EP1154518B1 - Integrated antenna for mobile telephones - Google Patents

Abstract

The antenna (1) has an earth plate (2) and a radiator (3) positioned parallel to the earth plate and electrically coupled to it at one end, with a voltage minimum obtained at this end at the lower resonance frequency of the antenna, a voltage voltage maximum obtained at the free end (6) of the radiator, which is capacitively coupled to a point along the radiator, for providing a further resonance frequency which is less than triple the first resonance frequency. An Independent claim for a mobile radio device is also included.

Description

The invention relates to a flat antenna assembly having a ground plane and a radiator, which is arranged at a distance substantially parallel to the ground plate, is connected to one of its end portions with this conductive and is not connected at its free end to the ground plate, wherein portions of the radiator in form the plan view of the ground plate at least approximately the shape of a letter C, including an approximately C-shaped shape with a non-round, angular shape, wherein at a lower resonant frequency of the antenna assembly at the connection of the radiator to the ground plate, a voltage zero point is present, and in the region of the free end of the radiator, a first voltage maximum is present, wherein the free end of the radiator is capacitively coupled to another point of the radiator.

Such antenna arrangements are also known as a plate antenna arrangement or patch antenna arrangement.

Are known integrated antennas for mobile phones based on the principle of the patch antenna. The external dimensions of such an antenna module are minimized in existing applications, for example by using a folded structure (eg C-patch). In addition to the single-resonant design (a single operating frequency band), other structures are known which enable operation in two defined frequency bands (such as in the two mobile radio bands of GSM900 and GSM1800 standards). Here, either two separate radiators are used or it is achieved by suitable measures that at the higher operating frequency only a particular radiator part is used. These procedures have the disadvantage that, in particular at the higher frequency, not the entire available antenna volume is used. This results in a low bandwidth of the antenna.

The document JP-11-251825 shows an antenna for two resonant frequencies having a radiator divided by a parallel resonant circuit (trap circuit). The radiator emits at the lower resonant frequency along its entire length. At a higher frequency, the trap circuit resonates and decouples the portion of the radiator (as viewed from the terminal on a ground plane) beyond the barrier circuit, so that the said portion does not radiate. The blocking circuit is essentially realized by a C-shaped notch in the otherwise formed as a plate radiator.

The document WO 00/02287 A & EP 1 011 167 A1 forms the basis for the preamble of claim 1. The document shows numerous antenna arrangements, including those shown in Figures 13 and 14, each having two radiators slightly different lengths, one for transmission mode and the other for receiving operation at slightly different frequencies. The radiators have in plan view of a ground plate approximately a C-shape with a grounded end and a free end. Figures 59 and 60 show a capacitive coupling of a radiator with other parts of the radiator, including Figure 60 also a capacitive coupling of the free end of each partial radiator of a dipole radiator with another location of the same partial radiator. Measures to be able to operate one of the aforementioned radiators with very different frequencies can not be found in the description of the aforementioned figures and otherwise not apparent.

The invention has the object of providing an arrangement of the type mentioned in such a way that it is suitable for two frequency ranges and allows a broadband construction.

This object is achieved according to the characterizing part of claim 1, characterized in that this other point, measured from the connection with the ground plate, approximately 1/3 of the unwound length of the radiator, so that a further, higher resonant frequency, wherein the said Ends of the Radiator is a voltage zero point or a second voltage maximum, occurs, which is smaller than three times the value of the first resonant frequency.

An advantage of the invention is that the entire radiator radiates at both frequency ranges. As a result, a relatively large bandwidth is possible even at the higher frequency, because a large radiator surface is available. There is also an advantage at the lower frequency because here as well the entire area available for the antenna can be used as a radiator. For powering a single point of the spotlight can be used.

It is also advantageous that the lower resonance frequency is reduced less than the higher resonance frequency. It is advantageous that the antenna can be kept small in size. Said other point of the radiator with which the capacitive coupling takes place is in the vicinity of the first voltage maximum on the radiator at the second resonant frequency. Of advantage is a particularly strong reduction of the higher resonance frequency with a small reduction of the lower resonance frequency.

In one embodiment of the invention, the capacitance value of the capacitive coupling is chosen such that the higher resonant frequency at least roughly corresponds to twice the lower resonant frequency. The suitability for operation in the bands 900/1800 MHz or 900/1900 MHz is advantageous.

In one embodiment of the invention, the shape of the radiator is chosen such that the free end of the radiator is adjacent to a location of the radiator corresponding to the desired other terminal of the capacitance. Before part of this are the possible short Verbindungsleitun conditions for the capacitor.

In one embodiment of the invention, the capacitive coupling is formed by a metal strip which, with the interposition of dielectric material, forms part of the length of the free end region and a part of the radiator on the other location provided for the capacitive coupling covered, such that the capacitive coupling is formed by a series connection of two capacitors. An advantage is the simple and space-saving design.

The invention also relates to a handheld radio, including transceivers, for at least one of the purposes: voice transmission, data transmission, image transmission, with an antenna characterized in that the antenna is formed by the antenna arrangement according to any one of the claims, substantially above are discussed. The advantage is that a simple transmission / reception circuit is possible. Also, a small size for the device is possible, please include.

Fig. 1

eine schematische perspektivische Ansicht eines Ausführungsbeispiels einer Antenne,

Fig. 2

eine graphische Darstellung der Spannungsverteilung über der Lange einer Antenne gemäß Figur 1, aber ohne Kondensator, bei zwei Resonanzfrequenzen,

Fig. 3

die Lage von zwei Resonanzfrequenzen der Antenne ge- mäß Figur 1 ohne Vorhandensein des Kondensators der Figur 1,

Fig. 4

im gleichen Frequenzmaßstab wie bei Figur 3 die veränderte Lage der Resonanzfrequenzen im Vergleich zu Figur 3 in Folge des Vorhandenseins des Kondensators der Figur 1

Fig. 5

eine Ansicht eines Hand-Funktelefon-Geräts mit Antenne, und

Fig. 5a

eine Einzelheit in Fig. 5 bei 20, vergrößert.

Further features and advantages of the invention will become apparent from the following description of embodiments of the invention with reference to the drawing, which shows details essential to the invention, and from the claims. The individual features may be implemented individually for themselves or for several in any combination in an embodiment of the invention. Show it:

Fig. 1

a schematic perspective view of an embodiment of an antenna,

Fig. 2

3 is a graph of the voltage distribution over the length of an antenna according to FIG. 1, but without a capacitor, at two resonance frequencies;

Fig. 3

the position of two resonance frequencies of the antenna 1 without the presence of the capacitor of FIG. 1,

Fig. 4

in the same frequency scale as in Figure 3, the changed position of the resonance frequencies in comparison to Figure 3 due to the presence of the capacitor of Figure 1

Fig. 5

a view of a handheld cellular phone device with antenna, and

Fig. 5a

a detail in Fig. 5 at 20, enlarged.

In FIG. 1, the antenna arrangement 1 has a ground plate 2. This is just the example. At a distance from the ground plate 2, a radiator 3 is arranged on the largest part of its length parallel to the ground plate 2 and held by suitable means, not shown, at a constant distance from the ground plate 2. These means are in a first embodiment, which was realized in Fig. 1, some arranged between the radiator 3 and the ground plate 2 spacers made of insulating material. In another embodiment, said means are a plate of dielectric material disposed between the radiator 3 and the ground plane 2. The radiator 3 is a total of multiple angled. One end of the parallel to the ground plate 2 extending part of the radiator 3 is connected through a portion 3a (shorting plate), which is perpendicular to the ground plate 2, conductively connected to the ground plate 2 over its entire width. The section 3a is followed by a section 3b of the radiator 3, perpendicular to this extends to the section 3b, a section 3c, which runs parallel to a longitudinal edge of the rectangular in the example ground plate 2, parallel to this section 3b extending Section 3d and the section 3d is followed at a distance from the section 3c and parallel to this running a section 3e. The sections 3b to 3d together form approximately the shape of a letter C. In the embodiment is also at the end of section 3e, which is close to the shorting plate 3a, another section 3f is arranged, which lies much closer to the section 3b than the section 3d and extends to the vicinity of the section 3c. The sections 3b to 3f form a planar, angular, spiral-like arrangement. The antenna shown may also be referred to as a flat antenna, plate antenna or patch antenna.

The entire radiator 3 with said sections 3a to 3f is in one embodiment of the invention made in one piece from a thin metal sheet by stamping and bending. In another embodiment, the radiator is applied as a metallization on the upper side and an edge surface of the above-mentioned insulating plate of dielectric material.

The supply of the radiator 3 takes place in the transmission and reception case via a feed line 5, which is arranged at a distance from the short-circuiting plate 3a and connected to the radiator 3 (in the example the section 3b), wherein the distance is selected such that a desired characteristic impedance for the supply results. Since a relatively low characteristic impedance is generally desired (order of magnitude of 50 ohms), the feed line 5 is relatively close to the short-circuit plate 3a in comparison to the entire developed length of the radiator 3. At the short-circuit plate 3a facing away from the end portion 6, in the example exactly at the free end of the radiator 3, more precisely of the section 3f, on the one hand, and on one, in the embodiment exactly opposite, point 7 of section 3c on the other hand, a capacitor 8 is connected.

The height h corresponding to the length of the shorting plate 3a, in which the majority of the radiator 3 is located above the ground plate 2, is small compared to one quarter of the wavelength of the high frequency with which the antenna arrangement 1 to be operated.

The above-mentioned low-impedance supply of the feed line 5 is symbolized in Figure 1 by a coaxial cable 9, which is brought from below to the ground plate 2. The outer conductor of the coaxial cable 9 communicates with the conductive visible surface of the ground plate 2, and the center conductor of the coaxial cable 9 is in communication with the feeding line 5.

In practice, the coaxial cable 9 will often be much shorter than shown, or it may possibly omit the coaxial cable entirely, because the electronic circuit to be connected to the antenna assembly 1 is in embodiments of the invention immediately below the ground plane 2. In further embodiments of the invention, the ground plate 2 is formed by the substantially continuous metallization of a printed circuit board, on the underside of which are the circuit components of a printed circuit.

To explain the mode of operation of the antenna arrangement of FIG. 1, reference is first made to FIG. 2, which is based on an antenna according to FIG. 1, but without a capacitor. On the horizontal axis, the distance d from the connection point of the shorting plate with the ground plate is applied to the free end of the radiator 3, with the other end of the shorting plate 3a (i.e., the connection to the ground plate 2) being at d = 0. The vertical axis indicates the principal profile of the voltage or field strength when the antenna arrangement is supplied with high frequency at two different frequencies.

Curve 10 in FIG. 2 shows the voltage profile when the antenna arrangement without capacitor is fed to the first, lowest resonance frequency of the radiator 3, which then is present when a quarter of the wavelength corresponds to the effective length of the radiator 3 including the shorting plate. For simplicity, the influence of the dielectric constant of an insulating plate (as a spacer or carrier of the radiator) in these explanations should be neglected. When fed to the feed line 5 with this first resonance frequency, the voltage thus at the free end of the radiator, according to a developed length 1 has a first maximum and at the lower end of the shorting plate the value 0.

The next higher resonant frequency occurs when at the end at 6, when the feed frequency is increased again, a maximum occurs. This is the case when the length 1 of the radiator 3 corresponds to a value of 3/4 of the wavelength of the feeding high frequency. This second-mentioned resonance frequency occurs at a higher frequency compared to the first resonant frequency by a factor of 3.

Such a device (without a capacitor) is useless if it is to be used to provide a portable electromagnetic wave transceiver with an antenna arrangement intended to operate in two frequency ranges which differ widely in their frequency ( but not by a factor of 3), for example differ in their frequency roughly by a factor of 2. Such frequency ranges are common for so-called GSM radiotelephones in which a lower frequency range (devices according to the standard GSM 900) roughly at 900 MHz, and a next higher frequency range (device standard GSM 1800) at roughly 1800 MHz. The said antenna arrangement can thus, if it has the properties according to FIG. 2, not be operated in resonance at both said frequencies.

The embodiment shown in Fig. 1 makes such Dual band operation possible.

In practice, the said antenna arrangements are so narrow-banded that even for those mobile phones operating exclusively according to the GSM900 standard and in which the transmission and reception are carried out in bands separated by a frequency gap, they are transmitted and received by means of a feed point Wiring a vote must be made. This problem is not addressed by the present invention, and this problem is not necessarily solved by the invention.

Rather, the invention eliminates the need to switch specifically for a change between two frequency bands (e.g., as described between 900 MHz and 1800 MHz) in the region of the antenna. For feeding a single feed line 5 is used.

In the arrangement of Figure 1, the arrangement is now made so that the connection point 7 of the capacitor 8 is approximately at a developed length of one third of the total length of the radiator 3. The other terminal of the capacitor 8 is, as already stated, connected to the free end of the radiator 3. The capacitor 8 is thus connected between two points of the radiator 3, in which the voltages (read on the curve 10 of Figure 2) differ relatively little in operation with the low resonance frequency, in particular far less than half the voltage at the free end This relatively low voltage drives a capacitive current through the capacitor 8 and influenced in terms of a frequency reduction, this lower resonant frequency (curve 10) of the antenna assembly 1 relative to the state without capacitor 8 relatively little.

In contrast, during operation of the antenna arrangement 1 at the higher resonant frequency, the capacitor 8 without any switching now between two points (the same points 6 and 7 as before), between which a relatively large voltage difference prevails, which is far greater than the voltage at the free end of the radiator 3. It results here for the eye readily apparent from Fig. 2 that the capacitor 8 is applied to a voltage which is twice the voltage at the free end of the radiator 3. At the higher resonance frequency, therefore, the effect of the capacitor 8 in the sense of a frequency reduction or antenna extension is much stronger than at the lower resonance frequency.

Since also the lower resonance frequency is somewhat influenced in the sense of an antenna extension (frequency reduction), the length 1 will be made slightly shorter compared to the case without a capacitor, so that the slight reduction in frequency of the lower resonance frequency then to the desired resonance frequency, in the example to the resonance frequency in Area of the GSM 900 leads.

As already mentioned, the higher resonance frequency is reduced much more strongly, so that with a suitable selection of the size of the capacitor 8, this higher resonance frequency has the value required for GSM 1800.

The general teaching for the connection of the capacitor 8 is that it should be connected to the radiator in such a way that it influences the higher resonance frequency more strongly (namely reduced) than the low one. More specifically, the teaching is that the connection of the capacitor is such that the voltage acting on it is higher at the higher resonant frequency than at the lower resonant frequency. In the special case, the capacitor 8 is connected approximately where the two opposite-phase maxima of the voltage curve lie at the second resonance frequency.

It should be noted that there is currently another GSM standard operating at an even higher frequency, at about 1900 MHz (GSM 1900). This frequency also falls within the framework of the strongly deviating, in particular very roughly twice the frequency of the first resonant frequency and is therefore also to be realized by the invention.

The frequency ranges for GSM 900 are about 880 to 960 MHz, for GSM 1800 about 1710 to 1880 MHz, for GSM 1900 about 1850 to 1990 MHz.

The location of the resonance frequencies without presence of the capacitor 8 is shown in FIG. S ₁₁ is the reflection factor measured at the feed point. At the resonance frequencies f1 and f2, the reflection factor is considerably lower than at other frequencies, because at these resonance frequencies the antenna radiates a large part of the supplied high-frequency power. The frequency f2 has three times the value of the frequency f1. FIG. 4 shows the state as it results through the capacitor 8. The frequency f'1 has decreased only slightly compared with f1 and therefore has approximately the value f1, the higher resonance frequency f'2 has decreased considerably compared to f2 in FIG.

The person skilled in the art knows that further influences (housing of the handheld radio, in particular a GSM radiotelephone, the effect of a hand holding the device and other influences) are lengths that are operated in a non-installed state due to a theoretical consideration or to an antenna arrangement , can result, noticeably change. Therefore, fine adjustments may still be necessary in comparison with the design rules for the design explained here.

The provided in the arrangement of Figure 1 five radiator sections 3b to 3f form in plan view, approximately the shape of the small letter "e". Therefore, the name e-patch is suggested for this arrangement.

The antenna arrangement 1 is designed so that it fills a limited available space with as much high frequency leading radiator surface. This is also served by the section 3f following the section 3e, which contributes to the unwound radiator length 1 (which is slightly smaller than the individual sections measured along the respective center line) and offers a practical connection possibility for the condenser 8 because of its proximity to the section 3c. At the lower resonance frequency at which the radiator 3 is a λ / 4 radiator, the radiator 3 acts as a radiator over its entire length. But this is also the case at the higher resonance frequency. Again, the radiator 3 radiates with all its sections 3a to 3f, so not only with a shorter length. This is an important advantage, because the antenna arrangement is relatively broadband even at the higher resonance frequency. In contrast, as mentioned above, a switchable adaptation of the antenna may be required to optimally adapt the antenna arrangement to the reception area of GSM 1800 on the one hand and to the transmission area of GSM 1800 on the other hand. It should be understood that these embodiments are immediately applicable even if the antenna is dimensioned for GSM 1900 rather than GSM 1800, or if other standards such as AMPS are used.

In particular, it should be noted that in the embodiment of Fig. 1 for the connection of the capacitor 8, no significant parts of the surface of the radiator 3 are lost. The capacitor 8 can be easily switched between the areas 6 and 7.

Preferred is an embodiment of an antenna arrangement 1 '(Figure 5) in which the capacitor 8 is formed by a sheet metal strip 20 approximately of the width of the portion 3f that overlaps the gap between the free end at 6 and the portion 3c with sufficient overlap the two adjacent sections 3c and 3f is laid and with the interposition of dielectric material (plastic film 22, see Fig. 5a) is connected at a defined distance with these parts. There are two capacitors are formed in this way, which are connected via a relatively wide and short and thus low-inductance connection line in series.

In particular, variables in the optimum dimensioning of the antenna are the capacitance value of the capacitor 8 and the connection point 7. For example, it may be useful to connect the capacitor at a position of the section 3c for which the value d of FIG. 2 is slightly greater than the length 1 / 3, because at such an increase of the distance from the ground plane, the voltage acting at the higher resonant frequency on the capacitor (because the point d = 1/3 is at the maximum of the curve 11) changes only slightly, whereas the corresponding one Voltage of the curve 10 (lower frequency range) changes more, so that in this way the influence of the capacitor on the lower resonance frequency can be somewhat reduced.

FIG. 5 shows in a simple representation a partially broken-down handheld radio device 15, namely a mobile radio telephone, which contains the antenna arrangement 1 'described above as antenna. In this antenna, the capacitor is realized by a metal strip 20 placed over the parts 3c and 3f with the interposition of an insulating layer as a series connection of two capacitors. The short-circuit plate 3a is disposed toward the upper end of the housing of the radiotelephone. The handheld radio is in the example for the areas GSM 900 and GSM 1800 designed. The antenna assembly is housed entirely inside the housing of the radiotelephone, so it is an integrated antenna.

In a particular embodiment of the antenna arrangement of Fig. 1 for a cellular telephone for the GSM 900 and GSM 1800 ranges, the radiator occupies a space of about 5 cm x 4 cm x 0.5 cm (the latter being the length of the shorting plate).

From the observation of Fig. 1, it is understood that, while maintaining the radiator length and the 1/3 to 2/3 length division by the terminal 7 of the capacitor and the close vicinity of the area 6 and 7, the radiator sections are changed substantially in shape can, without leaving the principle of invention.

Short leads to the capacitor 8, as described, mean little space and relatively low losses. The low space consumption allows dimensioning for the widest possible bandwidth.

It should also be emphasized that the feeding of the antenna arrangement for both frequency bands takes place at the same circuit point, namely at the connection point of the feed line 5 to the emitter 3.

If one wanted to lower the higher resonant frequency in the arrangement according to FIG. 1 by omitting the capacitor 8 there and by switching on a capacitor between the free end of the radiator 3 and ground, this would also result in a considerable reduction of the lower resonant frequency , and at the 3: 1 frequency ratio between the higher and lower resonant frequencies, little would change so that such a circuit would not be useful.

Claims (6)

1. Flat antenna arrangement with an earth board (2) and a radiator (3), arranged at a distance substantially parallel to the earth board (2), connected conductively thereto by one of its end regions and not connected to the earth board (2) by its open end,
   wherein in the horizontal projection on to the earth board sections of the radiator (3) form at least approximately the shape of a letter C, with the inclusion of an approximately C-shaped form with a non-round, angular shape,
   wherein at a lower resonance frequency of the antenna arrangement (1) there is a voltage zero point at the connection of the radiator (3) to the earth board (2) and there is a first voltage maximum in the area of the open end of the radiator,
   wherein the open end (6) of the radiator is capacitively coupled to another point (7) of the radiator,
   characterised in that this other point (7), measured from the connection to the earth board (2), is approximately 1/3 of the unwound length of the radiator (3), so a further, higher resonance frequency occurs, wherein there is a voltage zero point or a second voltage maximum at said ends of the radiator (3), which is smaller than three times the value of the first resonance frequency.
2. Antenna arrangement according to claim 1, characterised in that the capacitance value of the capacitive coupling is chosen in such a way that the further resonance frequency corresponds at least in rough approximation to double the lower resonance frequency.
3. Antenna arrangement according to one of the preceding claims, characterised in that the open end of the radiator is adjacent to the point of the radiator corresponding to the other connection of the capacitive coupling.
4. Antenna arrangement according to one of the preceding claims, characterised in that the capacitive coupling is formed by a metal strip (20, Fig. 5), which overlaps part of the length of the open end region and part of the radiator at the other point provided for the capacitive coupling with intermediate positioning of dielectric material in such a way that the capacitive coupling is formed by a series circuit of two capacitors.
5. Antenna arrangement according to one of the preceding claims, characterised in that a feed (feed line 5) of the antenna arrangement is provided at the same connection on the radiator (3) for several frequency bands.
6. Hand radio device (15), with the inclusion of transceivers for at least one of the purposes of voice transmission, data transmission and picture transmission, with an antenna, characterised in that the antenna is formed by the antenna arrangement (1) according to one of the preceding claims.

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