EP2608316A1 - Assembly with a flat top antenna for emitting or receiving circular and linear polarised electromagnetic waves - Google Patents

Abstract

The arrangement has a plane antenna (A) for radiating or receiving a circular polarized electromagnetic wave. The plane antenna comprises two feed points that are spaced from each other. A fragment (SP) is provided for dividing a radio frequency signal into two phase shifted signal components. An output of the fragment is interconnected with one of the feed points. Two switches are provided in the plane antenna for selective radiation or receipt of the linear polarized electromagnetic wave in a signal path between the outputs of the fragment and feed points. An independent claim is included for method for emitting or receiving circular and linear polarized electromagnetic waves.

Description

The invention relates to an arrangement with a Flächenantentenne according to the preamble of patent claim 1.

Electromagnetic waves propagate in space depending on the design of the radiating antenna with a fixed polarization. Here, a distinction is made between linear polarization and circular polarization.

Especially for applications in the RFID area (RFID = Radio Frequency Identification) are used in applications in the UHF area surface antennas or patch antennas, depending on the design for a fixed polarization direction, z. B. linear vertical, linear horizontal or circular, are constructed. If the propagation conditions of the electromagnetic wave require a specific type of polarization or orientation for the respective application, a specific type of construction must be used depending on the application or, in the case of the linearly polarized applications, the antenna must be aligned in accordance with the desired polarization direction.

By choosing the feed points of a surface antenna, this has either a linear vertical or horizontal polarization. As mentioned, the orientation of the linear polarization mode can be changed by the mechanical rotation of the antenna unit, for example by 90 °. A circular or elliptical type of polarization can be achieved by the known method of superposing phase-shifted linear polarization types.

In many applications, in particular in the RFID field, the spatial position of an RFID tag (RFID data carrier) is variable to a read / write device. This means that depending on the orientation of the corresponding antennas (antenna of the read / write device and antenna of the RFID TAG's) to each other an optimal radio contact can be given either in a linear-vertical, linear-horizontal or circular polarization. Therefore, it is common to provide a read / write device with several differently oriented antennas ("antenna diversity") that can be switched electronically. These antennas are mounted regularly spaced from each other to avoid mutual interference. Furthermore, it is customary to mount at least the antennas for the linear application in a pivotable manner in order to be able to influence the respective spatial orientation of the linearly polarized electromagnetic wave manually or with a motor-operated pivoting member.

From the publication: Forster et al. "Optimization of Circularly Polarized Microstrip Antenna Elements" - ITG Symposium "Antennas", Starnberg, April 1996 a planar antenna for generating a circularly polarized electromagnetic wave is known, wherein two spatially separated feed points are each connected to an output of a splitter, this splitter is arranged to separate an electromagnetic signal into two mutually phase-shifted portions.

The use of multiple antennas, which are possibly also pivotally mounted, is associated with a high hardware cost, the often manual alignment of the individual antennas, especially in industrial applications often cumbersome and costly.

It is therefore an object of the present invention to propose an antenna which differs as possible without changing the mechanical structure or the mechanical orientation can radiate or receive polarized electromagnetic waves.

The solution of the problem provides for the use of a so-called surface or patch antenna, which has two spatially separate feed points, with which two mutually orthogonal wave propagation modes can be generated. For this purpose, a flexible connection is provided, with a control of the two feed points with preferably equal and mutually phase-shifted by 90 ° portions of the radiation or receiving circularly polarized electromagnetic waves is possible, and according to the invention by switching the same antenna with a linear vertical or horizontal polarization can be operated without the unit must be changed mechanically.

The solution of the problem provides in particular an arrangement with an area antenna according to the patent claim 1. In this case, an arrangement with an area antenna for emitting or receiving a circularly polarized electromagnetic wave, preferably in the UHF RFID frequency band, proposed, wherein the planar antenna has two spaced-apart feed points, wherein a splitter for dividing a high-frequency signal into two mutually phase-shifted signal components is provided, and wherein each one output of the splitter is connected to one of the feed points. In this case, a switch is provided for selectively radiating or receiving a linearly polarized, electromagnetic wave in a signal path between the outputs of the splitter and the feed points of the surface antenna. Depending on the setting of the switches, this arrangement can be operated with a circular, a linear-vertical or with a linear-horizontal polarization without mechanical intervention, so that the provision of separate antennas for linear and circular polarization unnecessary. Another advantage is that the antenna gain for a reference dipole is identical regardless of the polarization.

Advantageous embodiments of the arrangement according to the invention are specified in the dependent claims. The features and advantages described here can be realized either individually or in combination with each other.

Advantageously, the feed points are arranged in such a way that mutually orthogonal wave propagation modes are produced, wherein advantageously the two signal components to be transmitted or to be received are also phase-shifted by 90 ° relative to one another. In this way, it is easily possible to radiate or receive both circularly polarized waves and to transmit or receive mutually orthogonal linearly polarized waves.

Particularly good symmetry properties arise when the antenna has a square designed reference surface and a square designed radiating element. In such a geometry can be in conjunction with the connection to the spatially separate feed points particularly well mutually orthogonal wave propagation modes (vibration modes) produce.

Advantageously, a control device or control electronics is provided for the actuation of the switches, wherein the control device is configured such that for the emission or for receiving a circularly polarized wave, both switches are closed, and that for emitting or receiving a linearly polarized wave in Dependence of a desired orientation of the shaft of one of the two switches is closed. For this purpose, electronic switches are advantageously used, which can be switched accordingly fast, which are wear-free and their operation requires little energy. Particularly advantageously, the switches are designed non-reflective, thereby avoiding that in "open" switch, a reflected back signal in the splitter is superimposed on the signal of the alternative signal path and thus for unwanted interference provides. A retroactive effect on a transmission electronics (transmit power amplifier) can be avoided. To reduce reflection at the switch, it must be terminated in the "open" state with regard to the "non-feeding" side with the characteristic impedance of the feeding line.

In the linear application, a signal due to the splitter attenuation of the signal (eg by 3dB) can be avoided if the switches are designed as a changeover switch, and if in addition at least two further switches are provided, which are arranged such that in the use of the arrangement for Radiation or for receiving a linearly polarized electromagnetic wave of the splitter is not arranged in the active signal path.

In an advantageous embodiment, the splitter is designed as a passive component such that the arrangement can be used alternatively or alternately for transmitting and / or receiving linearly or circularly polarized electromagnetic waves. In an alternative embodiment, the alternate transmission and reception of electromagnetic waves may be enabled by providing two different active splitters, one for the transmit case and one for the receive case, for alternate use.

Embodiments of the inventive arrangement will be explained below with reference to the drawings.

Figur 1

eine für die erfindungsgemäße Anordnung geeignete planare Antenne in einer Draufsicht,

Figur 2

die planare Antenne in einer seitlichen Ansicht,

Figur 3

ein Prinzipschaltbild einer erfindungsgemäßen Anordnung für eine zirkulare Polarisationsart,

Figur 4

das Prinzipschaltbild für einen linearvertikalen Betrieb,

Figur 5

das Prinzipschaltbild für einen linearhorizontalen Betriebsfall,

Figur 6

eine alternative Verschaltung der Anordnung für einen linear-vertikalen Betriebsfall und

Figur 7

die alternative Ausgestaltung der Anordnung für einen linear-horizontalen Betriebsfall.

Showing:

FIG. 1

a planar antenna suitable for the arrangement according to the invention in a plan view,

FIG. 2

the planar antenna in a side view,

FIG. 3

a schematic diagram of an arrangement according to the invention for a circular polarization,

FIG. 4

the block diagram for a linear-vertical operation,

FIG. 5

the block diagram for a linear horizontal operating case,

FIG. 6

an alternative interconnection of the arrangement for a linear-vertical operating case and

FIG. 7

the alternative embodiment of the arrangement for a linear-horizontal operating case.

In the Figures 1 and 2 As antenna A, a planar patch antenna for the UHF range of an RFID application, namely for an RFID read-write device, is shown. The planar antenna consists of a preferably square base area GP (ground plane) and a likewise preferably square radiation element P (patch) arranged above it, wherein two feed points F1, F2 ("feed") spaced apart from one another are arranged on the radiator surface P. The in the FIG. 1 Arrows shown here indicate the oscillation axes resulting from the feed points F1, F2. These are aligned orthogonal to each other, which means that based on the representation in the FIG. 1 by feeding a signal at the feeding point F1, a horizontally polarized electromagnetic wave can be radiated, and by feeding at the feeding point F2, a vertically polarized orientation can be obtained.

In the FIG. 3 a schematic circuit (circuit diagram) is shown, wherein the basis of the FIG. 3 introduced designations and components, if provided with the same reference numerals, to apply to the following drawings. In the FIG. 3 and the following figures is from the Figures 1 and 2 already known antenna A, wherein the feed points (not shown) F1, F2 via switches SH, SV (switch horizontal, switch vertical) are connected to a splitter SP, said splitter SP with a (not shown) transmitting / receiving electronics a (not shown) RFID read / write device is connected. The splitter SP, also referred to as "hybrid coupler / power splitter", shares the signal to be transmitted in two mutually phase-shifted by 90 ° to sub-signals, these sub-signals are passed through the switch SH, SV on the feed points F1, F2. Based on the original signal, the sub-signals are attenuated by at least 3dB, because the splitter SP is a passive component, so that, of course, a maximum of half the original signal strength can be present at each output of the splitter SP. Due to the passive design of the splitter SP can be used unchanged for the reception of electromagnetic waves, which of course reverses the signal flow direction. In the in the FIG. 3 In the case shown, both switches SH, SV are closed, so that due to the orthogonal orientation of the wave propagation modes generated by the feed points F1, F2 and due to the phase shift, which is achieved by the use of the splitter SP, radiated altogether a circularly polarized wave can be received. Apart from the use of the here closed switch SH, SV corresponds to the arrangement and mode shown here of the known generation of circularly polarized electromagnetic waves. The switches SH, SV are electronic switches which are used in the examples shown in the FIGS. 3, 4 . 5 be discussed as opener or closer can be executed. They are controlled by means of dashed lines indicated control lines CHC, CVC (circular / linear control, vertical / horizontal control). An unillustrated control electronics or control logic is used for the switching effected by means of the switch SH, SV a polarization, which will be explained with reference to the following drawings.

In the FIG. 4 is the one from the FIG. 3 known arrangement, in which case the switch SH is open, while the switch SV is closed. This results in a sole control of the feed point F2, so that only a vertically-linearly polarized electromagnetic wave is radiated or received by the antenna A. The switch SH is designed non-reflective, which means with the switch SH open, the high-frequency signal led out of the connection "3dB / 0 °" is not reflected back into the splitter SP. This is done by terminating the corresponding line through the open switch SH by means of the characteristic impedance of the feed line. In this constellation, the signal "open" is applied to the switch SH through the control line CHC, while the control line CVC carries the signal "closed".

In the FIG. 5 is that to the FIG. 4 suitable counter-example shown, wherein the switch SV is open and the switch SH is closed, so that a linear-horizontal polarized electromagnetic wave can be radiated or received.

Based on FIGS. 4 and 5 can be seen that according to FIG. 4 with two switches SV, SH arrangement for emitting or receiving circularly polarized electromagnetic waves can be switched by means of simple control signals for a linear-horizontal or linear-vertical operating case. The arrangement, in particular the antenna A, does not need to be changed mechanically for this purpose. By using non-reflective electronic switches SV, SH, which, for example, have integrated a 50-ohm terminating resistor, the power divider, that is to say the splitter SP, is correctly terminated in an exemplary embodiment in 50-ohm technology. This leaves a high decoupling of the two signal branches. For the circular polarization two equal signal components are required, so that a power split by means of the splitter SP results. Therefore, the circular antenna A shown here has an antenna gain that is about 3dB lower (relative to a reference dipole) than a linear antenna without splitter SP.

Another configuration or connection occurs when the power division and thus the splitter SP is bypassed by other electronic switches SE, SL and for the respective polarization (linear-horizontal, linear vertical) necessary feed points F1, F2 are connected directly. This will be discussed with reference to the following figures.

In the FIGS. 6 and 7 are different from the arrangement of the FIGS. 3, 4 . 5 additional switches SE ("signal input") and SL ("switch linear") are provided. The known from the preceding figures switch SV, SH are now designed as a changeover switch SVL, SHL; Similarly, the other switches SE, SL are designed as a changeover switch. The sketched control lines are now labeled CLC, VHC (circular-linear control, vertical-horizontal control). By further switches SE, SL in conjunction with the design of the previous switch as a changeover switch SHL, SVL allows bypassing (shutdown) of the splitter SP in linear polarization. It is in the FIG. 6 that switching state is shown which allows the radiation or the reception of a linear-vertical polarized electromagnetic wave, while in the FIG. 7 the linear-horizontal application is shown. In both figures, it can be seen that the power attenuation due to the splitter SP no longer occurs in the case of linear polarization.

Claims (7)

Arrangement with an area antenna (A) for emitting or receiving a circularly polarized electromagnetic wave,
wherein the planar antenna (A) has two feed points (F1, F2) arranged at a distance from one another,
wherein a splitter (SP) is provided for dividing a high-frequency signal into two mutually phase-shifted signal components, and
wherein in each case one output of the splitter (SP) is connected to one of the feed points (F1, F2),
characterized,
in that a switch (SH, SV) is provided in each case for selectively emitting or receiving a linearly polarized electromagnetic wave in a signal path between the outputs of the splitter (SP) and the feed points (F1, F2) of the planar antenna (A). Arrangement according to claim 1,
characterized,
that the feed points (F1, F2) are arranged such that mutually orthogonal wave propagation modes arise, and
that the two signal components are phase-shifted by 90 ° to each other. Arrangement according to one of the preceding claims, characterized
that the antenna (A) has a square configured reference plane (GP) and a square ausgestaltetes radiating element (P). Arrangement according to one of the preceding claims, characterized
in that a control device is provided for the actuation of the switches (SH, SV), wherein the control device is configured in such a way that both switches (SH, SV) are closed for the purpose of emitting or receiving a circularly polarized wave, and for emitting or receiving a linearly polarized wave in dependence of a desired orientation of the shaft of one of the two switches (SH, SV) is closed. Arrangement according to one of the preceding claims, characterized
that the switches (SH, SV) are carried out non-reflective. Method according to one of the preceding claims, characterized in that
that the switches (SH, SV) are designed as changeover switches, and in that two further switches (SE, SL) are provided, which are arranged such that in use the arrangement for emitting or receiving a linearly polarized electromagnetic wave to the splitter (SP) is not located in the active signal path. Arrangement according to one of the preceding claims, characterized
in that the splitter (SP) is designed as a passive component such that the arrangement can be used alternatively or alternately for transmitting and / or receiving linearly or circularly polarized electromagnetic waves.

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