US3900875A

US3900875A - FM-CW fuze system

Info

Publication number: US3900875A
Application number: US099320A
Authority: US
Inventors: David F Scheets
Original assignee: US Department of Navy
Current assignee: US Department of Navy
Priority date: 1961-03-29
Filing date: 1961-03-29
Publication date: 1975-08-19
Anticipated expiration: 1992-08-19

Abstract

2. In a fuze system the combination comprising: a random turnaround triangular generator having an output; an amplitude modulator having a first input coupled to the output of said triangular generator a second input and an output; a low frequency sin wave generator having an output coupled to the second input of said modulator; a transmitting antenna; an oscillator having an input coupled to the output of said modulator and an output coupled to said transmitting antenna; a mixer having first and second inputs and an output a receiving antenna coupled to the first input of said mixer, the second input of said mixer being coupled to the output of said oscillator; a low level amplifier having an input coupled to the output of said mixer and having an output; a firing circuit having an input; a phase detector having a first input coupled to the output of said low level amplifier, a second input coupled to the output of said sin wave generator and an output coupled to the input of said firing circuit.

Description

O United States Patent 11 1 n 3,900,875 Scheets Aug. 19, 1975 [54] FM-CW FUZE SYSTEM EXEMPLARY CLAIM [75] lm'emm: David Schefl5- Commh Calif 2. In a fuze system the combination comprising: a ran- 73 Assignec; The United sun f America as dom turnaround triangular generator having an outrepresemed b h Secretary f h put; an amplitude modulator having a first input cou- Navy, Washington. DC. pled to the output of said triangular generator a second input and an output; a low frequency sin wave [22] Flledi generator having an output coupled to the second 21 Appl 99 320 input of said modulator; a transmitting antenna; an oscillator having an input coupled to the output of said modulator and an output coupled to said transmitting [52] Cl 343/7 PF; 02/702 Pi 343/18 E antenna; a mixer having first and second inputs and an F42C 13/04 output a receiving antenna coupled to the first input Field Search of said mixer, the second input of said mixer being 7 E; 102/702 702 P coupled to the output of said oscillator; a low level amplifier having an input coupled to the output of said [561 References (fled mixer and having an output; a firing circuit having an UNITED STATES PATENTS input; a phase detector having a first input coupled to 1841764 mass Harvey 343/14 the uutput 0f said low lcwl amplifiersecond input 2358.862 ll/l96t1 Reymim. 343/14 coupled to the output of said sin wave generator and 19653496 3/1950 343/14 an output coupled to the input of said firing circuit. 3 ()7(i l-ll l/l9fi3 Williams 343/l4 3.l()9.l72 lO/Wo] Hardinger et all 343/14 Primary Exmm'ner-T. Ht Tubbesing Attorney. Agent. or Firm Richard S. Sciascia: Joseph M. St. Amand; T. M, Phillips 5 Claims 3 Drawing Figures PHASE TUNED DETECTOR AMPLIFIER FIRING ClRCUlT FIG. I

RUBY 9 I975 SET 1 UF 2 12 l3 '0 f f f RANDOM TURNAROUND AMPLITUDE TRIANGULAR MODULATOR OSCILLATOR GENERATOR SIN WAVE GENERATOR l9 l8 I? f f v f I LOW LEVEL BALANCED BANDPASS MIXER DISCRIMINATOR AMPLIFIER 22 l 2l PHASE TUNED DETECTOR AMPLIFIER FIRING CIRCUIT I DAVID F. SCHEETS INVENTOR.

BY mnifw ATTORNEYS PATENTEDAUBISIBTS 3.900.875

SHEET 2 OF 2 24 26 IO H l l VARIABLE TURNAROUND IMPEDANCE TRIANGuLAR oscILLAToR MODULATOR GENERATOR SWEEP GENERATOR I8 I? r' f f f Low LEvEL m fi BANDPASS MIxER N To AMPLIFIER 22 I f 1 r PHASE TUNED DETECTOR AMPLIFIER 23 7 FIG. 2

FIRING CIRCUIT No sE GENERATOR BANDPASS FILTER r r r K l I REAGTANGE VIDEO TUBE AND MIxER UMTER --p INTEGRAToR o oscILLAToR FIG. 3

DAVID F. SCHEETS INVENTOR.

ATTORNEYS FM-CW FUZE SYSTEM The invention herein described may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to a FM-CW fuze sys tem and more particularly to a FM-C W fuze system with improved counter counter-measures and low altitude capabilities. This is accomplished by transmitting a noise-like dual modulated signal and comparing the return of this signal first with the undelayed transmitted signal and then with a second modulating source to insure that the signal which activates the firing circuit is in response to a target reflected signal rather than a spurious signal.

Accordingly. an object of the present invention is to provide a fuze system wherein jamming signals which may cause spurious firing are filtered out.

Another object is to provide a fuze system wherein removal of sea return and barrage jamming energy at a low level and before saturation.

A further object is to provide a fuze system wherein the return signal is filtered from the noise background by comparing the signal with a modulated frequency signal.

Other objects and many of the attendant advantages of this invention will become readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. I is a block diagram ofa fuze system embodying the invention.

FIG. 2 is a block diagram of a modification of FIG.

FIG. 3 is a block diagram of a further modification of FIG. I.

Referring now to the drawings there is shown in FIG. I a fuze system having an oscillator 10 coupled to a transmitting antenna I I. Oscillator I0 is modulated by a combined modulated signal which originates in a random turnaround triangular generator I2. The signal from generator I2 is amplitude modulated in modulator 13 by a sin wave signal from sin wave generator 14. The receiving portion of the fuze system includes a receiving antenna [6, mixer I7, band pass amplifier l8, balanced discriminator l9, tuned amplifier 21. and phase detector 22. Oscillator 10 is coupled as an input to mixer 17. to provide a local oscillator signal. Sin wave generator 14 is also coupled as an input to phase detector 22. The output of detector 22 is coupled to firing circuit 23.

Random turnaround triangular generator l2 may be of any of several triangular generators with random triggering as for example the triangular generator of FIG. 5-20 shown and described on page 86 of Digital Techniques for Computation and Control. Klein et al.. Instruments Publishing Co.. 1948: and random triggering circuit shown on page I25 of General Radio Company's catalogue P. Balanced discriminator I) may be of the type shown in FIG. 29.7 of Radiotron Dcsigners Handbook, Fourth edition; and firing circuit 23 may be any well known gating circuit. as for example. the silicon controlled switch. for passing a firing pulse voltage to the detonator of a warhead.

In operation, the output frequency of generator 14 should be much lower than the lowest average turn- (ill T A cos (m t If f(l:)dt)

where 0),, is the instantaneous carrier frequency and f( t) is the instantaneous frequency deviation. This signal is reflected from a target (not shown) and returns at a time. 1'. later than the transmitted signal B cos (t 1) f (t) dc) The return signal is mixed with the undelayed signal from oscillator 10 and a term at the difference frequency is generated Y -C cos (w 't' E (t) dt'.)

The difference frequency is equal to the derivative of the angular velocity or:

I: f (1:) dt

tll

As stated above/(1) is the instantaneous frequency deviation of oscillator Ill. The frequency deviation of a klystron is proportional to the repeller voltage.

Since the repelle signal is a random turnaround voltage the average A 1' will be considered. Between turnaround points the voltage is linear in time with slope k or k. This slope is equal to twice the average peak voltage 2 ET. divided by one-half the average period. A 772. of the repeller voltage. The average period is inversely proportional to the average frequency. Thus equation (2) becomes:

Substitution into equation I l results in In FIG. 1 T1: the output of generator 12 is amplitude modulated with sin ml. The term l M sin w!) is then inserted in equation (5) resulting in:

where 6 1-= average frequency of the signal out of mixer l7. T average frequency deviation of oscillator 10.

average frequency of generator 12. M 7r amplitude modulation of the signal output of generator 12.

r time delay of signal to reach a target at range I) and return ZD/C speed of light The amplified signal from amplifier 18 which is modulated from generator 14 before transmission is fed to the balanced discriminator l9. Balanced discriminator I) eliminates jamming signals and sea clutter which energy is uniformly distributed about the discriminator center frequency producing equal positive and negative signals thus cancelling each other. Frequencies other than that of the signal modulation produced by the sinewave generator are eliminated in the tuned amplifier 2] which is tuned to the frequency of the sinewave generator 14. The signal is then compared with the phase of the direct signal from sinewave generator 14 by the synchronous detector 22 to produce a firing pulse for actuating firing circuit 23.

In FIG. 2 the modulating signal is generated by applying the sin wave signal of generator 14 to a variable impedance device 24 such as may be a component of a phantastron which in turn modulates the turnaround triangular generator 26. Since the fundamental frequency of generator 26 which may be a phantastron, is determined by impedance element 24, the output modulating frequency of generator 26 will vary sinusoid-ally about a center frequency.

An alternate frequency modulating generator is shown in FIG. 3. A noise generator 27, which may be any well known type. is coupled through a bandpass filter 28 to a mixer 29. A reactance tube and oscillator 31 is also coupled to mixer 29 which is excited by generator 14 (see FIGS. l and 2). The noise spectrum generated in generator 27 is varied about a center frequency by heterodying it in mixer 29 with the sinusoidally variable frequency generated by reactance tube oscillator 31. The difference frequencies from the output of mixer 29 are coupled through video limiter 32 and integrator 33 to produce a random turnaround triangular voltage to modulate oscillator 10. Limiter 32 may be of the standard circuit No. 6, page 42. M.-

STD439A(WEF), Mar. l, 1960, US. Government Printing Otfice.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

I. In a fuze system the combination comprising, a source of high frequency energy, an amplitude modulator coupled to said source of high frequency energy, a source of low frequency energy coupled to said amplitude modulator for amplitude modulating the high frequency energy from said high frequency energy source. a transmitting antenna, an oscillator coupled to said amplitude modulator and to said transmitting antenna and being responsive to said amplitude modulated high frequency energy for generating a frequency modu lated signal to be radiated in the direction of a target, a receiving antenna for receiving an echo of said transmitted energy. mixer circuit means having first and second inputs and an output, said receiving antenna being coupled to the first of said mixer circuit inputs, the output of said oscillator being coupled to the second of said mixer circuit inputs. a phase detector circuit having first and second inputs. circuit means coupling the output of said mixer to the first input of said detector, circuit means coupling said low frequency source to the second input of said detector. whereby said detector produces an output pulse when the inputs thereto are in phase.

2. In a fuze system the combination comprising: a random turnaround triangular generator having an output; an amplitude modulator having a first input coupled to the output of said triangular generator a second input and an output; a low frequency sin wave generator having an output coupled to the second input of said modulator; a transmitting antenna; an oscillator having an input coupled to the output of said modulator and an output coupled to said transmitting antenna; a mixer having first and second inputs and an output a receiving antenna coupled to the first input of said mixer. the second input of said mixer being coupled to the output of said oscillator; 21 low level amplifier having an input coupled to the output of said mixer and having an output; a firing circuit having an input; a phase detector having a first input coupled to the output of said low level amplifier, a second input coupled to the output of said sin wave generator and an output coupled to the input of said firing circuit.

3. In a fuze system the combination comprising an oscillator. circuit means for generating a combined random noise signal with a low frequency amplitude modulation coupled to said oscillator for frequency modu lating said oscillator. transmitting means coupled to said oscillator for radiating the output of said oscillator in the direction of a target in the presence of clutter. receiving circuit means for receiving reflections of said signal from said target and said clutter and including circuit means coupled to said low frequency source for comparing the returned signal with the low frequency modulation to remove said clutter reflected signals from said system.

4. The system of claim 3 wherein said generating circuit means comprises a variable impedance device, a turnaround triangular generator and a sin wave generator, said variable impedance device being coupled to being coupled as a first input to said mixer circuit. said reactance tube and oscillator coupled as a second input to said mixer. a low frequency sin wave generator coupled to said reactance tube and oscillator for producing a sinusoidally modulated signal.

Claims

1. In a fuze system the combination comprising, a source of high frequency energy, an amplitude modulator coupled to said source of high frequency energy, a source of low frequency energy coupled to said amplitude modulator for amplitude modulating the high frequency energy from said high frequency energy source, a transmitting antenna, an oscillator coupled to said amplitude modulator and to said transmitting antenna and being responsive to said amplitude modulated high frequency energy for generating a frequency modulated signal to be radiated in the direction of a target, a receiving antenna for receiving an echo of said transmitted energy, mixer circuit means having first and second inputs and an output, said receiving antenna being coupled to the first of said mixer circuit inputs, the output of said oscillator being coupled to the second of said mixer circuit inputs, a phase detector circuit having first and second inputs, circuit means coupling the output of said mixer to the first input of said detector, circuit means coupling said low frequency source to the second input of said detector, whereby said detector produces an output pulse when the inputs thereto are in phase.

3. In a fuze system the combination comprising an oscillator, circuit means for generating a combined random noise signal with a low frequency amplitude modulation coupled to said oscillator for frequency modulating said oscillator, transmitting means coupled to said oscillator for radiating the output of said oscillator in the direction of a target in the presence of clutter, receiving circuit means for receiving reflections of said signal from said target and said clutter and including circuit means coupled to said low frequency source for comparing the returned signal with the low frequency modulation to remove said clutter reflected signals from said system.

4. The system of claim 3 wherein said generating circuit means comprises a variable impedance device, a turnaround triangular generator and a sin wave generator, said variable impedance device being coupled to said turnaround triangular generator and said sin wave generator being coupled to said variable impedance device for varying the impedance sinusoidally.

5. The system of claim 3 wherein said generating circuit means comprises a noise generator, mixer circuit, a reactance tube and an oscillator, said noise generator being coupled as a first input to said mixer circuit, said reactance tube and oscillator coupled as a second input to said mixer, a low frequency sin wave generator coupled to said reactance tube and oscillator for producing a sinusoidally modulated signal.