input impedance can also be adapted individually to a specific installation situation.

To achieve these objects, there is provided a microwave antenna comprising a substrate having at least a first resonant wiring pattern and a plurality of wiring sections substantially meandering on a first end face of the substrate and a second wiring pattern, the substrate being substantially parallelepiped, and the first wiring pattern forming first and second line sections on the first end face of the substrate and the second line section along at least part of its length is formed by a first, substantially rectangular metallic surface, the two line sections spaced a distance equal to the frequency spacing between the first resonant frequency of the fundamental mode and the second resonant frequency at the first harmonic of the fundamental mode determines the second conductive pattern intended for operating the antenna in a third frequency band and a third Le itungsabschnitt and a third, substantially rectangular metallic surface is formed on the first end face of the substrate.
The microwave antenna is characterized according to claim 1 by a supply to the second end face of the substrate and a along the circumference at least one of the first, second and third side surface of the substrate extending supply line for feeding the first and second conductor structure.
A particular advantage of this solution is that the frequency of the fundamental mode can be adjusted by the total length of the interconnect structure, and the frequency spacing between the fundamental mode and the first harmonic by the said distance so that the antenna is a dual-band antenna in GSM900 and GSM1800. Operate the band.

The subclaims have advantageous developments of the invention to the content, These are characterized by the fact that the frequency spacing can be adjusted even better and a surface mounting of the antenna together with other components on a printed circuit board is possible, so that the production can be significantly simplified and accelerated ,

In addition, an independent adjustment of the frequency of the fundamental mode or the first harmonic can be made, without thereby appreciably affecting the other of these two frequencies.

Another advantage is that the antenna can even be operated in three frequency bands, whereby a supply via a common feed is possible.

With the embodiments according to claims 2 and 3, a vote of the individual resonance frequencies of this three-band antenna can be made.

Fig. 1

eine schematische Darstellung eines Beispiels einer ersten Antenne;

Fig. 2

ein an der Antenne gemessenes Reflektionsdiagramm;

Fig. 3

eine schematische Darstellung eines Beispiels einer zweiten Antenne;

Fig. 4

eine Darstellung des Beispiels einer zweiten Antenne auf einer Schaltungsplatine;

Fig. 5

eine schematische Darstellung einer erfindungsgemäßen Antenne auf einer Schaltungsplatine; und

Fig. 6

ein an der erfindungsgemäßen Antenne gemessenes Reflektionsdiagramm.

Further details, features and advantages of the invention will become apparent from the following description of preferred embodiments with reference to the drawing. It shows:

Fig. 1

a schematic representation of an example of a first antenna;

Fig. 2

a reflection diagram measured on the antenna;

Fig. 3

a schematic representation of an example of a second antenna;

Fig. 4

a representation of the example of a second antenna on a circuit board;

Fig. 5

a schematic representation of an antenna according to the invention on a circuit board; and

Fig. 6

a measured at the antenna according to the invention reflection diagram.

The antennas described are of their basic type so-called "printed wire antennas" in which a conductor track is applied to a substrate. In principle, these antennas are thus wire antennas which, in contrast to microstrip line antennas, do not have a metallic surface forming a reference potential on the rear side of the substrate.

The examples and embodiments described below comprise a substrate of a substantially block-shaped block whose height is smaller by a factor of 3 to 10 than its length or width. On the basis of this, in the following description, the upper and lower (large) surfaces of the substrates in the representations of the figures are to be referred to as first upper and second lower end surfaces, respectively, and the surfaces perpendicular thereto as first to fourth side surfaces.

Alternatively, however, it is also possible, instead of a cuboid substrate, to select other geometric shapes, such as, for example, a cylindrical shape, to which a corresponding resonant strip conductor structure having, for example, a spiral shape is applied.

The substrates can be produced by embedding a ceramic powder in a polymer matrix and have a dielectric constant of ε _r > 1 and / or a permeability of μ _r > 1.

In detail, the example of a first antenna according to FIG. 1 comprises a substrate 1, on the surface of which a first printed conductor structure 31 - 39 is applied, which is fed via a feed 40. At a lower end surface of the substrate are solder pads 21 to 25, which are also referred to as footprints and with which the substrate 1 by surface mounting (SMD) can be soldered onto a circuit board (PCB).

The printed conductor structure is formed by a plurality of individual printed on the substrate line sections. In detail, these are a first and a second section 31, 32, which extend substantially parallel and along the length of the upper end face of the substrate 1, wherein the second section 32 merges into a rectangular metallic surface 39.

A third section 33, which likewise extends in the longitudinal direction of the substrate 1, is considerably shorter in comparison. The first and second sections 31, 32, as well as the second and third sections 32, 33 are connected at their longitudinal ends, each with a fourth or fifth section 34, 35 extending in the direction of the width of the substrate 1, so that a meandering History of these sections 31 to 35 results.

On the right in the figure 1 (first) side surface 11 of the substrate 1 extends a sixth line section 36 which establishes a connection between the third section 33 and a seventh section 37 adjoining the lower end face of the substrate in its longitudinal direction. This seventh section 37 extends substantially parallel to the first and second line sections 31, 32 in the direction of in the 1 front (second) side surface 12 of the substrate and has a length which substantially corresponds to the length of the third portion 33 which lies in perpendicular projection over it on the upper end face of the substrate 1. The seventh section 37 is adjoined by an eighth section 38 extending in the direction of the width of the substrate, which merges into the feeder 40 in the form of a metallization plate.

Via the feed 40 located on the lower end face of the substrate 1, electromagnetic energy is coupled into the antenna. For this purpose, the lead in the surface mounting is soldered to a corresponding conductor on the circuit board (Figures 4 and 5). The feed or coupling does not necessarily have to lie on the second side surface 12 of the substrate 1.

The feeder 40 merges at the second side surface 12 into a first line segment 41, which will be explained later.

The resonance frequencies of this antenna can be adjusted in a known manner over the entire length of the printed conductor structure. For the application of this embodiment z. In a dual-mode mobile phone, the lowest resonant frequency, i. the fundamental mode is set to coincide with the lower of the two frequencies at which the antenna is to be operated. The next higher resonance frequency, ie the first harmonic, must then be such that it coincides with the higher operating frequency. This means that the frequency spacing of the first harmonic to the fundamental mode must be set according to the distance of the two operating frequencies, wherein the frequency of the fundamental mode must remain substantially unchanged.

This can be achieved by two independent measures.

On the one hand, the distance of the first harmonic from the fundamental mode can be changed by changing the distance between the first and second line sections 31, 32. For this purpose, the lengths of the fourth and fifth line sections 34, 35 enlarged or reduced accordingly. Alternatively, it is also possible to increase this distance, in particular with built-in antenna by laser trimming by one or both line sections 31, 32 are partially removed along their opposite edges with a laser beam.

On the other hand, this frequency shift can also be adjusted by changing the length of the seventh line section 37 on the lower end face of the substrate 1.

Qualitatively, the frequency spacing decreases with a reduction of the distance between the first and the second line section 31, 32 and by shortening the length of the seventh line section 37.

In one possible implementation of this first antenna, the dimensions of the substrate 1 are approximately 17 × 11 × 2.0 mm ³ . The material chosen for the substrate 1 has a relative permittivity ε _r = 18.55 and a tanδ = 1.17 × 10 ^-4 . This corresponds approximately to the HF properties of a commercial NP0-K17 ceramic (Ca _0.05 Mg _0.95 TiO ₃ ceramic). The printed circuit trace was made using silver paste and has a total length of about 55.61 mm. The width of the line sections is about 0.75 mm, while the dimensions of the rectangular metallic surface 39 at the end of the second line section 32 are about 11.0 × 4.5 mm ² .

At a length of the seventh line portion 37 of, for example, 6.25 mm, the frequency spacing of the first harmonic from the fundamental mode is about 820 MHz. With a length of this line section 37 of 5.75 mm results in a distance of 873 MHz.

With a length of the fourth line section 34 and thus with a distance between the first and second line sections 31, 32 of 3.0 mm, said frequency spacing is 900 MHz, while with a length of the fourth line section 34 of 2.5 mm a frequency spacing of 878 MHz. Such an antenna is thus suitable for dual-band operation in the frequency bands GSM900 and GSM1800.

Figure 2 shows the ratio R measured at the feed 40 of this antenna between the power reflected at the antenna and the power supplied to the antenna (reflection coefficient) as a function of the frequency F in MHz. It can be clearly seen that the two resonances lie within the GSM900 and GSM1800 bands and, in addition, the bandwidth is sufficient to operate effectively within both frequency bands.

This example of a first antenna, in addition to the surface mount capability (SMD) inherent in all embodiments, has the significant advantage that the frequency spacing of the first harmonic from the fundamental mode can be desirably adjusted.

FIG. 3 shows an example of a second antenna. In this illustration, the same or corresponding elements and components as in FIG. 1 are designated by the same reference numerals. Reference is made to the description in connection with Figure 1, and only the differences are explained below.

In this example, with the first printed conductor structure according to FIG. 1, in addition to the already mentioned first line segment 41, a second line segment 42 is connected in the form of a stub line which is located on the upper end face of the substrate 1 and extends from the first line section 31 in the direction of the first side face 11 of the substrate extends.

The resonance frequency of the antenna in the fundamental mode can be adjusted by changing the length of the first line segment 41 in the direction of the upper end face of the substrate 1. The frequency of the first harmonic is only slightly influenced by such a setting. Furthermore, by changing the length of the second line segment 42 in the direction of the first side surface 11, the frequency of the first harmonic can be adjusted. This setting in turn affects the frequency in the basic mode only slightly.

The mode of operation of this adjustment of the resonant frequency in the fundamental mode is based on the fact that the electric field strength for the fundamental mode in the region of the first line segment 41 is relatively high, but relatively low for the first harmonic, and the latter thus remains essentially unaffected. An extension of the first line segment 41 thus leads to a strong influence on the resonant frequency of the fundamental mode. The frequency of the first harmonic remains essentially unaffected.

Similarly, the second line segment 42 is configured and arranged to increase or decrease a volume of high electric field intensity at the first harmonic, thereby shifting the harmonic in frequency, with the fundamental mode being substantially unaffected since it is at the relevant point has a low electric field strength.

The main advantage of this example is that the frequencies of the fundamental mode and the first harmonic can be set independently of each other. Furthermore, the modification of the antenna design required for this is only slight, and the antenna is fully functional even without this change. In order to adapt to the specific installation situation, therefore, only the dimensions of the first line segment 41 or the second line segment 42 must be changed, which is relatively easy even when installed, for example by laser trimming, i. Ablation of a part of the relevant segment 41, 42 is possible with a laser beam.

In a realization of this second antenna, the dimensions of the substrate 1 are approximately 17 × 11 × 2.0 mm ³ . The material chosen for the substrate 1 has a relative permittivity ε _r = 21.55 and a tanδ = 1.17 × 10 ^-4 . This corresponds approximately to the high frequency properties of a commercial NP0-K21 ceramic. The printed circuit trace was made using silver paste and has a total length of about 55.61 mm. The width of the line sections is about 0.75 mm, while the dimensions of the rectangular metallic surface 39 at the end of the second line section 32 are about 11.0 × 4.5 mm ² .

With a length of the first line segment 41 of 1.5 mm in the direction of the upper end face of the substrate, the frequency of the fundamental mode is about 928 MHz. Decreasing the length to 0.4 mm results in a frequency of the fundamental mode of 975 MHz. This corresponds to a change of 47 MHz, whereby the frequency of the first harmonic only changes by 9 MHz.
If, by analogy, the length of the second line segment 42 is approximately 0.75 mm, the result is a frequency of the first harmonic of approximately 1828 MHz. If you increase the length to 3.75 mm, this resonance frequency is about 1800 MHz. This corresponds to a change of 28 MHz, whereby the frequency of the fundamental mode shifts by less than 1 MHz.

FIG. 4 schematically illustrates a printed circuit board (PCB) 100 to which the antenna 110 has been applied along with other devices in areas 120 and 130 of the surface mount (SMD) board 100. This is done by shallow soldering in a Wellenlötbad or with a reflow process, whereby the solder pads (footprints) 21 to 25 and the feeder 40 are connected to corresponding solder pads on the board 100. Among other things, this also creates an electrical connection between the feeder 40 and a conductor 111 on the circuit board 100, via which the electromagnetic energy to be radiated is supplied.

FIG. 5 shows an embodiment of the antenna 110 according to the invention, which is shown mounted on a circuit board 100. Again, the same or corresponding elements as in the illustration according to Figure 4 are again denoted by the same reference numerals, so that in this respect can be dispensed with a new description and only the differences are to be explained.
In this embodiment of the invention, in addition to a first printed conductor structure 51, 52, a second printed conductor structure 60, 61 is additionally applied to the substrate 1, which are fed via a common feed 40 and a common feed line 45. The feeder 40 is located in this embodiment on a long first side surface 11 of the substrate 1 and is soldered onto the conductor 111.

To the feeder 40, the feeder pipe 45 is connected, which runs along the circumference of the substrate 1 at the first, second and third side surface 11, 12, 13, until it is at the opposite third side surface 13 at approximately half their length in the direction of extends upper first end face of the substrate and feeds the applied there first metal wiring pattern. This structure comprises a first line section 51 extending in the direction of the first side face 11 and a second line section in the form of a first, substantially rectangular metallic face 52 (patch) connected to its end.

From the feeder 40, a first tuning stub 53 continues, which extends on the first side surface 11 of the substrate 1 in the form of a second, substantially rectangular metallic surface in the direction opposite to the feed line 45 and for tuning the first metallic interconnect structure 50 , 51 is provided on a first operating frequency band. At the end of the feed line 45 is further followed by a second tuning stub 54 running along the third and fourth side surfaces 13, 14 of the substrate for a second operating frequency band.

The feed line 45 feeds via a branch at about half the length of the second side surface 12, the second metallic wiring pattern 60, 61, which is provided for operating the antenna in a third frequency band. This structure comprises a third line section 61 extending in the direction of the fourth side face 14 and a third, substantially rectangular metallic face 62 (patch) connected to the end thereof. If necessary, tuning stubs can also be printed for this second interconnect structure 60, 61, but they are not provided here.

The first trace structure 51, 52 in this embodiment is for tuning and operating the antenna in the GSM900 and GSM1800 bands, while the second trace structure 61, 62 is for operating the antenna in the BT (Bluetooth) band at 2480 MHz.

The position and length of the first metallic surface 52 and of the first line section 51 on the upper end face of the substrate 1 essentially determines the impedance matching to 50 ohms and the position of the resonant frequencies relative to one another. These frequencies are chosen so that (as in the first and second embodiments of the antenna) the fundamental mode lies in the GSM900 band and the first harmonic lies in the GSM1800 band. The tuning of the impedance matching and the two resonance frequencies to the concrete installation situation, which is given for example by the nature of the housing and its influence on the resonance behavior, takes place through the two tuning stubs 53, 54. By shortening these stubs (z. B. by laser trimming), the two resonance frequencies can be shifted to higher values, which at the same time a more critical coupling of the microwave energy can be achieved.

By appropriate positioning and dimensioning of the third metallic surface 62, the resonance frequency of this structure is tuned to the BT band, although other frequency bands (for example, PCS1900 or UMTS) can of course be covered for other applications.

The particular advantage of this embodiment according to the invention, in addition to the possibility of surface mounting, the particularly small dimensions and the other advantages mentioned above is that with this antenna, a three-band operation of a corresponding mobile device is possible.

In one implementation of this embodiment of the antenna according to the invention, the substrate 1 had the dimensions 15 × 10 × 3 mm ³ . The resonant frequencies of this antenna were 943 MHz for the GSM band, 1814 MHz for the GSM 1800 (DCS) band and 2480 MHz for the BT band. The course of the reflection coefficient R over the frequency F shown in FIG. 6 also shows that the bandwidths of the resonances are large enough to be able to operate the antenna in the three bands. Furthermore, it has been found that the same resonant frequencies can also be achieved with a 13 × 10 × 2 mm ³ substrate, thereby achieving a volume reduction of 42.2% relative to the first mentioned substrate.

Claims (6)

1. A microwave antenna with a substrate (1) having at least one, first resonant conductor track structure and a plurality of conductor portions (51, 52) which extend in a substantially meandering arrangement on a first end face of the substrate (1), and a second conductor track structure (61, 62), the substrate (1) substantially having the shape of a rectangular block, while the first and second conductor portions (51, 52) forming the first conductor track structure lie on the first end face of the substrate (1), the second conductor portion being formed along at least part of its length by a first, substantially rectangular metal surface (52), wherein

   - the two conductor portions (51, 52) have a mutual distance which defines the frequency distance between the first resonance frequency of the fundamental mode and the second resonance frequency at the first harmonic of the fundamental mode,

   - the second conductor track structure (61, 62), which is designed to operate the antenna in a third frequency band, is formed by a third conductor portion (61) and a third, substantially rectangular metal surface (62) on the first side face of the substrate (1),

   characterized by a feed terminal (40) at the second end face of the substrate (1), and by a feed line (45) extending along the circumference at at least one of the first, second, and third side faces (11, 12, 13) of the substrate (1) for supplying the first and second conductor track structures (51, 52; 61, 62).
2. A microwave antenna as claimed in claim 1, characterized in that a first tuning stub line (53) for a first frequency band is connected to the feed terminal (40), which first stub line (53) extends as a substantially rectangular metal surface along the first side face (11) of the substrate (1).
3. A microwave antenna as claimed in claim 1, characterized in that a second tuning stub line (54) for a second frequency band is connected to the end of the feed line (45), which second stub line (54) extends at least along the third side face (13) of the substrate (1).
4. A microwave antenna as claimed in claim 1, characterized in that the first conductor track structure is provided for operating the antenna in the GSM900 or GSM 1800 (DCS 1800) frequency band, and the second conductor track structure is provided for operating the antenna in a 2480 MHz frequency band in accordance with the Bluetooth standard.
5. A printed circuit board, in particular for surface mounting of electronic components, characterized by a microwave antenna (110) as claimed in any one of the preceding claims.
6. A mobile telecommunication device, in particular for dual-band or multiband operation, characterized by a microwave antenna as claimed in any one of the claims 1 to 4.

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