US3048844A

US3048844A - Radiant energy scanner

Info

Publication number: US3048844A
Application number: US606909A
Authority: US
Inventors: Robert M Ashby
Original assignee: North American Aviation Corp
Current assignee: North American Aviation Corp
Priority date: 1956-08-29
Filing date: 1956-08-29
Publication date: 1962-08-07
Anticipated expiration: 1979-08-07

Description

Aug. 7, 1962 R. M. ASHBY RADIANT ENERGY SCANNER 5 Sheets-Sheet 1 Filed Aug. 29, 1956 90E on i a m m 9 4 MN q mm mm mmxwi o mommw A mmtim mmEim mmsi A $5:

m m N w IN VEN TOR.

ROBERT M. ASHBY AT TO RN EY Aug. 7, 1962 R. M. ASHBY RADIANT ENERGY SCANNER 3 Sheets-Sheet 2 Filed Aug. 29, 1956 INVEN TOR. ROBERT M. ASHBY QQ XWW ATTORNEY 1962 R. M. ASHBY 3,048,844

RADIANT ENERGY SCANNER Filed Aug. 29, 1956 3 Sheets-Sheet s FEED HORN l9 (a) RELATIVE PHASE FEED HORN 2o FEED HORN l9 (b) RELATIVE AMPLITUDE FEED HORN 2o I (D)BEAMPOSITION:I: 4 gi; 1:; I,

I I Ki l ROTATION 0F PHASE SHIFTER INVENTOR.

ROBE RT M. ASHBY ATTORNEY United States atent Qfltice 3,048,844 RADIANT ENERGY SCANNER Robert M. Ashby, Pasadena, Calif., assignor to North American Aviation, Inc. Filed Aug. 29, 1956, Ser. No. 606,909 16 Claims. (Cl. 343-777) This invention relates to a radiant energy scanner, and more particularly it relates to the microwave portion of a conical radar scanner.

In a radiant energy scanning device, it is desirable to provide a minimum of equipment and a minimum of mechanical motion. In most scanning systems particular care must be taken to dynamically balance the mechanical elements to avoid the undesired effects of vibrations on the scanning system and other associated equipment. An early type of conical scanning was provided by a device in which the microwave portion was displaced slightly from the focal point of the reflector, causing the lobe of the transmitted energy to likewise be displaced from the axis of the reflector. The microwave feed portion then was rotated and the lobe thus caused to move in a conical scan. Such a device was not balanced mechanically. Also, it did not make full use of the reflecting capabilities of the reflector. This invention provides conical scanning without the rotation of the reflector or the microwave feed portion. Conical scanning is obtained by varying the illumination of the microwave feed apertures. This variation of aperture illumination is accomplished by the rotation of the polarization of electromagnetic waves within a resolver. The antenna feed does not rotate and it may be placed substantially at the focal point of the reflector.

In one embodiment of the invention the conical scanner is adapted to transmit the lobe directly on the reflector axis as may be desired for monopulse type operation in which control scanning is not used.

By the theorem of reciprocity the device may scan in conical fashion so as to receive any radiant energy as well as to transmit it. Scanning, as used herein, therefore, includes both reception and transmission.

It is, therefore, an object of this invention to provide an improved conical scanning device.

It is another object of this invention to provide a radiant energy scanner having a minimum of rotating equipment.

It is still another object of this invention to provide a conical scanner utilizing waves of rotating polarization.

It is another object of this invention to provide a conical scanner which may be readily adjusted for monopulse operation.

A further object of this invention is to provide an antenna wave-guide section producing a circularly polarized wave.

Still another object of this invention is to provide an antenna wave-guide section producing a rotating linearly polarized wave.

Other objects of invention will become apparent from the following description taken in connection with the accompanying drawings, in which FIG. 1 is a block diagram of the device of the invention;

FIG. 2 is an illustration of one phase shifter portion of the device of the invention;

FIG. 3 is an illustration of the device of the invention partially in cross section;

FIG. 4 is a diagram of phase, amplitude and beam position;

FIG. 5 is an illustration of the rotatable phase shifter of the invention showing another position of the phase shifter;

FIG. 6 is a front view of a reflector;

And FIG. 7 is a cut-away end view of waveguide 8 illustrating orthogonal takeoifs.

In FIG. 1, an antenna feed 1 is shown illuminating a reflector 2. In the transmission mode, the signals transmitted by antenna feed 1 are received from range duplexer 3 through A phase shifter 4, and A 90 rotating phase shifter 5, and a A 90 phase shifter 6. In the energy reception mode, antenna feed 1 provides signals to phase shifter 6, phase shifter 5, phase shifter 4, and range duplexer 3, and azimuth and elevation error duplexer 7.

FIG. 2 is an illustration of A 90 fixed phase shifter 4 of FIG. 1. A linearly polarized wave enters waveguide section '8 at the nearer opening 9, and is illustrated as vector A. A fixed dielectric slab 10 resolves this vector into its two components, the vectors A, and A,,. One lies normal to the dielectric slab, the other is parallel to the plane of the slab. The slab is chosen so that its length and dielectric constant produce a 90 time phase lag in the component A, which is parallel to the plane of the slab. The A 90 phase shifter is a fixed dielectric slab 10 or a metallic slab of suitable dimensions to cause the vector A; to be delayed 90 along the length of waveguide 8 behind the vector A This results in a circularly polarized wave at the output end 11 of Waveguide 8. It will be noted that the phase shifter slab is at a 45 angle with the input linear vector A. The time phase relationship of the vectors A, and A, at the output end are also illustrated. Explanation and clarification of the concept illustrated in FIG. 2 may be obtained from Hyper and Ultra High Frequency Engineering, by Sarbacher and Edson, pp. 101 et seq.

Referring now to FIG. 3, illustrating the conical scanner, it can be seen that the A 90 fixed phase shift is accomplished by metal fins 12 and 13 which have the same effect as the dielectric slab 10 of FIG. 2. Subsequent to this phase shifter are illustrated two rotating A 45 phase shifters 14 and 15, rotated by motor 16. In conical scan, phase shifters 14 and 15 are maintained in alignment and therefore form a rotating A 90 phase shifter. As the outgoing wave is received in waveguide 23, it is passed through duplexer 3 and section 21 to section 4 of the Waveguide. Up to this point, the outgoing wave is linearly polarized. At it passes through section 4 it becomes circularly polarized, as explained in reference to FIG. 2. As the wave leaves section 5, due to the two rotating 45 phase shifters, the wave is rotating and linearly polarized. Waveguide 17 and waveguide 18 take ofl? from phase shifter 5 at right angles with respect to each other. FIG. 7 illustrates the similar

orthogonal takeoff apertures

35 and 36 of

waveguides

21 and 24. The orthogonal takeoff apertures of waveguides 17 and 18'are similarly located. The rotating linearly polarized wave is extracted through two orthogonal waveguide takeofis 17 and 18 which guide the energy to

feedhorns

19 and 20. The apertures of the two feed horns are located near the focus of the paralbolodial reflector. The one horn 19 is above and to the right of the reflector axis, while the other horn 20 is below and to the left of the reflector axis.

Such disposition is termed herein as being :laterally and' vertically spaced apart. An additional 90 phase shift section 6 is inserted in the waveguide leading to horn 20; or alternately, the length of the waveguide to feedhorn 20 may be made correspondingly longer to cause a 90 phase shift in the relative outputs of

feedhorns

19 and 20. As subsequently explained herein, the transmitted lobe 33 rotates about central axis 34 as illustrated to provide conical scan.

FIG. 4 shows the phase, amplitude and beam position of the radio frequency fields at the apertures of

feedhorns

19 and 20 as a function of the rotating phase shifter. Due to the relative geometry of the waveguide takeoffs 17 and 18, as the phase shifter 5 rotates, there is a phase shift of 180 between the waves extracted at takeoffs 17 and 18. This is due to the inherent coupling geometry that two orthogonal takeoffs present to the rotating linear polarization. At zero radians rotation, FIG. 4a, the 90 phase lag in the waveguide takeoif 18 establishes a relative 90 phase lead in the wave that is radiated from horn 19 with respect to the wave radiated from horn 20. However, for positions of the phase shifter between and 1r there is a shift to 90 phase lag. It is observed, FIG. 4b, that the amplitude of the radio frequency wave at horn 20 follows a sine wave distribution as a function of the rotation angle; whereas the amplitude of the radio frequency at feedhorn 19 follows a cosine distribution. This amplitude modulation of the energy being fed into the horns is caused by the resolver-like action of the cylindrical section of the waveguide and the two orthogonal takeoifs during this mode of operation. there is the position of the rotating A 90 phase shifter 5 (the two A 45 phase shifters) for which the linear polarization incident upon the orthogonal takeoffs 17 and 18 will be aligned with the waveguide takeoff 17 which feeds horn 19. At this position, there will be a maximum of energy coupled into the horn 19, while there is no energy coupled into the horn 20, because the waveguide takeofi feeding horn is at right angles to the linearly polarized Wave. Let this position of the phase shifter, the zero position in FIG. 4, be considered as the reference. By rotating the A 90 phase shifter the polarization of the transmitted wave is rotated so as to couple equally into both waveguide takeofls. At this point, both horns will receive waves of equal amplitude. An additional rotation of the A 90 phase shifter will bring the linearly polarized transmitted wave in the cylindrical section into alignment with the waveguide takeofl feeding born 20. At this point, a maximum power is radiated from horn 20 whereas no power is radiated from horn 19. As the A 90 phase shifter is rotated still further, the energy is transferred again from horn 20 to 19 in a sinusoidal manner.

FIG. 4c also shows the orientation of the beam in space for this type of excitation. When there is no energy being radiated from horn 20, the transmitted beam is essentially down, as shown in FIG. 4. This is caused by the fact that horn 19 is located above the axis and the radiation therefrom, upon striking the reflector, is transmitted outwardly below the axis. The

distances horns

19 and 20 are laterally displaced from the focal point of the reflector introduce errors which may be minimized as explained later with reference to FIG. 6. The deflection of the conical beam in azimuth is obtained because the excitation of the feedhorns are out of phase which was mentioned previously. When the phase shifter is rotated to the position equal energy is radiated from both

horns

19 and 20, but they are out of phase and the transmitted beam is radiated to the left of the antenna axis. As the phase shifter rotates to position all of the radiated energy appears to come from the horn 20 which is located below the axis of the reflector; therefore, the beam is reflected upwardly and appears above the antenna axis. When the phase shifter is located at %1r, the radiated beam is to the right of the antenna axis, and when the phase shifter reaches the point 1r, the beam is again in the down position. It should be observed from FIG. 4 that the antenna conical scan rate is twice the rotation rate of the phase shifter 5.

During reception, the antenna pattern, by the theorem of reciprocity, is the same as for transmission so that the For example,

reflected energy returns by the same path through the waveguides and the phase shifters where it is coupled in the normal manner to a conventional receiver designed to operate with a conical scanning system.

FIG. 5 illustrates how the device of the invention is used in the more conventional monopulse scanning if desired. This is done by simply rotating the two A 45 slabs 14 and 15 so that they are oriented at right angles to each other. Eflectively then, they cancel each other. They may either be held stationary or rotated in this relative relation.

In the monopulse transmission, the circularly polarized wave is received at the orthogonal takeofls 17 and 18, FIG. 3, and equal energy is coupled into both

horns

19 and 20. However, there is an inherent time phase lag of the wave in horn 19 relative to the wave in horn 20 that is associated with the circularly polarized wave within the cylindrical section. This lag is cancelled by the phase shift section 6 in feedhorn 20. Since the tw horns are then radiating equal energy in time phase, the transmitted beam appears directly on the axis as is desired for monopulse operation.

In monopulse reception, the antenna radiation pattern associated with the range receiver is the same as the transmission pattern. Because of the vertical offset of

horns

19 and 20, the energy reflected from a target off axis in elevation will excite the

horns

19 and 20 essentially in time phase but with unequal amplitudes. Due to the waveguide between horn 20 and takeoff 18 being longer than between horn 19 and takeoif 17, these waves are in quadrature upon arrival at the circular portion of the waveguide. Since the waves are not equal in amplitude, they excite an elliptically polarized wave in the round guide. This elliptically polarized wave may be thought of as being composed of two circularly polarized waves of opposite sense and of unequal magnitude. As these circularly polarized waves pass the fixed phase shifter in section 4, they are transformed into two linearly polarized components in space quadrature. One of these components is coupled into waveguide takeoff 21 and provides range information to duplexer 3. Duplexer 3, in turn, passes the signal t an output waveguide 22 which is connected to the range receiver of the device. The other linearly polarized component couples into waveguide takeolf 24 and corresponds to the elevation error signal. If the target is off axis in azimuth, the two feedhorns 19 and 20 are excited by waves of approximately equal amplitude but different in phase. At the circular portion 8 of the Waveguide, the waves from

horns

19 and 20 result in excitation of the two essentially equal amplitude components at right angles in the round guide but with time phase differing up to 90, depending upon the azimuth error angle. The composite wave in the round guide may be resolved again into two components which couple into

waveguide takeoifs

21 and 24. That portion coupling into output waveguide 21 is, again, the range reference. The energy in waveguide takeoff 24 contains the azimuth error information and is in time phase quadrature with the elevation error information contained within the same channel. These azimuth and the elevation error signals are propagated in waveguide takeoff 24 and pass through :duplexer 7 and out waveguide 25 to the error receiver of the device. After detection and intermediate frequency amplification, the azimuth and elevation error signals are then separated in a quadrature error detector (not shown). As with other systems, the relative phase of the signal in the sum channel, waveguide 22, may be used to determine whether the signal in the error channel comes from a target above or below the antenna axis or to the left or to the right in azimuth.

A practical reflector may be a paraboloid or an elliptical paraboloid. The previous discussion indicated that the azimuth error information resulted from the phase difference in the excitation of

horns

19 and 20. To eliminate the off axis in azimuth amplitude variations in the

horns

19 and 20 excitation, the two halves of the reflector are separated, as shown in FIG. 6, to result in the center of phase of each horns radiation lying along the vertical line containing the half paraboloid vertex. The two half paraboloids are then joined in region 32 by a parabolic cylinder.

A signal off axis in elevation results in a small amount of time phase difference in the signals excited in the

horns

19 and 20. There is no way of eliminating the resulting azimuth channel cross-coupling component. Therefore, the distance 32 is made slighty wider or narrower than the distance between feedhorns 1'9 and 26 in FIG. 6 so as to result in an amount of azimuth to elevation channel crosscoupling of a magnitude and direction to compensate for the elevation to azimuth channel cross-coupling.

A compact conical scanner, readily adaptable to monopulse operation, is thus obtained with no externally moving parts.

Although the invention has been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of this invention being limited only by the terms of the appended claims.

I claim:

1. A conical scanning device comprising means for resolving an electromagnetic wave to feed two signal channels comprised of two waveguides terminating in two laterally and vertically displaced feedhorns, with electromagnetic waves of sinusoidally-varying amplitudes and a relative time phase difference of 90, and means for reversing the relative phase in said channels between lead and lag every 90 of said sinusoidally-varying waves.

2. A conical scanning device comprising means providing an electromagnetic wave, a pair of signal channels comprised of two waveguides, means for coupling said electromagnetic wave into said waveguides with sinusoidally-varying amplitudes and a relative time phase difference of 90, the relative phase in said channels reversing between lead and lag every 90 of said sinusoidally-varying waves, a pair of feedhorns located laterally and vertically apart, each of said feedhorns connected to a respective waveguide.

3. A conical scanning device comprising means providing an electromagnetic wave, a pair of waveguides, means for coupling two components of said electromagnetic wave into said Waveguides with sinusoidally-varying amplitudes, said components being displaced in time phase with respect to each other, and a pair of feedhorns located laterally and vertically apart, each of said feedhorns connected to a respective waveguide, reflector means cooperatively associated with said feedhorns.

4. A waveguide, a rotatable 90 phase shifter located within a section of said waveguide, said waveguide comprised of two 45 phase shifting sections, means for displacing each of said 45 phase shifting sections relative to the other and means for rotating said phase shifter.

5. In a radiant energy scanner, a waveguide, means providing a circularly polarized wave to said waveguide, a rotatable 90 phase shifter adapted for continuous rotation, said phase shifter being located in said waveguide, and two waveguide takeoffs located with respect to each other so as to receive orthogonal components of the output wave from said phase shifter and antenna feed means connected to receive the output provided by both said takeotfs.

6. In a radiant energy scanner, a waveguide, means providing a circularly polarized wave to said waveguide, a rotatable 90 phase shifter adapted for continuous rotation, said phase shifter being located in said waveguide, and two waveguide takeofis located orthogonally with respect to each other so as to receive orthogonal components of the output wave from said phase shifter and antenna feed means connected to receive the output provided by both said waveguide takeoffs.

7. The combination recited in claim 6 wherein said antenna feed means includes a first antenna feed connected 6 to receive the output provided by one of said waveguide takeoffs, and a second antenna feed connected to receive the output provided by the other of said waveguide takeolfs, and a phase shifter located in one of said antenna feeds.

8. In a radiant energy scanner, a waveguide for receiving a linearly polarized wave, a fixed 90 phase shifter located in said waveguide and oriented at 45 with respect to said linearly polarized wave, a rotatably 90 phase shifter located in said waveguide, two waveguide takeolfs orthogonally located with respect to each other so as to receive orthogonal components of the output of said waveguide, and antenna feed means comprising two channels connected to receive respective orthogonal component outputs of said waveguide.

9. In a radiant energy scanner, a waveguide for receiving a linearly polarized wave, a fixed 90 phase shifter located in said waveguide and oriented at 45 with respect to said linearly polarized wave, a rotatable 90 phase shifter located in said waveguide, two waveguide takeolfs orthogonally located with respect to each other and connected to receive the outputs of said rotatable 90 phase shifter, a first feedhorn connected to receive the output of one of said takeoifs, a second feedhorn connected to receive the output of the other of said takeoffs, a reflector, said feedhorns being located laterally and vertically apart substantially at the focal point of said reflector.

10. The combination recited in claim 9 wherein is included a 90 phase shifter between one of said takeoffs and the feedhorn connected to receive its output.

11. In a radiant energy scanner, a Waveguide for receiving a linearly polarized wave, a fixed 90 phase shifter in said waveguide located at 45 with respect to said linearly polarized wave, a rotating 90 phase shifter located in said wave guide, first and second takeoffs connected at one end of said waveguide, said takeofis located orthogonally with respect to each other, third and fourth waveguide takeoffs connected at the other end of said waveguide, said third and fourth takeoffs located orthogonally with respect to each other, and first and second antenna feed means connected to receive the outputs provided by said first and second takeofis, respectively.

12. The combination recited in claim 11 wherein said rotating 90 phase shifter comprises a plurality of sections adapted to be rotated with respect to each other.

13. The combination recited in claim 11 wherein said rotating 90 phase shifter comprises two 45 phase shifters adapted to rotate in alignment and further adapted to be rotated in a position in which said shifters are located at right angles with respect to each other.

14. In a radiant energy scanner, a waveguide for receiv ing a linearly polarized wave, a fixed 90 phase shifter in said waveguide located at 45 with respect to said linearly polarized wave, a rotating 90 phase shifter located in said waveguide, first and second takeoffs connected at one end of said waveguide, said takeoffs located orthogonally with respect to each other, third and fourth waveguide takeoifs connected at the other end of said waveguide, said third and fourth takeoifs located orthogonally with respect to each other, first and second antenna feedhorns connected to receive the outputs of said first and second takeoifs, a 90 phase shifter connected between the output provided by one of said takeoffs and one of said feedhorns, a reflector, said feedhorns being disposed laterally and vertically apart substantially at the focal point of said reflector.

15. In a radiant energy scanner, a waveguide for receiving a linearly polarized wave, a fixed 90 phase shifter in said waveguide located at 45 with respect to said linearly polarized wave, a rotating 90 phase shifter located in said waveguide, first and second takeoifs connected at one end of said waveguide, said takeoffs located orthogonally with respect to each other, third and fourth waveguide takeoffs connected at the other end f i N p a wave from said phase shifter, antenna feed means con- 10 nected to receive the output provided by both said waveguide takeofis, said antenna feed means including a first antenna feed connected to receive the output of one of said waveguide takeoffs, and a second antenna feed connected to receive the output of the other of said waveguide takeoifs, and a 90 phase shifter located in one of said antenna feeds, said antenna feeds comprising feedhorns located laterally and vertically apart.

References Cited in the file of this patent UNITED STATES PATENTS 2,438,119 Fox Mar. 23, 1948 FOREIGN PATENTS 1,102,590 France May 11, 1955 OTHER REFERENCES Electronics, June 1952, pages 156, 158, 162, 166.