WO2007036839A2

WO2007036839A2 - Automotive radar transmitter and radar signal generating method

Info

Publication number: WO2007036839A2
Application number: PCT/IB2006/053369
Authority: WO
Inventors: Wilhelmus M. C. Dolmans
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2005-09-27
Filing date: 2006-09-19
Publication date: 2007-04-05
Also published as: WO2007036839A3

Abstract

The present invention relates to a RADAR transmitter for use in automotive vehicles, a method for generating a respective RADAR transmission signal and a modulation signal for control of an oscillating means for generation of the RADAR transmission signal. The RADAR signal, which may be generated according to the method of the invention by the transmitter by using a control signal for control of an oscillating means according to the invention, has a frequency spectrum with predetermined frequencies omitted such that it can easily comply with applicable regulations specified by the respective authorities. Therefore, the method, transmitter and modulation signal of the invention may also be used in any other RADAR applications where a frequency modulated RADAR signal is to be used and certain regulations with respect to the allowed use of transmission frequencies are to be met.

Description

Automotive RADAR transmitter and RADAR signal generating method

The present invention relates to a RADAR transmitter, a method for generating a respective RADAR transmission signal for such an RADAR transmitter and a RADAR oscillator modulation signal.

It is known to use Radio Detection and Ranging (RADAR) devices in automotive vehicles. Such RADAR devices also called RADAR sensors may basically be used for detection of distances and/or relative velocities of other objects in the whole area around an automotive vehicle. The measuring signals received by those RADAR sensors may be used in particular for accident avoidance, for collision avoidance, for an adaptive cruise control as well as for an automatic cruise control for stop-and-go traffic. Also the use in a parking aid system for detection of objects within blind spots of the driver's vision or behind the automotive vehicle is possible.

Preferably, broadband RADAR sensors within the 24 GHz band are a good option for RADAR sensors in the circumference of automotive vehicles as well as for detection of hazardous situations in the automotive vehicle traffic. Recently, the EU- commission and the respective official authorities for frequency regulations have given the starting signal for the use of RADAR technology in automotive vehicles, when the permission to car manufacturers has been granted for use of the radio frequency spectrum around the 24 GHz waveband for automotive RADAR sensors. However, the frequency band close to the 24 GHz waveband is traditionally used by radio astronomy, e.g. earth-exploration satellite services, and telecom services, e.g. a number of telecommunication providers need this frequency band for UMTS services. In recognition of the possible interference caused by automotive RADAR to these services, the specified emission levels are to be reduced accordingly. Therefore, for the ultra-wide band spectrum in Europe for short-range automotive RADAR around 24 GHz, which is 5 GHz wide, as well as in the United States, where the Federal Communications Commission (FCC) has also provided regulations for the 24 GHz automotive RADAR, strong restrictions apply to the frequency range of 23.6 GHz to 24 GHz. With reference to Fig. 1, which shows as example the respective US regulations for the allowed spectral Effective Isotropic Radiated Power (EIRP) for ultra- wide band signals according to the FCC. The FCC has defined emission rules for the 23.6 GHz to 24 GHz band with predetermined increasing steps to be fulfilled regarding the minimum suppression up to the year 2014. These minimum suppression levels are required for a RADAR emitting device for a certain antenna beam angle with respect to horizontal emissions. The following table 1 provides these limits.

Table 1

For example, table 1 is to be read as follows: in the year 2005 up to 2010, a 25 dB suppression is specified for emissions radiated in elevation angles above 30 degrees. In practice, i.e. in the known prior art, these suppression limits are reached by using sophisticated antenna configurations, which are special designed to have side-lobes towards these elevation angles. However, antennas having high antenna gain in the desired direction and at the same time placing side-lobes in the unwanted direction are bulky and costly.

A known method to generate wideband RADAR signals is usage of frequency- modulated continuous-wave (FMCW) signals as RADAR transmission signal. For instance, the frequency of a voltage-controlled oscillator is swept from a start frequency f min up to an end frequency f max in a periodically manner, i.e. continuously. For example, such periodicity in the modulation of the transmission frequency f tx can be achieved by use of a triangular waveform for the modulation signal U mod, as illustrated in Fig. 2, used to steer a voltage-controlled oscillator, as illustrated in Fig. 3. However, the use of such a prior art FMCW RADAR signal requires the use of the afore-mentioned bulky and costly transmit antennas.

It is therefore an objective of the present invention to provide a RADAR transmitter for use in automotive vehicles and/or a respective method for generating of a RADAR transmission signal by which the necessary signal suppression according to the afore-mentioned regulations can be achieved without use of costly and/or bulky antennas. A RADAR transmitter according to present invention comprises generation circuitry for generating a RADAR transmission signal, which is periodically frequency- modulated, an output connected to a RADAR transmit antenna, wherein the generation means are configured to omit predetermined frequencies in the RADAR transmission signal such that the RADAR transmission signal is a frequency-modulated continuous wave RADAR signal with frequency gaps corresponding to the predetermined frequencies. Present invention further describe, a method for generating a RADAR transmission signal, comprising steps of controlling an frequency generation circuitry by a modulation signal such that to generate a periodically frequency-modulated RADAR signal with a predetermined lowest and a predetermined highest frequency, wherein certain values of the modulation signal correspond to certain frequencies of the frequency-modulated RADAR signal; and omitting predetermined frequencies within the periodically frequency- modulated signal.

As to the transmitter of the present invention, the generation circuitry further comprises oscillator circuitry for generating the RADAR transmission signal, wherein the oscillator circuitry is controlled by a predetermined periodical modulation signal. Advantageously a voltage-controlled oscillator may be used by which a frequency-modulated continuous wave RADAR signal can be generated. The used modulation signal for controlling the generating means may be any periodical signal, wherein certain values of the modulation signal correspond to certain frequencies of the generated frequency-modulated RADAR signal. Preferably, the modulation signal has a waveform, which is one of a triangle, a saw tooth, and a sinusoidal waveform. As to a first aspect of the present invention, the used modulation signal comprises predetermined gaps, which correspond to the predetermined omitted frequencies (e.g. forbidden frequencies according to applicable regulations) in the RADAR transmission signal. That is advantageously by not using those modulation signal values, which correspond to those frequencies, which are to be omitted, i.e. suppressed, the oscillator means do not generate these forbidden frequencies.

According to a first embodiment of the first aspect the modulation signal is a continuous steering signal for the oscillator means. During the respective predetermined gaps the modulation signal is switched off. In a second embodiment of the fist aspect of the present invention the modulation signal remains constant during the predetermined gap. That is the oscillator means generate during the predetermined gap a RADAR signal with a constant frequency. This frequency may correspond to a lower border frequency of the predetermined frequency gap or to a higher boarder frequency of the predetermined frequency gap. Advantageously, the so generated periods with a constant frequency in the continuous RADAR transmission signal can be used as RADAR pulses for additional measurements, for instance, as pulse Doppler RADAR in which the Doppler frequency shift can be used, for instance, as means for discriminating moving objects from fixed targets. Thus, a moving target indication (MIT) comes along with the achieved suppression of forbidden frequencies.

According to a second aspect of the present invention, the transmitter further comprises a switch in the signal path of the RADAR signal between the oscillator means and the output, the switch being controlled by a predetermined periodical switch signal. The switch may comprise at least two switch positions, wherein at a first switch position the signal path is connected to the output of the transmitter, i.e. to the RADAR transmit antenna. At a second switch position the RADAR signal path is basically not connected to the output of the transmitter, preferably the RADAR signal path is connected to a dummy element.

As to the switch signal, it is configured such that the switch is switched to the second switch position to pass frequencies of the RADAR transmission signal, which belong to the predetermined frequencies to be omitted to the dummy element. That is the power of the RADAR signal vanishes in the dummy element and thus, again no forbidden frequencies are transmitted by the RADAR transmitter.

Basically, in the RADAR transmitter according to the second aspect of the invention, the predetermined periodical modulation signal may be generated by saw tooth generator. Advantageously, such a saw tooth generator may be implemented together with the oscillator means. Preferably, the predetermined periodical switch signal is generated by a first microcontroller. Additionally, the predetermined periodical modulation signal may be generated by a second microcontroller. It goes without saying that both the predetermined periodical switch signal and the predetermined periodical modulation signal may be generated by a common third microcontroller. The use of one or more microcontrollers allows an easy alterable system design, which may be adjusted by changing the respective programming of the respective microcontroller.

According to the introduction, the predetermined suppressed frequency band is preferably defined by a lower boundary of 23.6 GHz and a higher boundary of 24 GHz, i.e. frequencies in the range between 23.6 GHz to 24 GHz should be suppressed. The suppression is at least 25 dB, most preferably 35 dB.

As to the method for generation of the desired RADAR transmission signal, the suppressing of predetermined frequencies within the periodically frequency-modulated signal may be achieved according to the first aspect of the invention by omitting predetermined values of the control signal, which correspond to predetermined frequencies to be suppressed.

Alternatively or additionally, the suppressing of predetermined frequencies within the periodically frequency-modulated signal is achieved according to the second aspect of the present invention by switching the signal path of the periodically frequency- modulated signal such that the predetermined frequencies to be omitted, i.e. suppressed, are guided to a dummy device.

It is noted that it is further possible to combine both the suppression according to the first and according to the second aspect of the invention. Accordingly, the objective of the present invention can further be solved by use of and by a modulation signal for controlling an output frequency of an oscillation circuitry for generating a frequency modulated RADAR signal, the modulation signal being predetermined and periodical with predetermined range defined by a maximum and a minimum value, wherein certain values of the modulation signal correspond to certain output frequencies of the oscillation means, and wherein predetermined values of the predetermined range of the modulation signal are omitted such that within a frequency spectrum of the output frequencies of the oscillation means frequencies corresponding to the omitted predetermined values of the modulation signal are suppressed.

According to further embodiment the modulation signal, the signal comprises gap portions in the course of time, which correspond to the omitted predetermined values.

According to another embodiment the modulation signal, the signal comprises periodical portions, in which the modulation signal is constant.

A RADAR transmission signal generated by the method or by the use of the modulation signal for controlling an output frequency of an oscillation circuitry according to the present invention can preferably be used in a RADAR device for automotive vehicles. The invention will be better understood in consideration of the following detailed description of the embodiment thereof in connection with the accompanying drawings, in which:

Fig. 1 shows the US regulations for the allowed spectral EIRP for ultra- wide band signals according to the FCC;

Fig. 2 shows a prior-art triangle signal for control of a voltage-controlled oscillator;

Fig. 3 is a simplified block diagram of a FMCW RADAR transmitter of the prior art; Fig. 4 is a waveform of a first periodical modulation signal for control of a voltage-controlled oscillator of the RADAR device according to a first embodiment of the present invention;

Fig. 5 is a waveform of a second periodical modulation signal for control of the voltage-controlled oscillator of the RADAR device according to a second embodiment of the present invention;

Fig. 6 shows a possible implementation of a RADAR transmitter of the present invention, in which a periodical modulation signal for control of the voltage-controlled oscillator according to the present invention is used; and

Fig. 7 shows further implementations for a RADAR transmitter of a RADAR device according to the present invention.

Now reference is made to Fig. 2, which shows a conventional periodical modulation signal U mod for control of a voltage controlled oscillator. By using the periodical modulation signal U mod of Fig. 2 a frequency modulated continuous waveform (FMCW) RADAR signal f tx according to the prior art can be generated. The waveform of Fig. 2 will be called herein as waveform A. The diagram shows also the frequency sweep of the output frequency f tx of a respective voltage-controlled oscillator, the bias voltage of which is controlled by the corresponding modulation signal U mod such that the oscillator is controlled to continuously sweep between a minimum frequency f min and a maximum frequency f max according to waveform A to generate the FMCW RADAR signal.

Fig. 3 shows a simplified block diagram of a RADAR transmitter of a prior art FMCW RADAR transmitter. A voltage-controlled oscillator (VCO) 110 is controlled by a respective modulation signal CRL, i.e. a control voltage, by which the VCO 110 is controlled such said output frequency signal f tx has the waveform A, shown in Fig. 2. The FMCW RADAR signal is input to a power amplifier 120 and the amplified RADAR signal is supplied to a RADAR transmit antenna 130. Since the general configuration of a FMCW RADAR transmitter is known, it is herein not described in further detail. However, further basic information on RADAR systems can be gathered, for instance, from "Introduction to RADAR systems" of Merrill I. Skollnik, McGraw-Hill, Inc.

As mentioned above, the general idea of the present invention is to adjust the generation of a FMCW-RADAR signal such that a predetermined frequency band, e.g. from 23.6 GHz to 24 GHz, is omitted and thus, frequencies of this predetermined frequency band are sufficiently suppressed as, for instance, demanded by the regulations laid down by the respective authority, e.g. as shown in Fig. 1. According to the present invention, there are provided several solutions how such required suppression can be achieved.

According to a first aspect of the present invention the waveform of the frequency modulated continuous wave RADAR signal generated and output by a voltage- controlled oscillator is modified such that an interrupt from a first frequency f_l to a second frequency f_2 is provided within the waveform of the RADAR signal. A first embodiment of the invention is illustrated in Fig. 4, in which a waveform B for the frequency modulated continuous wave RADAR signal f tx is interrupted from a first frequency f_l to second frequency f_2. In a second embodiment according to the present invention a waveform C, shown in Fig. 5, the frequency modulated continuous wave RADAR signal f tx remains for a while at the particular first frequency f_l until the forbidden frequency band is passed and then the frequency sweep is continued with the second frequency f_2.

As a result, the waveforms B and C of Fig. 4 and Fig. 5, respectively, have a frequency gap (B) or a frequency stay (C) at a particular frequency, e.g. f_l. As a result, no emission will occur from first frequency f_l to the second frequency f_2 by use of these waveforms. Hence, the required emission levels in a predetermined frequency band, e.g. in the 23.6 GHz to 24 GHz band, can be easily met.

In the following a possible implementation of the waveform B and C, respectively, will be discussed. According to the first embodiment of the invention the bias voltage by which the voltage-controlled oscillator (Fig. 3, 110) is controlled by one of the specific waveforms B or C, shown in Fig. 4 or Fig. 5, respectively. Now reference is made to Fig. 6, in which a simplified configuration/set-up of a RADAR transmitter for FMCW- RADAR system according to the present invention is shown. The difference between Fig. 6 and Fig. 3 is the fact that a microcontroller 205 is used for generating the required modulation signal by which the voltage-controlled oscillator 210 is controlled. By means of the microcontroller 205 the waveform B of Fig. 4 or the waveform C of Fig. 5 may easily be implemented in the microcontroller 205. For example, the microcontroller 205 may have a digital memory in which the required form of the control signal for the voltage-controlled oscillator is stored in digital format. It may also be possible to have a microcontroller 205, a output signal of which can be programmed by definition (i.e. programming) of particular characterizing parameters of the required waveform, e.g. a lowest value and a highest value of the required modulation signal as well as the range of values which correspond to the frequencies to be suppressed or omitted, respectively. That is according to the present invention the microcontroller 205 generates a control voltage CRL l for the voltage- controlled oscillator 210 according to the desired waveform B of Fig. 4 or waveform C of Fig. 5 such that the output of the voltage-controlled oscillator 210, i.e. the FMCW RADAR signal complies with the restrictions which apply in the predetermined frequency range, e.g. 23.6 GHz to 24 GHz as illustrated in Fig. 1. The generated RADAR signal is amplified by a power amplifier 220 and than supplied to respective RADAR transmit antenna 230.

According to a second aspect of the present invention, the desired waveform B for frequency modulated continuous wave RADAR signal f tx, as illustrated in Fig. 4, may also be generated by use of a switch, which is provided within the signal path of the RADAR signal between the voltage-controlled oscillator output and the respective RADAR transmit antenna. Basically, such a switch should be suitable to switch the used extreme high frequency (EHF) signal. For instance, an EHF pin-diode may be a suitable switch. Also a MEM switch, i.e. micro electronic-mechanic switch, may be used.

As shown in Fig. 7, a RADAR device 200 according to the present invention for use in an automotive vehicle comprises a voltage-controlled oscillator 210 which is, according to a first configuration, controlled by a standard control signal CRL according to the prior art, i.e. the voltage-controlled oscillator 210 generates a standard FMCW RADAR signal at the output which has the waveform A, as shown in Fig. 2. The FMCW RADAR signal is then input to the power amplifier 220 and amplified. Next, the amplified FMCW RADAR signal is supplied to a radio frequency switch 240, which is controlled by the microcontroller 205. According to the present invention the microcontroller 205 controls the radio frequency switch 240 such that only those parts of the FMCW RADAR signal passes the switch 240 from the respective input 242 to the antenna output 244 and is supplied to the RADAR transmit antenna 230. During the times, when the FMCW RADAR signal contains or carries, respectively, frequencies from the predetermined frequency band, which is to be omitted or suppressed, the microcontroller 205 actuates the radio frequency switch 240 such that the FMCW RADAR signal is passed from the switch input 242 to the dummy output 246. Hence, no forbidden frequency is supplied to the RADAR transmit antenna 230 and thus, the required suppression, e.g. 35dB, within the predetermined frequency band, for instance 23.6 GHz to 24 GHz, can easily be achieved.

For a perfect coordination of the voltage-controlled oscillator 210 and the radio frequency switch 240, the microcontroller 205 may be further configured such that the microcontroller 205 controls the voltage-controlled oscillator 210 via a modulation signal CTR l (instead of the control signal CRL by modulation signal generator 215) as well as the radio frequency switch 240 via the control signal CTR 2. This configuration is also illustrated by Fig. 7. Accordingly, a time delay that is due to the traveling time of the FMCW RADAR signal from the voltage control oscillator 210 up to the radio frequency switch 240 may easily be taken into account in the respective control program of the microcontroller 205. It is worth noting that in this implementation it would also be possible to use both aspects of the present invention simultaneously. That is the microcontroller 205 controls the voltage-controlled oscillator 210 via the modulation signal CRL l, which is a modulation signal B or C, respectively, according to the present invention, as illustrated in Fig. 4 or Fig. 5. Further, the microcontroller 205 actuates the switch 240 via the switching control signal CRL 2. By the present invention a RADAR transmitter for use in automotive vehicles, a method for generating a respective RADAR transmission signal and a modulation signal for control of a oscillating means for generation of the RADAR transmission signal has been disclosed. The RADAR signal, which may be generated according to the method of the invention by the transmitter by using a control signal for control of an oscillating means according to the invention, has a frequency spectrum with predetermined frequencies omitted such that it can easily comply with applicable regulations specified by the respective authorities. It goes without saying that the method, transmitter and modulation signal of the invention may also be used in any other RADAR application where a frequency modulated RADAR signal is to be used and certain regulations with respect to the allowed use of transmission frequencies are to be met.

Finally, but yet importantly, it is noted that the term "comprising" when used in this specification including the claims is intending to specify the presence of stated features, means, steps or components, but does not exclude the presence or additions of one or more other features, means, steps, components or groups thereof. Further, the word "a" or "an" before an element in a claim does not exclude the presence of a plurality of such elements. Moreover, any reference sign does not limit the scope of the claims. Furthermore, it is to be noted that "coupled" is to be understood that there is a connection between those elements, which are coupled, that is "coupled" does not mean that those elements are to be directly connected.

Claims

CLAIMS:

1. RADAR transmitter for use in automotive vehicles comprising generation circuitry for generating a RADAR transmission signal, which is periodically frequency- modulated, an output connected to a RADAR transmit antenna, wherein said generation circuitry is configured to suppress predetermined frequencies in said RADAR transmission signal such that said RADAR transmission signal is frequency-modulated continuous wave RADAR signal with frequency gaps corresponding to said suppressed predetermined frequencies.

2. Transmitter according to claim 1, wherein said generation circuitry comprises oscillator circuitry for generating said RADAR transmission signal, said oscillator being controlled by a predetermined periodical modulation signal.

3. Transmitter according to claim 2, wherein said modulation signal has one of a triangle, saw tooth, sinusoidal waveform.

4. Transmitter according to claim 2 or 3, wherein said modulation signal comprises further predetermined gaps corresponding to said predetermined suppressed frequencies of said RADAR transmission signal.

5. Transmitter according to one of the claims 2 to 4, wherein said modulation signal remains constant during said gap.

6. Transmitter according to one of the claims 2 to 4, wherein said modulation signal is switched off during said gap.

7. Transmitter according to one of the preceding claims, wherein said transmitter further comprises a switch in the signal path of said RADAR signal between said oscillator circuitry and said output, said switch being controlled by a predetermined periodical switch signal.

8. Transmitter according to claim 7, wherein said switch comprises at least two switch positions, wherein in a first switch position said signal path is connected to said output and in a second switch position said RADAR signal path is connected to a dummy element.

9. Transmitter according to claim 8, wherein said switch signal is configured such that said switch is switched to said second switch position to pass frequencies of said RADAR transmission signal which belong to said predetermined suppressed frequencies to said dummy element.

10. Transmitter according to one of the preceding claims, wherein said predetermined periodical switch signal is generated by a first microcontroller.

11. Transmitter according to one of the preceding claims 7 to 10, wherein said predetermined periodical modulation signal is generated by saw tooth generator.

12. Transmitter according to one of the preceding claims 1 to 10, wherein said predetermined periodical modulation signal is generated by a second microcontroller.

13. Transmitter according to one of the preceding claims 1 to 9, wherein said predetermined periodical switch signal and said predetermined periodical modulation signal is generated by a third microcontroller.

14. Devices according to one of the preceding claims, wherein said predetermined frequency band is 23.6 to 24 GHz and the suppression is at least 25dB.

15. Method for generating a RADAR transmission signal, comprising the steps of: controlling a frequency generation circuitry by a control signal for generating a periodically frequency-modulated signal with a predetermined lowest and a predetermined highest frequency, wherein certain values of said control signal correspond to certain frequencies of said frequency-modulated signal; and suppressing predetermined frequencies within said periodically frequency- modulated signal.

16. Method according to claim 15, wherein said suppressing of predetermined frequencies within said periodically frequency-modulated signal is achieved by omitting predetermined values of said control signal which correspond to predetermined frequencies to be suppressed.

17. Method according to claim 15, wherein said suppressing of predetermined frequencies within said periodically frequency-modulated signal is achieved by switching a switch in the signal path of said periodically frequency-modulated signal such that said predetermined frequencies to be suppressed are guided to a dummy device.

18. Method according to one of the claims 15 to 17, wherein said RADAR transmission signal is used for a RADAR device of an automotive vehicle.

19. A modulation signal for controlling an output frequency of a oscillation means for generation of a frequency modulated RADAR signal, said modulation signal being predetermined and periodical with a predetermined range defined by a maximum and a minimum value, wherein certain values of said modulation signal correspond to certain output frequencies of said oscillation means, characterized in that predetermined values of said predetermined range of said modulation signal are omitted such that within a frequency spectrum of said output frequencies of said oscillation means frequencies corresponding to said omitted predetermined values of said modulation signal are suppressed.

20. Signal according to claim 19, wherein said modulation signal comprises gap portions in the course of time, which correspond to said omitted predetermined values.

21. Signal according to claim 19, wherein said modulation signal comprises periodical portions, in which said modulation signal is constant.