Antenna

The invention relates to an antenna according to the preamble the Ansrpuches. 1

Among the antennas that used for small wireless modems are located insbesonder the magnetic loop antennas: These include a closed, usually circular or rectangular conductor piece whose length is significantly smaller than the wavelength. The conductor piece is connected at an input to a transmitter output and its other end is terminated by a head capacity, such that the conductor loop and head capacity form a resonant circuit whose resonant frequency with the operating frequency of the transmitter matches. The head capacity can also by an air or a Dielectric filled gap at the corresponding end of the be formed conductor piece.

Ei ne such loop antenna is described in DE 195 45 394 A1. It is characterized by very low Dimensions. But now with a magnetic Loop antenna radiation resistance and thus the the radiation efficiency proportional to the square the space enclosed by the conductor surface (antenna surface), small and typically is 10 mOhm. In order for a such an antenna to obtain a good efficiency, must all loss resistances in the antenna is very small be. Difficult is the critical RF resistance of Leitstückes and the RF resistance of head capacity.

Antennas mentioned in DE 195 45 394 A1 Type are typically for Wireless remote readout of electronic consumption meters (heat cost allocators, Water meters, heat meters, gas meters, electricity meters, etc.). The Wireless remote readout occurs usually in the most of Europe approved for that purpose Radio bands at 433.92 MHz or 868-870 MHz. Looks of this approval conditional criteria from, would also Frequency bands in the range between 200 and 3000 MHz usable.

Such frequencies already be resistors conventional capacitive components several tens of milliohms. Because of the relatively low radiation resistance of the antenna would all other resistors of the conductor piece and Kopfkapzität range from a few milliohms are, making wide conductor dimensions necessary.

Now, to be as small as possible such antennas, in practice considerably smaller than a quarter of the wavelength. Often also used for Wireless remote readout Devices disposed in the vicinity of larger metal surfaces, Count about housing with gas / electricity meters, heating for heat cost allocators, water pipes in water and heat quantity counters. This also adversely affects on from radiation. Other influences on the Radiation effected by furniture, curtains and people. The consumption meters are battery operated normally, wherein a functionality of the long-life battery desired over the entire calibration period of time (5 to 12 years) becomes.

The present invention is therefore to an antenna specify that a small dimensions has high efficiency.

This object is achieved by a erfindunngsgemäß Antenna with the features specified in Claim first

An antenna according to the invention is a magnetic loop antenna, However it comes, otherwise as the antenna after DE 195 45 394 A1 from headless capacity. The length the conductor piece, which limits the antenna surface, is at least 1.5 times the circumference of the antenna surface. This yields circumferentially extending Portions of the conductor piece which are adjacent to each other. The Benachbartsein can in relation to the limit the antenna surface in the radial direction or relative on the antenna surface perpendicular direction or in a combination of these two directions be given.

The adjacent guide portions of the conductor piece are hereinafter also referred to as "overlap" which term includes that the corresponding Head piece portions not touching each other need. The important thing is that the conductor sections adjacent to each other so closely that it Feldverkopplungen comes between the conductor sections.

The addressed Feldverkopplung causes that the conductor portion in the overlapping area more like a Double line behaves. Thus, the propagation speed decreases well below the speed of light from. The lowering of the speed of propagation (or the wavelength of the current distribution in the conductor portion) right in the individual according to the distance of the conductor sections and the number of turns of the antenna (ratio between length of the conductor piece and the scope of Antenna face). According to the invention, the overlapping Conductor portions guided so that a reduction of the propagation velocity to approximately 0.8-fold that propagation speed obtained, which in no overlapping line sections conductor piece adjusts.

Through the immersion position of the turns and the type and, the overlap of the conductor sections (and the obtained thereby shortening factor) can then realize antennas with a diameter only 1/20 amounts to 1/30 of the wavelength. The size of such Antenna is thus similar to small as that of a classic Loop antenna with top capacitance, but a the quality of the antenna debilitating head capacity is not required, rather, the magnetic coupling the overlapping conductor portions for setting the resonance conditions with small antenna dimensions responsible for.

In practice, one can with inventive antennas obtain a working resonance quality from 10 to 300.

Thus, an inventive antenna in use with the receiving antennas as a low-loss prefilter serve high operating resonance quality, or if as a transmitting antenna as a filter to suppress the broadcast of surface and sub-shafts of the transmission frequency serve.

In comparison with a loop antenna, the radiation resistance the antenna of the invention is significantly higher (in Ohm range) so that the conductor resistance is not long is as critical. Thus one can also antenna easily realized from wire. Geometric tolerances are not critical for the same reason.

Because of their properties can be an inventive Antenna good even at a small distance (a few Mm) before use a metal surface, and also capacitive influences of the antenna (for example, by a Hand) are only small.

The realization of performing a loop substantially Conductor piece, by appropriately bent Wire, by milled conductor pieces or printed Interconnects effected, the latter on a insulating Carriers are arranged, which, for example, a plastic housing or may be a plastic cover.

Advantageous developments of the invention are in the dependent claims indicated.

Is measured to the length of the conductor piece of claim 2, we obtain a good reduction in the velocity of propagation of the electromagnetic waves along the conductor piece and thus a very compact geometry the antenna with mechanical or simple construction of Antenna, which can thus be produced inexpensively.

The development of the invention as claimed in claim 3 is getting more compact dimensions of the antenna.

A spacing of the overlapping portions of the conductor piece, as set forth in claim 4, has proven itself in practice especially. You get a good reduction in the velocity of propagation. At the same time, the antenna structure is compact and the adjacent out conductor portions can be precisely to lead.

allows the development of the invention according to claim 5 the realization of antennas, in which the total length of the conductor piece is an integral multiple the half wavelength is. By changing the winding sense is in each case after the half-wavelength achieved that the magnetic fields which are different from the Portions of the conductor piece are produced, quantitatively are added.

In the antenna according to the invention flow at the ends the conductor piece no current, so that these ends alternatively connect (claim 6) or electrically leave open can (claim 7), as from other points, eg ease of fabrication, mechanical Strength of the antenna, is desirable.

According to claim 8 the conductor piece needs to feed the transmission energy or for extracting the received Energy not to be additionally interrupted. A inductive coupling with the transmitter or receiver, the cooperating with the antenna, is also in view a radical adaptation of antenna and transmitter or receiver advantageous.

The geometries of the antenna surface in Claim 9 are indicated, are particularly well suited for the Realsierung of antennas that no pronounced directivity have, as in the Wireless remote readout desired by flowmeters, because the the provided installation orientation with Wireless remote readout Flowmeters with regard to local needs (Radiator surface, wall surface) must take place and not the transmission ratios to a remote readout Central can be adapted.

Alternatively, you can with the features specified in claim 10 Geometries of the antenna surface directivity achieve the antenna.

Hereinafter, the invention by means of embodiments with reference to the drawing, in which explained. Therein:<dl tsize="8"><dt>Figure 1:</dt><dd>a perspective view of a first Antenna with associated feed device, wherein portions of the antenna forming Conductor piece, the entire length of a half Wavelength corresponds, guided axially spaced are;</dd><dt>Figure 2:</dt><dd>a view similar to Figure 1, in which However, a modified antenna is shown, wherein portions of the antenna forming Conductor portion are spaced radially;</dd><dt>Figure 3:</dt><dd>a view similar to Figure 1, in which However, the total length of the antenna forming Conductor piece is a wavelength equal; and</dd><dt>Figure 4:</dt><dd>a view similar to Figure 3, in which However, the dimension of a practice Bespieles is registered.</dd></dl>

In Figure 1 a magnetic loop antenna is registered, having a conductor portion 10th This includes 1.75 Turns, seen in axial direction, a square Antenna area A enclose. The edge length A surface of the antenna is designated by a.

assigned the various edges of the antenna surface A Portions 12 of the conductor piece 10 are similar out, wherein the pitch of the windings with p denotes is.

It can be seen that in each case two sections 12 of the Conductor portion 10 overlap in the axial direction, except the forwardmost portion of the individually is the winding planes and bridged.

The axial distance p of the conductor portions 12 is in Range 1-5 wire diameters. This results in the area of ​​three sides of the antenna surface A a magnetic coupling of conductor portions 12, and thus a reduction in the propagation speed of the electromagnetic radiation along the length of conductor 10. The corresponding reduction factor k (wavelength the current distribution in the conductor piece 10 / wavelength the electromagnetic radiation in a vacuum) may be between be selected 0.2 and 0.8, depending on how small the pitch p is chosen and how far the conductor sections 12 overlap in the circumferential direction.

Thus, the antenna shown in Figure 1 small dimensions exhibit, although it is a no capacity working in resonance W / 2-antenna (W = wavelength) concerns.

To feed the formed by the conductor portion 10 Antenna loop is provided a coupling loop 14, which also defines a square area, the however, is much smaller than the antenna area A.

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

The transmitter 16 is powered by a 20 Flowmeters ago controlled and transmitted at longer intervals the count of the consumption meter in 20 serial binary representation. Details about the Works of such consumption meter can the DE 195 45 394 A1, DE 30 44 262 A1, DE 42 25 042 A1 or DE 44 22 281 A1 are taken on the reference is made in this respect.

The conductor portion 10 is dimensionally stable and can, for example, about an insulator (not shown), the middle of the twice provided conductor sections 12 packs, at a not shown supporting structure (eg printed circuit board or Housing) to be set.

2 shows a modified antennas for Wireless remote readout shown by flowmeters, to differs from that of Figure 1 in that the Leiterabsschnitte 12 arranged under radial distance are. Such an arrangement is particularly good to realize on printed circuit boards. The conductor portions 10 can there easily from a continuous Copper layer are etched, as the coupling loop 14th

The antenna according to Figure 3 differs from that characterized by Figure 1, that the total length of the conductor piece 10 corresponds to a wavelength. A positive Superimposing the produced by the conductor sections 12 to achieve partial magnetic fields, the conductor portion 10 first been folded and the resulting folded Conductor arrangement is then formed additionally as shown in Figure 1 for a simple conductor piece.

Thus, the current direction will change to the current node.

Figure 4 gives precise dimensions of a practical embodiment. The characteristics of the shown there W antenna are as follows:<tables><table><tgroup cols="2"><tbody><row><entry align="left">Edge length a</entry><entry align="right">25.00 mm</entry></row><row><entry align="left">Wire diameter d</entry><entry align="right">0.63mm</entry></row><row><entry align="left">Pitch p</entry><entry align="right">6,40 mm</entry></row><row><entry align="left">Edge length of the coupling loop</entry><entry align="right">8,50 mm</entry></row><row><entry align="left">Distance of coupling loop</entry><entry align="right">6.60mm</entry></row><row><entry align="left">coupling capacitor</entry><entry align="right">6.20 pF.</entry></row></tbody></tgroup></table></tables>

Thus the following properties are obtained:<tables><table><tgroup cols="2"><tbody><row><entry align="left">Q₀</entry><entry align="left">430</entry></row><row><entry align="left">Operating Q_B</entry><entry align="left">215 (R_i = 50 ohms)</entry></row><row><entry align="left">Input impedance Ze / Ohm</entry><entry align="left">56 + jx 0</entry></row><row><entry align="left">resonant frequency</entry><entry align="left">433.9 MHz</entry></row><row><entry align="left">Radiation resistance R_s</entry><entry align="left">2.79 Ohm</entry></row><row><entry align="left">Loss resistance R_a</entry><entry align="left">0.55 Ohm</entry></row><row><entry align="left">efficiency</entry><entry align="left">83%</entry></row><row><entry align="left">Free space wavelength l</entry><entry align="left">690 mm</entry></row><row><entry align="left">Length ratio a / l</entry><entry align="left">1 / 27.6.</entry></row></tbody></tgroup></table></tables>

The antennas described above are thus typical W / 2 antennas, but have considerably smaller dimensions as typical known W / 2 antennas. Of the by Kopfapazitäten distinguish closed loop antennas they are distinguished by the absence of a head capacity and by a significant improved performance.

Among the conventional helical antennas, the plurality a of turns have, these are different, that its total length is an integral multiple of W is that a symmetrical power supply is provided (at Helix antennas unilateral feed) and that the winding pitch is small, so that a magnetic Coupling of adjacent conductor sections obtained.

Here, the antennas described above are characterized by a mechanically simple compact structure of.

In the embodiments described above was the Antenna area A substantially square. It is understood that the limiting surface of the antenna instead may be selected to be circular. Such antennas have a circumferentially substantially constant Charakterisitk. If one selects the antenna surface A rectangular or oval, can be a Richtcharakterisitk circumferentially achieve variable directivity.