Antenna arrangement for receiving and transmitting electromagnetic waves of different polarizations

Description

[0001] The invention relates to an antenna arrangement for receiving and transmitting electromagnetic waves of different polarizations, as well as a corresponding method and a coupler circuit.

[0002] Such antenna arrangements can include a feed network. A feed network serves to couple signals from a transceiver unit into an antenna structure at more than one feed point with minimal loss. The feed network, for example, uses a coupler circuit to ensure that predefined portions of the input signal are present at the network outputs with a desired phase angle, thus achieving the desired polarization of the transmitted signal. The lower the losses in the network (for signal splitting and transmission), the higher the amplitude of the output signal(s) fed to the antenna. This effect is particularly pronounced in RFID antennas, since the same antenna (of the RFID reader) is used for both transmitting and receiving.

[0003] Depending on the application, different polarizations can be advantageous. If the orientation of a transponder is unknown, using a circularly polarized antenna—that is, an antenna that receives and transmits circularly polarized electromagnetic waves—offers significant advantages because the variance in the transponder's orientation can be better compensated for, thus improving information readability. However, since transponders in most cases only have a linearly polarized antenna, the transponder can (ideally) only receive half of the electromagnetic wave's energy.In applications where the transponders have a predetermined, known orientation to the reader, it would therefore be advantageous to use an antenna with linear polarization in the reader, so that with correct orientation (of the reader in relation to the transponder) the transponder can absorb more energy, thus achieving a greater identification range.

[0004] Consequently, there is a need for an antenna arrangement that can generate signals of different polarization.

[0005] The paper by Ferrero et al., "A Novel Quad-Polarization Agile Patch Antenna," May 1, 2009, XP011257126, describes a microstrip antenna design capable of generating vertical, horizontal, and right- or left-hand circular polarization using a tunable coupler. This is achieved by changing the coupler's operating mode through switching the bias of two varactor diodes. The paper by Bergeron Jarrah et al., "Microstrip antenna system for arbitrary polarization reconfigurability," April 6, 2014, XP032643050, refers to a microstrip antenna system that enables dynamic polarization changes. It employs a network consisting of a PIN diode switch, a variable power distributor, and two variable phase shifters to adjust phase and amplitude.

[0006] One of the problems underlying the invention is to provide an improved antenna arrangement as well as an improved method for receiving and transmitting electromagnetic waves of different polarization and a corresponding coupler circuit.

[0007] This task is solved by the subject matter of the independent claims.

[0008] The invention relates to a coupler circuit according to claim 1, an antenna arrangement according to claim 11, and a method for transmitting electromagnetic waves of different polarization according to claim 12.

[0009] In other words, as in claim 1, the first and third nodes, as well as the second and fourth nodes, are fixed and preferably directly electrically coupled to one another via the first and third lines, respectively. The electrical connection between the first and second nodes, as well as between the third and fourth nodes, can be selectively established via the first switching device or the second switching device. For example, the first switching device can be configured such that an electrical connection between the first and second nodes can be established via the second line (and, in particular, the first switching device). This state is described below as the coupling state of the switching device. However, the first switching device can also be operated in such a way that there is no electrical connection between the first and second nodes, which is referred to below as the decoupling state.This applies accordingly to the second switching device and the third and fourth nodes.

[0010] The signal input can preferably only be coupled to either the first coupler input or only to the second coupler input.

[0011] According to a first embodiment, the coupler circuit can be operated in a decoupling mode and in a coupling mode, wherein the coupler circuit in the decoupling mode is configured such that the first and second switching devices are operated in a decoupling state, so that the signal input is only connected to the first or second coupler output.

[0012] In decoupling mode, the antenna is preferably configured to emit a linearly polarized electromagnetic wave. Furthermore, in coupling mode, the coupler circuit can be configured such that the first and / or second switching device is operated in a coupled state, so that the signal input is connected to the first and second coupler outputs, and the antenna in coupling mode is preferably configured to emit a circularly polarized or elliptically polarized electromagnetic wave.

[0013] In decoupling mode, for example, the first node is electrically coupled to only one other node, namely the third node. The second node can accordingly only be electrically coupled to the fourth node. The input signal, present at either the first or second coupler input, is then only passed on to one coupler output, either the first or the second. The antenna therefore receives the input signal at only one feed point, which preferentially results in the generation of a linearly polarized electromagnetic wave by the antenna.

[0014] In coupling mode, an input signal at one coupler input can be split across both coupler outputs. For this example, we assume an input signal at the first coupler input, and thus at the first node. We also assume, for this example, that the first through fourth lines each generate a phase shift of 90°.

[0015] In coupling mode, the input signal can travel from the first node to the third node via the first line, experiencing a phase shift of 90°. Simultaneously, the input signal can travel via the second and third lines to the fourth node, experiencing two phase shifts of 90° each, for a total of 180°. The input signal is thus split between two feed points of the antenna, with the signals at these two feed points exhibiting a 90° phase shift relative to each other. This allows, for example, the transmission of a circularly polarized wave.

[0016] The antenna array is thus capable of setting different operating modes by means of the first and second switching devices, in which different output signals are provided at the coupler outputs by determining the forwarding of the input signal, for example, a high-frequency signal, based on the state of the switching devices. In particular, the operating state of the first and second switching devices determines at which coupler outputs an output signal is provided. Furthermore, depending on the operating state of the switching devices, the phase and / or amplitude of the output signals of the coupler outputs, especially with respect to the input signal, can be set, with the state of the switching devices determining whether the input signal is split or not. The operating state of each switching device can be controlled, for example, by means of a control system for the antenna array.When the term "phase shift" is used below, it refers specifically to a phase shift with respect to the input signal, unless otherwise stated.

[0017] The phase shift of the output signals at the first and second coupler outputs, relative to the phase of the input signal, depends primarily on the electrical length of the lines. The "electrical length" of an electrical line refers to the length of the line through which the signal is transmitted. Electrical signals propagating through lines are subject to various phase shifts, delays, and distortions. The phase shift depends particularly on the electrical length of the line. Hereinafter, the term "electrical length" can also be used synonymously with a phase shift caused by an electrical line or component.

[0018] Furthermore, the amplitude of the output signals at the first and second coupler outputs depends in particular on the impedance of the lines and on the amplitude of the input signal.

[0019] By utilizing the aforementioned properties, the high-frequency signal present at the signal input can be forwarded and adapted by means of the coupler circuit in such a way that different output signals are provided at the coupler outputs.

[0020] In the following, it is assumed that the signal input is connected to the first coupler input. However, the same functionality of the coupler circuit can also be achieved if the signal input is connected to the second coupler output, in which case the output signals described below would be reversed. In particular, depending on which coupler input the input signal is applied to, a polarization direction, i.e., left-circulating or right-circulating, and / or a polarization angle, for example of a linearly polarized electromagnetic wave, can be defined.

[0021] If the switching device is operated in coupling mode, i.e., when the first and / or second switching device is in the coupled state, meaning in a state where an electrical connection exists between the first and second nodes and / or the third and fourth nodes, for example, by closing a switch of the respective switching device, the processing of the high-frequency signal present at the signal input can be carried out as follows: The input signal can be routed via the first coupler input and the first line to the first coupler output, so that an output signal is present at the first coupler output which corresponds to a converted, in particular phase-shifted and amplitude-modified, input signal. The output signal of the first coupler output thus exhibits, in particular, a phase shift corresponding to the electrical length of the first line and a corresponding amplitude.

[0022] Furthermore, the input signal can be routed to the second coupler output via two possible paths. The input signal can be routed to the second coupler output via both paths if both the first and second switching devices are operated in the coupled state. Alternatively, the input signal can be routed to the second coupler output via only one of the two paths if one of the two switching devices is operated in the decoupling state and the other in the coupled state. The following describes the case where the input signal is routed to the second coupler output via both paths.

[0023] The input signal can, for example, be routed via a first path from the first node via the second line to the second node and from the second node via the third line to the fourth node. Furthermore, the input signal can be routed via a second path from the first node via the first line to the third node and from the third node via the fourth line to the fourth node. In particular, at the fourth node, the input signal routed via the first path and the second path are combined, so that the output signal at the second coupler output corresponds to the sum of the signals transmitted via the first path and the second path. In particular, the electrical length of the first path, i.e.,The combined electrical length of the second line, including the electrical length of the first switching device and the third line, is at least substantially equal to the electrical length of the second path, i.e., the combined electrical length of the first line and the fourth line, including the electrical length of the second switching device. In particular, the phase shift of the signals transmitted via the first path and the second path is thus equal. Furthermore, the cumulative impedances of the first path and the second path, i.e., the combined impedance of the second and third lines and the combined impedance of the first and fourth lines, can also be at least substantially equal in magnitude.

[0024] In particular, the phase shift of the combined output signal of the second coupler output corresponds to the phase shift of the signals transmitted via the first and second paths. The amplitude of the output signal of the second coupler output is determined, in particular, by the impedances of the respective lines. For example, the output signal of the second coupler output exhibits a phase shift and amplitude corresponding to the electrical length of the first and / or second path.

[0025] The output signal of the first coupler output and the output signal of the second coupler output can therefore have different phase shifts and, depending on the impedance of the lines, also different amplitudes. Accordingly, the output signal of the first coupler output and the output signal of the second coupler output can be fed into the antenna, for example a patch antenna, via the antenna feed points to generate and transmit a circularly polarized or elliptically polarized electromagnetic wave. To generate a circularly polarized or elliptically polarized polarization, for example, two feed lines from the feed points are attached to the antenna, offset from each other by 90°. A 90° offset of the feed points can be provided, for example, in a patch antenna, with the angle being measured, for example, from a center point or centroid of the antenna.The arrangement of the feed points can be chosen, for example, depending on the phase of the output signals and the output impedance (matching) of the coupler circuit. In particular, with a patch antenna, the position of the feed point, e.g., between the patch center (approx. 0 ohms) and the patch edge (approx. 200 ohms), is chosen so that the impedance is matched to the impedance of the coupler circuit.

[0026] As mentioned above, in a symmetrical patch design (e.g., circle, square, octagon, etc.), the geometric angle of the feed point arrangement in the patch antenna can also correspond to the phase angle of the feed signals. For example, two input signals with a 90° phase offset are preferably fed into two orthogonally arranged feed points. With asymmetrical patch contours, e.g., a rectangle, triangle, oval, etc., other orientations are conceivable.

[0027] In the coupled state, the coupler circuit can therefore be operated as a branchline coupler.

[0028] If the switching device is operated in decoupling mode, i.e., when the two switching devices are in a decoupling state, meaning an electrical connection between the first and second or the third and fourth nodes is interrupted (for example, by opening a switch on one of the respective switching devices), the high-frequency signal present at the signal input can be fed in as follows: The input signal can be routed via the first coupler input and the first line to the first coupler output, so that the first coupler output provides an output signal corresponding to a converted, in particular phase-shifted and amplitude-modified, input signal. The output signal of the first coupler output thus exhibits, in particular, a phase shift and amplitude corresponding to the electrical length of the first line.Due to the decoupling state of the switching devices, the input signal cannot be routed to the second coupler output, thus isolating the second coupler output. Specifically, the input signal is essentially routed entirely to the first coupler output. The output signal of the first coupler output can be fed into the antenna via a feed point, resulting in the generation and transmission of a linearly polarized electromagnetic wave. For example, a feed line to the feed point(s) may be positioned in a straight line or at a specific angle to the antenna's orientation. The resulting radiation can be linearly polarized, for example, horizontally, vertically, or at any other angle, depending on the orientation of the feed line.

[0029] The second coupler input can be short-circuited to ground in both operating modes of the coupler circuit, particularly via a terminating resistor, to generate the best possible termination, especially total reflection of the transmission signal.

[0030] The antenna arrangement according to the invention thus makes it possible to switch between a linear polarization mode, i.e., decoupling mode, and a circular or elliptical polarization mode, i.e., coupling mode. This allows the polarization to be flexibly changed depending on the specific application. For example, if an indefinite number of transponders are to be identified using an antenna arrangement such as an RFID reader, the RFID reader can identify an initial number of RFID transponders in a first "coarse" read operation using circularly polarized RF waves, and then, in a second "fine" read operation, identify further RFID transponders that could not be identified in the first read operation due to their lower transmission power using linearly polarized RF waves, which have a higher transmission power than the circularly polarized RF waves.

[0031] A further advantage of the invention lies particularly in the fact that a standard branchline coupler can be adapted with just a few additional components to generate linear, circular, or elliptical polarization. The invention can therefore be implemented particularly cost-effectively and in a space-saving manner.

[0032] The antenna can, in particular, comprise a double bifilar helix antenna, a patch antenna, a cross-fed antenna, or a quadrature antenna. The electromagnetic waves emitted by the antenna can further comprise microwaves, infrared waves, RF waves, and / or laser beams or the like. The high-frequency input signal can also have a wavelength of less than 500 cm, less than 100 cm, or less than 50 cm, in particular 32 cm. Preferably, the high-frequency input signal can have a frequency in an ISM (Industrial, Scientific and Medical) band, in particular in the frequency range between 902 and 928 MHz.

[0033] According to a further embodiment, an electrical length of the first conductor essentially corresponds to an electrical length of the third conductor, wherein the electrical length of the first and / or third conductor each corresponds to an electrical length L1, wherein an electrical length of the second conductor essentially corresponds to an electrical length of the fourth conductor, wherein the electrical lengths of the second and fourth conductors each correspond to an electrical length L2, wherein an electrical length of the first switching device essentially corresponds to an electrical length of the second switching device, wherein the electrical lengths of the first and second switching devices each correspond to an electrical length LS, wherein a phase shift L2S caused jointly by the electrical lengths L2 and LS corresponds at least essentially to an odd integer multiple of 90°.The same can also apply to L1, i.e., that L1 causes a phase shift which corresponds at least essentially to an odd integer multiple of 90°.

[0034] Thus, in coupling mode, it can be ensured that the output signal of the first coupler output is phase-shifted by an electrical length L1, while the output signal of the second coupler output is phase-shifted by an electrical length L12S = L1 + L2S. In particular, the phase shift between the output signal of the first coupler output and the output signal of the second coupler output corresponds to the electrical length L2S, which is an odd integer multiple of 90°, specifically 90°. Therefore, the signals fed into the two antenna feed points also have a phase shift of 90° relative to each other, resulting in the transmission of a circularly polarized or at least elliptically polarized electromagnetic wave.It is also possible, in principle, for the second and fourth lines and the first and second switching devices to be configured such that the phase shift L2S assumes a value that does not correspond to an odd integer multiple of 90°. In such a case, an elliptically polarized electromagnetic wave results. The electrical lengths L2 and Ls are specifically matched so that the phase shift L2S does not assume a value that corresponds to an even integer multiple of 180°, since in this case a linearly polarized electromagnetic wave would be generated.

[0035] According to a further embodiment, the first and third lines each have a first impedance Z 1, in particular one of essentially the same magnitude, wherein the second and fourth lines each have a second impedance Z 2, in particular one of essentially the same magnitude, wherein the first impedance Z 1 and the second impedance Z 2 are selected such that output signals with essentially the same amplitude are output at the first coupler output and at the second coupler output.

[0036] In particular, the impedances Z1 and Z2 are matched. When matching the impedances, an impedance ZS of the switching device can also be taken into account, wherein the first and second switching devices preferably have essentially equal impedances. When matching the impedances, it is also taken into account, for example, that the output signal of the second coupler output in coupling mode is generated based on a combination of the input signal routed via the first path and the second path. Z2 can, for example, be 50 ohms, so that Z1 assumes a rounded value of 35.35 ohms. The coupler circuit can, for example, be configured such that the power of the input signal is divided into two parts of equal amplitude, i.e., output signals, each of which has 3 dB less power compared to the input signal.

[0037] According to a further embodiment, the coupler circuit can be operated in a partial coupling mode in which the first switching device is operated in the coupling state and the second switching device in the decoupling state or vice versa, wherein the antenna is configured to emit an elliptically polarized electromagnetic wave in the partial coupling mode.

[0038] In partial coupling mode, the input signal can only be routed to the second coupler output via either the first or the second path. Consequently, this also affects the amplitude of the second coupler output's output signal. Specifically, the amplitude of the first coupler output's output signal is not equal to the amplitude of the second coupler output's output signal. Furthermore, the phase shift between the first coupler output's output signal and the second coupler output's output signal in partial coupling mode can also be a non-odd integer multiple of 90°. This can result in the electromagnetic wave generated by the antenna exhibiting elliptical polarization. More precisely, to generate elliptical polarization, preferably only one of the two switches is operated in coupling mode, resulting in signals with a 90° phase shift at the coupler circuit's outputs.Due to the impedance differences between L1 and L2, different amplitudes can result. For example, in a symmetrical patch structure, feeding signal into two orthogonal feed points with a 90° phase shift and unequal amplitudes results in an elliptical polarization. By using the coupler circuit in partial coupling mode, an additional, i.e., elliptical, polarization can be generated, which may be desirable in some applications, for example, when only a predefined area needs to be sampled with higher transmit power.

[0039] According to a further embodiment, the first switching device is arranged at one end of the second line closer to the first line, in particular in the immediate vicinity of the first node, and the second switching device is arranged at one end of the fourth line closer to the third line, in particular in the immediate vicinity of the fourth node, or the first switching device is arranged at one end of the second line closer to the third line, in particular in the immediate vicinity of the second node, and the second switching device is arranged at one end of the fourth line closer to the first line, in particular in the immediate vicinity of the third node.

[0040] Furthermore, the first switching device is arranged between a first sub-line of the second line and a second sub-line of the second line and / or the second switching device is arranged between a first sub-line of the fourth line and a second sub-line of the fourth line.

[0041] In particular, the first sub-conductor of the second conductor and the second sub-conductor of the second conductor are configured such that a phase shift caused jointly by an electrical length L21 of the first sub-conductor of the second conductor, by an electrical length L22 of the second sub-conductor of the second conductor, and by the switching device essentially corresponds to an odd integer multiple of 90°. This also applies, in particular, to the electrical length L41 of the first sub-conductor of the fourth conductor and an electrical length L42 of the second sub-conductor of the fourth conductor. In particular, the impedances of the first and second sub-conductors are of equal magnitude for the second conductor and / or for the fourth conductor.

[0042] Alternatively to the invention, the first and / or second switching device, in the decoupling state, can be configured to connect the first or second sub-line to a ground line, i.e., a line element short-circuited to ground. In particular, the ground line has an impedance ZM and is short-circuited to ground at one end. This additional line element can optimize the transmission loss, i.e., the isolation of the second coupler output, in decoupling mode, since mismatches of the coupler circuit, in particular of the impedances, the electrical lengths of the lines, and the switching devices, can be partially compensated.

[0043] Furthermore, the first and / or second switching device, in the decoupling state, is configured to connect the first or second sub-line to an additional open-ended line. That is, instead of an uncontacted open port on the first and / or second switching device, the first or second sub-line is connected to the additional line, which has an open end and an impedance Z3. In this embodiment as well, the additional line element in decoupling mode can optimize the transmission loss, i.e., the isolation of the second coupler output, since mismatches in the coupler circuit, particularly in the impedances, the electrical lengths of the lines, and the switching devices, can be partially compensated.

[0044] In particular, the choice of the additional conductor element, i.e., whether the ground conductor or the additional conductor is used, can depend on the type of switching device, especially on the phase response or phase shift of the transmitted signal generated by the switching device. The ground conductor and / or the open-ended additional conductor are designed such that total reflection of the high-frequency signal occurs through the ground conductor and / or the additional conductor.

[0045] According to another embodiment, the conductors include microstrip lines, coplanar lines, stripline lines, and / or coaxial lines. Particularly in coupler circuits with microstrip lines, the microstrip lines are generally designed to utilize the largest possible substrate height, as this minimizes line losses. However, if the distance to a ground plane (reference ground) of the microstrip line is increased, the conductor width of the microstrip line must be increased to maintain the same impedance. Consequently, in such a case, the microstrip line occupies more area on the substrate. Therefore, especially in coupler circuits using microstrip lines, there is a need to save space on a circuit board. Consequently, the advantages of the invention are particularly evident when using microstrip lines.

[0046] According to a further embodiment, the first and / or second switching device each comprises an SPDT semiconductor switch (SPDT for "Single Pole Double Throw", i.e., a changeover switch), a mechanical switching relay, or a PIN diode. In particular, the transmit power of the antenna arrangement depends on and / or is limited by the type of switching device.

[0047] According to another embodiment, the coupler inputs are connected to a DPDT switch (DPDT stands for "Double Pole Double Throw"), which is configured to couple the signal input to either the first coupler input or the second coupler input and to short-circuit the other coupler input to ground. When the signal input is connected to the first coupler input, the input signal is passed to the first coupler output in decoupling mode, and the second coupler output is isolated. Conversely, when the signal input is connected to the second coupler input, the input signal is passed to the second coupler output in decoupling mode, and the first coupler output is isolated.

[0048] According to a further embodiment, the antenna arrangement also includes a control device configured to selectively control the DPDT switch, the first switching device, and / or the second switching device. The control device is thus able to switch the coupler circuit into different operating modes, i.e., coupling mode, decoupling mode, or partial coupling mode. In particular, the control device can automatically adjust the operating mode of the coupler circuit based on the antenna's reception, i.e., switch from linear to circular or elliptical polarization and vice versa. Furthermore, the control device can control the respective switching devices based on the amplitude of the input signal.For example, with a high input signal amplitude, it can be advantageous to operate the coupler circuit in coupling mode, as the division of the input signal and the associated loss of transmit power are acceptable in order to reach a larger number of potential receivers of the antenna's transmit signal. Conversely, with a low input signal amplitude, it can be beneficial to operate the coupler circuit in decoupling mode to achieve a higher transmit power of the antenna's transmit signal.

[0049] Another aspect of the invention relates to an RFID reader (RFID for Radio Frequency Identification) comprising an antenna arrangement of the type described herein. The RFID reader includes an evaluation unit that sends read signals in the form of input signals to the signal input of the antenna arrangement in order to transmit radio signals to RFID tags, wherein the evaluation unit is configured to evaluate signals emitted by RFID tags and received via the antenna arrangement.

[0050] The descriptions of the antenna arrangement apply accordingly to the coupler circuit, the RFID reader, and the method. This applies in particular to embodiments and advantages.

[0051] Different embodiments of the invention are described below with reference to the drawings. The drawings show: Fig. 1A and 1Bone coupler circuit in a coupling mode and a decoupling mode; Fig. 2 form; a coupler circuit according to a further embodiment; Fig. 3 a coupler circuit according to a further embodiment; Fig. 4 a coupler circuit according to a further embodiment; and Fig. 5 an antenna arrangement with a coupler circuit.

[0052] The embodiment in Fig. 4 The coupler circuit according to the invention is shown. The other figures serve to better understand the invention, but are not covered by the scope of protection. Fig. 1A und 1B show a coupler circuit 12 for use in an antenna arrangement 80 (not shown) for receiving and transmitting electromagnetic waves of different polarization, wherein the coupler circuit 12 is in Fig. 1A in pairing mode and in Fig. 1B The coupler circuit 12 operates in decoupling mode. It comprises a first coupler input 24 connected to a first node 16, a second coupler input 26 connected to a second node 18, a first coupler output 28 connected to a third node 20, and a second coupler output 30 connected to a fourth node 22. The first and third nodes 16 and 20 are further electrically coupled to each other via a first line 32, and the second and fourth nodes 18 and 22 are electrically coupled to each other via a third line 36. Furthermore, the first and second nodes 18 and 20 can be electrically coupled via a second line 34 by means of a first SPDT switch 40, and the third and fourth nodes 20 and 22 can be electrically coupled via a fourth line 38 by means of a second SPDT switch 42.

[0053] Each line has a corresponding impedance 46, 48, 50, 52, where the impedances 46 and 50 of the first line 32 and the third line 36 are equal and each have an impedance value of Z1. Furthermore, the impedances 48 and 52 of the second line 34 and the fourth line 38 are equal and each have an impedance value of Z2. The relationship Z1 = 0.707 * Z2 holds for impedances Z1 and Z2. This impedance dimensioning ensures that the amplitudes of the two output signals of the coupler outputs 28 and 30 are essentially equal.

[0054] Each line 32, 34, 36, 38 also has an electrical length, which indicates the phase shift of the transmitted signal caused by the line. In this case, the electrical lengths 54, 58 of the first and third lines 32, 36 each correspond to an electrical length L1, which corresponds to a phase shift of 90°. Furthermore, the electrical lengths 56, 60 of the second and fourth lines 34, 38 each correspond to an electrical length L2, wherein the electrical length L2 and the electrical length LS of the first and second SPDT switches 40, 42 are dimensioned such that the electrical length L2S = L2 + LS corresponds to a phase shift of 90°.

[0055] As shown in 1A and 1B, the SPDT switch 40 is located at one of the ends of the second line 34 closer to the first line 32 in the immediate vicinity of the first node 16, and the second of the SPDT switches 42 is located at one of the ends of the fourth line 38 closer to the third line 36 in the immediate vicinity of the fourth node 22.

[0056] In pairing mode, which is in Fig. 1A As shown, the SPDT switches 40, 42 are in a coupling state, i.e., the SPDT switches 40, 42 are closed and connect the first and second nodes 16, 18 via the second line 34 and the third and fourth nodes 20, 22 via the fourth line 38. When an input signal 44 is applied to the first or second coupler input 24, 26, the input signal 44 is thus split, so that an output signal is present at the first and second coupler outputs 28, 30, respectively, which has a reduced signal power compared to the input signal 44.

[0057] In the following, it is assumed that the input signal 44 is applied to the first coupler input 24, whereby in the case that the input signal 44 is applied to the second coupler input 26, the operation of the coupler circuit 12 applies accordingly.

[0058] The input signal 44 at the first coupler input 24 is routed from the first node 16 via the first line 32 to the third node 20 and thus to the first coupler output 28, whereby the output signal of the first coupler input 24 is phase-shifted by 90° with respect to the input signal 44 and its amplitude is reduced.

[0059] Secondly, the input signal 44 present at the first coupler input 24 is routed to the second coupler output 30 via two different paths 43, 45. The input signal 44 is routed to the second coupler output 30 via a first path 43, namely from the first node 16 via the second line 34 to the second node 18 and from the second node 18 via the third line 36 to the fourth node 22, and via a second path 45, namely from the first node 16 via the first line 32 to the third node 20 and from the third node 20 via the fourth line 38 to the fourth node 22. The signal transmitted via the first path 43 and the signal transmitted via the second path 45 is phase-shifted by 180° with respect to the input signal 44 at the fourth node 22 and phase-shifted by 90° with respect to the output signal of the first coupler output 28, and its amplitude is reduced.The signal transmitted via the first path 43 and the signal transmitted via the second path 45 are combined and added at the fourth node 22, so that the sum of the two signals is present as the output signal at the second coupler output 30. The output signal of the second coupler output 30 also has a phase shift of 180° with respect to the input signal 44 and 90° with respect to the output signal of the first coupler output 28. Furthermore, the amplitude of the output signal of the second coupler output 30 corresponds to the amplitude of the output signal of the first coupler output 28.

[0060] The output signals of the first and second coupler outputs 28, 30 can then be used in coupling mode to be fed into the patch antenna 64 via feed points 92, 94, 96, 98 of a patch antenna 64 (not shown) in order to generate and transmit a circularly or elliptically polarized RF wave.

[0061] In decoupling mode, which is in Fig. 1B As shown, the SPDT switches 40, 42 are in a decoupling state, i.e., the SPDT switches 40, 42 are open, so that an electrical connection between the first and second nodes 16, 18 via the second line 34 and between the third and fourth nodes 20, 22 via the fourth line 38 is interrupted. When an input signal 44 is applied to the first or second coupler input 24, 26, the input signal 44 is therefore no longer split, but is routed from the first node 16 via the first line 32 to the third node 20 and thus to the first coupler output 28, whereby the output signal of the first coupler input 28 is phase-shifted by 90° with respect to the input signal 44 and has a reduced amplitude. The second coupler output 30 is thus isolated, i.e., no output signal is provided via the second coupler output 30.

[0062] The output signal of the first coupler output 28 can be used in decoupling mode to be fed into the patch antenna 64 via feed points 92, 94, 96, 98 of the patch antenna 64 (not shown) in order to generate and transmit a linearly polarized RF wave.

[0063] Fig. 2 bis 4 further embodiments of the coupler circuit 12 are shown, wherein the coupler circuit 12 is shown only in coupling mode for the sake of simplicity.

[0064] Fig. 2 shows a coupler circuit 12, which differs from the coupler circuit 12 of the Fig. 1A differs in that the SPDT switches 40, 42 in Fig. 2 along the second line 34 or the fourth line 38 more centrally than in Fig. 1A are arranged. The first SPDT switch 40 is arranged between a first sub-line 66 of the second line 34 and a second sub-line 68 of the second line 34, and the second SPDT switch 42 is arranged between a first sub-line 70 of the fourth line 38 and a second sub-line 72 of the fourth line 38.

[0065] Fig. 3 shows a coupler circuit 12, which differs from the coupler circuit 12 of the Fig. 2 differs in that the first and second SPDT switches 40, 42 in the decoupling state connect the first sub-line 66, 70 of the second and fourth lines 34, 38 respectively to a ground line 74, which is connected to ground, wherein an impedance 76 of the ground line 74 has an impedance value ZM.

[0066] Fig. 4 shows a coupler circuit 12, which differs from the coupler circuit 12 of the Fig. 2 differs in that the first and second SPDT switches 40, 42 in the decoupling state connect the first sub-line 66, 70 of the second and fourth lines 34, 38 with an additional line with an open end 78.

[0067] The additional conductor element of the Fig. 3 and 4 , i.e. the ground line 74 and the additional line with open end 78, can optimize the transmission attenuation, i.e. the isolation of the second coupler output 30, in decoupling mode, since mismatches of the coupler circuit can be compensated for by this.

[0068] Fig. 5 Figure 80 shows an antenna arrangement, in particular an RFID antenna arrangement, with a coupler circuit 12 for receiving and transmitting RF waves of different polarizations. The antenna arrangement 80 comprises a signal input 82 with a high-frequency input signal 44, wherein the signal input 82 is connected to a DPDT switch 84, which couples the signal input 82 to a first coupler input 24 of the coupler circuit 12 and connects a second coupler input 26 of the coupler circuit 12 to ground. Alternatively, the DPDT switch 84 can switch the signal input 82 to the second coupler input 26 and connect the first coupler input 24 to ground, thereby changing, for example, the polarization angle and / or the polarization direction of the RF wave, depending on the position of the DPDT switch 84.

[0069] The in Fig. 5 The coupler circuit 12 shown corresponds to the coupler circuit 12 of the Fig. 1A or 1B. As already described above, the coupler circuit 12 can be operated in coupling mode or in decoupling mode. In Fig. 5 The coupler circuit 12 is operated in coupling mode, such that an output signal is output at the first coupler output 28 to a first antenna coupler 85, which splits the output signal of the first coupler output 28 and feeds the split signals via respective feed lines 88 to a first feed point 92 and a third feed point 96 opposite the first feed point 92. Furthermore, an output signal is output at the second coupler output 30 to a second antenna coupler 86, which splits the output signal of the second coupler output 30 and feeds the split signals via respective feed lines 90 to a second feed point 94 and a fourth feed point 98 opposite the second feed point 94. The phase shift between the output signal of the first coupler output 28 and the output signal of the second coupler output 30 corresponds to 90°, while the amplitudes of the two signals are essentially the same.In particular, the supply lines 88 of the first and third feed points 92, 96 are arranged offset by 90° to the supply lines 90 of the second and fourth feed points 94, 98, thereby polarizing the resulting RF wave circularly or elliptically.

[0070] When the coupler circuit 12 is operated in decoupling mode, the input signal 44 is not split, but is routed from the first node 16 via the first line 32 to the third node 20 and to the first coupler output 28. The second coupler output 30 is then isolated, i.e., no output signal is provided via the second coupler output 30. The output signal of the first coupler output 28 is, as in coupling mode, provided to the first antenna coupler 85, which splits the output signal of the first coupler output 28 and feeds the split signals via the respective feed lines 88 to the first feed point 92 and the third feed point 96. No signals are fed via the second and fourth feed points 94 and 98, so the resulting RF wave is linearly polarized. Bezugszeichenliste

[0071] 12 Coupler circuit 14 Antenna arrangement 16 First node 18 Second node 20 Third node 22 Fourth node 24 First coupler input 26 Second coupler input 28 First coupler output 30 Second coupler output 32 First line 34 Second line 36 Third line 38 Fourth line 40 First SPDT switch 42 Second SPDT switch 43 First path 44 Input signal 45 Second path 46 First line impedance 48 Second line impedance 50 Third line impedance 52 Fourth line impedance 54 First line electrical length 56 Second line electrical length 58 Third line electrical length 60 Fourth line electrical length 64 Patch antenna 66 First sub-line of the second line 68 Second sub-line of the second line 70 First sub-line of the fourth line 72 Second Sub-conductor of the fourth line 74 Ground line 76 Impedance of the ground line 78 Additional open-ended line 79 Impedance of the additional open-ended line 80 Antenna arrangement82 Signal input 84 DPDT switch 85 First antenna coupler 86 Second antenna coupler 88, 90 Feed lines 92 First feed point 94 Second feed point 96 Third feed point 98 Fourth feed point

Claims

1. A coupler circuit (12) for transmitting a polarized electromagnetic wave from an antenna, which can be connected to coupler outputs (28, 30) of the coupler circuit (12), wherein the coupler circuit (12) comprises the following features: a first coupler input (24) connected to a first node (16); a second coupler input (26) connected to a second node (18); a first coupler output (28) connected to a third node (20); and a second coupler output (30) connected to a fourth node (22), wherein the first and third node (16, 20) are electrically coupled to one another via a first line (32), wherein the second and fourth node (18, 22) are electrically coupled to one another via a third line (36), wherein the first and second node (16, 18) can be electrically coupled via a second line (34) by means of a first switching apparatus (40), wherein the third and fourth node (20, 22) can be electrically coupled via a fourth line (38) by means of a second switching apparatus (42), wherein the coupler circuit can be coupled to a signal input (82) via the first coupler input (24) or via the second coupler input (26), wherein the first switching apparatus (40) is arranged between a first subline (66) of the second line (34) and a second subline (68) of the second line (34) and / or wherein the second switching apparatus (42) is arranged between a first subline (70) of the fourth line (38) and a second subline (72) of the fourth line (38), characterized in that the first and / or second switching apparatus (40, 42) is / are configured in a decoupling state to connect the respective first or second subline (66, 68, 70, 72) to an additional line with an open end (78).

2. A coupler circuit (12) according to claim 1, wherein the coupler circuit (12) can be operated in a decoupling mode and in a coupling mode, wherein the coupler circuit (12) is configured in the decoupling mode such that the first and second switching apparatus are operated in the decoupling state so that the signal input (82) is only connected to the first (28) or second coupler output (30), wherein the antenna is configured in the decoupling mode to transmit a linearly polarized electromagnetic wave, wherein the coupler circuit (12) is configured in a coupling mode such that the first and / or second switching apparatus is / are operated in a coupling state so that the signal input (82) is connected to the first (28) and second coupler output (30), wherein the antenna is configured in the coupling mode to transmit a circularly polarized or elliptically polarized electromagnetic wave.

3. A coupler circuit (12) according to one of the preceding claims, wherein an electrical length (54) of the first line (32) substantially corresponds to an electrical length (58) of the third line (36), wherein the electrical length (54, 58) of the first and / or third line (36) corresponds to an electrical length L1 in each case, wherein an electrical length (56) of the second line (34) substantially corresponds to an electrical length (60) of the fourth line (38), wherein the electrical length (56, 60) of the second and / or fourth line (38) corresponds to an electrical length L2 in each case, wherein an electrical length of the first switching apparatus substantially corresponds to an electrical length of the second switching apparatus, wherein the electrical length of the first and second switching apparatus corresponds to an electrical length LS in each case, wherein a phase offset L2S caused jointly by the electrical lengths L2 and LS substantially corresponds to an odd integer multiple of 90°.

4. A coupler circuit (12) according to any one of the preceding claims, wherein the first and third line (32, 36) each have a first impedance, wherein the second and fourth line (34, 38) each have a second impedance, wherein the first impedance and the second impedance are selected such that output signals with substantially the same amplitude are output at the first coupler output (28) and the second coupler output (30).

5. A coupler circuit (12) according to claim 2, wherein the coupler circuit (12) can be operated in a partial coupling mode in which the first switching apparatus is operated in the coupling state and the second switching apparatus is operated in the decoupling state or vice versa, wherein the antenna is configured to transmit an elliptically polarized electromagnetic wave in the partial coupling mode.

6. A coupler circuit (12) according to any one of the preceding claims, wherein the first switching apparatus is arranged at an end of the second line (34) that is closer to the first line (32) and the second switching apparatus is arranged at an end of the fourth line (38) that is closer to the third line (36) or the first switching apparatus is arranged at an end of the second line (34) that is closer to the third line (36) and the second switching apparatus is arranged at an end of the fourth line (38) that is closer to the first line (32).

7. A coupler circuit (12) according to any one of the preceding claims, wherein the lines comprise microstrip lines, coplanar lines, stripline lines, waveguides and / or coaxial lines.

8. A coupler circuit (12) according to any one of the preceding claims, wherein the first and / or second switching apparatus each comprises / comprise an SPDT semiconductor switch (40, 42), a mechanical switching relay or a PIN diode.

9. A coupler circuit (12) according to any one of the preceding claims, wherein the coupler inputs (24, 26) are connected to a DPDT switch (84) which is configured to couple the signal input (82) to the first coupler input (24) or the second coupler input (26) and to short-circuit the respective other coupler input (26, 24) to ground.

10. A coupler circuit (12) according to claim 9, wherein the DPDT switch (84), the first switching apparatus and / or the second switching apparatus are configured to be selectively controlled by a control apparatus.

11. An antenna arrangement (80), in particular an RFID antenna arrangement, for receiving and transmitting electromagnetic waves of different polarization, said antenna arrangement (80) comprising: an antenna which has at least two feed points (92, 94, 96, 98) arranged spaced apart from one another, wherein the antenna is configured to transmit a polarized electromagnetic wave; a signal input (82) for a high-frequency input signal (44); a coupler circuit (12) according to any one of the preceding claims that is coupled to the signal input (82), wherein the signal input (82) can be coupled to the first coupler input (24) or to the second coupler input (26), wherein the first and second coupler output (28, 30) are each connected to one or more feed points (92, 94, 96, 98) of the antenna.

12. A method for transmitting electromagnetic waves of different polarization that comprises: a high-frequency input signal (44) being applied to a coupler circuit (12) according to any one of the claims 1 to 10, a polarized electromagnetic wave being transmitted by an antenna connected to the coupler circuit (12), wherein the type of polarization of the electromagnetic wave is changed by switching the first and / or second switching apparatus of the coupler circuit (12).