Radar

Claim 2

In an apparatus for locating targets by a radar system operating with very short electromagnetic waves, particularly for locating low-flying targets so that the antenna radiation pattern of said system touches ground, wherein a speed selection is combined with a distance selection, the line interval of the operating spectrum being greater than 2(vmax/ lambda ), where vmax the maximum radial speed of the target relative to the system and lambda the operating wave length of the system, the combination which comprises: means for phase modulating a carrier frequency fo with a modulation frequency f1 for producing a frequency spectrum containing substantially only the frequencies fo - f1, fo, and fo + f1; means for pulse modulating said frequency spectrum with a frequency f2; means for transmitting the thus-modulated frequency spectrum; means for converting the echo signal, which if it has been reflected by a target which is travelling radially with respect to the transmitter antenna has been frequency shifted relative to the transmitted signal by an amount corresponding to the Doppler frequency, to an intermediate frequency; means for applying the thus-obtained intermediate frequency to a phase modulator for phase modulating the former with said frequency f1, the latter being applied to said phase modulator via a first adjustable phase shifter; means for applying the output of said phase modulator to a keying unit which is keyed by said frequency f2 via a second adjustable phase shifter; means for adjusting said second phase shifter for producing coincidence between the received signal and the keying pulse, the latter serving as a Selection pulse; means for adjusting said first phase shifter for neutralizing the frequency modulation of the transmitter by counter-modulation in said phase modulation which countermodulation has been shifted so that the distance of the target is obtained by adjustment of said phase shifter; and means for applying the distance selected output of said keying unit to a Doppler frequency filter for extracting from said signal intelligence concerning the speed of the target.

Claim 3

Apparatus as defined in claim 1, further comprising means for mechanically coupling said phase shifters such that the adjustable running times for f1 and f2 are equal.

Claim 4

Apparatus as defined in claim 1, wherein said intermediate frequency is fine-adjusted for purposes of speed selection such that the demodulated output voltage of said Doppler frequency filter is a maximum.

Claim 5

Apparatus as defined in claim 1, further comprising means for extracting from the received signal intelligence concerning the bearing of the target.

Claim 6

Apparatus as defined in claim 4, wherein said intelligence concerning the bearing of the target is obtained from the Doppler frequency filter.

Claim 7

In an apparatus for locating targets by a radar system operating with very short electromagnetic waves, particularly for locating low-flying targets so that the antenna radiation pattern of said system touches ground, wherein a speed selection is combined with a distance selection, the line interval of the operating spectrum being greater than 2(vmax/ lambda ), where vmax the maximum radial speed of the target relative to the system and lambda the operating wave length of the system, the combination which comprises: means for phase modulating the carrier frequency fo of the operating spectrum with a modulation frequency f1 which is in fixed relationship relative to said carrier frequency for producing a frequency spectrum containing substantially only the frequencies fo - f1, fo, and fo + f1; means for pulse modulating said frequency spectrum with a pulse repetition frequency f2 which is in fixed relationship relative to said carrier frequency; means for transmitting the thus-modulated frequency spectrum; means for converting the echo signal, which if it has been reflected by a target which is travelling radially with respect to the transmitter antenna has been frequency shifted relative to the transmitted signal by an amount corresponding to the Doppler frequency, to an intermediate frequency; means for applying the thus-obtained intermediate frequency to a phase modulator for phase modulating the former with a frequency f1'' derived from a frequency fs generated by an adjustable fixed frequency generator, the range of adjustability of said frequency fs depending on fo and the maximum radial target speed to be encountered; means for applying the output voltage of said phase modulator to a keying unit which is keyed by a frequency f2'' derived from said fixed frequency generator; means for phase shifting the frequencies f1'' and f2'' for neutralizing the frequency modulation of the received signal by corresponding counter modulation in said phase modulator and for producing coincidence in said keying unit between the received signal and the frequency f2''; means for comparing the phase position of a reference voltage ff derived from said carrier frequency with the phase position of an indicator voltage ff'' which is phase-fixed relative to a voltage of said frequency fs of said fixed frequency generator for determining the target distance; and means for mixing the distance selected signal with said fixed frequency fs derived from said fixed frequency generator, the latter being finely regulated such that the output voltage of a Doppler frequencY filter which is connected to the last mixer stage is a maximum.

Claim 8

In an apparatus for locating targets by a radar system operating with very short electromagnetic waves, particularly for locating low-flying targets so that the antenna radiation pattern of said system touches ground, wherein a speed selection is combined with a distance selection, the line interval of the operating spectrum being greater than 2(vmax/ lambda ), where vmax the maximum radial speed of the target relative to the system and lambda the operating wave length of the system, the combination which comprises: means for phase modulating the carrier frequency fo of the operating spectrum with a modulation frequency f1 which is in fixed relationship relative to said carrier frequency for producing a frequency spectrum containing substantially only the frequencies fo - f1, fo, and fo + f1; means for pulse modulating said frequency spectrum with a pulse repetition frequency f2 which is in fixed relationship relative to said carrier frequency; means for transmitting the thus-modulated frequency spectrum; means for converting the echo signal, which if it has been reflected by a target which is travelling radially with respect to the transmitter antenna has been frequency shifted relative to the transmitted signal by an amount corresponding to the Doppler frequency, to an intermediate frequency; means for applying the thus-obtained intermediate frequency to a phase modulator for phase modulating the former with a frequency f1'' derived from a frequency fs generated by an adjustable fixed frequency generator, the range of adjustability of said frequency fs depending on fo and the maximum radial target speed to be encountered; means for applying the output voltage of said phase modulator to a keying unit which is keyed by a frequency f2'' derived from said fixed frequency generator; means for phase shifting the frequencies f1'' and f2'' for neutralizing the frequency modulation of the received signal by corresponding counter modulation in said phase modulator and for producing coincidence in said keying unit between the received signal and the frequency f2''; means for comparing the phase position of a reference voltage ff derived from said carrier frequency with the phase position of an indicator voltage ff'' which is phase-fixed relative to a voltage of said frequency fs of said fixed frequency generator for determining the target distance; and means for mixing the distance selected signal with said fixed frequency fs derived from said fixed frequency generator, the latter being finely regulated such that the output voltage of a Doppler frequencY filter which is connected to the last mixer stage is a maximum.

Claim 9

Apparatus as defined in claim 6, wherein the fixed frequency generator is finely regulated by the output voltage of said Doppler frequency filter.

Claim 10

Apparatus as defined in claim 6, wherein the fixed frequency generator is finely regulated by the output voltage of a phase modulator which has applied to it, via two parallel channels, signals derived from frequencies f2'' and f2'''', said frequency f2'''' being in synchronism with said frequency f2'' and phase-shifted relative thereto by 90*, said frequencies being added such that the output signal of said phase modulator is proportional to the difference between the distance of the target and the distance stored in said fixed frequency generator.

Claim 11

Apparatus as defined in claim 6 further comprising means for applying the distance and speed selected signal to an evaluating unit for extracting from said signal intelligence concerning the bearing of the target.

Claim 12

A radar system comprising, in combination: a carrier frequency generator; a first phase modulator connected to the output of said carrier frequency generator; a modulation frequency generator having its output connected to said first phase modulator; a first keying unit connected to the output of said first phase modulator; a pulse repetition frequency generator having its output connected to said first keying unit; a transmitting antenna connected to the output of said first keying unit; a receiving antenna; a mixer and I.F. amplifier connected to the output of said receiving antenna; an oscillator having its output connected to said mixer and I.F. amplifier; a second phase modulator connected to the output of said mixer and I.F. amplifier; a second keying unit connected to the output of said second phase modulator; a first phase shifter having its input connected to said modulation frequency generator and its output to said second phase modulator; a second phase shifter having its input connected to said pulse repetition frequency generator and its output to said second keying unit; a transmission interconnecting said phase shifters and having a transmission ratio equal to the ratio of the frequency of said modulation frequency generator to the frequency of said pulse repetition frequency generator; and measuring means connected to the output of said second keying unit; said system thereby producing an operating spectrum generating a signal containing intelligence which is a function of both the speed and distance of a target, the line interval of the operating spectrum being greater than 2(vmax/ lambda ), or, if targets travelling toward or away from the system are to be located, 4(vmax/ lambda ), where vmax the maximum radial speed of the target relative to the system and lambda the operating wave length of the system.

Claim 13

A radar system comprising, in combination: a carrier frequency generator; a first phase modulator connected to the output of said carrier frequency generator; a modulation frequency generator having its output connected to said first phase modulator; a first keying unit connected to the output of said first phase modulator; a pulse repetition frequency generator having its output connected to said first keying unit; a transmitting antenna connected to the output of said first keying unit; a receiving antenna; a mixer and I.F. amplifier connected to the output of said receiving antenna; an oscillator having its output connected to said mixer and I.F. amplifier; a second phase modulator connected to the output of said mixer and I.F. amplifier; a second keying unit connected to the output of said second phase modulator; a first phase shifter having its input connected to said modulation frequency generator and its output to said second phase modulator; a second phase shifter having its input connected to said pulse repetition frequency generator and its output to said second keying unit; a transmission interconnecting said phase shifters and having a transmission ratio equal to the ratio of the frequency of said modulation frequency generator to the frequency of said pulse repetition frequency generator; and measuring means connected to the output of said second keying unit; said system thereby producing an operating spectrum generating a signal containing intelligence which is a function of both the speed and distance of a target, the line interval of the operating spectrum being greater than 2(vmax/ lambda ), or, if targets travelling toward or away from the system are to be located, 4(vmax/ lambda ), where vmax the maximum radial speed of the target relative to the system and lambda the operating wave length of the system.

Claim 14

A radar system as defined in claim 10, further comprising a Doppler frequency filter connected to the output of said second keying unit.

Claim 15

A radar system as defined in claim 11, further comprising an evaluating unit connected to the output of said Doppler frequency filter.

Claim 16

A radar system comprising, in combination: a carrier frequency generator; first and second frequency dividers connected to said carrier frequency generator for deriving from the carrier frequency a pulse repetition frequency f2 and a modulation frequency f1, respectively; a first phase modulator connected to the output of said carrier frequency generator and to the output of said second frequency divider; a first keying unit connected to the output of said first phase modulator and to the output of said first frequency divider; a transmitting antenna connected to the output of said first keying unit; a receiving antenna; a mixer and I.F. amplifier connected to the output of said receiving antenna; an oscillator having its output connected to Said mixer and I.F. amplifier; a second phase modulator connected to the output of said mixer and I.F. amplifier; a second keying unit connected to the output of said second phase modulator; a mixer connected to the output of said second keying unit; an adjustable fixed frequency generator for generating a frequency fs and having its output connected to said last-mentioned mixer; a phase shifter connected to the output of said fixed frequency generator; third and fourth frequency dividers connected to the output of said phase shifter for deriving from said frequency fs generated by said fixed frequency generator a reference frequency f2'' and a reference frequency f1'', respectively, the output of said third frequency divider connected to said second keying unit and the output of said fourth frequency divider being connected to said second phase modulator; a Doppler frequency filter connected to the output of said last-mentioned mixer; and a control circuit connected to the output of said Doppler frequency filter for producing a fault signal proportional to the Doppler frequency, the output of said control circuit being connected to the input of said fixed frequency generator for adjusting the same in response to the speed of the target; said system thereby producing an operating spectrum generating a signal containing intelligence which is a function of both the speed and distance of a target, the line interval of the operating spectrum being greater than 2(vmax/ lambda ), or, if targets travelling toward or away from the system are to be located, 4(vmax/ lambda ), where vmax the maximum radial speed of the target relative to the system and lambda the operating wave length of the system.

Claim 17

A radar system comprising, in combination: a carrier frequency generator; first and second frequency dividers connected to said carrier frequency generator for deriving from the carrier frequency a pulse repetition frequency f2 and a modulation frequency f1, respectively; a first phase modulator connected to the output of said carrier frequency generator and to the output of said second frequency divider; a first keying unit connected to the output of said first phase modulator and to the output of said first frequency divider; a transmitting antenna connected to the output of said first keying unit; a receiving antenna; a mixer and I.F. amplifier connected to the output of said receiving antenna; an oscillator having its output connected to Said mixer and I.F. amplifier; a second phase modulator connected to the output of said mixer and I.F. amplifier; a second keying unit connected to the output of said second phase modulator; a mixer connected to the output of said second keying unit; an adjustable fixed frequency generator for generating a frequency fs and having its output connected to said last-mentioned mixer; a phase shifter connected to the output of said fixed frequency generator; third and fourth frequency dividers connected to the output of said phase shifter for deriving from said frequency fs generated by said fixed frequency generator a reference frequency f2'' and a reference frequency f1'', respectively, the output of said third frequency divider connected to said second keying unit and the output of said fourth frequency divider being connected to said second phase modulator; a Doppler frequency filter connected to the output of said last-mentioned mixer; and a control circuit connected to the output of said Doppler frequency filter for producing a fault signal proportional to the Doppler frequency, the output of said control circuit being connected to the input of said fixed frequency generator for adjusting the same in response to the speed of the target; said system thereby producing an operating spectrum generating a signal containing intelligence which is a function of both the speed and distance of a target, the line interval of the operating spectrum being greater than 2(vmax/ lambda ), or, if targets travelling toward or away from the system are to be located, 4(vmax/ lambda ), where vmax the maximum radial speed of the target relative to the system and lambda the operating wave length of the system.

Claim 18

A radar system as defined in claim 13, further comprising a fifth frequency divider connected to said carrier frequency generator for deriving from the carrier frequency a phase-fixed reference voltage ff; a sixth frequency divider connected to the output of said phase shifter for deriving from the fixed frequency an output voltage ff'' which is phase-shifted by an amount corresponding to the distance of the target; and means for comparing the phases of ff and ff''.

Claim 19

A radar system as defined in claim 14, wherein said control circuit comprises a discriminator having its input connected to said Doppler frequency filter.

Claim 20

A radar system as defined in claim 15, wherein said control circuit comprises means deriving from said third frequency divider a signal f2'''' which is in synchronism with said reference frequency f2'' and which is phase-shifted by 90* relative thereto; and means for adding said frequencies f2'' and f2'''' such that the output signal of said second phase modulator is proportional to the difference between the distance of the target and the distance represented by the fixed frequency generated by said fixed frequency generator, the output of said last-mentioned means being applied to said fixed frequency generator for controlling the same.

Claim 21

A radar system as defined in claim 15, wherein a first pulse former is interposed between said third frequency divider and said second keying unit for delivering to the latter said reference frequency f2'' and wherein said control circuit comprises: a second pulse former connected to the output of said third frequency divider and deriving therefrom a reference frequency f2''''; a third keying unit connected to the output of said second phase modulator and to the output of said second pulse former; an additional mixer connected to the output of said fixed frequency generator and to the output of said third keying unit; an additional Doppler frequency filter connected to the output of said additional mixer; an additional phase shifter connected to the output of said additional Doppler frequency filter; an addition circuit connected to the output of the first-mentioned Doppler frequency filter and to the output of said additional phase shifter; and a phase meter connector to the output of said first-mentioned Doppler frequency filter and to the output of said addition circuit, the output of said phase meter being connected to the input of said fixed frequency generator for controlling the same.

Claim 22

A radar system as defined in claim 17, further comprising an integrator interposed between the output of said phase meter and the input of said fixed frequency generator.