GB2302227A - Millimeter wave sensor - Google Patents

Description

n I C- l 1 -, r 1 T.1 p. 17 n.

1 - 1, n--s-nn flurnhern 2302227 The invention relates to a millimetrc--ij3ve ( Translator's note: can also mean "an extremely high frequency,,) sensor in accordance with the definition of the snecips of claim 1.

Such a sensor has heen put forward as an Fl-!711-radar in the article of 'larconi lectronic nevices Ltd. hy n.n.

H i 11 i an s at t h t2 'I 10 P C ong--ess 1 nng in I I jp S -l a d e n. The ramn linearisation of its frPquencV modulation is achieveH hy a frPquency requInting circuit, for which a small nroDortion is -ecounlr?d from the outn,ijt nath of the voltage-controllahle mil-limetre-uave oscillator and is compared as actual value in a renu I at -2r m it h t l-);:? -f P l ue, p rp-ri;=t p r m ine r.4 hy t h e ran p nenerat,i7, tn, o'tain a correcting renulatinq deviation. As a re-ult of the frenuency renulation of the oscillator control with t2mporal voltage ramps, sunplied from a verv line,r sautonth npnerator, as d?sir.,7,1-value course, the p-rohle.ms are sunposTr' tn he avoided which uould '3e present in the case nf ELAD ORIGINAL boo- 1 a controlled (thus not realised in the clnse(l rpgulating circuit) linearisation of the contrnl characteristic of the oscillator: Plamelv having to stare ai,jay control characteristics through which the non- linearity of the oscillator, voltage-controllable in its output frequency, would precisely he compensated. This is because, for this, an entire family of characteristics as a 'unction of the operating temperature of the oscillator would h3ve to he stored away, in order in the case of varying working temperattir,s to switch over hF-ti,ieen the associated sets. of charanteristics. The expenditure for the prnqramming and for the provision of appropriate storage canacity and switch-over mechanisms would, however, be considerahle; and it has heen shown that as a result of such switch-over procedures the mode of operation of the sensor is impaired more especially when it is used in two-channel manner in active and in passive operation radiometer) for example as a radar and as a as is known for instance from IIS-13S 3 qm ?n7 Indeed, a good linearisation of the frequency sweep can also he realised by a phase regulating loop, as is known for instance from!)E-!Iq 13 42 n97, but also already descrihed hy L.A. Hofrmann Pt al in TEEE Trans., Vol. MTT-17, No. 12, 1 Decemher lnr,173, pages 1145 to 1140.The circuitrywise necessary expenditure for such nhase regulating circuits can, however, 3 not he justified more especially when it is a matter of small-size and chean sensors for non-stationary use, such as in narticular radar/radiometer combinations fnr seeker-fuze 1 1 C. - munition (see 'n-9S '12 n7 P07) or for vehicle warning and information mechanisms. This applies accordingly to the basically affordet! possibility of achieved a periodical and strictly linear frequency cnur!-, p ovpr time not h\l means of en oscillator i.ihich is controllable with respect to its output frequency, hut hy a cirruitrywise much more complex frequency syntlipgizpr.

'lore esnecially in the case of military use in munitions it has, in addition to this, to be taken into account that on the one hand proprammahle read-only stores of hiqi caracity, for the deposit of control characteristics 11 over the temperature as ambient parameter), in militarily-qualifie; version are very expensive; and that in addition to this through the temperaturp-deDendent sets of characteristics neitlier tlie r9all%/ ocrurring aqeinq phenomena in their effect on the oscill-tnr oneration are detectahle, nor even 9nvironmRnt-dictat9d disturl-)ancgs, such as occur for instance hy rpason of the hiqh departure acceleration upon the firing of munition f7om a weapon 13arrel. nifferently from tmperature influences that are to he expected, such other ter environmental influences ', hiqi mechanical stressinq aft 4 storage time o-F many years) cannot be predetermined in a sufficiently accurate manner for the linear frequency control, to be striven after, of the oscillator output frequency in the time-accelerator procedure and by test loadings. In production-technoloqy respects it would anyuay be disadvantageous that besides the complex programming-in of the sets of characteristics into a read store (PPTI) for the later oscillator control each oscillator could be individually measured and then he handled ( installed) only in pairs with its modulation control store, which would severely restrict the flexibility of production and would complicate the sQare-part logistics.

In recognition of these factors, the problem underlying the invention is, in the case of a sensor of the type in accordance ijith the species, to ensure the linear time--lenendencv of the output frequency hy measurps which are simpler in prodtiction-tpchnolony and circuit-technnlnqy resnects.

In accordance with the invention, this problem is essentially solved in that the sensor of the type in accordance with the species is designed in accordance with the characterising part of claim 1.

In accordance with this solution, only immediately at the start of use or else during operation of the sensor is an item of correction information for the compensation of the non-linearity of its frequency modulation over the control voltage obtained in that the oscillator is operated temporarily, while (still) no sensor evaluation is being effected, in the closed frequency regulating circuit, in order with stationarily steadystate operating conditions to obtain from the comparison of the actualfrequency course with the desired-frequency course a modification of the temporal ramp of the modulation control voltage and to transfer same into a rpad-write store; wherewith the regulating circuit is then split up ( translator's note: can also mean "separated up") and the oscillator is controlled with this item of correction information which applies exactly to the actual operating factors. In this way not only is the circuittechnology and control-technology exnenditure for obtaining and selecting different control characteristics which are dependent upon different enviromenal factors abolished; there is abolished more particularly any disturbance of the sensor mode of operation which would stem from the operation of the frequency requlating circuit or from switch-overs of control characteristics. Above all now the enviromental influences which have actually occurred directly prior to the putting 6 into operation of the oscillator ( such as previous shock stresses and actual ambient temperature) are taken into account, because the one set of items of correction information, ascertained for the actual control from temporary regulation, have only just heen picked up and stored.

This one, crucial set of items of correction information for the linearisation of the output frequency fluctuation can he deposited in a correspondingly small and cheap volatile store which is overwritten when, after a certain operating period of time for instance as a distance radar set on a motor vehicle a switch-back is made temporarily to closed frequency regulating circuit, in order to ohtain actual items of correction information by reason of interim disturbing influences in the oscillator. In the production cycle upon the production of the sensor thus still no characteristics need to be detected and he stored away in a copious manner, because only the control liehaviour is picked tip immediately prior to use of the sensor and only this is then stored away for the oscillator control.

If the temporal frequency course behind the oscillator, measured for instance in the return branch of the regulating circuit, is stored away as correction imnfo-rmation, before 7 the circuit is then opened, there is effected for the measuring operation the oscillator control from the sawtooth generator, the ramp voltage of which is modified by the correction information. The continuous operation of the sawtooth generator can, however, be dispensed with if the modified ramp is stored away as the control voltage in front of the oscillator, before for the entry into the measurement the regulating circuit is opened.

Additional alternatives and further developments as well as further features and advantages of the invention will become apparent from the further claims and, also taking into account what is set forth in the abstract, from the following description of preferred examples of realisation with regard to the solution in accordance with the invention which are shown in the drat.iing, along with a restriction to that which is essential, in a highly ahstracted manner as a sinqlp-pole block wiring diagram. The sale Figure of the drawing shows a millimetre-tiave sensor ijith a 'Frequency regulatinn, loop, which, here ( for exDlanation) optionally in front of or behind the comparison paint, can be split up for the controlled operation of the linear-frequency-modulated oscillator.

The linear-frequency-riodulnted continuous-wave-signal 9 millimetre-wave sensor 11 shown in circuitry respects is designed for simultaneous active and passive operation; i.e. it works on the one hand actively in the sense of the radiation of transmission energy 12 and reception, time-offset thereagainst, of reflection energy 13 as a radar set and, preferably by way of the same antenna 14, as a radiometer for the reception of microwave extraneous radiation 15. In an evaluation circuit 16, which is connected by way of a circulator as transmission/reception stuitch-point ( translator's note: can also mean llduplexerll 17 suhsequent to the antenna 14, there is effected a frequency-wise splitting-up of the reception information 19 into a radar channel and a radiometer channel frequency-offset thereagainst f. not executed in more detail in the drawing). In the radar channel the modulation frequency of the reflection energy 13 is compared with the actual transmission frequency lq lying thereabove, in order in known 'per sel manner to be able to draw conclusions, from the difference between these two instantaneous modulation frequencies, regarding the reflector distance ( translator's note: can also mean "range").

For this, the oscillator ?n which is modulable in its output or transmission frequency 1n by voltage control ( in the case of which it can lip a matter of a varactor-tunpd 9 ( translator's note: varaktorabgestimrTiten) VCn or of an oscillator which is tunable by way of its supply voltage) is controlled from a sawtooth generator 21 with a ramp voltage ur(t) which rises in a highly linear manner over the time t and the sawtooth-course repetition cycle of which ( thus the ramp period thereof) is predetermined from a timing generator 22.

Since, of course, the modulation characteristic of a voltage-controlled maximum-frequency generator 2n is not linear ( thus the output transmission frequency 10 does not depend linearly upon the input or modulation voltage u), there arises in fact a non-linear frequency course f(t) as oscillator output frequemncy 1q over the ramp period. This assumes the striven-after linearly rising course only when a control signal us(t) deviating accordingly opposingly from the ideal ramp course ur(t) is fed in. This can be obtained by way of a difference former 27 from a comparison of the ideal modulation signal ur(t) with the actual frequency modulation f(t), the frequency course f of which over the time t is converted by means of a frequency discriminator 24 into an equivalent voltage course over the time u(t). The difference voltage ud(t) resulting therefrom is added to the ideal ramp signal ur(t) in an adder 25, so that the distorted control voltage us(t) arises for the compensation of the non- - 19 linearities of the oscillator 2n. Hpon decoupling of the (output) frequency 19, that is to he returned, by means of a directional counler 2n- hetween oscillator Pn and (transmission) antenna 14 and upon switch- on of a filter amplifier 27 in front of the frequency-controllahle oscillator 2', thus a closed frequency regulatinn circuit 29 for achieving a time-linearly rising transmission frequency 10 is afforded.

9y reason of unavoidahle couplings, the function of such a regulatinq circuit 2n does, of course, disturh the simultaneous passive mode of ooeration (measuring operation) of the sensor 11, thus in the microwave spectrum the radiometric mode of operation thereof in the evaluation circuit 1. in orc.er to avoid items of misinformation, the function of the evaluation circuit lr is therefore initially hlocked by tj3y of a si, jitchinq signal E1 from a supernrdinated function cycle control 2n, when the oscillator 2n is operated in tne closed frequency renulating circuit 2n. If stahle, steady-st.nte conditions with respect to the function of the regulating circuit 2q h3ve occurred, by way of a switch-over siqnal E2 the effect is hrounht ahout that an item of correction information 3r is taken over by way of a converter 31 into a store 32 and the regulating circuit 2.9 is split up 5y way of a changL--,jver switch 37, in order to control the - 1 1 oscillator 20 from then on in an unregulated manner in accordance with the correction information 30 just obtained from the regulating circuit 2P. In the case of this it is a matter of the modified ramp of the control voltage us(t), if the stare 32, behind the adder 25 for the ideal ramp voltage ur(t) and the compensation difference voltage ud(t), and thus its change-over switch 33 in the control channel in front of the oscillator 2n, lies; or it is a matter in the case of the stored-aijay correction information 30 of the actual frequency course u(t), if the store 32 lies behind the oscillator 2n, and the change-over switch 33 in front of the desired-value/actual-value comparator 23 for the splitting- up of the repulating circuit return. However, also (not taken into account in the drawing) the difference voltage ud(t) can be stored away as correction information (30) and again the regulating-circuit return by way of the change-over switch 33 be opened, upon operation of the sawtooth generator 21 also in the measuring operation of the oscillator 2n.

It is crucial that from the function of the closed regulating circuit 2n an item of correction information 3n can he obtained and stored away, by way of which then the modified control voltage us(t) for a frequency modulation, linear over the time, of the output and transmission frequency 19 is achieved, without needing in the measuring 12 - operation still the function of the (disturbing the radiometric evaluation) closed regulating circuit 28.

In the case of the store 32 it can be a matter of a read-write store (RAM) which is fed by way of the converter 31 with a temporally equidistant sequence of digitized (coded) voltage values of a ramp function us(t). These are then read out cycliically - controlled by way of the timing generator 222' - and changed back by way of a converter 31 into time-dependently varying voltage impulses, in order to carry out the voltage control of the oscillator 20 or respectively of the filter amplifier 27 connected prior to it. The store 32 can, however, also be realised as a shift register, the length of which corresponds to the number of voltage values to be stored away over a ramp and the width of which corresponds to the coding bit width. In the case of the converter 31 it can he a matter of separate analog/diqital and digital/analog converters; since these are, however, for the writing-in of the correction information n and the reading-out e.g. for the control voltage us(t) operated in a non-overlapping manner, also a converter working in both directions (in accordance with the so-called weighing method, see 11. Tietze, Ch. 9chenk, Halbleiter-Schaltungstechnik, Springer-Verlag, ln97, Rerlin-Heidelberg, New York, Tokyo, 6th edition, parles 767 to - 13 772) can be used, which can realise both an analog/digital and a digital/analog conversion.

The instant of the appearance of the change-over signal E2 for the termination of the operation of the closed regulating circuit 29 after storing-away of the then precisely ascertained, actual correction information 3n can be generated from the superordinated function cycle control 29 a certain space of time after appearance of the switch-on signal El and thus depend indirectly upon the appearance of a number of sawtooth ramps of the generator 21, which is at least mnecessary in order to achieve a stably steady-state behaviour of the regulating circuit 29. More especially when as the correction information 30 the voltageconverted modulation stroke ( translator's note: can also mean 11swing") f(t) = u(yt) in the return of the regulating circuit 29 is enlisted (bottom left in the drawing), it is advantageous to issue the change-over signal E21 when the switch-on frequency drift of the output frequency f(t) hehind the oscillator ?n has gone hack to a predetermined minimum. This can he ascertained circuitrywise in a particularly simple manner if the store 32 is organised as a shift register, so that a specific frequency value (for instance the lowest modulation frequency at the start of a ramp period) is compared with the associated next-following frequency value (thus the next-following ramp), by the last cell of the shift-register store 32 and the actual input value thereof being sswitched to a difference former 34. Only when the onset frequency of the next ramp corresponds sufficiently with that of the preceding ramp is from the difference former 34 by way of an internal threshold interrogation the switch-over signal E21 issued to the switch 33 for the splitting-up of the closed regulating circuit ?R.

Instead of this or in addition, by way of a temperature monitor 35 the working temperature of the oscillator 20 can be measured and a switch-on signal Ell be issued only (or respectively thereabove the previously mentioned central switch-on signal El be released only) when by reason of approximately achieved operating temperature of the oscillator 2n generally now a specified mode of operation of the oscillator 20 and thus a stable mode of operation of the regulating circuit 29 can be expected; with the issuance of the switch-over signal E21 when the temporal gradient, ascertained in a differencing stage 36, of the temperature change falls helow a predetermined minimum, thus when by reason of constant operating temperature of the oscillator 2n also an output frequency f(t) rid of temperature dirft can he expected.

Furthermore, the temperature monitor 35 can supply an item of temperature information 37 which is infraposed as temperature-dependent initial bias to the ramp voltage ur(t), for instance by additional injection into the adder 29 behind the sawtooth generator 21. If this additional voltage behaves conversely to the variation of the working-temperature fluctuation of the oscillator 2n, it is thereby ensured that this starts to oscillate reliably and rapidly even at particularly low temperatures. This is particularly of interest if the multi-channel microwave sensor 11 is used for instance as a distance warning radar with simultaneous radiometer operation for the detection of special road-traffic conditions, such as for instance the formation of ice or the risk of aquaplaning and thus unter 2Xtreme temperature factors. In order then to be able to compensate for ageing- and vibration-occasioned influences, detrimental to the frequency constancy of the modulable oscillator 2n, even over fairly long times of utilisation, it is advantageous to trigger periodically and/or in each case upon start-up of the motor vehicle (or respectively of its sensor 11) a switch-on signal El, in order to obtain in accordance with the actual ageing and ambient factors for the operation of the oscillator ?n a brought-up-to-date iten of correction information 30 for the linearisation of the frequency sweep.

1 16 rlaims 1. A linear-frequency-modulated continuous-wave-signal millimetre-wave sensor (11), more especially for a non-stationary radar/radiometer combination, with a voltage-controlled oscillator (12) in a frequency regulating circuit (29), characterised in that provided for the closed regulating circuit (29) is a store (32) for the reception of an item of correction information (30), dependent upon the actual output frequency (19) of the oscillator (29), along with stationary operation of the oscillator (2n) in the closed regulating circuit (29), which is thereupon opened by a change-over switch (33) contained in the regulating circuit (28), in order to control the oscillator (2n) in the non-closed circuit from the store (32).

2. A sensor according to claim 1, characterised in that a volatile readwrite store is provided as the store (32).

3. A sensor according to claim 1 or 2, characterised in that the store (32) is connected prior to the oscillator (23) and behind the desiredvalue/actual-value comparator (23) of the closed regulating circuit (2P) to this.

4. A sensor according to claim 1 or 2, characterised in that the stare (32) is connected behind the oscillator (2n) and in front of the desiredvalue/actual-value comparator (23) of the closed regulating circuit (28) to this.

9. A sensor according to one of the preceding claims, characterised in that one input of the change-over switch (33) is connected to the input and one input of the changeover switch (33) is connected to the output of the store (32).

5. A sensor according to claim 5, characterised in that the change-over switch is placeable by a switch-on signal (E1) to the input and by a change-aver signal (E2) to the output along with splitting-up of the input to the store (32) of the store (32).

7. A sensor according to claim 6, characterised in that a switch-over signal (E2) is supplied from a superordinated function cycle control (2q) when the closed regulating circuit (28) has been operated over a predetermined space of time.

P. A sensor according to claim fi, characterised in that an item of switch-over information (E21) is supplied from a - 1 9 - difference former (34) when upon operation of the oscillator (2n) x in the closed regulating circuit (28) mutually associated frequencies (f) of consecutive modulation ramps fall below a predetermined difference from one another.

9. A sensor according to claim 5, characterised in that a switch-over signal (E21) is supplied from a temperature monitor (35) when the temporal temperature gradient of the operating temperature of the oscillator (2n) operated in the closed regulating circuit (29) falls below a predetermined value.

1n. A sensor according to one of the preceding claims, characterised in that a temperature-dependent initial bias is infraposed to the output signal (ur(t)) of the satitooth generator (21) for the frequency modulation of the output frequency (1q) of the oscillator (2n) from a temperature monitor (35).

11. A sensor according to one of the preceding claims, characterised in that it is designpd as a combined radar/radiometer sensor (11) with a common transmission/reception antenna (1) for 13oth channels.

X9 Amendments to the claims have been f lied as follows 1. A linear-frequency-modulated continuous-wave-signal millimetre-wave sensor having a measuring function and comprising a voltage-controlled oscillator for producing the continuous-wave signal which oscillator Is acted upon from a store with correction information in accordance with the deviation of the actual course of the oscillator output frequency from a predetermined course of the output frequency, characterised In that during generation of 10 correction information the oscillator, frequency-modulated by way of a saw-tooth generator, is operated in a closed frequency regulating circuit and the store is fed with correction information from the frequency regulating circuit until the frequencies in consecutive frequency15 modulation ramps fall below a predetermined difference from one another, whereupon the closed frequency regulating circuit is opened and a switch-over Is made to a measuring operation with control of the modulation saw-tooth generator by the just stored correction information.

2. A sensor according to claim 1, characterised in that a volatile readwrite store is provided as the store.

3. A sensor according to claim 1 or 2, characterised in that the store is connected prior to the oscillator and behind a desired-value/actual-value comparator of the closed regulating circuit.

4. A sensor according to claim 1 or 2, characterised in that the store (32) is connected behind the oscillator and in f ront of a des i redvalue/ actual -value comparator of the closed regulating circuit.

5. A sensor according to any one of the preceding claims, characterised in that the switch-over is made by a change over switch, and in that one input of the changeover switch is connected to the input of the store, and another input of the change-over switch is connected to the 10 output of the store.

6. A sensor according to claim 5, characterised in that the change-over switch is placeable by a switch-on signal to the input of the store and by a change-over signal to 15 the output of the store accompanied by a splitting-up of the input to the store.

7. A sensor according to claim 6, characterised in that a switch-over signal is supplied from a superordinated 20 function cycle control when the closed regulating circuit has been operated in the closed condition over a predetermined space of time.

8. A sensor according to claim 6, characterised in that an item of switchover information supplied by a difference former for the frequencies of consecutive modulation ramps determines the opening of the frequency regulating circuit for the transition from the operation of correctioninformation generation to the measuring operation.

9. A sensor according to claim 6, characterised in that a switch-over signal is supplied from a temperature monitor when the temporal temperature gradient of the operating temperature of the oscillator operated in the closed regulating circuit falls below a predetermined value.

10. A sensor according to one of the preceding claims, characterised in that a temperature-dependent initial bias is infraposed to the output signal of the sawtooth generator for the frequency modulation of the output frequency of the oscillator from a temperature monitor.

11. A sensor according to one of the preceding claims, characterised in that it is designed as a combined radar/ radiometer sensor with a common transmission/reception antenna for both channels.

12. A sensor substantially as hereinbefore described with reference to the accompanying drawing.