HUP0100955A2 - Antenna - Google Patents

Abstract

Antenna with a conductor (10) surrounding the antenna surface (A), the length of which corresponds to an integer multiple of the half-wavelength of the current distribution in the conductor (10). The conductor (10) has a length corresponding to at least 1.5 times the circumference of the antenna surface (A), and viewed axially and/or radially, the overlapping sections (12) of the conductor (10) are located so close to each other that the current distribution in the conductor (10) its wavelength corresponds to a maximum of 0.8 times the vacuum wavelength of the electromagnetic field generated by the current distribution. HE

Description

3667R

P 01 00955

PUBLICATION COPY .....-

P 0 100955

Antenna

The invention relates to an antenna having a conductor surrounding an antenna surface, where the length of the conductor corresponds to an integer multiple of the half-wavelength of the current distribution in the conductor.

Antennas used for small radio modems include magnetic loop antennas, which are usually circular or rectangular conductors with a length significantly shorter than the wavelength. The conductor is connected to the input of a transmitter output, and the other end is terminated with a head capacitance in such a way that the conductor loop and the head capacitance create a resonant circuit with a resonant frequency equal to the operating frequency of the transmitter. The head capacitance can also be formed by a gap filled with air or dielectric placed at the corresponding end of the conductor.

Such a loop antenna is known from the patent specification DE 195 45 394 A1, which is distinguished by its extremely small dimensions. However, in the case of a magnetic loop antenna, the radiation resistance and thus the radiation efficiency are proportional to the square of the area enclosed by the wire (antenna surface), and are therefore small and typically below 10 mOhm. In order to achieve good efficiency in the case of such an antenna, all loss resistances in the antenna must be very small. The difficulty is the critical high-frequency resistance of the wire and the high-frequency resistance of the head capacitance.

Antennas of the type known from the patent specification DE 195 45 394 A1 are typically used for radio-controlled remote reading of electronic consumption meters (heat cost allocators, water meters, heat meters, gas meters, electricity meters, etc.). Radio-based remote reading is mostly carried out in the 433.92 or 868 - 870 MHz frequency bands licensed for this purpose almost throughout Europe. If we disregard the criteria for licensing, the frequency bands between 200 and 3000 MHz could also be used.

At frequencies below -2, the resistance of even the usual capacitive components is a few tens of mOhm. Due to the rather low radiation resistance of the antenna, all other resistances of the wire and the head capacitance should also be in the range of a few mOhm, which requires large wire sizes.

However, such antennas should be as small as possible, in practice this means significantly smaller than the wavelength. Devices used for radio remote reading are often placed in close proximity to larger metal surfaces, which can be e.g. metal housings of measuring devices in the case of gas and electricity meters, or radiators in the case of heating cost allocators, and water pipes in the case of water meters and heat meters. This also has a negative effect on the radiation. Radiation is also affected by furniture, curtains and the human body. Meters are mostly battery-operated, and the functionality of these durable elements must be maintained for the entire period of verification (which is 5-12 years).

With the present invention, we therefore aim to provide an antenna that has high efficiency even in small dimensions.

The solution to the problem according to the invention is an antenna with a conductor surrounding the antenna surface, the length of which corresponds to an integer multiple of the half-wavelength of the current distribution in the conductor. According to the invention, the conductor has a length corresponding to at least 1.5 times the circumference of the antenna surface, and the overlapping sections of the conductor, viewed in the axial direction and/or radial direction, are located so close to each other that the wavelength of the current distribution in the conductor corresponds to at most 0.8 times the vacuum wavelength of the electromagnetic field generated by the current distribution.

The antenna according to the invention is a magnetic loop antenna, which, however, unlike the antenna known from the patent specification DE 195 45 394 A1, does not have a head capacity. The length of the wire delimiting the antenna surface is at least 1.5 times the circumference of the antenna surface. Thus, we obtain sections of the wire running in the circumferential direction, which are adjacent to each other. This adjacency is radially relative to the boundaries of the antenna surface

-3 can be specified either in the vertical direction relative to the antenna surface or by a combination of the two.

The routing of conductor sections adjacent to each other is briefly referred to below as "overlapping", although this term implies that the corresponding conductor sections do not have to touch each other. What is important is that the conductor sections are close enough to each other that field couplings are created between the conductor sections.

The above field coupling results in the conductor acting more like a double conductor in the overlapped section. This reduces the propagation speed well below the speed of light. The reduction in the propagation speed (or the wavelength of the current distribution in the conductor) is adjusted to the distance between the conductor sections and the number of turns of the antenna (ratio between the length of the conductor and the circumference of the antenna surface). According to the invention, the overlapped conductor sections are routed in such a way that the propagation speed in the conductor without overlapped conductor sections is reduced by about 0.8 times.

By adjusting the number of turns and the way the conductor sections are overlapped (and the resulting shortening factor), antennas can be produced whose diameter is only between 1/20 and 1/30 of the wavelength. Such an antenna is thus similarly small in size as a classic loop antenna with head capacitance, but at the same time there is no need for head capacitance that degrades the quality of the antenna, but the inductive coupling of the overlapped conductor sections is all the more necessary for setting the resonance conditions in such small-sized antennas.

In practice, antennas according to the invention can achieve a performance factor of between 10 and 300.

Thus, the antenna according to the invention can serve as a low-loss prefilter with excellent performance factor when used as a receiving antenna, and as a filter to suppress the radiation of the main wave and its harmonics of the transmitting frequency when used as a transmitting antenna.

Compared to ring antennas, the radiation resistance of the antenna according to the invention is significantly higher (in the Ohm range), so the conductor resistance is far less critical. This means that it can be simply made of wire.

-4- ··’·· the antenna can be adjusted. Geometric tolerances are also not critical for the same reason.

Due to its properties, the antenna according to the invention can be used well in front of metal surfaces even within a small distance (a few millimeters), and the capacitive influence of the antenna (e.g. by hand) is also low.

The conductor, which essentially forms a loop, can be produced using suitably bent wire, milled conductor or printed conductor tracks, the latter being placed on an insulating substrate, which can be, for example, a plastic housing or a plastic housing cover.

If the length of the conductor is 1.75 — 3.5 times the circumference of the antenna surface, then a significant reduction in the propagation speed of electromagnetic waves along the conductor is achieved and thus a very compact geometry of the antenna is achieved with even simpler mechanical construction, which allows for affordable production.

It serves to achieve more compact dimensions of the antenna if the wavelength of the current distribution in the conductor is not less than 0.2 times the wavelength in vacuum of the electromagnetic field generated by the current distribution.

It has been found to be particularly advantageous that the radial and/or axial distance between the radially and/or axially offset sections of the conductor is 1 to 5 times the conductor size in the respective direction, thus achieving a significant reduction in the propagation velocity. The antenna structure is also compact and the adjacent conductor sections can be precisely guided.

The integer multiple is preferably greater than 1, and the direction of winding of the conductor is reversed at intervals corresponding to half the wavelength of the current distribution. This allows the production of antennas in which the total length of the conductor is an integer multiple of half a wavelength. By changing the direction of winding after half a wavelength, we achieve that the magnetic fields generated by the different sections of the conductor are added together.

In the case of the antenna according to the invention, no current flows at the ends of the conductor, so these ends can be connected or electrically isolated as desired.

-5- .:..

can be left open as desired for other considerations, such as ease of manufacture or mechanical strength of the antenna.

If the antenna includes an inductive power supply cooperating with the conductor, the conductor does not require any further interruption for the supply of transmitting energy or the decoupling of received energy. The inductive coupling of the transmitter or receiver cooperating with the antenna is also advantageous with regard to the residual coupling of the antenna and the transmitter or receiver.

The geometries of rectangular or circular antenna surfaces are particularly suitable for producing antennas with a small characteristic directional characteristic, which is desirable for remote reading of consumption meters, since the installation orientation of consumption meters equipped with remote reading must be adjusted to local needs (radiator surface, wall surface) and not to the transmission conditions of the remote reading center.

Alternatively, the directional characteristics of the antenna can be created by using rectangular or oval geometries of the antenna surface.

Below, preferred embodiments of the invention are described by way of example with drawings, where the

Figure 1 is a perspective view of a first antenna with an associated power supply, where the full length conductor sections of half a wavelength forming the antenna are axially offset, the

Figure 2 is a view similar to Figure 1, but showing a modified antenna in which the conductor sections forming the antenna are radially offset, the

Figure 3 is a view similar to Figure 1, in which the total length of the conductor forming the antenna is equal to one wavelength,

Figure 4 is a view similar to Figure 3, including the dimensions of the practical embodiment.

In Figure 1, we see a magnetic loop antenna that has 10 conductors.

The latter has a pitch of 1.75, which defines a rectangular antenna surface A when viewed in the axial direction. The antenna surface A has the edge length.

-6The sections 12 of the conductor 10 assigned to the different edges of the antenna surface A have similar lines, the twists have a thread pitch p.

It can be seen that the two sections 12 of the guide 10 always overlap each other in the axial direction, except for the front section, which stands alone and bridges the torsion planes.

The axial distance p of the conductor sections 12 is between 1 and 5 wire diameters. This creates an inductive coupling of the conductor sections 12 in the region of the three sides of the antenna surface A, thereby reducing the propagation speed of the electromagnetic radiation along the conductor 10. The appropriate shortening factor k (wavelength of the current distribution of the conductor 10 / wavelength of the electromagnetic radiation in vacuum) can be selected between 0.2 and 0.8 depending on how small the distance p is chosen and to what extent the conductor sections 12 overlap each other in the circumferential direction.

This allows the antenna shown in Figure 1 to have smaller dimensions, although it is a W/2 antenna (W = wavelength) operating in resonance without capacitance.

The antenna loop formed by the guide section 10 is fed by a coupling loop 14, which also defines a rectangular surface, which is, however, significantly smaller than the antenna surface A.

One end of the coupling loop 14 is directly connected to one terminal of a transmitter 16. The other terminal of the coupling loop 14 is connected to the other terminal of the transmitter 16 via a coupling capacitor 18.

The transmitter 16 is controlled by a consumption meter 20 and transmits the reading of the consumption meter 20 in serial binary representation at longer intervals. Details of the operation of such a consumption meter are described in the patent specifications DE 195 45 394 A1, _DE 30 44 262 A1, DE 42 25 042 A1 or DE 44 22 281 A1.

The conductor 10 can be attached to a supporting structure (not shown) (e.g. a printed circuit board or housing) with an insulating member (not shown) surrounding the conductor sections 12, e.g. the double-shaped conductor sections.

Figure 2 shows a modified antenna for radio remote reading of consumption meters, which differs from that shown in Figure 1 in that the conductor sections 12 are offset in the radial direction. This arrangement is particularly suitable for production on a printed circuit board. The conductors 10 can simply be omitted from a continuous copper layer on a printed circuit board, as can the coupling loop 14.

The antenna of Figure 3 differs from that shown in Figure 1 in that the total length of the conductor 10 corresponds to one wavelength. In order to achieve the positive addition of the magnetic partial fields generated by the conductor sections 12, the conductor 10 is first folded in half and the resulting folded conductor arrangement is subsequently shaped like the single conductor shown in Figure 1. This reverses the direction of the current at the current nodes.

The exact dimensions of a practical embodiment are shown in Figure 4. The typical dimensions of the W-antenna shown there are as follows.

the edge length: 25.00mm d wire diameter 0.63mm p thread pitch 6.40mm coupling loop edge length: 8.50mm coupling loop distance 6.60mm coupling capacitor: 6.20 pF

This provides the following properties.

Qo quality factor: operating quality factor: Ze/Ohm input impedance: R _s radiation resistance: R _a loss resistance: efficiency:

I outdoor wavelength:

a/l aspect ratio:

430

215(Rj = 50 Ohm) 56 + j x 0

2.79 Ohm 0.55 Ohm 83 % 690 mm 1/27.6

The antennas described above are therefore typically classified as W/2 antennas, but are significantly smaller in size than the typical W/2 antennas.

-8•ί.. ,.· ·..· ··/·· known W/2 antennas. These are distinguished from loop antennas terminated with a head resistor by the lack of head capacitance and the significantly better quality factor.

They differ from traditional helix antennas with numerous twists in that their total length is an integer multiple of W (wavelength), symmetrical feeding occurs (in helix antennas, unilateral feeding), and the path distance is small, so inductive coupling of adjacent conductor sections can be achieved.

The antennas described above also stand out for their mechanically simple, compact design.

In the exemplary embodiments described above, the antenna surface A was essentially square. It is understood that the shape of the antenna surface could instead be circular. Such antennas have essentially constant characteristics in the circumferential direction. If the antenna surface A is formed in a square or oval shape, a directional characteristic that varies in the circumferential direction can be achieved.

Claims (10)

-9Patent claims 1. An antenna with a conductor surrounding an antenna surface, the length of which corresponds to an integer multiple of the half-wavelength of the current distribution in the conductor, characterized in that the conductor (10) has a length corresponding to at least 1.5 times the circumference of the antenna surface (A), and the overlapping sections (12) of the conductor (10) viewed in the axial direction and/or radial direction are located so close to each other that the wavelength of the current distribution in the conductor (10) corresponds to at most 0.8 times the vacuum wavelength of the electromagnetic field generated by the current distribution. 2. Antenna according to claim 1, characterized in that the length of the conductor (10) is 1.75 - 3.5 times the circumference of the antenna surface (A). 3. An antenna according to claim 1 or 2, characterized in that the wavelength of the current distribution in the conductor (10) is not less than 0.2 times the wavelength in vacuum of the electromagnetic field generated by the current distribution. 4. Antenna according to any one of claims 1-3, characterized in that the radial and/or axial distance between the radially and/or axially offset sections (12) of the conductor (10) is 1-5 times the size of the conductor (10) in the corresponding direction. 5. Antenna according to any one of claims 1-4, characterized in that the integer multiple is greater than 1, and the winding direction of the conductor (10) is reversed in sections corresponding to half the wavelength of the current distribution. 6. Antenna according to any one of claims 1-5, characterized in that the ends of the conductor (10) are electrically connected to each other. 7. Antenna according to any one of claims 1-6, characterized in that the ends of the conductor (10) are electrically open. 8. An antenna according to any one of claims 1-7, characterized in that it comprises an inductive feeding device (14) cooperating with the conductor (10). 9. Antenna according to any one of claims 1-8, characterized in that the antenna surface (A) is rectangular or circular. 10. Antenna according to any one of claims 1-8, characterized in that the antenna surface (A) is rectangular or oval. (4 sheets of drawings, 4 figures) The authorized person GÖDÖLLE, KÉKES, MÉSZAROS the TAILOR Patent and Trademark Office 1024 Budapest, Keleti Károly u. 13/b Kereszty Marcell