NZ208213A - Resonant waveguide slot array - Google Patents

Resonant waveguide slot array

Info

Publication number
NZ208213A
NZ208213A NZ20821384A NZ20821384A NZ208213A NZ 208213 A NZ208213 A NZ 208213A NZ 20821384 A NZ20821384 A NZ 20821384A NZ 20821384 A NZ20821384 A NZ 20821384A NZ 208213 A NZ208213 A NZ 208213A
Authority
NZ
New Zealand
Prior art keywords
waveguide
line
elements
transducer
frequency
Prior art date
Application number
NZ20821384A
Inventor
R F Frazita
A R Lopez
Original Assignee
Hazeltine Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US06/497,350 external-priority patent/US4554551A/en
Priority claimed from US06/497,349 external-priority patent/US4554550A/en
Application filed by Hazeltine Corp filed Critical Hazeltine Corp
Publication of NZ208213A publication Critical patent/NZ208213A/en

Links

Classifications

    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01QANTENNAS, i.e. RADIO AERIALS
    • H01Q3/00Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system
    • H01Q3/26Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture
    • H01Q3/267Phased-array testing or checking devices

Landscapes

  • Waveguide Aerials (AREA)
  • Variable-Direction Aerials And Aerial Arrays (AREA)

Description

Priori?/ iXr.vir;;: ^ -.15-83 Complete Specification Filed: ^T-P.T&^s Class: .HO.VQk^ ./)&,.
Publication Date: ... ?. .P.99X $$J., P.O. Journal, Mc: ..\30 1 2082 1 3 N .Z .No.
NEW ZEALAND Patents Act 3953 COMPLETE SPECIFICATION "RESONANT WAVEGUIDE APERTURE MANIFOLD" We, HAZELTINE CORPORATION, a corporation organized and existing under the laws of the State of Delaware, United States of America, 500 Commack Road, Commack, New York 11725, United States of America, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement : - (followed by lA) .X • 7082 13 >?v. 1 RESONANT WAVEGUIDE APERTURE MANIFOLD ! ! ^ 2 The invention relates generally to 3 phase-stable manifolds and, in particular, a resonant 4 waveguide for monitoring a scanning beam antenna essentially independent of temperature and frequency ^ 6 over a practical range and for monitoring a scanning 7 beam antenna at a scan angle which is not aligned with 8 the boresight direction of the antenna, 9 Slotted waveguides are sometimes used as aperture manifolds which couple to the radiated 11 signal of a phased-array antenna to monitor its 12 performance. Such waveguide manifolds are used in 13 Microwave Landing System (MLS) ground systems for 14 producing a signal equivalent to a signal viewed by a ,Oj 15 receiver at a specific angle within the coverage 16 volume of the ground system. Ideally, such waveguide 17 manifolds provide a far-field view of the scanning 18 beam of the ground system and, additionally, measure 19 the antenna insertion phase and amplitude associated with each individual array element.
J' ,-y.:1', • 2082 1 1 Waveguide manifolds used to monitor 2 elevation and azimuth scanning beams of an MLS ground 3 system have been waveguides which propagate travellin 4 waves and, consequently, the phasing characteristics /r-N 5 are frequency and temperature dependent. The result 6 is that the scan angle of the beam monitored at the 7 waveguide output is also temperature and frequency 8 dependent. Furthermore, for monitoring MLS azimuth ,^\ 9 scanning, a travelling wave manifold does not inherently monitor the zero degree course over the 11 MLS operating frequency bandwidth. This is because 12 the beam pointing characteristic of a travelling 13 wave manifold is frequency and temperature dependent. 14 It is an object of this invention to provide a resonant waveguide aperture manifold that 16 forms a beam at a scan angle that is independent 17 of temperature and frequency. 18 The apparatus according to the invention 19 comprises a transmission Jine for directing electromagnetic energy in a predetermined frequency 21 range. Associated with the line are elements such 22 as coupling slots or holes. The line may be 23 associated with groups of elements such 24 as coupling slots or holes wherein adjacent groups have different phase. Each group has N 203213 elements wherein adjacent elements have different phase, N being a positive integer greater than one.
A transducer is associated with the line for converting energy having a frequency within the predetermined frequency range into an electrical signal having a corresponding frequency and vice versa. The transducer has an impedance which is matched to the line as if the line had non-reflecting terminations coupled to the first and second ends thereof. First means creates a short circuit at the first end of the line and second means creates a short circuit at the second end of the line.
For a better understanding of the present invention, together with other and further objects, reference is made to the following description, taken in conjunction with the accompanying drawings, and its scope will be pointed out in the appended claims.
Figure 1 is a longitudinal cross-sectional view of a travelling waveguide according to the prior art.
Figure 2 is a simplified block diagram illustrating one use of an aperture manifold as described in copending New Zealand application Serial No. 204,522 filed June 10, 1983 for Scanning Antenna With Automatic Beam Stabilization, incorporated herein by reference. • 20821 1 Figure 3 is a longitudinal cross-sectional 2 view of a resonant waveguide according to the 3 invention. 4 Figure 4A is a perspective view of one side O w 5 of a resonant waveguide according to the invention 6 showing the slots therein. 7 Figure 4B is a perspective view of one side 8 of an asymmetric resonant waveguide according to 9 the invention showing the adjacent groups of slots of alternating phase wherein each group 11 has adjacent slots of alternating phase. 12 Figure 5 is a transverse cross-sectional 13 view of one resonant waveguide according to the 14 invention illustrating its rectangular configuration.
Figure 6 is a transverse cross-sectional 16 view of another resonant waveguide according to the 17 invention illustrating its ridged rectangular 18 configuration. 19 Figure 7 is an amplitude diagram of an incident wave propagating within a waveguide according 21 to the invention. 22 Figure 8 is a phase diagram of an incident 23 wave propagating within a waveguide according to the 24 invention. *7* * 7082 f 3 1 Figure 9 is an amplitude diagram of a 2 reflected wave propagating within a waveguide 3 according to the invention. 4 Figure 10 is a phase diagram of a reflected wave propagating within a waveguide 6 according to the invention. 7 Figure 11 is a diagram of the standing 8 wave generated within a resonant waveguide according 9 to the invention.
Figure 12 is one illustration of the 11 resonant waveguide according to the invention coupled 12 by means of slots to the radiating waveguide column of 13 an MLS azimuth antenna. 14 Figure 13 is another illustration of a resonant waveguide according to the invention coupled 16 by means of holes to the radiating waveguide column of 17 an MLS azimuth antenna. 18 Figure 14 is an illustration of a resonant 19 waveguide according to the invention coupled by means of slots to the radiating waveguide column of an MLS 21 elevation antenna. 22 As shown in figure 1, a prior art 23 travelling wave manifold 100 made of conductive 'O 24 material is provided with an output transducer such as connector 101 which receives a wave propagating along rt • 'I , ^ ^ o 3213 1 propagation path 102 which is terminated in absorber 2 103 or other non-reflecting terminating means at the 3 far end. Side 10A functions as a short circuit which A reflects waves propagating to the left. Side 105 of waveguide 100 is provided with weakly coupled input 6 slots 106, 107, 108, 109, 110, 111, 112 and 113 having 7 spacing d. The phase relationship between adjacent 8 slots 106 and 107 is given by the following formula: 9 -*107 = ^106 + — d ± 71 xg As shown by the formula, the phase of slot 11 107 as compared to the phase of slot 106 12 ^106^ is dePenclent upon the spacing d and the 13 waveguide wavelength (^g)- All other adjacent slots 1A have similar phase relationships. Since spacing d is temperature dependent (conductive material such as 16 copper or aluminum expands or contracts with 17 temperature variations) and the waveguide wavelength 18 Ag is frequency dependent, travelling wave manifold 19 100 is both frequency and temperature dependent.
The monitored beam pointing angle, 0 , for 21 the travelling wave manifold having slots of 22 alternating phase is defined as the pointing angle 23 of a beam detected by the travelling wave manifold 2A 100. The connector 101 acts as a transducer providing an electrical output signal when excited 26 by a wave travelling along the waveguide 100 77FEBt9S7 1 2 3 4 6 7 8 9 11 12 13 14 16 17 18 19 21 208213 as a result of excitations imparted at the manifold slots. By reciprocity, it may be defined as the conjugate of the pointing angle of a beam radiated by the manifold output slots as a result of excitations imparted by the manifold input connector. The monitored beam pointing angle is given by: 8 = arc sin where /u - UoVW2'- Vo/2df) XQ = reference free space wavelength (design center) Xco = waveguide cutoff wavelength f = reference frequency f = frequency of excitations This equation gives the explicit relationship between the monitored beam pointing angle, frequency and coupling slot spacing. The invention relates to: (a) microwave landing systems which use wide scanning phased array antenna systems having a sharp cutoff of the element pattern, such as are disclosed by Richard F. Frazita, Alfred R. Lopez and Richard J. Giannini in U.S. Patent No. 4,041,501; and (b) calibration of a system having plural signal carrying channels. 208213 1 Referring to Figure 2, generally such antenna systems 2 include one or more radiating elements forming an 3 array 1 in which the elements are arranged along an 4 array axis and are spaced from each other by a given distance. Each of the elements is coupled to a power 6 divider 8 via a corresponding one of a plurality 7 of phase shifters 9 connected to the elements by 8 distribution network 2. Wave energy signals from 9 signal generator 11 and power divider 8 are supplied to antenna elements 1 by phase 11 shifters 9 such that a proper selection of the 12 relative phase values for phase shifters 9 causes 13 antenna elements 1 to radiate a desired radiation 14 pattern into a selected angular region of space.
Variation of the relative phase values of the phase 16 shifters 9 is accomplished by beam steering unit 10 17 via control line 22 and causes the radiated antenna 18 pattern to change direction with respect to angle A in 19 space. Therefore, phase shifters 9 and beam steering unit 10 together form means 2 for scanning a beam 21 radiated by the antenna elements of array 1 as a 22 result of the supplied wave energy signals from 23 generator 11 coupled to the elements of array 1 by 24 power divider 8 and distribution network 2. 208213 1 The properties of a scanning antenna and 2 techniques for selecting design parameters such as 3 aperture length, element spacing and the particular 4 configuration of the distribution network 2 are well known in the prior art. A review of these parameters 6 is completely described in U.S. Patent No. 4,041,501. 7 In order to stabilize the be.am pointing 8 angle of the radiated beam, an aperture manifold 4 is 9 associated with the antenna elements of array 1.
Manifold 4 may be any means for forming a signal 11 provided by output 12 which represents a beam pointing 12 angle of the radiated beam. Preferably, manifold 4 is 13 a highly phase stable waveguide or manifold, such as 14 the invention, coupled to the array 1 and center-fed to avoid inherent frequency (phase) and temperature 16 effects. Center feeding also eliminates first-order 17 dependence on frequency and absolute temperature 18 variations. 19 As used herein, manifold 4 refers to any type of device for sampling signals including a 21 waveguide, a printed circuit network, a coaxial line 22 network or a power combiner. A phase stable manifold 23 is, by definition, one in which the beam formed by 24 summing of the slot excitations is insensitive to frequency and temperature changes and is used in 2082 1 3 1 combination with a phased arrray In accordance with 2 this invention to detect bias error at a specific 3 angle. Manifold 4 is equivalent in function to a 4 probe located in space at a specific angle with respect to the phased array. A manifold in accordance 6 with the present invention may be a slotted waveguide 7 configured to monitor radiated energy such that there 8 is equal, non-zero phase and equal amplitude at all 9 sample points (i.e. slot locations) of the manifold.
The output 12 of manifold 4 is coupled to 11 means 5, associated with means 3, for controlling the 12 scanning of the radiated beam in response to the 13 output 12 of manifold 4. 14 Figure 3 illustrates a resonant waveguide 200 according to the invention. Waveguide 200 is 16 provided with a first end 201 terminating in a short 17 circuit such as a conductive sheet of metal 18 perpendicular to the sides of waveguide 200 and a 19 second end 202 terminating in a short circuit.
Waveguide 200 is center fed by a transducer which 21 converts an electrical signal Into electromagnetic 22 energy and vice versa. Preferably, the transducer is 23 any connector well known in the prior art such as 24 output connector 203 which receive waves propagating in both directions along path 204. Side 205 of * 208213 1 waveguide 200 is provided with slots 206, 207, 208, 2 209, 210, 211, 212, 213, and 214 for coupling to a 3 radiating antenna. Figure 4 illustrates a 180° 4 degree phase compensating pattern of the coupling slots which will be described below. Figures 5 and 6 6 illustrate preferred rectangular crossections of 7 waveguide 200. 8 As shown by Figure 7, an incident wave ^ 9 radiated by connector 203 has a constant amplitude along the entire length of waveguide 200. This 11 is because amplitude tapers in the travelling wave 12 caused by the coupling slots is counteracted and 13 eliminated by the resonance of waveguide 200. 14 Due to reciprocity, waveguide 200 may be used in either a transmitting or receiving mode. In 16 the transmitting mode, connector 203 is connected via 17 isolator 215 to a signal source (not shown). The 18 signal is converted by connector 203 to 19 electromagnetic wave energy which propagates along (3^ 20 waveguide 200 and is radiated by slots 206-214. In 21 the receiving mode, slots 206-214 are illuminated by 22 electromagnetic wave energy which propagates along 23 waveguide 200 and is converted by connector 203 into 24 an electrical signal. For convenience and according to convention, the invention has been described in a '.X 1 2 3 4 6 7 8 9 11 12 13 14 16 17 18 19 21 22 23 24 2U8213 t receiving mode. However, this disclosure should not be limited to any one mode and should be broadly construed to include both transmitting and/or receiving operations.
Figure 8 is an illustration of the incident phase J^nc of the wave radiated by connector 203 and illustrates that the phase along waveguide 200 is linearly changing.
Since short circuits 201 and 202 reflect the incident waves propagating within waveguide 200, figure 9 illustrates that the amplitude of the reflected wave Are^ is constant along the entire length of waveguide 200. Similarly, the phase of the reflected wave &ref propagating within waveguide 200 i is linearly changing with distance. The result, as illustrated in figure 11, is a standing wave having a ! - plurality of cells of alternating phase of zero degrees and 180 degrees between spacing d of the slots. / As shown in Figure 4A, each slot is located within one of the standing wave cells of waveguide 200 so that the resulting manifold output will be temperature and frequency independent as long as the variations in temperature and frequency are within the ■ i-' range such that there is one and only one slot or ' i 1 "7 C P ^0^7 1 / TLL w/ m 208213 1 group of slots located within each standing wave 2 cell. By alternating the direction and thereby the 3 phase of adjacent slots, the resulting manifold output 4 will provide equal phasing to all radiating elements.
This aperture manifold provides a beam forming 6 capability which is independent of frequency and 7 temperature since the phase within .each standing wave 8 cell is constant. To prevent transmission of the 9 reflected wave back through connector 203, isolator 215 is located within the line feeding connector 203. 11 As shown in Figure 4B, each slot is located 12 within one of the standing wave cells of waveguide 13 200. By alternating the direction and thereby the 14 phase of each group of slots, the resulting manifold output will have equal phase for each coupling slot 16 and will be temperature and frequency independent as 17 long as the variations in temperature and frequency are 18 within the range such that there is one and only one 19 slot or group of slots located within each standing wave cell. By alternating the direction and thereby 21 the phase of each group A, B, C and D of slots (N=2) 22 and by alternating direction and thereby the phase of 23 adjacent slots within each group, the resulting 24 manifold output will approximate an 11.25° beam pointing angle. This aperture manifold provides a 1 2 3 4 6 7 8 9 11 12 13 14 16 17 18 19 21 22 23 2'o8213 beam forming capability which is independent of frequency and temperature since the phase within each standing wave cell is constant. To prevent transmission of the reflected wave back through connector 203, isolator 215 is located within the line feeding connector 203.
The monitored beam pointing angle, 0, for resonant manifold 200 according to the invention, over the operational frequency bandwidth, is given by: 0 = arc sin m = 1, 2.... « md/^g where is the slot spacing in guide wavelengths.
Therefore, the phasing of manifold 200 is independent of frequency and coupling slot spacing over the operational frequency bandwidth. In the embodiment illustrated in Figure 4A, 0 = 0°(m =00 ) and the beam radiated is perpendicular to path 204. In the embodiment illustrated in Figure 4B, the beam pointing angle is generally not 0° and the beam radiated by manifold 200 is not perpendicular to path 204 because of the nonequal phasing of the groups of slots. For example, an MLS ground system having a center operating frequency of 5.06GHz (i.e. X = 2.33 inches) and a group spacing (dg) of 5.97" would have a { 17 FED 19C7 208213 f 1 monitored beam pointing angle of 11.25°. 2 However, slots 206-214 may be phased to 3 approximate any beam pointing angle desired. The 4 range of the actual beam pointing angles which the slots of a particular manifold may approximate are 6 limited by the physical configuration of the ^ 7 particular manifold. In any case, therefore, the 8 phasing of manifold 200 is independent of frequency 9 and coupling slot spacing over the operational frequency bandwidth. 11 In order to achieve the results described 12 above, input connector 203 is initially matched to 13 waveguide 200 as if each end of waveguide 200 14 terminated in a non-reflecting absorber as shown in the prior art illustrated in figure 1. Such a matched 16 connector 203 is employed with waveguide 200 17 terminating in short circuits as illustrated in figure 18 3 thereby resulting in the resonant standing wave as 19 shown in figure 11.
To achieve the in-phase condition of the 21 adjacent coupling slots of waveguide 200, the required 22 waveguide wavelength g is twice the spacing d 23 between coupling slots 206-214. This spacing d is 24 determined by the radiating characteristics of the phased array antenna associated with waveguide 200 and o K - '7 % 2 082 13 1 is typically slightly larger than 1/2 wavelength. For 2 the Microwave Landing System elevation phased array 3 antenna, ridge leading as shown in Figure 6 is used to 4 obtain this result. In particular, opposing ridges ^ 5 250R and 260R are located within waveguide 200R for ^ 6 eliminating odd mode resonance which may disturb the 7 amplitude and phase of the slot excitations. 8 The maximum length, L, of a manifold 9 according to the invention is limited by the operational frequency bandwidth of the phased array 11 antenna with which it is associated. To limit the 12 beam distortions caused by amplitude taper at the band 13 edges, length L should not exceed the value given 14 below: L < X f /2(f /(I - (1 - A f /A f )*) -— o o v max u oo co max7 f , /(I - (1 - A f /X f . )2)) min o o co min 16 For the ICAO standard Microwave Landing System 17 bandwidth, L is given approximately by: 18 Ag fc 2Af t 2082 t 3 1 where Af/fo iS the fractional design bandwidth plus 2 a margin for fabrication tolerances. 3 For Af/fo = .0165, L = 30.3 Ag. For larger arrays on 4 the order of 60 Ag, two similar manifolds can be ^j) 5 interconnected with equal length stable transmission 6 lines. 7 Figure 12 illustrates waveguide 200R in 8 association with waveguide 300 such as descibed by ^ 9 U.S. Patent No. 3,903,524, owned by Hazel tine Corporation. Waveguide 300 may be one of a 11 series of parallel waveguides forming the 12 azimuth antenna of a Microwave Landing System (MLS) 13 ground system. Such a ground system requires 14 monitoring to evaluate its performance. In order to provide such monitoring, waveguide 200R functions as a 16 manifold and is associated with each of the parallel 17 waveguides 300. Ridge loading in waveguide 200R in 18 the form of ridges 250R and 260R is used to match the 19 guide wavelength of waveguide 200 to the required spacing of radiating waveguides 300. Specifically, 21 waveguide 300 with polarized radiating slots 301 has a 22 non-polarized opening 302 coupled to slot 208R. Other . 23 vertical waveguides would be coupled to slots 206R and 24 207R. 1 2 3 4 6 7 8 9 11 12 13 14 16 17 18 19 2082.23 Figure 13 illustrates another MLS ground system coupling configuration having non-polarized holes 506R, 5D7R and 508R in broad wall 509R of waveguide 500R and having ridge 51oRon the wall 511R opposite broad wall 509R. The non-polarized holes are coupled to parallel radiating waveguides such as waveguide 300 by polarized slot 303. For this configuration the required 180 degree phase reversals between adjacent coupling holes is incorporated in the design of waveguide 300. Adjacent waveguides 300 have a 180° phase reversal at their input wave launchers i.e. slot 303.
Figure 14 illustrates another MLS ground system coupling configuration wherein slots 206, 206a, 207, 207a, 208, 208a, are coupled to dipole array 400 which may function as an MLS elevation antenna. Although this invention has been particularly described with regard to its function as an elevation manifold, it may be used as an azimuth manifold or other array monitor. 2 * > ,v ' < • 17 FEB 1987

Claims (14)

WHAT WE CLAIM IS:
1. An apparatus for monitoring radiated signals and having a transmission line for receiving electromagnetic energy in a predetermined frequency range, said line having first and second ends; and means for sampling the radiated signals, said means including slotted elements associated with said line; said apparatus characterized by: (a) a transducer having an impedance, said transducer associated with said line for converting electromagnetic energy having a frequency within the predetermined mino frequency range into an electrical signal having a corresponding frequency; (b) said transducer impedance being the impedance of said transducer when matched to said line when said line is terminated with substantially non-reflecting terminations coupled to the first and second ends thereof; (c) a first short circuit at the first end of said line; and (d) a second short circuit at the second end of said line whereby said transducer is not impedance matched to said line terminated with said first and second short circuits so that the transducer output is independent of changes in temperature and frequency within the predetermined frequency range.
2. The apparatus of claim ] wherein adjacent slotted elements have respective orientations which provide different phasing.
3. The apparatus of claim 2 wherein said transducer comprises an electrical connector projecting into said transmission line.
4. The apparatus of claim 3 further including a circuit for isolating from the transmission line any load, other than the line itself, connected to the connector.
5. The apparatus of claim 4 wherein said first short circuit comprises a first electrically conductive member substantially perpendicular to the sides of said waveguide and attached to the first end and said second short circuit comprises a second electrically conductive member substanti ally perpendicular to the sides of said waveguide and attached to the second end.
6. The apparatus of claim 1 comprising: groups of elements associated with said line wherein adjacent groups have different phases, each group having N elements wherein adjacent slotted elements within each group have respective orientations which provide different phasing, where N is a positive even integer greater than one. N j -2°- \ 20 AUG 1987 ^o. mi
7. The apparatus of claims 1 or 6 further including an apparatus for eliminating odd mode resonance thereby reducing amplitude and phase distortions resulting from excitations received by the elements.
8. The apparatus of any one of claims 1, 6 or 7 wherein said transmission line comprises an electrically conductive hollow member and said elements comprise openings in said member.
9. The apparatus of claims 5 or 8 wherein adjacent elements have opposite phases.
10. The apparatus of claim 8 wherein said electrically conductive hollow member is a linear waveguide of rectangular cross-section and said openings comprise a linear array of slots spaced apart by substantially one-half of a waveguide wavelength of said member at a signal frequency within the predetermined frequency range.
11. The apparatus of claim 7 wherein said apparatus for eliminating comprises a ridge located within said electrically conductive hollow member.
12. The apparatus of claims 7 or 11 wherein said openings are configured to provide a beam pointing angle of approximately 11.25°. '~r'- A*'
13. The apparatus of claims 7 or 12 wherein adjacent groups of elements have opposite phases and adjacent elements within each group have opposite phases.
14. An apparatus as claimed in claim 1 substantially as i loe cJ herein drgri-bod with reference to the accompanying drawings. HAZELTINE CORPORATION By Their Attorneys -22-
NZ20821384A 1983-05-23 1984-05-18 Resonant waveguide slot array NZ208213A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US06/497,350 US4554551A (en) 1983-05-23 1983-05-23 Asymmetric resonant waveguide aperture manifold
US06/497,349 US4554550A (en) 1983-05-23 1983-05-23 Resonant waveguide aperture manifold

Publications (1)

Publication Number Publication Date
NZ208213A true NZ208213A (en) 1987-10-30

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Family Applications (1)

Application Number Title Priority Date Filing Date
NZ20821384A NZ208213A (en) 1983-05-23 1984-05-18 Resonant waveguide slot array

Country Status (4)

Country Link
EP (1) EP0126626B1 (en)
AU (1) AU565039B2 (en)
DE (1) DE3486164T2 (en)
NZ (1) NZ208213A (en)

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AU565039B2 (en) 1987-09-03
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EP0126626B1 (en) 1993-06-16
DE3486164D1 (en) 1993-07-22

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