CA1111132A - Radar antenna systems - Google Patents
Radar antenna systemsInfo
- Publication number
- CA1111132A CA1111132A CA108,760A CA108760A CA1111132A CA 1111132 A CA1111132 A CA 1111132A CA 108760 A CA108760 A CA 108760A CA 1111132 A CA1111132 A CA 1111132A
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- Prior art keywords
- pair
- antenna according
- navigation antenna
- radiating
- feed
- Prior art date
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Abstract
ABSTRACT OF THE DISCLOSURE
The present invention relates to a doppler navigational radar antenna with automatic land-sea correction utilizing the production of two somewhat differently inclined mutually overlapping labe groups each having four lobes. The antenna comprises a plane radiation array group having individual radiators disposed in parallel rows. Each radiator having two ends which have respective feed points. Each radiator is either actually fed or fed by way of radiation at the feed points by a first pair of feed lines extending transverse to the rows of radiators and coupled thereto at the respective feed points at one end thereof and a second pair of feed lines extending transverse to the rows of radiators and coupled thereto at respective feed points at the other end thereof. One feed line of each pair has a different phase delay than the other feed line of the same pair.
The different phase delay is set correspondingly small so as to obtain the overlapping of the lobe groups.
The present invention relates to a doppler navigational radar antenna with automatic land-sea correction utilizing the production of two somewhat differently inclined mutually overlapping labe groups each having four lobes. The antenna comprises a plane radiation array group having individual radiators disposed in parallel rows. Each radiator having two ends which have respective feed points. Each radiator is either actually fed or fed by way of radiation at the feed points by a first pair of feed lines extending transverse to the rows of radiators and coupled thereto at the respective feed points at one end thereof and a second pair of feed lines extending transverse to the rows of radiators and coupled thereto at respective feed points at the other end thereof. One feed line of each pair has a different phase delay than the other feed line of the same pair.
The different phase delay is set correspondingly small so as to obtain the overlapping of the lobe groups.
Description
The present invention relates to radar antenna systems for use in Doppler navigation equipment with automatic land-sea error correction, the antenna system being designed to produce two slightly differently inclined groups of lobes (beam lobing), using a flat radiator array consisting of individ-ual radiators in parallel rows each end-fed at both ends, using feeder lines extending transversely to said rows.
In Doppler navigational systems, an aircraft or the like directs radar beams onto the earth's surface and measures the Doppler shift of the reflected waYes. In determining the well known frequency shift phenomena only those velocity components which are vectored back in the direction of the particular radar beam are effective. In order to obtain the velocity compon-ents necessary to determine movement in space, at least three measurements in different directions and more than one plane have to bc carried out. In systems using continuous measurement, this means that at least three beams are required, and a fourth beam is generally provided as a standby.
The known systems enable a relatively high degree of accuracy to be achieved in overland navigation, whereas over water an error occurs due to the dependence of the reflected energy upon the angle of incidence of the beam on the water. This error can be explained by the fact that the energy of the ground echo over l~md is virtually independent o the angle of incidence whilst the reflectcd energy over water varies substantially, both as a function of the angle of incidence of the beam on the water, and also as a function of the condition of the water surface tstate of the sea). Consequently the frequency spectrum of the echo signals is distorted relative to the frequency spectrum obtained over land ant this leads to an error shift in the measured centre frequency. Consequently, when flying over water a correction must be introduced.
In most of the systems thus far known, this correction is intro-ducod by operation of a so-called "land-sea" switch. However, this is only a compromise solution, and simply eliminates an average error over water, taking no account of the sea condition. Furthenmore, it imposes an additional work-load on the pilot, and requires that the pilot must be able to see the ground or have first-hand knowledge of the terrain over which he is flying.
- 1- ~, .
1111~32 The reflected energy is dependant upon the angle of incidence~
which differs for land and sea, so that an automat;c land-sea error correction can be derived. One known system employs Doppler navigational antenna to radiate one group of three or four variously inclined lobes onto the ground and a further set of three or four iobes, generally radiated with a time-staggered relationship to the first group, the lobes of this further group having inclinations slightly modified relative to the first group (beam lobing).
The energy difference between neighbouring beams will depend upon the sea condition, so that a correction which is actually dependent on this sea con-dition can be automatically derived.
In the known arrangements of this type, the two lobe groups haveeither been produced by two separate antenna systems side by side, or by two interleaved antenna systems. There is usually only a specific area available for the entire antenna arrangement, so that if separate antenna systems are used, then they can each be only half the size of a system used without beam lobing, and this leads to double the beam width in a plane, and is therefore less favourable. With two interleaved antenna systems, then a radiator of one system must be located between each two radiators of the other, and slotted waveguides may be used, for examplc. ~lthough thc overall arrangement is more compact, the resulting spacing between the individual radiators of either antenna system becomes so large that several main lobes are produced. Where two main lobes occur at an antenna input, then the signals from these two lobes are distinguished only by their different Doppler frequencies, and in the case of slow-flying aircraft such as helicopters for example, they can no longer be effectively separated from one another.
One object of the invention is ~o provide an antenna system for Doppler navigation equipment which avoids these drawbac~s.
In accordance with the present invention there is provided a doppler navigational radar antenna with automatic land sea correction utilizing the production of two somewhat differently inclined mutually over-lapping lobe groups each having four lobes, comprising a plane radiation array group having individual radiators disposed in parallel rows each ~11113Z
radiator having two ends having respective feed points, each radiator being actually fed or fed by wa~ of radiation at said feed points by a first pair of feed lines extending transverse to said rows of radiators and coupled thereto at the respective feed points at one end thereof and a second pair of feed lines extending transverse to said rows of radiators and coupled thereto at respective feed points at the other end thereof, one feed line of each pair having a different phase delay than the other feed line of the same pair, the different phase delay being set correspondingly small so as to obtain the overlapping of the lobe groups.
B
- 2a -Preferably, each radiator is fed at each end by a respective pair of feeder linesi one for each lobe group. One line of each feeder line pair is fed with the same phase delay, and a differing lobe group inclination in the longitudinal direction of the feeder lines is obtained in relation to that produced by the other two feeder lines. This enables a common antenna system to be used for producing the two lobe groups the two feeder lines of each feeder line pair being connected to one supply source or, in the case of a receiving station, to the receiver input.
The invention will now be described with reference to the drawings, in which:
Figure 1 schematically illustrates an aircraft provided with means for directing two lobe groups to the ground;
Figure 2 is a perspective view of one exemplary embodiment of ~n antenna system in accordance with the invention;
Figure 3 is a plan view illustrating the ground position of the eight main lobes ratiated by the antenna system shown in Figure 2; and Figures 4a to 4d are fragmentary details of four alternative coupling arrangements for feeding each slotted waveguide radiator of the embodi-mentS of the type shown in Figure 2, each view being a transverse cross-section at ono end of a radiator.
; Pigure 1 illustrates an aircraft 1 vertically above a ground loca-tion 2, and provided with a Doppler navigational equipment whose antenna system radiates a first lobe group 3 and a second lobe group 4, the respective inclina-tions of the lobes of the two groups 3 and 4 being slightly diferent in relation to the perpenticular between the aircraft and the ground. Fundamentally, only three measurements, i.e. three beams in different directions and more than one plane, are required, although it is advantageous to have a standby beam available.
Using the two lobe groups 3 and 4, it is possible to establish the dependence of the reflected energy upon the angle of incidence, a factor which differs in the caso of the sea from the land, so that the energy ratios of the received signals onable sn automatic l~nt-sea error correcticn to be derived.
The exemplary embodiment of a Doppler navigation antenna system ;
:
,, .
- .
1~113Z
in accordance with the invention shown in Figure 2 consists of an array of eleven rectangular waveguides 5, in whose narrow sides a plurality of slots 6 have been milled, which are slightly inclined in alterna~e directions. A
constant centre-to-centre spacing applies for the slots, and this is slightly greater than half a wavelength. If a wave is propagated through a slotted waveguide 5 of this type, then the output radiation is slightly inclined in relation to ~he waveguide input. Therefore, with a double-ended feed two oppositely inclined beams are produced. The beam direction and the radiation pattern are particularly dependent upon the frequency, the waveguide size, and upon the number, spacing and inclination of the slots. The output energy rises with increasing slot inclination, and it is advantageous to arrange for the inclination to increase towards the waveguide centre, to promote secondary lobe attenuation. One end of each of tha eleven waveguides 5 is connected and coupled to two feeder waveguides 7 and 8, the other end of each waveguide is connected to two guides 9 and 10. By suitable dimensioning, propagating waves develop in the feeder waveguides 7, 8, 9 and 10. The feeder waveguides of each pair have the same phase delay, that is, the delay is similar for the waveguides 7 and 9, and for the feeder waveguides 8 and 1OJ but the two wave-guides at the same end of the radiators~ one from each pair, have slightly different delays, i.e. that of the guide 7 differs from that of 8, and thus that of the guide 9 diffors from that of 10. This differenco is achieved eithor by giving them different cross-sectional dimensions or by introducing a dielectric. Feeder points 11, 12, 15 and 16 are located at the ends of the pair of feeder waveguides 7 and 9 for producing one group of lobes, whilst feeder points 13, 14, 17 and 18 are located at the ends of the two feeder wave-guides 8 and 10 for producing the second, differently inclined lobe group.
In Figure 3 shows the respective ground positions of the eight main lobes radiated by this antenna system when fed at the fe~der points correspondingly marked in Figure 2. The samo relationship applies to the case of a receiving ant~nna. A central point 2 represents the incidence of the perpendicular from the aircraft or the like to the ground. The two groups of lobes are differently inclined with respect to the longitudinal direction of _ 4 -.
~1~L113~
the feeder waveguidesO In the example illustrated, this direction corresponds with the direction of flight.
Figures 4a to 4d illustrate various possible ways of coupling each slotted waveguide radiator, these coupling arrangements serving simultane-ously to opti~ise the mutual decoupling of the two feeder waveguides where a pair of feeders is involved. In Figure 4a, two feeder waveguides 20 and 21 of a pair are arranged on opposite side walls 22 and 23 of a slotted radiator 24 which takes the form of a rectangular waveguide. Part of each of the waveguides 20 snd 21 projects into the slotted radiator 24, where it is coupled through slots 25 and 26. In the alternative arrangement shown in FiguTe 4b, a slotted radiator 27 merges at its end into a chamber 28, into which there partially penetrate two waveguidcs 29 and 30 of a feeder line pair. Figure 4c illustrates a slotted radiator 31 whose end forks into two arms 32 and 33, in each of which there penetrates a respective waveguide, 34 or 35, of a feeder line pair. In Figure 4d, instead of two waveguide feeders at each end, one feeder pair is used, a single waveguide 36 being provided for each end of esch radiatorO This waveguide 36 has sn a~nost square section, and carries two Hlo waves which are polarised in mutually perpendicular directions, as indicated by arrows 37 and 38. The respective delays or transit times are determined by the dimension in the particular H-plane, and differ from one another in accordance with the sido ratio of the cross-section of the waveguide 36. Coupling to a waveguide radiator 39 is effectod via two coaxial lines 40 and 41. The inner conductor 42 of the coaxial line 40 projects through a side wall 43 and ths inner conductor 44 of tho line 41 projects through a side wall 45, into the interior of the waveguide 36. At the other end of the coaxial line 40 and 41, the inner conductors 42 snd 44 penetrate into the interior of the slotted radiator 39.
It is also possible to employ a single feeder waveguide at each end, with a standard square, rectsngular or circular cross-section9 in which an electrically controlled phase-shift device is successively switched in or out to slter the lobe inclination.
Instead of rows of slotted radiators, other radiators, for example periodically curved conductors forming strip line radiators, dipole radiators, or slotted radiators in metal plates, Furthermore, the feeder lines need not take the form of waveguides, but can be coaxial lines, for example.
In Doppler navigational systems, an aircraft or the like directs radar beams onto the earth's surface and measures the Doppler shift of the reflected waYes. In determining the well known frequency shift phenomena only those velocity components which are vectored back in the direction of the particular radar beam are effective. In order to obtain the velocity compon-ents necessary to determine movement in space, at least three measurements in different directions and more than one plane have to bc carried out. In systems using continuous measurement, this means that at least three beams are required, and a fourth beam is generally provided as a standby.
The known systems enable a relatively high degree of accuracy to be achieved in overland navigation, whereas over water an error occurs due to the dependence of the reflected energy upon the angle of incidence of the beam on the water. This error can be explained by the fact that the energy of the ground echo over l~md is virtually independent o the angle of incidence whilst the reflectcd energy over water varies substantially, both as a function of the angle of incidence of the beam on the water, and also as a function of the condition of the water surface tstate of the sea). Consequently the frequency spectrum of the echo signals is distorted relative to the frequency spectrum obtained over land ant this leads to an error shift in the measured centre frequency. Consequently, when flying over water a correction must be introduced.
In most of the systems thus far known, this correction is intro-ducod by operation of a so-called "land-sea" switch. However, this is only a compromise solution, and simply eliminates an average error over water, taking no account of the sea condition. Furthenmore, it imposes an additional work-load on the pilot, and requires that the pilot must be able to see the ground or have first-hand knowledge of the terrain over which he is flying.
- 1- ~, .
1111~32 The reflected energy is dependant upon the angle of incidence~
which differs for land and sea, so that an automat;c land-sea error correction can be derived. One known system employs Doppler navigational antenna to radiate one group of three or four variously inclined lobes onto the ground and a further set of three or four iobes, generally radiated with a time-staggered relationship to the first group, the lobes of this further group having inclinations slightly modified relative to the first group (beam lobing).
The energy difference between neighbouring beams will depend upon the sea condition, so that a correction which is actually dependent on this sea con-dition can be automatically derived.
In the known arrangements of this type, the two lobe groups haveeither been produced by two separate antenna systems side by side, or by two interleaved antenna systems. There is usually only a specific area available for the entire antenna arrangement, so that if separate antenna systems are used, then they can each be only half the size of a system used without beam lobing, and this leads to double the beam width in a plane, and is therefore less favourable. With two interleaved antenna systems, then a radiator of one system must be located between each two radiators of the other, and slotted waveguides may be used, for examplc. ~lthough thc overall arrangement is more compact, the resulting spacing between the individual radiators of either antenna system becomes so large that several main lobes are produced. Where two main lobes occur at an antenna input, then the signals from these two lobes are distinguished only by their different Doppler frequencies, and in the case of slow-flying aircraft such as helicopters for example, they can no longer be effectively separated from one another.
One object of the invention is ~o provide an antenna system for Doppler navigation equipment which avoids these drawbac~s.
In accordance with the present invention there is provided a doppler navigational radar antenna with automatic land sea correction utilizing the production of two somewhat differently inclined mutually over-lapping lobe groups each having four lobes, comprising a plane radiation array group having individual radiators disposed in parallel rows each ~11113Z
radiator having two ends having respective feed points, each radiator being actually fed or fed by wa~ of radiation at said feed points by a first pair of feed lines extending transverse to said rows of radiators and coupled thereto at the respective feed points at one end thereof and a second pair of feed lines extending transverse to said rows of radiators and coupled thereto at respective feed points at the other end thereof, one feed line of each pair having a different phase delay than the other feed line of the same pair, the different phase delay being set correspondingly small so as to obtain the overlapping of the lobe groups.
B
- 2a -Preferably, each radiator is fed at each end by a respective pair of feeder linesi one for each lobe group. One line of each feeder line pair is fed with the same phase delay, and a differing lobe group inclination in the longitudinal direction of the feeder lines is obtained in relation to that produced by the other two feeder lines. This enables a common antenna system to be used for producing the two lobe groups the two feeder lines of each feeder line pair being connected to one supply source or, in the case of a receiving station, to the receiver input.
The invention will now be described with reference to the drawings, in which:
Figure 1 schematically illustrates an aircraft provided with means for directing two lobe groups to the ground;
Figure 2 is a perspective view of one exemplary embodiment of ~n antenna system in accordance with the invention;
Figure 3 is a plan view illustrating the ground position of the eight main lobes ratiated by the antenna system shown in Figure 2; and Figures 4a to 4d are fragmentary details of four alternative coupling arrangements for feeding each slotted waveguide radiator of the embodi-mentS of the type shown in Figure 2, each view being a transverse cross-section at ono end of a radiator.
; Pigure 1 illustrates an aircraft 1 vertically above a ground loca-tion 2, and provided with a Doppler navigational equipment whose antenna system radiates a first lobe group 3 and a second lobe group 4, the respective inclina-tions of the lobes of the two groups 3 and 4 being slightly diferent in relation to the perpenticular between the aircraft and the ground. Fundamentally, only three measurements, i.e. three beams in different directions and more than one plane, are required, although it is advantageous to have a standby beam available.
Using the two lobe groups 3 and 4, it is possible to establish the dependence of the reflected energy upon the angle of incidence, a factor which differs in the caso of the sea from the land, so that the energy ratios of the received signals onable sn automatic l~nt-sea error correcticn to be derived.
The exemplary embodiment of a Doppler navigation antenna system ;
:
,, .
- .
1~113Z
in accordance with the invention shown in Figure 2 consists of an array of eleven rectangular waveguides 5, in whose narrow sides a plurality of slots 6 have been milled, which are slightly inclined in alterna~e directions. A
constant centre-to-centre spacing applies for the slots, and this is slightly greater than half a wavelength. If a wave is propagated through a slotted waveguide 5 of this type, then the output radiation is slightly inclined in relation to ~he waveguide input. Therefore, with a double-ended feed two oppositely inclined beams are produced. The beam direction and the radiation pattern are particularly dependent upon the frequency, the waveguide size, and upon the number, spacing and inclination of the slots. The output energy rises with increasing slot inclination, and it is advantageous to arrange for the inclination to increase towards the waveguide centre, to promote secondary lobe attenuation. One end of each of tha eleven waveguides 5 is connected and coupled to two feeder waveguides 7 and 8, the other end of each waveguide is connected to two guides 9 and 10. By suitable dimensioning, propagating waves develop in the feeder waveguides 7, 8, 9 and 10. The feeder waveguides of each pair have the same phase delay, that is, the delay is similar for the waveguides 7 and 9, and for the feeder waveguides 8 and 1OJ but the two wave-guides at the same end of the radiators~ one from each pair, have slightly different delays, i.e. that of the guide 7 differs from that of 8, and thus that of the guide 9 diffors from that of 10. This differenco is achieved eithor by giving them different cross-sectional dimensions or by introducing a dielectric. Feeder points 11, 12, 15 and 16 are located at the ends of the pair of feeder waveguides 7 and 9 for producing one group of lobes, whilst feeder points 13, 14, 17 and 18 are located at the ends of the two feeder wave-guides 8 and 10 for producing the second, differently inclined lobe group.
In Figure 3 shows the respective ground positions of the eight main lobes radiated by this antenna system when fed at the fe~der points correspondingly marked in Figure 2. The samo relationship applies to the case of a receiving ant~nna. A central point 2 represents the incidence of the perpendicular from the aircraft or the like to the ground. The two groups of lobes are differently inclined with respect to the longitudinal direction of _ 4 -.
~1~L113~
the feeder waveguidesO In the example illustrated, this direction corresponds with the direction of flight.
Figures 4a to 4d illustrate various possible ways of coupling each slotted waveguide radiator, these coupling arrangements serving simultane-ously to opti~ise the mutual decoupling of the two feeder waveguides where a pair of feeders is involved. In Figure 4a, two feeder waveguides 20 and 21 of a pair are arranged on opposite side walls 22 and 23 of a slotted radiator 24 which takes the form of a rectangular waveguide. Part of each of the waveguides 20 snd 21 projects into the slotted radiator 24, where it is coupled through slots 25 and 26. In the alternative arrangement shown in FiguTe 4b, a slotted radiator 27 merges at its end into a chamber 28, into which there partially penetrate two waveguidcs 29 and 30 of a feeder line pair. Figure 4c illustrates a slotted radiator 31 whose end forks into two arms 32 and 33, in each of which there penetrates a respective waveguide, 34 or 35, of a feeder line pair. In Figure 4d, instead of two waveguide feeders at each end, one feeder pair is used, a single waveguide 36 being provided for each end of esch radiatorO This waveguide 36 has sn a~nost square section, and carries two Hlo waves which are polarised in mutually perpendicular directions, as indicated by arrows 37 and 38. The respective delays or transit times are determined by the dimension in the particular H-plane, and differ from one another in accordance with the sido ratio of the cross-section of the waveguide 36. Coupling to a waveguide radiator 39 is effectod via two coaxial lines 40 and 41. The inner conductor 42 of the coaxial line 40 projects through a side wall 43 and ths inner conductor 44 of tho line 41 projects through a side wall 45, into the interior of the waveguide 36. At the other end of the coaxial line 40 and 41, the inner conductors 42 snd 44 penetrate into the interior of the slotted radiator 39.
It is also possible to employ a single feeder waveguide at each end, with a standard square, rectsngular or circular cross-section9 in which an electrically controlled phase-shift device is successively switched in or out to slter the lobe inclination.
Instead of rows of slotted radiators, other radiators, for example periodically curved conductors forming strip line radiators, dipole radiators, or slotted radiators in metal plates, Furthermore, the feeder lines need not take the form of waveguides, but can be coaxial lines, for example.
Claims (15)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A doppler navigational radar antenna with automatic land-sea correc-tion utilizing the production of two somewhat differently inclined mutually overlapping lobe groups each having four lobes, comprising a plane radiation array group having individual radiators disposed in parallel rows each radi-ator having two ends having respective feed points, each radiator being actually fed or fed by way of radiation at said feed points by a first pair of feed lines extending transverse to said rows of radiators and coupled thereto at the respective feed points at one end thereof and a second pair of feed lines extending transverse to said rows of radiators and coupled thereto at respective feed points at the other end thereof, one feed line of each pair having a different phase delay than the other feed line of the same pair, the different phase delay being set correspondingly small so as to obtain the overlapping of the lobe groups.
2. A doppler navigation antenna according to claim 1, wherein said feed lines comprise coaxial conductors.
3. A doppler navigation antenna according to claim 1, wherein said feed lines comprise strip conductors.
4. A doppler navigation antenna according to claim 1, wherein said radiating arrays group comprises hollow wave guide slot radiating arrays.
5. A doppler navigation antenna according to claim 1, wherein said radiating arrays group comprises dipole radiating arrays.
6. A doppler navigation antenna according to claim 1, wherein said radiating arrays group comprises periodically curved line radiating arrays.
7. A doppler navigation antenna according to claim 1, wherein said radiating array group comprises slot radiating arrays.
8. A doppler navigation antenna according to claim 1, wherein each pair of feed lines comprises hollow wave guides.
9. A doppler navigation antenna according to claim 8, wherein the individual wave guides of each pair of said feed lines have different cross-sectional dimensions.
10. A doppler navigation antenna according to claim 8, wherein the individual wave guides of each pair of said feed lines have different dielectric characteristics.
11. A doppler navigation antenna according to claim 8, wherein the radiating arrays comprise hollow wave guides of rectangular cross-section and the wave guides of each pair of feed lines are coupled to said radiating arrays on opposite side walls of said radiating hollow wave guides.
12. A doppler navigation antenna according to claim 8, wherein each of said radiating arrays comprise hollow chambers at their end, and said wave guides of said feed lines are coupled to said radiating arrays within said chambers.
13. A doppler navigation antenna according to claim 8, wherein each radiating arrays comprise a hollow wave guide having fork-shaped ends, and each of said hollow wave guide feed lines is coupled to each said radiating array within respective branches of the fork-shaped ends.
14. A doppler navigation antenna according to claim 8, wherein each feed line pair is formed of a single hollow wave guide of rectangular cross-section adapted to guide two waves polarized perpendicularly with respect to one another to effect different time delays of the two wave structures in accordance with the side walls relationships of the hollow wave guide cross-section.
15. A doppler navigation antenna according to claim 14, comprising a pair of coaxial lines each having an inner conductor and an outer conductor, said outer conductors connecting adjacent side walls of said single hollow wave guide to oppositely disposed walls of radiating array hollow wave guide, and said inner conductors following the same paths and extending into the radiating array hollow wave guides.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA108,760A CA1111132A (en) | 1971-03-26 | 1971-03-26 | Radar antenna systems |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA108,760A CA1111132A (en) | 1971-03-26 | 1971-03-26 | Radar antenna systems |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1111132A true CA1111132A (en) | 1981-10-20 |
Family
ID=4089168
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA108,760A Expired CA1111132A (en) | 1971-03-26 | 1971-03-26 | Radar antenna systems |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1111132A (en) |
-
1971
- 1971-03-26 CA CA108,760A patent/CA1111132A/en not_active Expired
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