WO2001056110A1

WO2001056110A1 - Rod antenna for a mobile radio telephone

Info

Publication number: WO2001056110A1
Application number: PCT/DE2001/000260
Authority: WO
Inventors: Johannes Jahn; Andreas Kirsch; Carmen Wagner
Original assignee: Siemens Aktiengesellschaft
Priority date: 2000-01-24
Filing date: 2001-01-23
Publication date: 2001-08-02

Abstract

The invention relates to a rod antenna (10) for a mobile radio telephone (mobile phone) the power of which is minimized in an antenna near field (N) in any predetermined range (T1, T2; R1, R2), in which the mobile radio telephone user's head is located, while the power is maximized in an antenna remote field (F) in a predetermined angle range (T3, T4) by adjusting an array of antenna elements by near-optimum determination of the surface current density.

Description

description

Rod antenna for a mobile radio device

The invention relates to a rod antenna for a mobile radio device (cell phone). Commercial mobile radio devices with rod antennas have a uniform radiation pattern. Here, a considerable amount of energy is absorbed by the body and in particular by the head of the cell phone user. This share is of the order of 38% of the input power. Approximately 12% of the power fed in is absorbed by the hand of the mobile phone user. Since neither conductor losses nor dielectric losses occur, only a maximum of 50% of the electrical power fed into the rod antenna of a corresponding mobile radio device is actually radiated.

A mobile radio antenna is known from [1], which consists of a plurality of antenna elements which can be switched by a simple controller in such a way that directional radiation takes place. In addition, a shield in the form of a plate in sandwich construction reduces the radiation into the user's head. It is particularly disadvantageous that a large part of the power is lost as a result of the shielding by means of a plate and that a radiation direction is predetermined by the plate.

In [2] a mobile phone rod antenna is described, which consists of two elements. The aim here is to align these two antenna elements (mechanically or electronically) so that a directional effect is created. This directional antenna inevitably reduces the radiation in the user's head.

In [3], too, a directional effect with an adjustable main beam direction is achieved with an antenna array. The aim here is to reduce the transmission power, which inevitably reduces the exposure of the user to electromagnetic radiation.

In [4] the aim is to reduce the electromagnetic pollution for the user by reducing the transmission energy itself. The same goal is also pursued [5], whereby an attempt is made to implement five different radiation directions with the help of antenna arrays. So-called patch antennas are known to improve the antenna characteristics with regard to a reduction in the strain on the head while at the same time improving the transmission quality, and are usually arranged on the inside of the rear wall of the mobile phone housing. Such patch antennas result in a reduction in the power absorbed in the head of the mobile phone user from an order of magnitude of 38% to approximately 7%. However, the power absorbed in the hand of the mobile phone user increases from approx. 12% to an order of magnitude of 23%. With such patch antennas, approximately 68% of the electrical power is actually emitted.

Knowing these circumstances, the invention has for its object to provide a rod antenna, the power in the near field within an arbitrary predetermined angular range, in which the head of the mobile phone user is located, minimized and at the same time the power in the far field in an arbitrarily predetermined Angular range is maximized.

This object is achieved in that the rod antenna has antenna elements which extend in the longitudinal direction of the rod antenna and which are equally wide and equally spaced from one another in the circumferential direction of the rod antenna, the individual antenna elements being controlled electronically by selecting a suitable surface current density such that the antenna Near field is minimized within a first angular range and the antenna far field is maximized within a second angular range.

The rod antenna according to the invention has the advantage that its antenna characteristic is significantly improved or optimized in such a way that the influence of the electromagnetic waves on the head, i.e. the load on the head of the mobile phone user is drastically reduced or minimized and at the same time a substantial improvement in the transmission quality is achieved by the maximized antenna far field, because with the same electromagnetic energy the transmission quality of the mobile radio device designed with the rod antenna according to the invention is improved. Both the far field and the near field of the antenna are taken into account.

A further advantage is to control the rod antenna by a suitable choice of the surface current density in such a way that the radiation is maximized over a wide angular range while the radiation to the body of the user is minimized without the use of additional fixed structures. Controlling the surface current density of the antenna elements leads to significantly improved radiation characteristics that have not been achieved so far. This rod antenna can be used in various networks, such as in the D network (frequency range between 880 and 960 MHz) or in the E network (frequency range between 1710 and 1880 MHz), since the surface current density can be set depending on the transmission frequency. This means that the rod antenna can be used in both dual-band and triple-band cell phones because it can be optimally reconfigured when the network is changed by automatically selecting the surface current density.

One embodiment consists of the fact that an orientation can be specified in accordance with the selected form of the mobile radio device, so that the near field and the far field are aligned as a function thereof. An example is a common cell phone with a microphone and speaker on one side; this side can be roughly specified as a near field, since a user will only hold the cell phone to his head in this orientation. The opposite side - without a microphone or loudspeaker - is suitable as a default for the far field, since the head of the user does not reduce the transmission power in this radiation direction. These near-field and far-field orientations can automatically be associated with the shape of the mobile radio device.

The rod antenna according to the invention can have a hollow cross section, and the antenna elements can be provided on the outer surface of the hollow rod antenna. Another possibility is that the rod antenna has a full cross-section and that the antenna elements have a cross-section in the form of an annular segment. In these two designs of the rod antenna according to the invention, the radiated power in the near-field antenna, i.e. in the area of the head of the mobile phone user and his body, minimized and at the same time maximized the radiated power in an area remote from the body (far-field antenna). The areas can be selected variably in both the radial and azimuthal directions of the rod antenna.

Further details, features and advantages also emerge from the following description of exemplary embodiments of the rod antenna according to the invention which are shown schematically and not drawn to scale on an enlarged scale.

Show it

Figure 1 is a view of a first embodiment of the rod antenna with a hollow cross-section in the viewing direction from above;

Figure 2 shows the rod antenna according to Figure 1 in a side view;

Figure 3 shows another embodiment of the rod antenna in a view similar to Figure 1 with a full cross section; Figure 4 shows the rod antenna of Figure 3 in a side view (similar to

Side view according to Figure 2); Figure 5 is a schematic representation of the rod antenna to illustrate various parameters for defining the antenna near field and the antenna far field; Figure 6 shows a far field characteristic of the rod antenna corresponding to the

Figures 3 and 4;

FIG. 7 shows a near-field characteristic of the rod antenna according to FIGS. 3 and 4;

FIG. 8 shows a far field characteristic of a rod antenna similar to FIG. 6, as is shown schematically in FIGS. 1 and 2, and

9 shows a representation of the near-field characteristic of a rod antenna according to FIGS. 1 and 2, which is associated with the far-field characteristic according to FIG. 8.

Figures 1 and 2 show schematically greatly enlarged and not to scale, a design of the rod antenna 10 for a mobile radio device (cell phone), which - as can be seen from Figure 1 - has a hollow cross section 12. On the outer surface 14 of the rod antenna 10, strip-shaped antenna elements 16 are provided which extend in the longitudinal direction of the rod antenna 10 and which are of the same width in the circumferential direction of the rod antenna 10 and are evenly spaced from one another. The strip-shaped antenna elements 16 are each individually connected together with an electronic circuit device 18 (see FIG. 2), the mode of operation of which is explained in more detail below in connection with FIGS. 5 to 9, and which is provided for the individual antenna elements 16 electronically in this way to drive that the antenna near field N (h) minimizes within a first azimuth or polar angle range Tl and T2 between the radial distances R1 and R2 and the antenna far field F (h) within a second azimuth or polar angle range 3 and T4 (see FIG. 5) is maximized. The rod antenna is also schematically illustrated in FIG. 5 with the reference number 10. R is the radial distance from the rod antenna 10 and t is the polar angle.

FIGS. 3 and 4 show, in addition to the schematic representations similar to FIGS. 1 and 2, a second embodiment of the rod antenna 10 for a mobile radio device (cell phone). In this embodiment, the rod antenna 10 has a full cross section 20. The antenna elements 16 of the same width in the circumferential direction of the rod antenna 10 and equally spaced from one another in this case have a cross-section in the form of an annular segment and, like the antenna elements 16 of the rod antenna 10 according to FIGS. 1 and 2, are spaced apart, ie electrically insulated. In this embodiment of the rod antenna 10, too, the antenna elements 16 are contacted individually with an electronic circuit device 18, the mode of operation of which is explained below in connection with FIGS. 5 and 6 to 9.

FIG. 5 illustrates - as has already been explained - the rod antenna 10 in the plane of the drawing. T1 and T2 indicate the polar angles and R1 and R2 the radii of an annular sector 22 in which the radiation of the rod antenna 10, i.e. the antenna near field N (h) should be minimal. The polar angles T3 and T4 define the area, i.e. the antenna far field F (h) in which the radiation from the rod antenna 10 is as strong as possible, i.e. should be maximized.

The optimal surface current densities result from solving an optimization problem, which is described below.

In order to better take into account the inhomogeneity of the head of the mobile phone user, averaging over the wave numbers from k 1 to & ₂ corresponding to the respective mobile phone frequencies is carried out for optimization in the close range. If N and F denote the near-field and far-field operators of the respective antenna model, the technical problem leads to an optimization problem with two objectives:

under the constraints

/ ι GE ² ([0, 2τr], C)

II h | - <1

Inscribed here

L ² ([0, 2τr], C) describes the space of the complex-valued functions integrable on [0, 2π] and he L ([0, 2π], C) describes the third component of the surface current density J of the respective antenna element 16. This surface current density J is optimized according to the invention. We are looking for Edgeworth Pareto optimal points of this optimization problem. Depending on the antenna type, the optimization problem of the above formula (1) is of a special form.

In the case of the full-cross-section rod antenna, the radiation behavior is mathematically described by an external Neuman problem using known near-field and far-field operators. If H "'denotes the first-order Hankel functions, the optimization problem arises for the rod antenna with a full cross-section

n = - oo

The rod antenna with a hollow cross-section is the basis of the transmission problem. The optimization problem arises with the known formulas for the near-field and far-field operators for this antenna type

71 = - 00

OO

2π | Λn | ² ≤ l-

Here J _n denotes the Bessel function of the 1st kind of nth order.

The optimization problems (2) and (3) mentioned above cannot be solved in the present form on a computer because they are infinite series. The function h is solved on a computer by finite Fourier series

h (t) w ^ (x _n + zy _n ) exp (int) for t G [0, 2π] n = - l approximated. x _n describes the real part and y _n the imaginary part of the corresponding Fourier coefficient. The natural number l, which should be large, can be chosen arbitrarily. The larger the number l, the more accurate the approximation.

Thus, the optimization problem arises from the original problem according to the mathematical formula (2) above

under the constraints x _n , y _n eR (neZ, \ n \ <l) x _m , y _m ER (eZ, | | <Z)

2τr E (+ ύ) ^~ 1 ≤ 0. n = - l and results from the optimization problem (3)

under the constraints x _n , y _n R (n € Z, | n | <Z) x _m , y _m GR (meZ, | m | <J)

2τr ∑ (+ y) -l <0.

Since these are finite Fourier sums, the optimization problems (4) and (5) can be solved with the help of a computer. They are set up so flexibly that both antenna types according to the invention, ie rod antennas with a hollow cross-section and rod antennas with a full cross-section, as described above, for different frequency ranges, ie for different networks, can be optimized. This applies to both existing and future networks. The wave numbers k of the D network with the frequency range from 880 to 960 MHz are, for example, between 18 and 21 cm ^-1 and in the E network with the frequency range between 1710 and 1880 MHz between 35 and 40 cm ^-1 .

In the following, optimized antennas are presented, which were calculated on a computer using the above procedure. With the help of Polak's modified method, discretization points d are determined, which are Edgeworth-Pareto optimal points. For each discretization point d and the wavenumber

FIGS. 6 and 8 show the radiation characteristics of the respective rod antenna for the far field and in FIGS. 7 and 9 the near field.

FIG. 6 illustrates the radiation characteristic of a rod antenna 10 with a full cross section and antenna elements 16 with a circular segment cross section for the far field, and FIG. 7 shows the radiation characteristic of said antenna 10 for the near field.

For the D network there are e.g. with the parameter values:

l 5

19 k ₂ 21

R ₂ = 20 cm τ_ = 1/2 TΓ τ ₂ = 3/2 TΓ τ ₃ = 7/4 TΓ τ ₄ = 9/4 TΓ

the far-field radiation characteristic shown in FIG. 6 and the near-field radiation characteristic shown in FIG. The following Fourier coefficients apply, for example, to a discretization point d = 25 h = (0.01300055383495 + 0.04331750467401 + 0.01893142334700z 0.04040158189752z 0.08653143526568 + 0.12848449976889 + 0.05666391450014z 0.06285070605292z 0.15702229613280 + 0.16680136017128 + 0.06254469475927z 0.06153526635706z 0.15691981020013 + 0.12841034377474 + 0.06264305387827z 0.06309460517844z 0.08650155561591 + 0.04331147429367 + 0.05688947067973z 0.04056573006974z 0.01299653980904 + 0.01890570205347z)

The values corresponding to these Fourier coefficients are processed with the aid of the electronic device 18 (see FIGS. 2 and 4).

For the E network, the result is

l 5

R ₂ = 20 cm

for a rod antenna 10 according to FIGS. 3 and 4, similar far-field and near-field radiation characteristics.

FIGS. 8 and 9 illustrate a far-field and near-field radiation characteristic of a rod antenna 10 according to FIGS. 1 and 2, for example for the D network l = 5 h = 20 k ₂ = 20

In the case of such a rod antenna 10 according to FIGS. 1 and 2, the parameter values result for the E network

l 5 h 38 k ₂ 38

similar radiation characteristics.

It follows from the above that the performance of the rod antenna 10 can be minimized in the near field and maximized in the far field.

For the jth strip-shaped antenna element 16 according to FIGS. 1 and 2, the surface current is

.lambda..sub.n

^Λ (* j) = ∑ (pn + <-ynn)) e ⁽ chosen ⁱⁿ n = —l, the Fourier coefficients x _n + iy _{n being determined} according to the method described above. The strip-shaped antenna elements 16 are - as described has been fed with different surface currents, which is done with the aid of the electronic circuit device 18. If the respective frequency band is changed during transmission, so the surface currents of the individual antenna elements 16 are suitably changed with the aid of the optimal Fourier coefficients. This has the advantage that the optical shape of the rod antenna 10 remains unchanged when the frequency changes. The rod antenna 10 is electronically reconfigured by a suitable choice of an optimal surface current for the current frequency.

This applies not only to the rod antenna 10 with a hollow cross section 12, but also in the same way for a rod antenna 10 with a full cross section 20, as is schematically illustrated in FIGS. 3 and 4. Here too, the surface current becomes the j-th antenna element 16

set. With this configuration of the rod antenna 10 as well, the surface current h (tj) can be suitably set or changed as a function of frequency with the aid of the electronic circuit device 18 without the geometric shape of the rod antenna 10 having to be changed.

bibliography

[1] WO 94/28595

[2] DE 42 21 121 Cl

[3] DE 44 10 174 AI

[4] DE 297 22 794 ul

[5] WO 99/27610

Claims

claims

1. rod antenna (10) for a mobile radio device

(a) with antenna elements (16) which extend in the longitudinal direction of the rod antenna (10) and which are approximately the same width and approximately equally spaced from one another in the circumferential direction of the rod antenna (10),

(b) with a circuit device (18) which electronically controls the individual antenna elements (16) in such a way that an antenna near field (N) within a radius range (R, R) and a first angular range (Tι, T ₂ ) minimizes and a Antenna far field (F) is maximized over a second angular range (T ₃ , T_) by the circuit device (18) adjusting the surface current density.

2. rod antenna according to claim 1, wherein the mobile radio device is a cell phone.

3. rod antenna according to one of the preceding claims, wherein the rod antenna (10) has a hollow cross section (12).

4. rod antenna according to one of the preceding claims, wherein the antenna elements (16) on an outer surface (14) of the rod antenna (10) are provided.

5. Rod antenna according to one of the preceding claims, wherein the rod antenna (10) has a full cross-section (20) and the antenna elements (16) have a circular segment cross-section (22).

6. rod antenna according to one of the preceding claims, for use in different mobile radio networks.

7. rod antenna according to claim 6, which is automatically set when changing the mobile network.

8. rod antenna according to one of the preceding claims, in which an alignment of the antenna near field and the antenna far field takes place automatically on the basis of the orientation of the mobile radio device.