Method for Operating a Testing Device for Testing a Distance Sensor Operating with Electromagnetic Waves, and Corresponding Testing Device

Abstract

A method for testing a distance sensor includes: receiving an electromagnetic free-space wave as a receive signal; generating a simulated electromagnetic reflection signal therefrom; shifting a reflection frequency of the reflection signal by a Doppler frequency smaller than a signal bandwidth of the receive signal; converting the receive signal into a first work signal having a first work frequency smaller than a receive frequency of the receive signal; converting the first work signal into a second work signal having a second work frequency, wherein the difference between the first and second work frequencies is at least as large as the signal bandwidth plus the Doppler frequency; converting the second work signal into a third work signal having a third work frequency that corresponds to the first work frequency shifted by the Doppler frequency; increasing the third work signal by the conversion frequency; and radiating the third work signal.

Claims

1. A method for operating a testing device for testing a distance sensor operating with electromagnetic waves, comprising: receiving an electromagnetic free-space wave as a receive signal having a receive frequency and a signal bandwidth; generating a simulated electromagnetic reflection signal from the received electromagnetic signal; shifting a reflection frequency of the reflection signal by a Doppler frequency relative to the receive frequency, wherein the Doppler frequency is smaller than the signal bandwidth of the receive signal; converting the receive signal into a first work signal having a first work frequency, wherein the work frequency is smaller, by a conversion frequency, than the receive frequency of the receive signal; converting the first work signal into a second work signal having a second work frequency, wherein the absolute value of the difference between the first work frequency and the second work frequency is at least as large as the signal bandwidth; converting the second work signal into a third work signal having a third work frequency, wherein the third work frequency corresponds to the first work frequency shifted by the Doppler frequency; increasing the third work signal by the conversion frequency and, thus, converting the third work signal into the reflection signal; and radiating the third work signal.

2. The method according to claim 1, wherein the conversion of the receive signal into the first work signal is carried out by mixing the receive signal with a local oscillator signal of the conversion frequency.

3. The method according to claim 1, wherein a spectrum of the first work signal having a signal bandwidth is spaced from the frequency zero at least by the signal bandwidth.

4. The method according to claim 1, wherein the conversion of the third work signal into the reflection signal is achieved by mixing the third work signal with a local oscillator signal of the conversion frequency.

5. The method according to claim 4, wherein the local oscillator signal of the conversion frequency for mixing the receive signal and for mixing the third work signal is an identical local oscillator signal generated by a single local oscillator.

6. The method according to claim 1, wherein the second work frequency of the second work signal is smaller than the first work frequency of the first work signal.

7. The method according to claim 1, wherein the first work signal-St is converted into the second work signal by time-discrete sampling of the work signal at a sampling frequency and subsequent digital-to-analog conversion of the sampled work signal into an analog work signal.

8. The method according to claim 7, wherein the sampling frequency is greater than the signal bandwidth-s of the receive signal and that the first work signal is sub-sampled, thus, the sampling frequency is smaller than twice the greatest frequency in the spectrum of the first work signal.

9. The method according to claim 8, wherein the sampling frequency is greater than the greatest frequency in the spectrum of the first work signal-St.

10. The method according to claim 1, wherein the second work signal is converted into the third work signal by mixing with a first auxiliary signal having a frequency.

11. The method (1) according to claim 10, a first frequency of the first auxiliary signal corresponds to the sum frequency of the frequency of the first work signal, the frequency of the second work signal and the Doppler frequency.

12. The method according to claim 10, wherein the first auxiliary signal is generated by mixing a second auxiliary signal having a second frequency and a third auxiliary signal having a third frequency; and wherein the second frequency corresponds to the sum frequency of the frequency of the first work signal and the frequency of the second work signal; and wherein the third frequency corresponds to the Doppler frequency.

13. The method according to claim 12, wherein the second auxiliary signal is generated by a local oscillator having a fixed frequency and the third auxiliary signal having tunable frequency is generated by a tunable oscillator.

14. The method according to claim 1, wherein at least one of the generated signals is filtered out of a total spectrum by means of a suitable bandpass filter or by means of a suitable low-pass filter after a mixing operation.

15. The method according to claim 14, wherein, after mixing the second auxiliary signal with the third auxiliary signal, a very narrow-band band filter is used in order to filter out one of the two resulting mixed signals.

16. A testing device for testing a distance sensor operating with electromagnetic waves, comprising: a receiving element for receiving an electromagnetic free-space wave as a receive signal having a receive frequency and a signal bandwidth; a radiating element for radiating a simulated electromagnetic reflection signal having a reflection frequency; signal electronics configured to generate the reflection signal from the electromagnetic receive signal, the reflection signal having a reflection frequency shifted by a Doppler frequency to be simulated with respect to the receive frequency of the receive signal, wherein the Doppler frequency is smaller than the signal bandwidth of the receive signal; a first converter configured to convert the receive signal into a first work signal having a first work frequency, wherein the work frequency is smaller, by a conversion frequency, than the receive frequency of the receive signal, a second converter configured to convert the first work signal into a second work signal having a second work frequency, wherein the absolute value of the difference between the first work frequency and the second work frequency is at least as large as the signal bandwidth; a third converter configured to convert the second work signal into a third work signal having a third work frequency, wherein the third work frequency corresponds to the first work frequency shifted by the Doppler frequency, wherein the third work frequency corresponds to the first work frequency shifted by the Doppler frequency; and a fourth converter configured to increase the third work signal by the conversion frequency and thus convert the third work signal into the reflection signal and radiate the third work signal.

17. The testing device according to claim 16, wherein the conversion of the receive signal into the first work signal is carried out by means of a first converter designed as a mixer by mixing the receive signal with a local oscillator signal of the conversion frequency generated by a first local oscillator.

18. The testing device according to claim 16, wherein a spectrum of the first work signal generated by the first converter having a signal bandwidth is spaced from the frequency zero at least by the signal bandwidth.

19. The testing device according to claim 16, wherein the conversion of the third work signal into the reflection signal is achieved by the fourth converter, which is designed as a mixer, by mixing the third work signal with the local oscillator signal of the conversion frequency generated by the first local oscillator.

20. The testing device according to claim 16, wherein the second work frequency of the second work signal generated by the second converter is smaller than the first work frequency of the first work signal.

21. The testing device according to claim 16, wherein the first work signal is converted into the second work signal with an analog-to-digital converter contained in the second converter by time-discrete sampling of the work signal having a sampling frequency and subsequent digital-to-analog conversion of the sampled work signal into an analog work signal with a digital-to-analog converter contained in the second converter.

22. The testing device according to claim 21, wherein the sampling frequency of the analog-to-digital converter contained in the second converter is greater than the signal bandwidth of the receive signal, and the first work signal is sub-sampled, thus, is smaller than twice the greatest frequency in the spectrum of the first work signal.

23. The testing device according to claim 22, wherein the sampling frequency of the analog-to-digital converter contained in the second converter is greater than the greatest frequency in the spectrum of the first work signal.

24. The testing device according to claim 16, wherein the second work signal is converted into the third work signal by the third converter in the form of a mixer by mixing with a first auxiliary signaler having a first frequency generated by an auxiliary signal generator.

25. The testing device according to claim 24, wherein the first frequency of the first auxiliary signal generated by the auxiliary signal generator corresponds to the sum frequency of the frequency of the first work signal, the frequency of the second work signal and the Doppler frequency.

26. The testing device according to claim 24, wherein the first auxiliary signal is generated by the auxiliary signal generator by mixing a second auxiliary signal having a second frequency and a third auxiliary signal having a third frequency with an auxiliary signal mixer, wherein the frequency corresponds to the sum frequency of the first frequency of the first work signal and the second frequency of the second work signal and wherein the third frequency corresponds to the Doppler frequency.

27. The testing device according to claim 26, wherein the auxiliary signal generator includes a local oscillator with a fixed frequency and a tunable oscillator with a tunable frequency, and that the second auxiliary signal is generated by the local oscillator having a fixed frequency and the third auxiliary signal having a tunable frequency is generated by the tunable oscillator.

28. The testing device according to claim 16, wherein at least one of the generated signals is filtered out of a total spectrum by means of a suitable bandpass filter or by means of a suitable low-pass filter carried out after a mixing operation.

29. The testing device according to claim 28, wherein, after mixing the second auxiliary signal with the third auxiliary signal by means of the auxiliary signal mixer, a very narrow-band bandpass filter is used to filter out one of the two resulting mixed signals.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In detail, there is now a plurality of possibilities for designing and further developing the method according to the invention for operating a testing device for testing a distance sensor operating with electromagnetic waves and a related testing device. For this, reference is made to the following description of embodiments in conjunction with the drawings.

[0024] FIG. 1 illustrates a method known from the prior art for operating a testing device for testing a distance sensor operating with electromagnetic waves and such a testing device.

[0025] FIG. 2 illustrates a method according to the invention with frequency spectra of different signals.

[0026] FIG. 3 illustrates a method and a device according to the invention with a schematic signal flow diagram.

[0027] FIG. 4 illustrates a more detailed representation of the third converter in analog technology.

DETAILED DESCRIPTION

[0028] FIG. 1 shows a method 1 for operating a testing device 2 for testing a distance sensor 3 operating with electromagnetic waves and also a corresponding testing device 2. The method 1 and testing device 2 are used for testing the distance sensor 3, which, in this case, is a distance sensor 3 operating with radar waves. The distance sensor 3 has a transmitting and receiving device 4 for radiating radar signals and for receiving radar signals which have been reflected by an object in actual use. In the shown test situation, there is no actual object, but only the testing device 2 with the implemented method 1 for the simulation of an actual object in view of the distance sensor 3 to be tested. The method 1 and the testing device 2 are used for the generation and radiation of a simulated electromagnetic reflection signal S.sub.TX having a reflection frequency f.sub.TX.

[0029] The electromagnetic wave radiated by the distance sensor 3 is received as an electromagnetic free-space wave as a receive signal S.sub.RX having a receive frequency f.sub.RX. The receive signal S.sub.RX also has a signal bandwidth B. This is indicated in FIG. 1 by the uppermost frequency spectrum. The reflection signal S.sub.TX is generated from the electromagnetic receive signal S.sub.RX in a manner not shown here in detail, wherein the reflection frequency f.sub.TX is shifted by a Doppler frequency f.sub.D with respect to the receive frequency f.sub.RX, whereby the Doppler frequency f.sub.D is smaller than the signal bandwidth B of the receive signal S.sub.RX. This is indicated in the lower part by the second frequency spectrum of FIG. 1.

[0030] In the present case, the receive signal S.sub.RX has a center frequency f.sub.RX of 77 GHz and a bandwidth B of 1 GHz. The testing device 2 has a receiving element 5 for receiving the receive signal S.sub.RX. The testing device 2 has a radiating element 6 for radiating the simulated electromagnetic reflection signal S.sub.TX. In the example shown in FIG. 1, the receiving element 5 and the radiating element 6 are separate antennas, which need not necessarily be the case, but the receiving element 5 and the radiating element 6 may also be designed as a single common antenna. The testing device 2 comprises signal electronics 7 which generate the reflection signal S.sub.TX from the receive signal S.sub.RX. How this is carried out in the prior art is not described further here.

[0031] FIG. 2 now shows the method 1, with which a reflection signal S.sub.TX shifted by the Doppler frequency f.sub.D is generated from the receive signal S.sub.RX. The method is shown here using frequency spectra in which the various signals involved are represented in terms of frequency. In the uppermost frequency spectrum, it can be seen that the high-frequency receive signal S.sub.RX having a receive frequency f.sub.RX of 77 GHz is converted into a first work signal S.sub.1 with a first work frequency f.sub.1 of 2.1 GHz. The work frequency f.sub.1 is smaller here, by a conversion frequency f.sub.U, than the receive frequency f.sub.RX of the receive signal S.sub.RX. This first frequency conversion is carried out in order to be able to work in a smaller frequency range that is easier to handle in terms of circuitry. It has been recognized that a direct conversion of the receive signal S.sub.RX; into the reflection signal S.sub.TX is not possible, since the desired frequency offset around the Doppler frequency f.sub.D is extremely small compared to the bandwidth B of the receive signal S.sub.RX. A direct mixing of the receive signal S.sub.RX with a signal having the Doppler frequency f.sub.D or a time-discrete sampling of the receive signal S.sub.RX with a sampling rate f.sub.sample that is much smaller than the bandwidth of the receive signal S.sub.RX would lead to overlapping spectra in the frequency spectrum, so that the reflection signal S.sub.TX would no longer be a single-frequency, shifted receive signal S.sub.RX, but a completely different signal.

[0032] It is useful to look at FIG. 3 in parallel to FIG. 2, which, in addition to the signal course of the method 1, also simultaneously, schematically depicts the testing device 2. In FIG. 3, the means by which the various method steps in FIG. 2 are carried out are also shown here. For example, FIG. 3 shows that the receive signal S.sub.RX is converted into the first work signal S.sub.1 with a first converter 8.

[0033] It is now provided and shown in FIG. 2 in the medium frequency spectrum that the first work signal S.sub.1 is converted into a second work signal S.sub.2 having a second work frequency f.sub.2, wherein the absolute value of the difference between the first work frequency f.sub.1 and the second work frequency f.sub.2 is at least as great as the signal bandwidth B. This ensures that no overlapping bands occur in the frequency spectrum. In the present case, the second work frequency f.sub.2 of the second work signal is selected to be 0.6 GHz. The distance between the spectra is sufficiently large with the above-mentioned requirement of being able to manage without collisions of any frequency bands that might occur during the subsequent frequency shift of the second work signal S.sub.2. The first work signal S.sub.1 is converted into the second work signal S.sub.2 by a second converter 9 (FIG. 3).

[0034] In a further step, it is now provided that the second work signal S.sub.2 is converted into a third work signal S.sub.3 having a third work frequency f.sub.3, wherein the third work frequency f.sub.3 corresponds to the first work frequency f.sub.1 shifted by the Doppler frequency f.sub.D. In the example shown, the Doppler frequency f.sub.D has been added to the first work frequency f.sub.1, which corresponds to an approaching of an object to be simulated. Equally, the third work signal S.sub.3 could also be shifted in the other direction toward the first work frequency f.sub.1, i.e., towards lower frequencies, which corresponds to an object moving away. Since the third work frequency f.sub.3 was selected in dependence on the first work frequency f.sub.1, the third work signal S.sub.3 can now be increased by the conversion frequency f.sub.U, i.e., the conversion frequency f.sub.U that was used in the frequency spectrum shown at the top for conversion to a low frequency range, whereby the reflection signal S.sub.TX is generated and finally radiated. The second work signal S.sub.2 is converted into the third work signal S.sub.3 with a third converter 10. Accordingly, the third work signal S.sub.3 is increased by the conversion frequency f.sub.U with a fourth converter 11, whereby the reflection signal S.sub.TX is generated and radiated.

[0035] In the embodiment shown in FIG. 3, the receive signal S.sub.RX is converted into the first work signal S.sub.1 by mixing the receive signal S.sub.RX with a local oscillator signal S.sub.LO having the conversion frequency f.sub.U. The first converter 8 is therefore designed as a mixer. The local oscillator signal S.sub.LO is generated by a first local oscillator 12.

[0036] When the various signals are converted, the signal bandwidth B is retained in each case. In the embodiment shown (upper frequency spectrum in FIG. 2), the spectrum of the first work signal S.sub.1 is shifted such that it is spaced from the frequency 0 by more than one signal bandwidth B, because the smallest frequency of the spectrum of the first work signal S.sub.1 is 1.6 GHz. This plays a role in connection with the present embodiment (middle frequency spectrum in FIG. 2), since the second work frequency f.sub.2 of the second work signal S.sub.2 is smaller than the first work frequency f.sub.1 of the first work signal S.sub.1.

[0037] The clever selection of the work frequency f.sub.3 of the third work signal enables that the conversion of the third work signal S.sub.3 into the reflection signal S.sub.TX is achieved by mixing the third work signal S.sub.3 with the same local oscillator signal S.sub.LO of the conversion frequency f.sub.U. Consequently, the fourth converter 11 is designed as a mixer and is supplied with the local oscillator signal S.sub.LO generated by the first local oscillator 12. This makes the circuit design simple, since one and the same mix signal S.sub.LO can be used for input-side mixing-down of the receive signal and output-side mixing-up of the third work signal S.sub.3 to generate the reflection signal S.sub.RX.

[0038] As already mentioned, the second work frequency f.sub.2 of the second work signal S.sub.2 generated by the second converter 9 is smaller than the first work frequency f.sub.1 of the first work signal S.sub.1; this is possible without problems because sufficient distance to the zero frequency was left during the generation of the first work signal S.sub.1.

[0039] As indicated in FIG. 3, the first work signal S.sub.1 and the second work signal S.sub.2 are converted by time-discrete sampling of the work signal S.sub.1 having a sampling frequency f.sub.sample. Subsequent digital-to-analog conversion of the sampled work signal S.sub.1 produces an analog work signal S.sub.2. This is achieved by converting the first work signal S.sub.1 into the second work signal S.sub.2 with an analog-to-digital converter 13, which is part of the second converter 9, by time-discrete sampling of the work signal S.sub.1 having a sampling frequency f.sub.sample. Accordingly, the second converter 9 also comprises a digital-to-analog converter 14, which generates an analog work signal S.sub.2 from the sampled work signal S.sub.1. As explained in the general description section, the fact is taken advantage of here that when a signal in the frequency spectrum of the sampled signal is sampled in a time discrete manner, a periodically repeating sequence of the sampled signal occurs, both towards higher frequencies and towards lower frequencies. Since the work signal S.sub.1 has been shifted into a very small frequency range, the analog-to-digital converter 13 and the digital-to-analog converter 14 can operate with relatively low data rates. This also has a positive effect on the comparatively simple design of the testing device 2 and signal electronics 7 of the testing device 2. In another embodiment, the second converter 9 is designed as a digital signal processor (DSP), with which a corresponding analog-to-digital conversion or digital-to-analog conversion is implemented. In the embodiment shown, the sampling frequency f.sub.sample is greater than the signal bandwidth B of the receive signal S.sub.RX, which prevents the frequency bands in the frequency spectrum (not shown here in detail) from overlapping periodically, so that the sampled signal can be reconstructed perfectly. In the embodiment shown, the first work signal S.sub.1 is sub-sampled by the second converter 9. The sampling frequency f.sub.sample is implemented with 2.7 GHz and therefore smaller than twice the greatest frequency in the spectrum of the first work signal S.sub.1, the largest frequency here being 2.6 GHz. This subsampling results in frequency bands in a lower frequency range. Knowing that these frequency bands actually correspond to a higher frequency in the sampled signal, a perfect reconstruction of the sampled signal is also possible using the lower frequency band (digital down conversion).

[0040] In the embodiment shown, it is implemented that the sampling frequency f.sub.sample of the analog-to-digital converter 13 contained in the second converter 9 is greater than the greatest frequency in the spectrum of the first work signal S.sub.1, i.e., greater than 2.6 GHz. At the selected sampling frequency there is so-called folding, which leads to a reflection of the sampled frequency band (inverse position, see middle frequency spectrum in FIG. 2).

[0041] The Doppler frequency f.sub.D is introduced in the third converter 10. The configuration of the third converter 10 as well as the method implemented in it are shown in detail in a signal flow diagram in FIG. 4. In FIG. 4, the degree of detail of the illustration increases from left to right. The middle figure shows that the second work signal S.sub.2 is converted into the third work signal S.sub.3 by mixing with a first auxiliary signal S.sub.H1 having a frequency f.sub.H1. The third converter 10 is therefore essentially designed as a mixer or comprises such a mixer 15 as a central element. The first auxiliary signal S.sub.H1 is generated by an auxiliary signal generator 16.

[0042] The frequency f.sub.H1 of the first auxiliary signal S.sub.H1 generated by the auxiliary signal generator 16 corresponds to the sum frequency of the frequency f.sub.1 of the first work signal S.sub.1, the frequency f.sub.2 of the second work signal S.sub.2 and the Doppler frequency f.sub.D or the negative Doppler frequency −f.sub.D. Thus, a frequency shift of the receive signal S.sub.RX to a frequency increased by the Doppler frequency f.sub.D as well as to a frequency reduced by the Doppler frequency f.sub.D can be implemented. FIG. 4 also shows that the first auxiliary signal SH, is generated by the auxiliary signal generator 16 by mixing a second auxiliary signal S.sub.H2 having the frequency f.sub.H2 and a third auxiliary signal S.sub.H3 having the frequency f.sub.H3 with an auxiliary signal mixer 17. The frequency f.sub.H2 corresponds to the sum frequency of the frequency f.sub.1 of the first work signal S.sub.H1 and the Doppler frequency f.sub.D. The frequency f.sub.H3 of the third auxiliary signal S.sub.H3 corresponds to the Doppler frequency f.sub.D. The auxiliary signal generator 16 comprises a local oscillator 18 with a fixed frequency and a tunable oscillator 19 with a tunable frequency. The second auxiliary signal S.sub.H2 is therefore generated by the local oscillator 18 having a fixed frequency and the third auxiliary signal S.sub.H3 is generated by the tunable oscillator 19 having a tunable frequency. This tunable frequency is the Doppler frequency f.sub.D by which the receive signal S.sub.RX is to be shifted. The Doppler frequency f.sub.D is usually given by an environment simulation and changes constantly with the constantly changing driving situation simulated by an environment simulator.

[0043] As can be seen in particular from the illustration in FIG. 4, the signals generated are—at least partially—filtered out of an entire spectrum by means of a suitable bandpass filter 20 or by means of a suitable low-pass filter.

[0044] Here, it is implemented that after mixing the second auxiliary signal S.sub.H2 with the third auxiliary signal S.sub.H3 by means of the auxiliary signal mixer 17, a very narrow-band bandpass filter 20 is used to filter out one of the two resulting mixed signals; the present mixed signal has the frequency f.sub.1+f.sub.2+f.sub.D, as can be seen from the bottom illustration in FIG. 3.