Patent Application
20060082494
The invention relates to a method and an arrangement for testing at least one antenna, in particular a multiple antenna system in a vehicle.
As the number of antennas on vehicles increases, it is becoming necessary to carry out a functional test of the antenna system. Functional tests such as these are normally carried out in the removed state. A functional test with the antenna in the installed state has been particularly complex and required a particularly large amount of effort. For example, DE 196 18 333 A1 describes a circuit arrangement for functional testing of mobile broadcast radio receiving systems in the installed state. One disadvantage of this circuit arrangement is that it has a calibrated signal generator to produce a test signal, which signal generator transmits a discrete test signal exclusively at the frequency to which the receiver is tuned. Furthermore, the circuit arrangement is not suitable for diagnosis which accounts for external influences, such as snow or ice.
A system for testing a signal transmitter/receiver, for example for a receiving antenna, is disclosed in U.S. Pat. No. 6,005,891. In this case, a pseudo-random noise signal source is used as the test signal source. A complex circuit is used in the system to process a signal which has been reflected from a damaged receiving antenna and to compare this with the original test signal. A correlation receiver, among other items, is required for this purpose. However, this system is highly costly to produce, as a result of the use of the pseudo-random noise signal source, which produces a high-speed digital signal, as well as the correlation receiver. Furthermore, it is always necessary to know the level of the output signal from the pseudo-random noise signal source.
The invention is thus based on a method for testing at least one antenna in a vehicle, in which diagnosis can be carried out at all the frequencies in one band, for example a radio, TV, mobile radio or ISM band, at low costs and in a particularly simple manner. Furthermore, the invention provides a particularly simple arrangement for testing the antenna in the installed state. In the invention knowing the level of the test signal source is not necessary, thus making it possible to use a low-cost test signal source.
The advantages which are achieved by the invention are, in particular, that a noise signal from an uncalibrated noise source is injected into the antenna as a test signal by means of a controllable coupling module. If there is only a single antenna, the noise signal which is being reflected at the antenna input is evaluated as the received signal in a test module. For this purpose, the received signal is advantageously used to determine an instantaneous transmission coefficient, which represents the relevant antenna, at a predetermined frequency or at two or more frequencies in a band. The instantaneous transmission coefficient is compared with a reference transmission coefficient, which represents the transmission behavior of the noise source via the coupling module to the antenna and back to the receiver. A serviceable antenna produces minimal reflection at the antenna.
In the case of a multiple antenna system comprising two or more antennas, the noise signal transmitted between the antennas is analyzed and assessed alternatively or in addition to the noise signal which has been reflected at the respective antenna inputs. For this purpose, the noise signal is injected into the antenna or antennas from the uncalibrated noise source or test signal source by means of a coupling circuit, is received by an adjacent antenna, and is analyzed by means of a transmission matrix in the test module, in particular in the receiver, for example an audio or video tuner. Such functional monitoring or diagnosis using a simple uncalibrated noise source, which in the simplest case is formed by a source in the receiver itself, allows a particularly low-cost and simple arrangement. In particular, the production cost is particularly low. As a result of the use of already existing components in the receiver, the arrangement generally requires little space and, as a result of this and due to the integration of the test module, for example, in a vehicle, there is no need for complex test transmitters at the end of the production line or for servicing when the diagnosis or test method is used in the vehicle field.
Furthermore, the use of a noise signal as the test signal allows a diagnosis covering all the frequency bands to be carried out on the antenna or antennas. In particular, a test such as this based on a noise signal also allows evaluation relating to external influences on the serviceability of the antenna or antennas, such as snow or other external interference signals, which lead to incorrect diagnosis in the case of the conventional systems based on the prior art. In particular, this ensures that the antenna or antennas is or are tested and monitored in the installed state as well, and thus, for example, while a vehicle is being driven.
Preferred exemplary embodiments of the invention will be explained in more detail in the following text in conjunction with the drawing, in which:
FIGS. 3 to 5 show, schematically alternative embodiments of the circuit arrangement as shown in
FIGS. 7 to 14 show, schematically, various circuit arrangements for testing the serviceability of an individual antenna.
Mutually corresponding parts are provided with the same reference symbols in all of the figures.
In one advantageous embodiment, the noise source 18 may be in the form of a bipolar transistor in an amplifier circuit. With the diagnosis or test method proposed here, there is no need for a calibrated noise source. This makes it possible to avoid the complex determination of the instantaneous frequency response of the noise source 18, which is dependent on components and temperature. The RF switch 20 which can be driven is, for example, in the form of switching diodes. The number of switching diodes corresponds to the number of antennas 2 which are used as transmitting antennas 2(n) in the diagnosis mode. The number of transmitting antennas 2(n) used governs the evaluation confidence of the diagnosis.
The diagnosis circuit does not involve expensive production costs but can, for example, be accommodated on the board surface of the antenna amplifier module, by changing its layout. The data can be evaluated in the tuner or receiver 8 by an addition to the software, and there is no need for additional hardware. Depending on the nature and embodiment of the circuit arrangement 1, the receiver module 8 and the coupling module 10 may be formed by a common module. Furthermore, the individual modules may be in the form of software and/or hardware, depending on the function. In addition, the arrangement and combination of the individual modules may vary, depending on the requirement.
The switching diodes are driven by means of a digital counter 21. If the bit rate is low, a control signal DI transmits two voltage states from the receiver module 8 to the digital counter 21. The control signal DI can be transmitted along an already existing RF cable in the same way as is already done for driving a given FM diversity circuit. The counter 21 is switched onwards by one position on each positive edge of the control signal DI, so that all of the antenna branches A, B, . . . , Z are switched through successively. Once the final antenna branch Z has been switched through and the diagnosis is produced, the next positive edge causes the noise source 18 to be switched off or, alternatively, to be switched to a state in which no antenna branch A to Z is switched through. The next positive edge once again switches the first antenna branch A through in a new diagnosis cycle.
At least two rear windshield antennas 2 are successively connected as transmitting antennas 2(n) via the RF switch 20. In an antenna system 4 having at least two antennas 2, the serviceability of the antennas 2 is preferably measured by measurement of the near field transmission between the antennas 2. The reference transmission coefficients Üvinorm or factors for all the possible couplings between the antennas 2 form the transmission matrix 14. The instantaneous transmission coefficients Üvi are determined analogously to this on the basis of the transmission matrix 14, and are compared with the reference transmission coefficients Üvinorm. In this case, the antennas 2 are used both as transmitting antennas and as receiving antennas.
The transmission path is determined by transmission of the noise signal S via one of the antennas 2 as a transmitting antenna n and by reception of the received signal S′, which results from this, at one of the other antennas 2 as a receiving antenna m, and by reflection of the noise signal S at the antenna input of the relevant transmitting antenna n.
The evaluation on the basis of the transmission matrix 14 expediently allows identification of adverse affects, such as wetness, snow, external interference signals, which can affect two or more antennas 2. The test or diagnosis is carried out such that the transmission of the noise signal S from the respectively selected transmitting antenna 2(n) to the other adjacent rear windshield antennas 2, which form the receiving antennas 2(m), is tested in the receiver module 8, in particular for all frequency bands. Each antenna 2 is thus tested for its transmission behavior Üv in a number of frequency bands. The FM band, the highest TV band and the AM band are expediently analyzed, so that the operation of the antennas 2 can be tested and determined reliably and easily on the basis of the transmission behavior Üv. Since the transmission is further tested in different combinations of transmitting antennas n and receiving antennas m, it is possible to exclude external fault sources.
During operation of the circuit arrangement 1, the RF switch 20 does not allow any noise signal S on the antenna path 22 during normal antenna operation, when it is in the position 0. In the diagnosis or test mode, the RF switch 20 is switched successively to the positions 1 and 2, with the noise signal S being injected successively in to the antenna path 22 via coupling circuits 24, for example by means of T junctions or capacitively. There, the noise signal S is split into the noise signal S1, which is passed directly from the noise source 18 to the tuner 8, and the noise signal S2, which migrates to the relevant antenna 2 and is emitted at the antenna 2. Statements relating to the serviceability of the relevant antennas 2 can be made from the comparison of the received signal S2, which is received from the receiving antenna 2(m), with the noise signal S1, which is supplied directly for level evaluation. Furthermore, depending on the extent of the analysis, amplifier and filter circuits 26 which affect the transmission path and their influence on the transmission can be taken into account. Since two or more or all of the antennas 2 are used as transmitting antennas n, and all of the antennas 2 are used as receiving antennas m, the entire system can be represented by a transmission matrix 14 with a maximum size of n×m.
The determination of the transmission matrix 14 for a level evaluation and the measurement tolerance to be expected will be described in the following text with reference to
For level evaluation using the transmission matrix 14, the signal levels Si1, Si2 and Si3 are respectively detected at the ports I, II and III for level evaluation when two or more antennas i (i=1, 2, 3) are used as the transmitting antenna n. In the case of an antenna system 4 which is largely completely serviceable, that is to say it is optimally matched, minimal reflection occurs at the antenna inputs 2. The noise signal S whose level is Pr(f) is injected successively into each of the signal paths 22 of the antennas 2. Some of the noise power is emitted via the respectively connected antenna 2, while a further portion is passed via the respective filter amplifier circuit 26 in the path 22 directly to the receiver module 8. The level Pr(f) of the noise source 18 need not be known in advance before measurement, since it can be determined from the measurement evaluation by means of the test module 12 in the receiver module 8. The measurement results in the diagnosis process are thus not dependent on the tolerance of the noise source 18.
The assumed transmission coefficient or reference transmission coefficient Üvinorm(f), the filter amplifier circuit 26 with the narrowest tolerance δvi and the actual transmission coefficient on the basis of
Üvi(f) where Üvi(f)=Üvinorm(f)×(1+δvi(f)) [1]
are used as the basis for determination of the instantaneous noise power Pr.
The signal level S11, as detected in the level evaluation, for the first antenna 2 at the port I in accordance with
S11(f)=(Pr(f)/2)×Üv1(f)=(Pr(f)/2)×Üv1norm(f)×(1+δv1(f)) [2]
is used as the basis for determination of the noise level Pr(f) for a given measurement tolerance δv:
Pr(f)=2S11(f)/((Üv1norm(f))×(1+δv1(f)) [3]
Accordingly, the noise characteristics of the noise source 18 may differ individually for each component, may be dependent on the temperature, and need not be known in advance. This allows simple low-cost noise sources 18 to be produced. Once the noise level Pr(f) has been determined, the transmission coefficients Üv2(f) and Üv3(f) of the other filter amplifier circuits 26 can be determined from the respective signal levels S22 and S33.
Üv2(f)=2S22(f)/Pr(f); Üv3(f)=2S33(f)/Pr(f) [4]
By comparison with the reference transmission coefficients Üv2norm(f) and Üv3norm(f) or nominal values for the respective frequency bands, the serviceability of the respective filter amplifier circuit 26 can easily be deduced from these coefficients Üv2(f) and Üv3(f). The tolerance δv for the noise power Pr is also obtained from these coefficients Üv2(f) and Üv3(f). The transmission coefficients Üa12(f) and Üa13(f) between the antennas 2 make it possible to calibrate out the tolerances in the transmission path 28 on the basis that:
Üa12(f)=S12(f)/S22(f); Üa13(f)=S13(f)/S33(f) [5]
The indication tolerance in the receiver 8 is not included in this analysis, since the assessment of the antenna system 4 always relates to its sensitivity. Accordingly, if the sensitivity of the receiver 8 is high, the antenna system 4 may have correspondingly poorer transmission characteristics. The required quality of the antenna system 4 is thus always assessed as a function of the available tuner sensitivity using the diagnosis system or the circuit arrangement 1, so that entire systems 1 (receiver 8 and antenna system 4) with the same quality are always assessed to be the same.
The transmission coefficients Üa not only provide information about the serviceability of the antennas 2, but also about the extent to which the transmission path 28 between the antennas 2 is subject to interference. If, for example, the antennas 2 are covered with snow, then all of the transmission coefficients Üvi(f) are interfered with to the same extent, and the diagnosis algorithm identifies that it is not an antenna 2 which is faulty, but that all the transmission paths 28 are affected. The state of the antennas 2, for example the fact that the rear windshield 6 is covered with a foreign body, is deduced as a function of the magnitude of the instantaneous determined transmission coefficients Üvi(f).
The method described above for testing the serviceability of the antenna 2 is not dependent on the antenna type.
Alternatively or additionally, depending on the equipment fitted to the vehicle, it is also possible to investigate the serviceability of mobile telephone and/or GPS antennas via broadband coupling to TV, AM and FM antennas. In this case, it is irrelevant where and how the individual antennas 2 are integrated in the vehicle.
During operation of the circuit arrangement 1, as shown in one of the FIGS. 1 to 5, the total of n antennas 2 are successively connected as transmitting antennas. Depending on the number n of transmitting antennas 2, this results in a corresponding number m of receiving antennas 2, and thus in n×m level information items, which are preferably in the form of a level or transmission matrix 14, in order to represent the transmission behavior Üv. A permissible value range can be produced for each transmission coefficient Üvi in the transmission matrix 14, which:
If a permissible value range is exceeded, one or more antennas 2 is or are determined to be defective on the basis of the transmission matrix 14.
External interference effects, which affect one or more antennas 2, for example ice on the rear windshield 6, are advantageously analyzed and identified in the diagnosis process by dynamically matching the value ranges to the instantaneous reception situation.
Table 1, below, shows one example of a transmission matrix 14 for an antenna system 4 with four antennas 2.
where Ant n=the number of transmitting antennas, Ant m=the number of receiving antennas, TX=a transmitter, RX=a receiver, Pnm=the signal level.
Depending on the nature and the function of the circuit arrangement 1, the transmission matrix 14 has, as information items, level and/or frequency values which represent the reference transmission coefficients Üvinorm and/or instantaneous transmission coefficients Üvi for the relevant antenna combination. During a diagnosis, the instantaneous transmission coefficients Üvi are compared with the reference transmission coefficients Üvinorm for each of the antenna combinations 2(n, m). To do this, the transmission matrix 14 must be initialized, for example before initial use of the vehicle, such as at the time of production. Reference knowledge is generated for this purpose, on the basis of which a diagnosis can then take place. One possible method for knowledge generation and evaluation is described in the following text.
A diagnosis is carried out in a number of steps:
By way of example,
The measurement and diagnosis method will be explained in the following text with a reference to an example. The transmission behavior between different rear windshield antennas 2 in their near field is determined by means of a so-called network analyzer. The transmission behavior is measured by injecting the noise signal S into the antennas 2 successively. The vehicle roof, the C pillars and the rear cover with sheet steel parts electrically connected has been modeled in order to estimate the field behavior on the actual vehicle. Measurements have been carried out for intact antennas 2 as well as for defective antennas 2, for example for a discontinuity in the windowpane contacts and/or for a discontinuity in the antenna wires on the rear windshield 6. The influence of wetness on the transmission behavior has also been measured.
The transmission or noise signal S was injected directly into the antenna 2, with the antenna amplifier disconnected. The transmitting antenna 2 is thus not matched. If the transmitting antenna 2 is fed in a matched manner, the transmission factors are better. The values included in the following tables are the S21 transmission coefficients in dB, in each case measured at 100 MHz (FM). S21 transmission coefficients represent the transmission factor or transmission coefficients Üvi between the respective antennas 2 which are coupled via the near field. In addition to the normal situation in which the antennas 2 are serviceable, a number of types of fault situations, and their influence on the transmission factors, have been investigated. The fault situations were brought about by disconnecting the windowpane contacts, interrupting the windowpane antenna wires, influencing the near field of the antennas 2 by means of water on the windowpane, and by means of metal surfaces located in the near field of the antennas 2.
For the normal situation without any fault influence on an antenna system 4 which comprises six antennas 2 and is integrated in the rear windshield 6, the transmission matrix illustrated in Table 2 is obtained for the frequency f=100 MHz (FM band):
The instantaneous transmission coefficients Üvi determined by means of the transmission matrix 14 are all better than −25 dB and the required transmission powers to be expected for near field transmission are very low, measured with respect to the conventional far field transmission/reception situation.
In order to illustrate the detection of poor contacts with the antenna 2, the window pane contacts were made worse or were interrupted at the connections to the antennas FM1 and TV3 by the insertion of layers of paper of different thickness. As is shown in Table 2, the antenna combination FM1 and TV3 normally has a transmission coefficient Üvi of −22.37 dB.
Table 3 shows the influence of poor contacts on the transmission behavior in the form of a significant change in the transmission coefficients Üvi determined in this instance by means of the transmission matrix 14.
The final fault situation “metal sheet in front of the windowpane” in this case simulates an invalid state, as would occur, for example, as a result of conductive material such as ice or water on the rear windshield 6.
Furthermore, a discontinuity in the antenna wires as modeled, for example by cutting through the conductor track for the antenna TV3 or cutting through both conductor tracks for the antennas TV3 and FM2. In this case, the test or noise signal S is transmitted via the antenna FM2 or FM1, depending on the drive for the coupling or RF switch 20. The transmission coefficients Ü determined by means of the transmission matrix 14 are shown in the following Tables 4A to 4C.
All the fault situations can clearly be identified from a decrease or increase in the transmission factors Ü. The method described above thus allows the serviceability of individual antennas 2 to be diagnosed particularly easily and reliably. Further transmission characteristics or operating parameters may be taken into account, depending on the type of antenna. For example, the rise in the so-called cross-coupling factor S FM1→FM3 in the UHF band (800 MHz) in the event of a fault in the FM antenna can be explained by shortening of the electrically effective antenna length. In contrast, the same fault in the FM band leads to a corresponding reduction in the coupling.
In a further test of the antennas 2, they are analyzed for changes caused by the influence of water on the rear windshield 6, or by other objects in the vicinity of the rear windshield 6. As is shown in the Tables 5A and 5B, water spray has virtually no influence on the transmission behavior at 100 MHz. In contrast, if objects, in particular conductive objects, are arranged closely in front of the rear windshield 6, these changes are indicated in the diagnosis, since they represent a significant influence on the transmission behavior of individual antenna pairs.
The superimposition of the noise signals S1 and S2, comprising the noise signal S1 that is passed directly from the noise source 18 to the receiver 8, and the reflected noise signal S2, results in a characteristic frequency characteristic with notches, from which conclusions are drawn about the state of the antenna 2, and these are assessed. However, this is dependent on a calibrated noise source 18, whose frequency characteristic is known. The serviceability of the antennas 2 can be determined only by comparison of the frequency characteristic of the superimposition of the noise signals S1 and S2 with the frequency characteristic of the noise signal S1.
In order to allow the calibrated noise source 18 to be replaced by a lower-cost uncalibrated noise source 18, the static coupling circuit 24 has a switching function added to it, with additional positions 2 and 3 for the switchable coupling circuit 44, as is illustrated in
As an alternative to the switchable coupling circuit 44 or to the open switch, a superimposition of the noise signal S1 and of the noise signal S2 as reflected on a defined impedance Z can also be measured and analyzed for the reference measurement of the noise signal S1, with a calculation then being carried out back to the frequency characteristic of the pure noise signal S. The associated circuit arrangement 1 is illustrated, by way of example, in
The frequency characteristic of the illustrated embodiments in FIGS. 7 to 9 for single antenna systems 4 is detected and analyzed in a relatively wide frequency band, in order to ensure statements that are as good as possible about the serviceability of the antenna 2, since significant level changes do not necessarily occur in the area of the mid-frequency fm in the superimposed noise signal S1+S2 if the antenna 2 is damaged.
A directional coupling circuit 46, for example a directional coupler, as is illustrated in
In order to allow a low-cost uncalibrated noise source 18 to be used, a directional coupling network 48 with a switchable signal flow direction is used, as is illustrated in
FIGS. 12 to 14 now show modified forms of the arrangement shown in
The embodiment shown in
As a result of the use of this additional switch 51, it is now also possible to dispense with the RF switch 20. The resulting circuit is illustrated in
The advantages which are achieved by the invention are, in particular, that it is possible to use a noise generator 18 which can be integrated in the antenna module 10 as a transmitter. The tuner or transceiver, which has being switched to a diagnosis mode, can be used as the receiver 8. This results in a particularly low-cost transmitter. Since the receiver 8 already exists, software can be added to it for the diagnosis function.
As a further alternative embodiment of the invention, an additional antenna can be provided which, in contrast to the antenna 2, is not connected to the receiver module 8. The noise signal S is now injected into this additional antenna from the noise generator 18. The additional antenna then transmits this noise signal to the antenna or antennas 2. The respective received signal S′ or S2 which results from this is received and evaluated by the test module 12 in the receiver module 8.
As described above, the present invention discloses the use of a very simple low-cost test signal source for antenna diagnosis. This is achieved by using an economically advantageous low-price noise signal source whose power need not be known. The noise source is suitable for testing antennas in a number of frequency bands, for example AM, FM, TV, owing to its wide signal spectrum. The sequential use of a different antenna in each case as the transmitting antenna makes it possible to produce a transmission matrix which represents the near-field coupling between different antenna combinations. The signal power of the noise source or test signal source can be calibrated out by means of this transmission matrix. Accordingly, it is possible to use a simple, low-cost test signal source whose level, in contrast to all previous approaches, need not be known and need not be reproducible. The transmission matrix is additionally used to calculate out external influences which affect all or two or more of the antennas, such as an ice, snow or fallen-leaf coating on them all, as well as external interference signals. A directional coupler in a calibration circuit is used for an arrangement for single antenna systems. In this case, the reception level is measured for each of two or more switch positions in the arrangement at the tuner. The power of the low-price signal source can be determined and calibrated out from different level values. This calibration circuit may, of course, also be used for two or more antennas.
In summary, the present invention discloses a method for testing at least one antenna 2 having a receiver module 8 and a coupling module 16 which is arranged between the antenna 2 and the receiver module 8. In this case, the antenna 2 and the receiver module 8 are supplied with a noise signal S as a test signal, by means of the coupling module 16. An instantaneous transmission coefficient is then determined by means of a test module 12 on the basis of a superimposition of the noise signal S, S1 with a received signal S′, S2 which results from the noise signal, S, S1, and is compared with a reference transmission coefficient which is stored in a transmission matrix. Furthermore, an arrangement is likewise disclosed for carrying out the method according to the invention.
The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102 07 487.9 | Feb 2002 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP03/01314 | 2/11/2003 | WO | 9/30/2005 |
