WO2007090785A1

WO2007090785A1 - Electronically controlled antenna and associated method for application in a radio-based system

Info

Publication number: WO2007090785A1
Application number: PCT/EP2007/050988
Authority: WO
Inventors: Dariusz Mastela; Leif Wiebking; Thomas Zander
Original assignee: Siemens Aktiengesellschaft
Priority date: 2006-02-06
Filing date: 2007-02-01
Publication date: 2007-08-16
Also published as: DE102006005281A1

Abstract

The present invention relates to a radio-based system, in particular an RFID system or a radio locating system. The intention is to effectively reduce multi-path propagation effects. For this purpose, a base station antenna (8) is formed by means of a number of radiating elements (7). These radiating elements (7) are actuated electronically in terms of phase and/or amplitude in order to set a preferred direction of action of the antenna (8) by means of a feed network (11). The radiating elements (7) transmit or receive electromagnetic shafts with different phase states and amplitude states. The preferred direction of transmission or of reception is set electronically in this way. This invention is used in particular for RFID systems and radio locating systems which are based on a direct line of sight connection between a base station (1) and target objects (4). The intention is that it will be possible to carry out identification and locating processes in a highly reliable way.

Description

description

Electronically controlled antenna and associated method for use with radio-based systems

The present invention relates to a radio-based system, in particular an RFID system or generally a radio location system. The radio-based system comprises a base station for transmitting a base signal and / or receiving response signals and at least one target object for receiving the base signal and for outputting a response signal. Radio-based systems are all technical systems that use transmitters and / or receivable electromagnetic waves from antennas. These include, for example, radar waves used, for example, in the range of 500 MHz to 100 GHz, or waves used for RFID (Radio Frequency Identification), which are used, for example, in the range of 800 MHz to 2.4 GHz. Basic signals and response signals are such electromagnetic waves. Likewise, FMCW (Frequency Modulated Continuous Wave) radar is included.

It is well known that the radio-based systems are affected by effects of multipath propagation. Particularly disturbing are these effects in RFID (Radio Frequency

Identification) systems and radiolocation systems whose operation is based on a direct line of sight between a reader and transponders. Conventionally, the problems due to multipath propagation are solved by the use of hard gating algorithms or discrete exclusion criteria and / or tracking filters, for example the tracking of a fault ellipse in the "extended Kalman filter", as described for example in DE 103 36 084. This has the disadvantage that the short multipath propagation, with numeric

Computing alone, can not be excluded, lead to significant falsification of the location. Furthermore, by a destructive overlay of the reflected Fields a local damping or an extinction of the field are caused. With a local minimum, a passive RFID tag may not have enough power to run. Applications in a critical measurement environment with many metal objects in the vicinity of a reader can not be performed satisfactorily with a conventional system architecture.

Conventionally, so-called omnidirectional antennas are used in radio-based systems. Conventionally, in a radio system only an omnidirectional antenna is used, which by virtue of its isotropic characteristic has no robustness over multipath propagation. FIG. 1 shows how

Multipath propagation occurs, and indeed when the radio signal several paths lead to the antenna. Reflections, diffraction and scattering result in addition to the direct line of sight between the base station and a target object or transponder more

Propagation paths. Multipath propagation is a major problem with all wireless systems and these can significantly distort or render completely unusable a received signal. In addition, conventional antennas must be mechanically aligned in their main beam direction to a target. This is particularly disadvantageous.

It is an object of the present invention in a radio-based system or in a radio-based transmission system, for example in an RFID system or a radio location system in which in particular a direct line of sight between a base station, which has a reader, and target objects or transponders is necessary, the robustness effectively increase multipath propagation effects. In addition, the communication system in critical measurement environments, for example, with many metal objects, work safely. The object is achieved by a device according to the main claim and a method according to the independent claim. Further advantageous embodiments can be found in the subclaims.

A system architecture of a radio system is extended by an "intelligent" antenna. A phased array is used to eliminate unwanted effects due to

Reduce multipath propagation effectively. This "intelligent" antenna is an electronically controlled antenna that replaces a conventional omnidirectional antenna. According to the system according to the invention, a radio system is coupled to a phased or amplitude-controlled antenna or antennas whose beam is formed by phases or by amplitude coupling. The direction of radiation is controlled by the complex excitation coefficients of the radiating elements, and the radiation direction during transmission and reception can be changed by means of an electrical control signal in the azimuth. An antenna is formed by radiators, the plurality of which generates the antenna. The electronically controlled antenna enables an electrical adjustment of the preferred transmission direction and / or reception direction with simultaneous maximum focusing of the transmission power. Such an antenna has the advantage that the emitters can be pivoted virtually inertia-free, fast and arbitrary. There are no mechanical wear parts needed. The accurate electrical adjustment of the antenna allows tracking of various moving and stationary objects without emitting electromagnetic waves in unwanted directions. Due to the high profit and narrow clubs other Mehrwegausbreitungen from others

Azimuth effectively hidden. It is possible, even in a very difficult measuring environment, for example in an industrial enterprise, to identify by radio waves perform. Due to the high gain and the narrow lobes of the antenna, the noise reflected from metal objects are attenuated and thus practically excluded from a measurement. An effective direction may correspond to a main lobe in an antenna directivity diagram. Effective direction means transmitting and / or receiving direction of an antenna. An antenna can be made up of radiators.

According to an advantageous embodiment, a feed network for controlling the radiator switch and / or phase shifter and / or attenuators, which are controlled by a control device. The control of the switches and phase shifters or attenuators can be carried out digitally with the aid of a microcontroller. In this way, a control of the radiator can be done directly.

According to a further advantageous embodiment, the radiators are designed as microstrip antennas. In addition, the radiators can advantageously be arranged along a point-symmetrical geometry. Examples of point-symmetric geometries are circles, rings or spheres. Particularly advantageous is the arrangement of the antenna elements forming the antenna, that is, the radiator, on a metal cylinder, such as a copper cylinder. The plurality of microstrip antennas are arranged in a circular geometry on a copper cylinder. These microstrip antennas have the advantages of a low overall height, cost-effective production and good integrability. Due to a curvilinear geometry, the antenna can radiate in all directions. A cylinder used has the significant advantage that the individual radiators can only couple with the neighboring radiator.

According to a further embodiment, the radiators are controllable by means of a power distributor with a certain number of attenuators, each with a phase shifter and a switch by means of the feed network. This means, a number r of radiators (re N) is divided into a number s (se N) of attenuators with respective phase shifters and respective switches. A switch can be used to control (r / s) emitters ((r / s) e N). In this way, the construction of a fully electronically controlled antenna is particularly advantageously simplified due to the reduction in the number of required phase shifters and Dampfungsgliedern. In this way, the required number of elements is significantly reduced.

According to a further advantageous embodiment, the emitters associated with a switch are each adjacent to one another at the same distance along the emitter arrangement. In this way, in particular in the case of point-symmetrical emitter arrangements, all effective directions can be provided according to an advantageous geometry. In this way, a control is much easier.

Likewise, according to a further advantageous embodiment, the distances between all adjacent radiators are the same size. Due to symmetries, the drives and readouts are simplified.

According to a further advantageous embodiment, with all switches together, a group of s adjacent radiators can be controlled at any time. In this way, an active main lobe of the antenna can be efficiently generated. A group of s adjacent radiators produces a main lobe. A main lobe corresponds to a main direction of the entire antenna in an antenna directional diagram. In principle, a main lobe generated by means of a group can be regarded as a separate antenna.

According to a further advantageous embodiment, it is particularly expedient to control the group of s adjacent emitters such that the group passes through the entire emitter array. That is, the group "jumps" in each case by a radiator in the respective direction and thereby a moving main lobe is generated. In a cylindrical radiator arrangement, the main lobe can rotate in all effective directions.

According to a further advantageous embodiment, r = 16 individual radiators are used, which are divided into s = 4 switches, phase shifters and attenuators. A switch controls (r / s) = 4 spotlights. The total radiator number = r = 16. With this embodiment, a 360 ° effective range can be effectively "scanned". There is a circulation of a main beam lobe in each case by 360 °. In this way, the entire environment of a base station can be detected.

According to a further advantageous embodiment, a phase excitation is phase-coherent and / or an amplitude distribution corresponding to a Hamming amplitude distribution. In this way, a good balance can be achieved between the half width of the main lobe and the sidelobe suppression.

In accordance with a further advantageous refinement, multipath propagation effects are additionally enhanced by the use of tracking filters, namely the tracking of a tracking filter

Error ellipse reduced in square-root unscented caymanian filter (SR-UKF).

According to the independent claim, a method of operating a radio-based system according to the above embodiments is claimed.

According to an advantageous embodiment, an angle information of an orientation of the base station is generated by means of different effective directions of the antenna. In an FMCW radio-based radar system, in addition to a location, an angle information of an orientation of the base station by means of a phase and / or Amplitude electronically controlled antenna determines. In this case, an amplitude comparison approach can be used to determine the angle information. The signals Pl and P2 received in two directions of action from the antenna differ in amplitude. By determining the difference

ΔP = Pl - P2

it is possible to determine an angle information. In practice, however, signal strengths also vary depending on many factors, such as distance. However, these losses appear identical in both received signals. Considering a ratio r of the difference ΔP to the sum ΣP of the received signals

_ AP - Pl - P2 ΣP Pl + P2

eliminates the components that are present in both signals, while the angle-dependent components are retained. The measured ratio indirectly contains directional information which can be converted to an angle form by means of a function table.

The present invention is based on

Embodiments described in conjunction with the figures. Show it:

Figure 1 shows a radio system with a conventional antenna;

Figure 2 shows an embodiment of a phased array antenna;

3 shows an embodiment of a radio system with phased array antenna; Figure 4 shows an embodiment of a radiator having array antenna;

Figure 5 shows an embodiment of a feed network for a 16-element array antenna;

Figure 6 shows an embodiment of a switching principle of a group antenna according to the invention;

FIG. 7 shows an embodiment of a lobe formation when using a group of four;

8 shows an embodiment of a directional diagram of a

Single emitter when using a phased array antenna.

FIG. 1 shows an exemplary embodiment of a conventional radio system. As the base station 1, an omni-directional antenna 2 is used, which acts simultaneously in all directions. The base station 1 has a reading device 3. In the environment of the base station 1 target objects 4 are arranged. These target objects 4 can be transponders. Likewise, RFID tags are usable. Likewise, these target objects 4 can only be reflective objects. Target objects 4 may be passive, semi-passive or active. In the figure 1, a directly returning response signal is indicated by the reference numeral 5. Reference numeral 6 shows as an example of multipath propagation an indirectly returning response signal. This response signal 6 is reflected, for example, on a wall and also returned to the base station 1.

Figure 2 shows an embodiment of a phased array antenna. An antenna 8 is characterized by an arrangement of

Emitters 7 formed. These emitters 7 are arranged linearly in accordance with FIG. The emitters 7 form the antenna 8. The reference numeral 9 is a directional diagram 9 of the antenna 8 displayed. A main lobe 10 is clearly visible. A feed network 11 has a phase shifter 12 for each radiator 7. By means of a control device 13, the phase shifter 12 are driven, in particular by means of an adaptive scheme for the control of

Weightings. By means of the control device 13, the signals per strand of a radiator 7 are also detected. The feed network 11 also has an adder 14.

FIG. 3 shows an exemplary embodiment of an antenna 8 according to the invention. In this case, identical elements according to FIG. 1 have the same reference symbols. In contrast to the exemplary embodiment according to FIG. 1, instead of an omnidirectional antenna 2, a phased and / or amplitude-controlled antenna 8 is used. The possible and effective main lobes 10 are clearly visible in a directional diagram 9. An accurate electrical adjustment of an antenna 8 allows tracking of various moving or stationary objects 4 without emitting electromagnetic waves 6 in unwanted directions or receiving from unwanted directions. By means of a high signal gain and narrow lobes Mehrwegebreitungen or indirect signals 6 which arrive from other azimuth directions, effectively hidden.

Figure 4 shows an embodiment of a group antenna 8, which is formed from a plurality of radiators 7. This group antenna may also be referred to as a patch array antenna. The antenna 8 shown here has a multiplicity of microstrip antennas as radiators 7, which are arranged in a circular geometry on a copper cylinder 15. The cylinder 15 used has the advantage that the individual radiators 7 couple only with an adjacent radiator 7. According to this embodiment, 16

Emitter 7 is arranged on the copper cylinder 15. Other numbers of radiators 7 are also possible. Other Materials or metals, such as iron, are also suitable for the execution of a cylinder 15.

Figure 5 shows an embodiment of a feed network 11. According to this embodiment, in contrast to the embodiment of Figure 2, the required number of elements is reduced. In particular, a feed network 11 is used, which is operated on a 4-of-16 switch principle. Again, 16 radiators 7 (r = 16) are used, which are each arranged at equal intervals in a circle. The 16 emitters 7 of the antenna 8 are divided into four strands. Each strand is supplied via a power distributor 16, a base signal 17 of the base station 1. Each of the four strands has an attenuator 18, a phase shifter 12 and an I-to-4 switch 19. By means of a switch 19 four radiators 7 are driven. In this case, all radiators 7, which are controlled by means of a first position of the switches 19, form a group of four radiators 7 of the antenna 8 arranged one behind the other. When the switches 19 are switched to a second position, the group is indexed by four radiator positions in one direction of movement. The switches 19 can also be controlled in such a way that a group of (s = 4) four radiators 7 in each case by a radiator position in one

Movement direction is shifted. Thus, the group of radiators 7 rotate a cylinder 15. According to the embodiment according to FIG. 5, the total number of required phase shifters 12 and attenuators 18 can be particularly advantageously minimized from 16 to 4. Each radiator 7 is controlled individually via a one-to-four switch 19, a phase shifter 12 and an attenuator 18. The radiators 7 therefore transmit or receive electromagnetic waves having different phase and amplitude states. The

Control of the switches 19 and the phase shifter 12 is done digitally using a microcontroller 13. There may alternatively be another number s of radiators 7 per group and a different number s of strands are used. The number (r / s) of possible switch positions must be adjusted accordingly. Alternatively, for example, r = 20, s = 4, and (r / s) = 5.

FIG. 6 shows an exemplary embodiment of the movement of a main lobe 10. According to the exemplary embodiment according to FIG. 5, four 1-to-4 switches are controlled in such a way that a group of four of adjacent radiators 7 can be activated at any time. Depending on the control by means of a

Controller 13 may rotate a main lobe 10 around base station 1. According to the arrangement of the radiators 7 according to this embodiment, main lobes 10 can be generated in 16 positions around the base station 1. According to FIG. 6, the main lobe generated by means of four adjacent radiators 7 moves clockwise about one emitter position around the base station 1, thereby covering an area of action of 360 °. All possible positions of the main lobe 10 are shown in FIG. The three representations according to FIG. 6 show three beams which are formed in different effective directions. When 16 beams generated a circulation has taken place. According to the embodiment according to FIG. 6, it is particularly advantageous that, despite a circular geometry, a group of four can be regarded as a linear array antenna.

FIG. 7 shows an exemplary embodiment of parameters L, y _m and

ΔΦ for generating a lobe characteristic using a group of four radiators 7. An antenna 8 is formed such that a desired radiation pattern 9 for the antenna 8 is generated. This can be achieved by suitably varying the individual phase shifts and amplitude attenuations that produce a significant "beam forming". FIG. 4 shows the effective parameters L, y _m and ΔΦ. FIG. 8 shows a directional diagram for a group of four emitters 7. A phase-coherent phase drive and an amplitude drive according to a Hamming amplitude distribution, which correspond to the formula:

can achieve a good balance between a half width of the main lobe (Half Power Beam Width) and a

Side lobe level can be effected. A radiator 7 is constructed so as to cover an azimuth sector of 22.5 ° each. For a complete coverage area of 360 ° therefore 16 spotlights 7 are required. With groups of four controlled individual radiators 7, an antenna gain in the preferred direction of about 8 dB is effected. Each doubling of the number of radiators 7 causes an increase in antenna gain of 2 to 3 dB. At the same time, the absolutely radiated energy at the transmitting antenna remains the same, so it is always compliant with ISM standards. The energy received by the base station 1 is, in contrast, increased. With the proposed antenna 8, the influence of multipath propagation in the radio system can be effectively reduced.

Advantageously, according to the present invention, the robustness of a radio system can be effectively increased over multipath propagation effects. It also improves the overall accuracy and range of a system. Likewise, the use of the system in a critical electromagnetic environment is possible. A critical electromagnetic environment is characterized by the presence of many metallic objects in the vicinity of the base station 1. According to the present invention, a channel of approximately optimum capacity can be used.

Claims

claims

1. A radio-based system, in particular RFID system or radio location system, comprising - a base station (1) for emitting a base signal and / or receiving response signals (5), - at least one target object (4) for receiving the

Base signal and for outputting a response signal (5), characterized in that the base station (1) has an antenna (8) with radiators (7) for setting a preferred effective direction of the antenna (8) by means of a feed network (11) with respect to phase and / or amplitude can be controlled electronically.

2. Radio-based system according to claim 1, characterized in that the feed network (11) for controlling the radiator (7) comprises a switch (19) and / or phase shifter (12) and / or attenuators (18) driving the control device (13).

3. A radio-based system according to claim 1 or 2, characterized in that the radiators (7) are microstrip antennas.

4. Radio-based system according to one or more of the preceding claims 1 to 3, characterized in that the radiators (7) acting in all 360 "directions, for example, along a point-symmetrical geometry, are arranged.

5. Radio-based system according to one or more of the preceding claims 1 to 4, characterized in that the radiators (7) on a metal cylinder, such as a copper cylinder (15) are arranged.

6. Radio-based system according to one or more of the preceding claims 1 to 5, characterized in that r radiator (7), re N, by means of a power distributor (16) with s attenuators (18), se N, each having a phase shifter (12 ) and a 1-on (r / s) switch ((19), (r / s) e N, are controllable by the feed network (11).

7. Radio-based system according to claim 6, characterized in that each (r / s) radiator (7) can be controlled via each 1-to-r / s switch (19).

8. A radio-based system according to claim 7, characterized in that the one-to-r / s switch (19) associated (r / s) emitter (7) are each adjacent to each other at the same distance.

9. Radio-based system according to one or more of

Claims 1 to 8, characterized in that the distances between all adjacent radiators (7) are equal.

10. Radio-based system according to one or more of the preceding claims 6 to 9, characterized in that with all 1-to (r / s) switches (19) at any time a group of s adjacent radiators (7) can be controlled.

11. A radio-based system according to claim 10, characterized in that the group of s adjacent emitters (7) is controllable such that the group passes through the emitter array and thereby generates a moving effective direction, in particular main lobe (10).

12. Radio-based system according to one or more of the preceding claims 6 to 11, characterized in that r = 16 and s = 4 and (r / s) = 4.

13. Radio-based system according to one or more of the preceding claims, characterized in that the radiators (7) can be controlled by means of a phase-coherent phase excitation and / or a Hamming amplitude distribution.

14. A radio-based system according to one or more of the preceding claims, characterized by a sigma-point Kalman filter (SPKF), in particular a square-root unscented Kalman filter (SR-UKF), for additional suppression of multipath propagation effects.

15. A method for operating a radio-based system according to one or more of the preceding claims 1 to 14, characterized in that the base station (1) comprises an antenna (8) with radiators (7) by means of a feed network (11) with respect to phase and / or amplitude for generating effective directions of the antenna (8) are electronically controlled.

16. The method according to claim 15, characterized in that by means of different effective directions of the antenna (8) an angle information of an orientation of the base station (1) is generated.