WO1991008615A1 - Method et appareil pour produire un signal de balayage de frequence composite et a impulsions - Google Patents

Method et appareil pour produire un signal de balayage de frequence composite et a impulsions Download PDF

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Publication number
WO1991008615A1
WO1991008615A1 PCT/NO1990/000174 NO9000174W WO9108615A1 WO 1991008615 A1 WO1991008615 A1 WO 1991008615A1 NO 9000174 W NO9000174 W NO 9000174W WO 9108615 A1 WO9108615 A1 WO 9108615A1
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WIPO (PCT)
Prior art keywords
frequency sweep
signal
frequency
signals
sum
Prior art date
Application number
PCT/NO1990/000174
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English (en)
Inventor
Karsten Husby
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Sinvent As
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication date
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Publication of WO1991008615A1 publication Critical patent/WO1991008615A1/fr

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Classifications

    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03B—GENERATION OF OSCILLATIONS, DIRECTLY OR BY FREQUENCY-CHANGING, BY CIRCUITS EMPLOYING ACTIVE ELEMENTS WHICH OPERATE IN A NON-SWITCHING MANNER; GENERATION OF NOISE BY SUCH CIRCUITS
    • H03B23/00—Generation of oscillations periodically swept over a predetermined frequency range
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03B—GENERATION OF OSCILLATIONS, DIRECTLY OR BY FREQUENCY-CHANGING, BY CIRCUITS EMPLOYING ACTIVE ELEMENTS WHICH OPERATE IN A NON-SWITCHING MANNER; GENERATION OF NOISE BY SUCH CIRCUITS
    • H03B2200/00—Indexing scheme relating to details of oscillators covered by H03B
    • H03B2200/006—Functional aspects of oscillators
    • H03B2200/0092—Measures to linearise or reduce distortion of oscillator characteristics

Definitions

  • This invention relates to an essentially new method for generating a composite and pulse shaped frequency sweep signal (chirp signal) , and means for carrying out the method.
  • a primary use of the resulting sum of frequency sweep signals is to multiply these by another analog signal in order to perform a CFT transform.
  • the invention is not, however, restricted to this specific use, but has potential interest in all relationships where it is desired to employ a sum of overlapping frequency sweep signals.
  • the invention is, i.a. , particularly useful within the field of satellite communication, and in such case imple- mentet onboard a communication satellite, but the invention can also be employed in connection with other electronic equipment as for example radio links, mobile telephones and base stations.
  • the invention is intended for appli ⁇ cations within the field of communications, where a large bandwidth and a low power consumption are important.
  • CFT Crohn's disease
  • CZT CZT
  • a CFT Crohn's disease
  • Such a CFT combines elements from digital signal processing (in order to attain flexibility) with analog techniques (in order to attain a large bandwidth) .
  • the frequency sweep generator can be a part of such a CFT arrangement. Because of the large bandwidths and the long integration times which it is desirable to use, the time-bandwidth product will be high. This implies that the digital memory will be large, and the sampling frequency high. In particular the sampling frequency can become so high that components having a large power capacity must be used. For performing such a CFT there has up to now been a necessity to employ a relatively complicated linear multiplier.
  • the invention implies a form of undersampling in order to reduce both the sampling frequency and the number of sampling points.
  • This utilization of undersampling with resulting aliasing gives the high number of signals and frequences which it is desired to achieve here.
  • the invention has for an object to reduce the size of the required digital memory in the frequency sweep generator, to eliminate the need for an accurately con ⁇ trolled amplitude of the frequency sweep signal whether this be generated in a digital or an analog manner, to reduce the intermodulation, to reduce the sampling rate as well as to replace the linear mulitiplier by a non-linear multiplier in the case of multiplication as with CFT.
  • the essential novelty and fundamental of the method for generating a composite and pulse shaped frequency sweep signal mainly consists therein that the signal is built up by taking as a basis an elementary signal block comprising a small number of frequency sweep signals and having a limited extent as to period time (T s ) and period bandwidth (B s ) and that a number of elementary signal blocks being in the principle an infinite number, are assembled with coinciding frequency and phase at the transitions between the elementary blocks, so that there is generated a sum of continuous frequency sweep signals by repeating of the elementary block both in time and frequency.
  • T s period time
  • B s period bandwidth
  • Fig. 1 is a frequency-time diagram of a sum of frequency sweep signals with indications of an elementary block or blocks being a fundamental elementary building block for the sum of signals shown
  • Fig. 3 shows a simplified block diagram of a feasible form of generator/multiplier based on a time variable phase twister, for example for performing a CFT
  • Fig. 4 shows simplified curve shapes of signals at certain points in the diagram of Fig.
  • Fig. 5 in block diagram form shows another embodiment of a frequency sweep signal generator/multiplier with complex digital generation and harmonic pulsed local oscillator
  • Fig. 1 is a frequency-time diagram of a sum of frequency sweep signals with indications of an elementary block or blocks being a fundamental elementary building block for the sum of signals shown
  • Fig. 2 shows a similar diagram as in Fig. 1, but with an enlarged elementary block as represented by an oversampling
  • FIG. 6 shows simplified curve shapes of signals at certain points in the diagram of Fig. 5
  • Fig. 7 shows still another apparatus for carrying out the method according to the invention, namely a generator/multiplier based on a SAW filter as a main component
  • Fig. 8 shows simplified curve shapes of signals at certain points in the diagram of Fig. 7
  • Fig. 9 shows a block diagram of still a further form of generator based on a D/D converter
  • Fig. 10 illustrates simplified curve shapes of signals at certain points in the diagram of Fig. 9
  • Figs. 12A and 12B show the same signals as in fig.
  • Appendix I is a listing of a FORTRAN program BEVIS which serves to substantiate some of the mathematical background behind the method according to the invention.
  • Appendix II is a listing of a BASIC program for calculating function values according to the mathematical background given in the following description,
  • Appendix III is an example of running of the BASIC program with the result printed out
  • Appendix IV is another example of running the BASIC program with the result printed out.
  • a frequency sweep signal is an electric oscillation with a lineary increasing frequency as a function of time.
  • a single sweep or signal variation is shown as the line SI in Fig. 1.
  • Such signals can be described by means of an elementary signal block as shown at B2 in the figure.
  • This elementary block can serve as a "building block” for a sum of frequency sweep signals.
  • the time dimension or extent of the elementary block is the period time T s which is the shortest required time cycle for generating the frequency sweep signal.
  • the elementary block has an extent in frequency referred to as the period band B s which corresponds to the lowest required sampling frequency for generating the frequency sweep signal. This can be expressed as follows:
  • ⁇ is the sweep rate, i.e. change of frequency per second and C 0 is the "oversampling factor" seen in relation to the frequency spacing between the individual sweeps, i.e. B s in Fig. 1.
  • a complete frequency sweep signal (in the theory) can consist of a sum of infinitely many overlapping frequency sweeps, having a frequency from - » to + oo. According to the invention, this is generated by copying or repeating the elementary block both along the frequency and the time axis. Just this is achieved by complex sampling of a periodic signal, which constitutes a substantial feature of the method according to the invention.
  • Frequency sweep signal number n in Fig. 1 having a frequency from - oo to + oo can be written mathematically as follows:
  • T s sweep period [s]
  • a sum of many frequency sweeps can be expressed as a series of pulses.
  • These pulses can have shapes as for example illustrated in the diagrams of Figs. 11 to 14 of the drawings. This can be shown by means of a FORTRAN program BEVIS as listed in Appendix I. In this program the bandwidth of the frequency sweep signal is limited by a Banning window so that in the time domain the pulses will be sufficiently separated from each other.
  • BEVIS FORTRAN program
  • the bandwidth of the frequency sweep signal is limited by a Banning window so that in the time domain the pulses will be sufficiently separated from each other.
  • h(t) the impulse response
  • T S 2 C n /C 0
  • C n is the number of samples per cycle of duration T s and C 0 is the oversampling factor.
  • C n and C 0 are relatively primic integers having a highest common divisor equal to 1.
  • Lines 110 to 130 Read desired value of period time T s and an interval which indicate desired minimum and maximum limit of the sweep rate ⁇ .
  • Lines 140 to 190 Calculate the smallest possible C 0 which gives a sweep rate ⁇ in compliance with the maximum and minimum values. At the same time, calculate C n so that C n and C Q become relatively primic.
  • Lines 200 to 240 The most important parameters of the frequency sweep signal are then determined. Print out these.
  • Lines 250 to 290 Calculate the function p(k,C n ,C 0 ).
  • Lines 330 to 380 Calculate the phase of all samples from number 0 to sample number C n -1 and simultaneously normalize the phase so that sample number 0 has always the value 0 degrees. The amplitude of all samples is equal.
  • the total sum of frequency sweep signals can be regarded as composed of a number of individual sweeps Sll in analogy to the individual sweep SI in Fig. 1.
  • Within the elementary block B12 there is here included three individual sweep lines and the complete signal which it is desired to generate, is provided by repeating this elementary block in time and frequency.
  • the invention is carried out by first calculating the phase values in the elementary block by means of a program as for examle the BASIC program in Appendix II. Then these values are applied to a suitable apparatus which can also simultaneously bandlimit the frequency sweep signal by letting the pulses extend somewhat in time. The desired sum signal is then obtained by generating these pulses at the desired sampling rate (C n /T s ) and period time (T s ) .
  • the diagrams in Figs. 13 and 14 are corresponding polar diagrams.
  • the pulses are short, so that intersymbol interference is avoided.
  • Such a frequency sweep signal can be handled non-linearly.
  • the frequency sweep signal is a narrow-band signal, so that the different pulses interfere with each other.
  • the invention makes it possible to generate a sum of several frequency sweep signals at sampling rates being much lower than the bandwidth of the sweep signals, without employing parallel processing.
  • the sampling frequency of the generator When used in connection with a CFT and without oversampling (Appendix III) the sampling frequency of the generator will be equal to the processed bandwidth irrespective of the bandwidth of the sweep signal. This is a great improvement from previous frequency sweep generators. Since the bandwidth of the sweep signal typically can be 8 times wider than the processed bandwidth in a CFT (the useful band ⁇ width) ,. the reduction of sampling frequency when using this invention will be correspondingly large. Also the memory requirements will decrease correspondingly.
  • a further advantage consists therein that the amplitude of all sweep samples are equal, so that amplifiers having a non-linear characteristic can be used for amplifying and conveying the frequency sweep signal.
  • the frequency sweep signal shall be multiplied by the useful signal.
  • a traditional passive mixer can be employed for this operation.
  • the fact that the frequency sweep signal consists of short pulses can also be utilized for simplifying the local oscillator which can be used for up-converting the frequency of the sweep signal to a suitable IF.
  • the local oscillator runs continuously, but it can be implemented by means of a band pass filter which is pulsed for each sample.
  • the SAW filter can also be used as a frequency sweep generator directly.
  • One pulse for each frame is emitted into a crystal, and this gives C n pulses out, which can be limited in class C amplifiers (amplifiers having a high efficiency and a non-linear characteristic) . All the factors mentioned above are significant with respect to complexity, mass, volume and power consumption.
  • FIG. 3 shows an apparatus which performs this.
  • An analog band limited signal 1 is applied to a time varying phase twister 2 so that the relative phase between an output signal at 3 and the input signal at 1 will be given by the phase values, for examle from Appendix III.
  • a short pulse of signal 3 is admitted through sampler 4.
  • the length and the shape of this pulse determines the spectral configuration of the output signal 5.
  • Schematic curve shapes of the signals at 1,5,6 and 7 are shown in Fig. 4.
  • multiplying D/A converters for example, or an analog band pass filter having a controllable phase characteristic can be used.
  • Fig. 5 shows another embodiment.
  • a clock signal 12 is generated by a circuit 11.
  • the sequence circuit 14 which can be a common counter circuit, is clocked for example on a positive edge, whereas counter 13 can be clocked on a negative edge.
  • Counter 13 has also particularly fast and precise drivers at its output. Therefore, this counter generates fast transitions 15 having a high bandwidth each time the signal 12 goes negative.
  • the steep edges of signal 15 are filtered in a band pass filter 24 so as to result in short band pass pulses 16. In the ideal case this shall be a filter having a linear phase and a finite pulse response. If the pulse response of the filter is shorter than the period of clock 12, there will be no interference between the different band pass pulses 16.
  • An amplifier having a non-linear characteristic therefore can be used for ampli ⁇ fying the frequency sweep signal.
  • the pulses 16 are mutually displaced by 180 degrees.
  • Signal 16 is then split in a 90 degree hybrid 37.
  • Each of the two signals 8,9 are applied to a separate mixer 25,26.
  • the signals 8,9 are mixed each with a signal 18,17 being proportional to sinus and cosinus of the phase angles as given for example by Table III.
  • Sequence circuit 14 forms an address 10 which addresses two stores 31,32 for sinus and cosinus respectively.
  • the digital representation 34,33 for sinus and cosinus is fed to two digital-analog converters 36,35 which generate the analog sinus and cosinus voltage 18,17.
  • the mixing product 20,19 is a comlex representation of a sum of several frequency sweep signals as these are stored in stores 32 and 31 and adjusted with respect to frequency by filter 24. Mixing products 20,19 are added at 22 so as to give a real frequency sweep signal 27. This signal can be strongly amplified before it is conveyed to the mixer 23 which finally multiplies the frequency sweep signal by the input signal 28. Schematic curve shapes of the signals at 12,15,16,17,18,20 and 28 are shown in Fig. 6.
  • Fig. 7 shows a third alternative based on this invention.
  • short pulses 42 are fed at a regular rate from a clock generator 41 into a SAW filter (Surface Acoustic Wave filter) .
  • SAW filter 43 is configured in compliance with calculated phase values as described above. Pulses 42 are generated each T s second. For each input pulse 41, the SAW filter generates a number C n of pulses 44 out. The length of the pulse response of the SAW filter can be equal to T s .
  • Frequency sweep signal 44 can be non- linearly amplified before it is mixed with the input signal 45 in mixer 46 which can well be of the passive, non-linear type. Schematic curve shapes of the signals at 42,44 and 45 are shown in Fig. 8.
  • D/D- converters or socalled Digital-to-Delay-converters can be employed for generating digital pulses having controllable delays.
  • Such pulses used for the excitation of a band pass filter can form the heart of a frequency sweep generator.
  • Clock circuit 51 generates a clock frequency which forms the sampling rate for the desired frequency sweep. This clock is used for incrementing a sequence circuit 53 which can be a common counter.
  • Sequence circuit 53 generates an address 54 which is used for making a table look-up in a storage circuit 55.
  • D/D-converter 57 delays one edge of signal 52 in accordance with the digitally stored word 56.
  • Circuit 59 generates a short pulse 60 each time the delayed transition 58 arrives.
  • Pulse 60 is applied to band pass filter 61.
  • the bandwidth of the filter must be much smaller than the center frequency. In the ideal case this shall be a filter having a linear phase and a finite pulse response. If the pulse response of the filter is shorter than the period of clock 52, there will be no interference between the various band pass pulses 62.
  • An amplifier 63 having a non-linear characteristic can therefore be employed for amplifying the frequency sweep signal before it is conveyed further, for example to a non-linear mixer 65 of a conventional type. Schematic curve shapes of most of the signals in Fig. 9 are shown in Fig. 10.
  • the conventional digital frequency sweep generator which directly generates a frequency sweep by means of a D/A converter and band pass sampling. Such a generator can also make use of some of the advantages of this invention.
  • the number of quantizing levels can for example be reduced to 2, which is the same as completely removing the D/A converter.

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Abstract

Méthode de production d'un signal de fréquence composite et à impulsions. Ledit signal est établi en prenant pour base un bloc signal élémentaire (B2) comprenant un faible nombre de signaux de balayage de fréquence et ayant une portée limitée en période temps (Ts) et en période-largeur de bande (Bs). Un nombre, en principe infini, de blocs de signaux élémentaires (B2) sont assemblés avec une fréquence et une phase coïncidantes aux emplacements de transition entre les blocs élémentaires, de manière à créer une somme de signaux continus de balayage de fréquence par la répétition du bloc élémentaire (B2), à la fois en temps et en fréquence.
PCT/NO1990/000174 1989-11-24 1990-11-23 Method et appareil pour produire un signal de balayage de frequence composite et a impulsions WO1991008615A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
NO89894710A NO894710L (no) 1989-11-24 1989-11-24 Fremgangsmaate og anordning for generering av et sammensatt og pulsformet frekvenssveipsignal.
NO894710 1989-11-24

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WO1991008615A1 true WO1991008615A1 (fr) 1991-06-13

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0580461A1 (fr) * 1992-07-21 1994-01-26 Sextant Avionique Dispositif pour la conversion d'une grandeur électrique en une fréquence avec possibilité d'autocalibration de ladite conversion
WO2008093077A2 (fr) * 2007-01-31 2008-08-07 Qinetiq Limited Système de production d'un signal à faible bruit

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3794995A (en) * 1972-08-02 1974-02-26 Raytheon Co Modulation signal generator and apparatus using such generator
US3852746A (en) * 1972-11-14 1974-12-03 Raytheon Co Pulse compression radar
US3962653A (en) * 1973-12-27 1976-06-08 Telecommunications Radioelectriques Et Telephoniques T.R.T. Arrangement for simultaneously producing signals having an increasing frequency and signals having a decreasing frequency
US4309703A (en) * 1979-12-28 1982-01-05 International Business Machines Corporation Segmented chirp waveform implemented radar system
US4336511A (en) * 1979-04-09 1982-06-22 Sanders Associates, Inc. Method and apparatus for increasing the sweep rate of a linearly swept frequency oscillator

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3794995A (en) * 1972-08-02 1974-02-26 Raytheon Co Modulation signal generator and apparatus using such generator
US3852746A (en) * 1972-11-14 1974-12-03 Raytheon Co Pulse compression radar
US3962653A (en) * 1973-12-27 1976-06-08 Telecommunications Radioelectriques Et Telephoniques T.R.T. Arrangement for simultaneously producing signals having an increasing frequency and signals having a decreasing frequency
US4336511A (en) * 1979-04-09 1982-06-22 Sanders Associates, Inc. Method and apparatus for increasing the sweep rate of a linearly swept frequency oscillator
US4309703A (en) * 1979-12-28 1982-01-05 International Business Machines Corporation Segmented chirp waveform implemented radar system

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0580461A1 (fr) * 1992-07-21 1994-01-26 Sextant Avionique Dispositif pour la conversion d'une grandeur électrique en une fréquence avec possibilité d'autocalibration de ladite conversion
FR2694145A1 (fr) * 1992-07-21 1994-01-28 Sextant Avionique Dispositif pour la conversion d'une grandeur électrique en une fréquence avec possibilité d'autocalibration de ladite conversion.
WO2008093077A2 (fr) * 2007-01-31 2008-08-07 Qinetiq Limited Système de production d'un signal à faible bruit
WO2008093077A3 (fr) * 2007-01-31 2008-10-02 Qinetiq Ltd Système de production d'un signal à faible bruit
GB2450390A (en) * 2007-01-31 2008-12-24 Qinetiq Ltd Low noise signal generation system
GB2450390B (en) * 2007-01-31 2012-03-28 Qinetiq Ltd Low noise signal generation system
US8188911B2 (en) 2007-01-31 2012-05-29 Qinetiq Limited Low noise generator for frequency swept signals

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NO894710L (no) 1991-05-27
NO894710D0 (no) 1989-11-24

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