US3328800A

US3328800A - Slot antenna utilizing variable standing wave pattern for controlling slot excitation

Info

Publication number: US3328800A
Application number: US351320A
Authority: US
Inventors: Jerry A Algeo
Original assignee: North American Aviation Corp
Current assignee: North American Aviation Corp
Priority date: 1964-03-12
Filing date: 1964-03-12
Publication date: 1967-06-27
Anticipated expiration: 1984-06-27

Description

June 27, 1967 J. A. ALGEO 3,328,800

SLOT ANTENNA UTILIZING VARIABLE STANDING WAVE PATTERN FOR CONTROLLING SLOT EXCITATION Filed March 12, 1964 5 Sheets-Sheet 1 1 i7 1 L i 2 L 3 2 L I JL 46B ,Z/ L L 32 2/8 FIG.2 25 5 ,w/I

INVENTOR.

JERRY A. ALGEO i BY SIDNEY MAGNES AGENT June 2 7, 1967 J. A. ALGEO 3,328,800

SLOT ANTENNA UTILIZING VARIABLE STANDING WAVE PATTERN FOR CONTROLLING SLOT EXCITATION Filed March 12, 1964 5 SheetsSheet 2 so x 62 I- I 66A I L 5 &

83 v JL I 706 j sec sec 70 INVENTOR. JERRY A. ALGEO SIDNEY MAGNES AGENT no 0 t 00 m 8 2 6 w 3% m s 5 June 27, 1967 J. A. ALGEO SLOT ANTENNA UTILIZING VARIABLE STANDING WA PATTERN FOR CONTROLLING SLOT EXCITATION Filed March 12, 1964 INVENTOR JERRY A ALGEO SIDNEY MAGNES AGENT...

June 27, 1967 J. A. ALGEO 3,328,800

SLOT ANTENNA UTILIZING VARIABLE STANDING WAVE PATTERN FOR CONTROLLING SLOT EXCITATION Filed March 12, 1964 5 Sheets-Sheet 4 JERRY A. ALGEO SIDNEY MAGNES AGENT June 27, 1967 J ALGEO 3,328,800

SLOT ANTENNA UTILIZING VARIABLE STANDING WAVE PATTERN FOR CONTROLLING SLOT EXCITATION Filed March 12, 1964 5 Sheets-Sheet 5 FIG. l3

INVENTOR JERRY A. ALGEO FIG SIDNEY MAGNES AGENT.

United States Patent SLOT ANTENNA UTILIZING VARIABLE STAND- lNG WAVE PATTERN FOR CONTROLLING SLOT EXCITATION Jerry A. Algeo, Buena Park, Calif., assignor to North American Aviation, Inc. Filed Mar. 12, 1964, Ser. No. 351,320 9 Claims. (Cl. 343-768) This invention relates to antennas; and more particularly to antennas that can produce different radiation and reception patterns, and different types of energy-polarization.

It is well known that radar operates upon the echo principle. In operation, a radar station causes its antenna to transmit energy outwardly to impinge upon a target; the target reflecting some of the impinging energy in the form of a return, or echo, signal. The antenna receives the reflected echo signal; and equipment in the radar station processes the reflected energy to provide target information, such as the direction of, and distance to, the target.

The distance to the target is obtained by measuring the length of time that elapses between the transmission of the radar energy and the reception of the echo signal, the direction of the target being obtained-depending upon the radar system-from the echo signal or the direction in which the antenna is aimed.

As is well understood in the art, radar energy has the characteristic that it may be polarized, the energy may be linearly-polarized either vertically, horizontally, or at any intermediate angle; or it may be polarized elliptically, of which circular polarization is a special case.

The polarization of the radar energy enters into the operation of the radar system in the following manner.

Assume that an airplanes radar operator is interested -for navigational purposes-in knowing whether the plane is flying over water, desert, or mountainous terrain. It has been found that circularly-polarized radar energy causes the magnitude of the echo signal to vary With changes in terrain; and, in this case, the radar operator would therefore prefer to use circularly-polarized radar energy. If, however, he is primarily interested in the planes height above the ground, he would prefer to use linearly vertically-polarized radar energy, since this produces echo signals of substantially the same magnitude regardless of the type of terrain.

It has also been found that in a rain storm the echo signal depends on the size and shape of the raindrops of the storm. Therefore, if the radar operator is trying to obtain information about the location and extent of a rain storm, it is desirable to select the type of polarization that provides the strongest return echo signal from the raindrops themselves. If, on the other hand, the radar operator is interested in a target beyond the rain storm, it is desirable to select the type of polarization that pierces the rain storm, and is reflected by targets beyond the storm.

Thus, it is desirable to be able to change the polarization of the radar energy.

The type of polarization may be unimportant under other conditions, such as searching for, and tracking a target; but-under these conditions-an item of great importance is the radiation-pattern, that is, the amount of radar energy that is radiated in various directions.

For example, in the searching mode of operation, when the radar operator is trying to detect a target, the radiation-pattern is preferably a wide beam, so that any target within the beamwidth will produce an echo signal. Once the presence of a target within the beamwidth has been indicated, the radar operation is changed to a so- 3,328,800 Patented June 27, 1967 called tracking mode, wherein the radiation-pattern is changed to a narrow pencil-like beam that isused to pinpoint the direction of the target.

Other modes of radar operation require still different types of radiation-patterns.

It will be understood from the above discussion, that it is desirable to be able to change both the polarization and the radiation-pattern, depending upon particular op erating conditions.

It is therefore the principal object of the present invention to provide an improved antenna having means for providing selected combinations of polarization and radiation pattern.

The attainment of this object and others will be realized from the following specification, taken in conjunction with the drawings of which:

FIGURES 1, 2, 3, and 4 illustrate antennas for producing different types of radar-energy polarization;

FIGURES 6 and 9 illustrate different beam patterns;

FIGURES 5, 7, 8, 10, and 11 illustrate antennas for producing different beam patterns; and

FIGURES l2 and 13 illustrate antennas having different cross-sectional shapes.

Broadly speaking, the present invention contemplates an antenna in which there is established a standing-wave pattern of radar energy. By permitting the energy to escape from the antenna only at selected points therealong, the emergent energy has a given beamwidth which is polarized in a given manner. By permitting the energy to escape from the antenna only at other selected points, the emergent energy may have a diiferen-t beamwidth which is polarized in a different manner. Thus, by controlling the points from which the energy escapes, the combination of beamwidth and polarization of the energy can be selectively controlled.

Alternatively, the amounts of different types of polarization can be selectively combined, so that the emergent energy is polarized in still another manner.

The present invention contemplates control of the polarization by (1) establishing a standing-wave pattern that permits the energy to escape from given points, and thus provides emergent energy of a given polarization; and then (2) changing the standing-Wave pattern to one that permits the energy to escape from different points, and thus provides emergent energy of a different polarization.

In this way the instantaneous controlled standing-Wave pattern establishes the polarization of the radar energy.

The present invention also contemplates the production of particular radiation-patterns by establishing standingwave patterns that cause the energy to escape from given sets of points, the arrangement of the escape-points establishing the radiation-pattern or beamwidth.

Moreover, the present invention also contemplates a constantly-changing standing-wave pattern, so that the energy emerges in a constantly-changing combination of polarization and radiation pattern.

FIGURE 1 shows an antenna that radiates linearlypolarized energy. The antenna 20 comprises a hollow tubular waveguide 22, made of an electrically-conductive material such as copper or the like. Waveguides such as element 22 are ordinarily used to guide microwave energy from one point to another, hence their name waveguide. However, if the waveguide has an aperture (or slot) in the wall thereof, energy will tend to escape through the aperture. Moreover, if the waveguide has an array of slots or a set of intentionally-introduced apertures that are suitably sized, shaped, spaced, oriented, etc., the energy escaping from the various apertures will com bine to form a specific radiation-pattern; and the waveguide then acts as a radiating, or transmitting antenna. This will be more fully discussed hereinafter.

In FIGURE 1, antenna 20 comprises an aperturedwaveguide 22 having a shorting plate 24 of electricallyconductive material positioned at one end of waveguide 22. shorting-plate 24 physically and electrically closes the end of the antenna. It therefore produces an electrical short-circuit; and energy cannot escape from the closed end of the antenna 20.

shorting-plate 24 has the characteristic that when energy is applied to the open bottom-end of the antenna as in icated by arrow 25-the shorting-plate 24 reflects the energy in such a way that a voltage standing-wave" pattern is produced; the voltage standing-wave being represented by sinusoidal waveform 26.

It will be noted that sinusoidal waveform 26 has a positive maximum value at certain cross-sectional planes such as 28; that sinusoidal waveform 26 has negative maximum values at other cross-sectional planes such as 30; and that sinusoidal waveform 26 has an intermediate value of zero at other cross-sectional planes, such as 32.

The sinusoidal waveform 26 has a characteristic known as its wavelength, which extends between corresponding pointsfor example, from a zero value through a negative maximum value and a positive maximum value back to a zero value. A wavelength of waveform 26 is represented by the distance L.

It has been found that if a transverse slot-like aperture 34A is cut through the broad wall of the waveguide 22 at a cross-sectional plane 32 where the sinusoidal waveform 26 has a value of zero, then the standing-wave will be coupled to the aperture; and energy will escape through the aperture. The emergent energy will be polarized in a linear longitudinal manner as indicated by the arrow 38A, which has a longitudinal orientation.

If another transverse slot 34B is similarly positioned at a zero-valued plane 32 that is one wavelength from the first slot 34A, it too will permit the escape of energy; the energy from transverse slot 34B also being polarized in the same linear longitudinal manner, as shown by arrow 38A.

Thus, a group of

transverse slots

34A, 34B, etc. that are similarly positioned one-wavelength apart-or multiples of one-Wavelength apart-will permit the escape of energy that is similarly-polarized in a linear longitudinal manner.

If another transverse slot 34C is positioned at a zerovalued plane 32 that is spaced one-half wavelength from the first slot, or is spaced one-half wavelength from a transverse slot of the first set, it too will permit the escape of energy. If the slot 34C is positioned on the other side of the longitudinal axis of the antennas broad wall, the energy escaping from slot 34B will have the same linear longitudinal polarization, as shown by arrow 38C.

Thus a second group of

transverse slots

34C, 34D, etc., spaced one wavelength apart, half-a-wavelength from the slots of the first group, and staggered with respect to the slots of the first group, will permit the escape of energy that is similarly-polarized in a linear longitudinal manner.

In this way, a set of staggered transverse slots positioned one-half wavelength apart at the zero-valued points of the standing-wave pattern 26 converts the waveguide to an antenna; and the energy emerging from the above set of slots combines to form a radiation-pattern of linear longitudinal polarization; the radiation pattern itself to be discussed later.

If the antenna is positioned vertically, as shown in FIGURE 1, the energy emerging from the set of transverse slots will be linearly polarized vertically, as shown by the vertical arrows 38; whereas, if the antenna were positioned horizontally, the emergent energy would be linearly horizontally-polarizedthat is, arrows 38 would then be horizontal.

It should be noted that in order to produce the abovedescribed longitudinal polarization of the emergent energy, the shorting-plate 24 must be spaced from the first slot 34A by a distance that is equal to one-half a wavelength; or by a distance that is equal to an integral number of half-wavelengths. This spatial relation is necessary in order to place all of the lots simultaneously at the zerovalued points of the voltage standing-wave pattern 26.

While FIGURE 1 shows shorting-plate 24 positioned at the end of the antenna, and one-half wavelength from the first slot, the shorting plate could just as well have been positioned at any of the zero-valued cross sectional planes 32 in accordance with the above explanation; although this arrangement would dis-able the apertures on the side of the shorting-plate away from the entrypoint of the energy (arrow 25).

FIGURE 2 shows a similar antenna 40 that comprises an apertured rectangular waveguide 42 and a shortingplate 24 that produces a standing-wave indicated by sinusoidal waveform 26. It has been found that if a longitudinal slot-like aperture 46A is cut through the broad wall of the waveguide 42 at a cross-sectional plane 28 where the sinusoidal waveform 26 has a maximum positive value, then the standing-wave will be coupled to the aperture; and energy will escape through the aperture. The emergent energy Will now be polarized in a linear transverse manner as indicated by arrow 48A, which has a transverse orientation.

If another longitudinal slot 46B is similarly positioned at a maximum positive valued plane 28 that is one wavelength from the first slot 46A, it too will permit the escape of energy; the energy also being polarized in the same linear transverse manner, as shown by arrow 4813.

Thus, a group of

longitudinal slots

46A, 46B, etc., that are similarly positioned one-wavelength apart--or multiples of one-wavelength apartwill permit the escape of energy that is similarly-polarized in a linear transverse manner.

If another longitudinal slot 46C is positioned at a maximum-valued positive plane 28 that is spaced onehalf wavelength from a longitudinal slot of the first set, it too will permit the escape of energy. The energy in this case has the same linear transverse polarization if the slot 46C is positioned on the other side of the longitudinal axis of the antennas broad wall.

Thus, a second group of

longitudinal slots

46C, 46D spaced one wavelength apart, half a wavelength from the slots of the first group, and staggered with respect to the slots of the first group, will permit the escape of energy that is similarly-polarized in a linear transverse manner.

In this way. a set of staggered longitudinal slots positioned one-half wavelength apart at the maximum-valued points of the standing-wave pattern 26, converts the Waveguide to an antenna; and the energy emerging from the set of slots combines to form a radiation-pattern of linearly transverse polarization; the radiation-pattern itself to be discussed later.

If the antenna is positioned vertically, as shown in FIGURE 2, the energy emerging from the set of longitudinal slots will be linearly polarized horizontally, as shown by the vertical arrows 48; whereas, if the antenna were positioned horizontally, the emergent energy would be linearly vertically polarizedthat is, arrows 48 would then be vertical.

It should be noted that in order to produce the abovedescribed transverse polarization of the emergent energy, the shorting-plate 24 must be spaced from the first slot 46A by a distance that is equal to an odd multiple of quarter-wavelengths. This spatial relation is necessary in order to place all of the slots simultaneously at the maximum-valued points of the voltage standing-wave pattern 26.

To recapitulate, it may be understood that by positioning a set of suitably-oriented slots at selected locations relative to a standing-wave pattern, the emergent energy may be selectively polarized in a desired manner.

The above discussion has shown that it is possible for an antenna to produce either longitudinally or transversely-polarized emergent energy. FIGURE 3 shows how a single antenna can produce either type of polarization.

In FIGURE 3, antenna 60 comprises a waveguide 62, a shorting plate 64, and a first set of staggered

longi tudinal slots

66A, 66B, 66C, etc. that are spaced apart a distance of half a wavelength. As previously indicated, the set of longitudinal slots can produce emergent energy that is linearly transversely-polarized.

FIGURE 3 also shows a second set of staggered

transverse slots

70A, 70B, 70C etc., that are on the same cross sectional plane as the longitudinal slots 66; and are therefore also half a wavelength apart. As previously indicated, the transverse slots can produce emergent energy that is linearly longitudinally-polarized.

It will be noted that the slots of the two sets are so positioned that the slots form slot-

pairs

66A, 70A; 66B, 70B; 66C, 70C, etc. comprising one longitudinal slot 66 and one transverse slot 70 positioned at each cross-sectional plane; and that the slots-pairs are spaced apart by half a wavelength.

In FIGURE 3, when energy is introduced at the lower end of the antenna, the shorting-plate 64A establishes a standing-wave pattern 80 having zero points or nulls positioned at the slot-pairs. Therefore, the transverse slots 70 would emit longitudinally-polarized energy, as explained in connection with FIGURE 1.

However, the longitudinal slots 66, also positioned at the zero-valued point of the standing-wave pattern 80, do not permit any energy to escape through them.

Thus, for the location shown for shorting-plate 64A, the emitted energy would be longitudinally-polarized.

If the shorting plate is moved to the location 648, and energy is introduced at the lower end of the antenna, the dotted-line standing wave pattern 81 will be produced.

It will be seen that the maximum-valued points of the standing-wave pattern 81 are now at longitudinal slots 66, and the escape of transversely-polarized energy resulting, as explained in connection with FIGURE 2. However, the transverse slots 70 also positioned at the maximum-valved points of standing-wave pattern 81, and therefore they will not permit any (longitudinally polarized) energy to escape through them. Accordingly, for the 64B location of the shorting-plate (in FIGURE 3), the emitted energy would be transversely-polarized.

Thus, by inserting or withdrawing a removable shorting-plate at location 64B (in FIGURE 3), the emergent energy can be polarized in a transverse or in a longitudinal manner respectively.

It has been found that a maximum amount of energy escapes from the slot if the slot has a periphery that is approximately equal to the wavelength of the energy. In a typical case, the length of the slot is about onehalf of the wavelength, and the width of the slot is about one-twentieth of the wavelength,

It has also been found that progressively-more energy is permitted to escape as the slot is progressively offset from the center line of the broad wall of the antenna. Thus, by suitably positioning a plurality of suitablyshaped slots, the amount of escaping radiation can be controlled.

It was previously indicated that the amount of energy escaping through a slOt can be controlled by the size of the slot, and by the amount of offset from the longitudinal axis of the antenna. If the same mounts of perpendicularly-polarized energy escapes from the separate slots of a slot-pair, the emergent energy combines to produce socalled circularly-polarized energy.

In FIGURE 4, antenna 84 produces circularly-polarized energy by using a shorting-plate at the location indicated by reference character 64C, and by using slotpairs that are positioned one wavelength apart. The shorting-plate at this location, produces a standing-wave pattern indicated by the solid sinusoidal line 82.

It will be noted that each slot of the slot pairs is now positioned, relative to the standing-wave pattern 82, at

a point that is neither maximum-valued nor zero-valued. As a result of this particular intermediate value, equal amounts of energy escape through each slot of each slot pair; thus resulting in circularly-polarized energy.

The circularly-polarized energy has a characteristic known as right-handedness or left-handedness; which is established by the location of the slot-pair relative to the standing-wave pattern. In FIGURE 4, for example, each slot-pair is at a location that produces polarization of the same handness.

If the slot-pairs were placed at locations half-way between those illustrated, and were offset to the other side of the longitudinal axis of the broad wall of the antenna, they would produce polarization of the opposite handness. This same opposite handness can also be achieved by establishing a standing-wave pattern such as 83, by the use of a shorting-plate 64D. Thus by using inserta'ble shorting-plates, either right-handed or left-handed circularly-polarized energy can be produced.

It has been shown that the standing-wave patterns of FIGURE 4 produce circularly-polarized energy by causin-g equal amounts of energy .to escape from each slot of a slot-pair. If now, the standing-wave pattern were changedas by slightly re-positioning the shorting-plate, more energy would escape from one slot than from the other. The resultant emergent energy would no longer be circularly polarized; butwould now' be elliptically polarized.

It is therefore apparent that the antenna of FIGURE 4 maybe made to establish a standing-wave pattern that produces polarization having difierent degrees of ellipticity; each of which may be right-handed or left-handed.

It is well known that antennas generally act in a reciprocal manner. For example, if an antenna transmits only horizontally-polarized radiation, it will receive only horizontally-polarized radiation. Similarly, if an antenna transmits vertically-polarized radiation, it will receive only vertically-polarized radiation. In a like manner, if an antenna transmits elliptically'or circularly-polarized radiation, it will receive only elliptically-or circularly polarized radiation. Moreover, if the antenna transmits right-hande or left-handed-elliptically or circularly polarized radiation (controlled by the type of slot pairs selected), it will receive only the same type of radiation. This conforms to the theory of reciprocity.

The previously-disclosed antennas act in accordance with the theory of reciprocity; and as a result they have a number of novel uses.

'For example, if right-handed polarized energy is transmitted toward a rainstorm, the raindrops reflect the energy; and the echo signal comprises left-hand polarized energy. Thus, if the radar operator Wants information about the rainstorm, he establishes a standing-wave pattern that causes the antenna to transmit right-handed polarized energy; and he then changes the standing-wave pattern so that the antenna will receive the left-handed polarized radiation reflected by the raindrops. The radar system then provides information about the energy-reflecting raindrops.

If, however, the radar operator wants information about targets beyond the rainstorm, he establishes a standingwave pattern that causes the antenna to transmit righthanded polarized energy; and he maintains the same standing-wave pattern, so that the antenna receives the right-handed circularly-polarized energy that is reflected by the more-distant targets beyond the rainstorm. Thus, the radar system does not receive the echo signals from the raindrops; but does receive the echo signals from the targets.

Moreover, the radar operator can establish a standingwave pattern whose ellipticity is optimum for reflection, or rejection, or the raindrops echo signals.

Pulsed radar systems are also plagued by echo signals known ,as "second-time-around-signals. These echo signals are produced by objects that are farther away than the maximum range of interest represented by the pulse repetition period of the radar; and such echo signals, in response to a transmitted energy pulse, arrive at the radar station during the subsequent pulsing period, whereby a false target-range indication is provided.

The present invention obviates these signals in the following manner. For an initial pulse repetition period, for example, the radar operator establishes a standing-wave pattern that causes the antenna to produce, say, horizontally-polarized energy. The desired echo signals are therefore horizontally polarized. At the beginning of the next pulse repetition period, a different standing-wave is caused to be established; and the second-time-around echo signals (due to targets beyond the range of interest) are no longer accepted by the antenna. (Target signals received from targets at ranges greater than that represented by the interval of two successive pulse repetition periods are presumed to be so attenuated in signal strength as to be negligible.)

Thus, the present invention may be employed to obviate second-time-around signals.

Since, because of the previously-discussed theory of reciprocity, the transmission radiation-pattern is similar to the reception-pattern, the term beam-pattern will now be used to include both the transmission and reception patterns.

As previously indicated, it is frequently desirable to control the beam-pattern in which the emergent energy is radiated and received; and FIGURE shows one way of producing different beam-patterns, using the present inventive concept. In FIGURE 5, antenna 90 has a first set of slots 92-shown to be transverse, but which may be either transverse or longitudinalextending substantially from one end of the antenna to the other. When a suitable standing-wave pattern is established, by means such as the shorting-plate 94 as described above, the first set of slots 92 will emit energy that is polarized in a particular manner.

Due to the large longitudinal spatial distribution of the first set of slots 92 (e.g. the longitudinal distance between the upper and lower slots or extremities of the array of slots 92), when this set of slots is emitting energy, the antenna will act as a large aperture antenna; and will produce a corresponding narrow beam of polarized energy as indicated by the narrow beam-pattern 96 of FIG- URE 6, in a plane parallel to the longitudinal axis of antenna 90 (FIGURE 5).

Antenna 90 of FIGURE 5 also contains a second set of slots 100, which are oriented perpendicularly to the slots 92 of the first set; slots 100 being relatively few in number (e.g., the longitudinal array of slots 100 being shorter than the longitudinal array of slots 92). In accordance with the previous explanation, when a suitable standing-wave pattern is established, this second set of slots 100 will emit energy that is polarized perpendicularly to the energy from the first set of slots.

Due to the smaller spatial distribution of the second set of slots 100 (e.g., the longitudinal distance between the upper and lower slots or extremities of the array of slots 100), when the second set of slots is emitting energy, the antenna will act as a small aperture antenna; and will produce a corresponding wide beam, (as indicated by reference character 102 of FIGURE 6) in a plane parallel to the longitudinal axis of antenna 90 (FIGURE 5).

It may therefore be seen that, when suitably energized, the antenna 90 of FIGURE 5 can produce either a wide or a narrow beam of energy (in a plane parallel to the longitudinal axis of antenna 90), the polarization of the particular pattern depending upon the orientation of the energized slots.

It was indicated above, that antenna 90 of FIGURE 5 needs two different types of standing-wave patterns, in order to energize the two separate sets of slots. This result may be produced by using insertable shorting-plates as described previously; but in order to switch rapidly from one radiation-pattern to the other, a different method may be used, as follows.

In FIGURE 5, the shorting plate 94 reflects the incoming energy to establish a first standing-wave pattern that energizes the first set of slots. When it is desired to adjust the standing-wave pattern so as to energize the second set of slots, a set of electrically-conductive shortingpins 104 are inserted into the waveguide; these effectively forming a shorting-plate. Because of its location, the effective shorting-plate produced by the shorting-pins 104 now establishes a different standing-wave pattern, which energizes the second set of slots.

It may thus be seen that by inserting or withdrawing shorting-pins 104, either of two standing-wave patterns may be produced; each standing-wave pattern being capable of exciting a different set of slots. Since the shortingpins 104 can be rapidly inserted or withdrawn by actuation means such as a magnet 106, the antenna is able to produce a wide or a narrow beam of the desired polarization; and to quickly switch from one beam to the other. Accordingly, antenna 90 of FIGURE 5 is adapted for providing a selected combination of beamwidth and polarization.

It is evident that even the mechanical shorting-pin arrangement of FIGURE 5 has a limitation on the rapidity with which the pins can be inserted and withdrawn. This limitation is overcome in the arrangement of FIGURE 7, which also shows a different type of slot arrangement.

Here, antenna 110, instead of having longitudinal and transverse slots, has a set shown in solid lines, of pairs o oppositely

inclined slots

112A, 114A; 112B, 114B; 112C 114C; etc. Each slot of each pair couples to a standingwave; and each pair of inclined slots produces longitud' nally-polarized emergent energy.

Antenna 110 also has a second set, shown in dotted lines, of pairs of oppositely

inclined slots

116A, 118A; 116B, 118B; 116C, 118C; etc. Each slot of each pair couples to a standing-Wave; and each pair of inclined slots produces longitudinally-polarized emergent energy.

The first set of slots 112-114 has a large spatial coverage (corresponding to the array of slots 92 in FIGURE 5); while the second set of slots 116, 118 has a small spatial coverage (corresponding to the array of slots in FIGURE 5). Thus, when the first set of slots-having the large spatial coverage-is energized by a suitable standing-wave, the antenna acts like a large antenna, and produces a narrow beam. However, when the second set of slotshaving a small spatial coverageis energized by a different standing-wave, the antenna acts like a small antenna, and produces a wide beam.

Thus, antenna of FIGURE 7 is capable of producing both the narrow and

broad beams

96 and 102 of FIG- URE 6. It should be noted however, that in the case of antenna 110, both beams have the same linear polarization. Accordingly, antenna 110 of FIGURE 7 is adapted for providing a selected combination of beamwidth and polarization.

FIGURE 7 also shows another way of producing different standing-waves. One standing-wave is produced by a sorting-plate 119, as previously described. However, a plurality of electronically controlled waveguide switches, such as varactor-diodes 120, takes the place of the previously-described shorting-pins. These varactor-diodes have the characteristic that they can be activated (by means of passing a direct current therethrough) to serve as an effective microwave shorting-plate; or they can be deactivated (by adjusting or reducing the current therethrough) to serve as a matched impedancewhereby the antenna acts as though the varactor-diodes were not in the antenna at all.

Thus, when the varactor-diodes are activated, they have the effect of producing a standing-wave that energizes one set of inclined slots; whereas when the varactordiodes are matched, the physical shorting-plate 119 produces another standing-Wave that energizes the other set of inclined slots.

In FIGURE 7, the varactor-diodes, instead of being located near the end of the antenna, are instead located onehalf wavelength beyond the furthermost radiating aperture; this location providing improved operation of the smaller-number set of inclined slots.

It will be realized that varactor-diodes may be used in the antennas previously discussed. Referring back to FIG- URE 3, for example, varactor-diodes can replace the illus trated shorting-plates; and, in fact, a plurality of suitablylocated varactor-diodes may be used to produce effective shorting-plates at a plurality of locations intermediate to the illustrated shorting-plates. By suitably activating the varactor-diodes, a plurality of different standing-waves can be established; and the emergent energy can therefore be polarized in a wide variety of polarizations.

In addition, a set of varactors may be activated to act as continuously variable phase shifter; whereupon the polarization of the emergent energy will vary continuously through a given range of polarizations.

The previous discussion has shown how the disclosed antenna can provide a beam having a selected combination of beamwidth and polarization. Under some conditions, it is desirable to have two similar but not identical beams; one of the beams to be used for transmitting radar energy, while the other beam is used for receiving echo signals. FIGURE 8 schematically shows an arrangement for achieving this result.

Referring to FIGURE 8, there is illustrated an antenna 140 comprising a symmetrical T-shaped antenna structure; the energy being introduced into the stem-portion 142 of the T, and the horizontal-bar portion 144 of the T having two sets of paired inclined slots of the type previously described. One set of inclined slots is shown in solid lines, while the other set of inclined slots is shown in dotted lines.

When energy is applied through stem-portion 142 to antenna 140, the passive or physical shorting-plates 146 at the end of the horizontal bar of the T establish a continuous standing-wave between them; the standing-wave exciting the set of inclined slots shown in dotted outline in accordance with the previously-discussed principles. Because of the large spatial extent covered by the array of dotted-line slots, the antenna acts as a large antenna that has a narrow-beam transmission pattern.

When it is desired to receive echo signals, both varactordiodes 148 may be activated (by means well understood in the art) whereby they act as effective shorting-plates as previously described; the effective shorting-plates establishing a continuous standing-wave that activates the second set of inclined slots shown in the solid-line slots. The antenna again acts as a large antenna that has a narrow-beam reception pattern.

In order to establish slightly different transmission and reception patterns, each set of slots may have a slightly different arrangement than the other. For example, the slots of one set may be different in size, orientation, or offset, compared with the slots of the other set; so that one set of slots produces a transmission-pattern that is similar but slightly different from the reception-pattern produced by the other set of slots.

Monopulse radar systems use a concept known as sum and difference signals; corresponding to the even and odd distributions, respectively, of a target signal, as described, for example, in Introduction to Monopulse, by Rhoades (published by McGraw-I-Iill, 1959). The application of such concept employs two reception antenna patterns which are severally combined as shown in FIGURE 9, to provide the single long, narrow sum beam 130, shown in solid line and representing the sum of the two reception patterns, the two smaller lobes 132 shown by the dotted lines representing the difference between the two reception patterns.

The above-discussed theory of reciprocity also applies to an antenna that directly produces the sum and difference patterns of FIGURE 9. This means that where, by means of the invention, an antenna transmits a narrow sum beam, its reception-beam will also be narrow; that is, the antenna will be more sensitive to echo signals originating dead-ahead (corresponding to the boresight axis or axis of symmetry of a directional antenna), and will be lesssensitive to echo signals originating off to one side of the boresight axis.

Similarly if the antenna, by means of the invention, is caused to transmit a two-lobed difference beam, the reception response thereof will be sensitive to echo signals originating in such difference beam.

An antenna using the disclosed inventive concept can produce these sum and difference beam patterns; and the symbolic antenna representation of FIGURE 10 shows how this can be done. Here, antenna is similar to those previously discussed, in that it has two sets of inclined slots; one set of slots being shown in solid lines, while the second set of slots is shown in dotted lines.

The antenna 150 of FIGURE 10 produces a singlelobed narrow beam as follows. Varactor-diode 152 is activated to produce an effective shorting-plate, so that the antenna is symmetrical. Energy applied to the antenna coacts with the effective shorting-plate produced by varactor-diode 152 and the physical shorting-plate 154, to produce a continuous standing-wave between them. The standing-wave causes the solid-line slots to be energized, so that each half of the antenna produces a signal that is in-phase with the signal from the other half of the antenna. In this way the antenna produces a single-lobed pattern as described in connection with the previous illustration.

In accordance with the theory of reciprocity, incomingecho signals would enter the slots, and would establish a similar standing-wave. This standing-wave would be coupled to the stem-portion of the antenna; and would rovide sum-signals to utilizing equipment.

If it were desired to transmit the two-lobed difference beam, varactor-diode 152 would be de-activated, or matched (i.e., an applied current to the diode being controlled or adjusted, as required); and diode 155 would be activated to produce an effective shorting-plate. Under these conditions, the antenna would no longer be symmetrical. The left half of antenna 150 establishes a standing-wave that would radiate energy of a given polarization from the dotted-line inclined slots in the left half of the antenna.

However, the right half of the antenna of FIGURE 10 would act in a somewhat dilferent manner. It will be seen that the physical shorting-plate 156 is now three-quarters of a wavelength from the closest dotted-line slot. This arrangement would establish a standing-wave that would cause the dotted-line slots of the right half of the antenna to radiate energy that is out-of-phase (anti-phase) compared with the energy that would be radiated by the dotted-line slots of the left half of the antenna. Hence, the mutually anti-phase energy radiated from the two halves of antenna 150 would co-act to produce the twolobed ditference pattern 132 of FIGURE 9.

In accordance with the theory of reciprocity, incoming echo signals received by the antenna of FIGURE 10 would enter the slots, and would establish two similar anti-phase standing-waves. These anti-phase standing-' 1 ll ence manner-the received echo signals appearing at the stem portion in a manner determined by the instantaneous standing-wave, as established by the states of the varactordiodes.

In a preferred application of such arrangement, the varactor diodes would be gated in synchronism with the system trigger of a pulsed radar to provide a sum transmission pattern, and then alternately-gated in such combination, as to provide sampled sum and difference signals for amplification by a single channel amplifier, the output of the amplifier being switched between two output terminals (by electronic gating means well-known in the art) in synchronism with the gating of the varactors in order to separate the sum and difierence signals into two several and distinct monopulse receiver outputs. In this way, monopulse receiver gain tracking errors are avoided due to the time-shared use of a single common amplifier for the sum and difierence receiver signals. The arrangement of FIGURE 11 shows a time-duplexing arrangement for severally processing sum and difference antenna pattern signals at the antenna.

The antenna 160 of FIGURE 11.is similar to that of FIGURE 10, in that the antenna inherently has sum and difference patterns that are controlled by the state of varactor-diodes 152, as previously explained. In FIG- URE 11, however, a four-port microwave hybrid T or magic tee 162 is used, instead of the simple T of FIG- URES 9 and 10; the magic tee having two ports or

openings

171 and 172 thereof coupled to the antenna, a third port 163 symmetrically cooperates with the first two

ports

171 and 172 as to represent a sum port while a fourth port 164 is symmetrically cooperated with the first two as to represent a difference port.

The construction and arrangement of magic tees is well known in the art, being described for example at' page 572 in volume 12 of the Radiation Laboratory Series, Microwave Antenna Theory and Design, by Silver (published by McGraw-Hill, 1949).

Where the varactor diodes 152 are switched to alternate states a respective one of the two slotted arrays are coupled to the waveguide section 160, as previously explained. Hence, the beam pattern of the antenna of FIG- URE 11 is alternately a sum and difierence beam pattern.

Where varactors 152 are switched to a first state corresponding to a sum pattern during the application of a microwave energy pulse to sum port 163 of T 162, then a sum pattern of energy is radiated from the antenna of FIGURE 11. If the varactors 152 are maintained in said first state during the receiving interval subsequent to the occurrence of the transmitted pulse, then the sum receiving pattern provided by each of the left and right-hand sections of the slotted waveguide element of FIGURE 11, as applied to the corresponding first and second port of magic tee 164, will be ditierentially combined at the output of the difference or receiving port 164 to provide a mononpulse ditference signal.

If, however, the varactors 152 in FIGURE 11 are switched to a second state corresponding to a difierence antenna pattern, during the receiving interval, then the difierence pattern provided by each of the left and righthand sections of the slotted waveguide elements of FIG- URE 11 (as applied to the corresponding ports of magic tee 162) Will be differentially combined at the output of receiving port 164 to provide a monopulse sum signal.

Where the state of varactors 152 is cyclically alternated during a receiving interval of an associated radar system (not shown), then the antenna of FIGURE 11 may be employed as a time-shared monopulse receiving antenna for use in cooperation with a single channel mononpulse receiver. Further, where the varactors are maintained in the first state during the pulsing interval of a radar transmitter (not shown) in response to the system trigger thereof and then cyclically alternated between the first and second states during the receiving interval of the radar system, the antenna may be employed as a dup- 12 lexed, time-shared antenna in a pulsed radar system having a time-shared single channel monopulse receiver.

While the foregoing explanation has been given in terms of antennas comprising rectangular waveguides that have standing-waves produced therein, the present inventive concept is also applicable to circular, elliptical, or other cross-sectional waveguides that have standingwaves produced therein. For example, FIGURES 12 and 13 show a circular and an elliptical waveguide respectively, these waveguides having slot-pairs similar to those of a previous illustration. In the structures of FIGURES 12 and 13, the slot-pairs are spaced in accordance with the previous explanations; and suitably-positioned shortingplates, varactor-diodes, or the like, produce desired standing-waves that cause energy to escape through the slots.

Because of the difficulty of illustrating the complex standing-Waves that exist in these types of waveguides no detailed explanation will be given; but use of the abovedescribed principles and types of slots will convert waveguides of other than rectangular cross sections into antennas capable of producing various types of polarization and beam patterns.

Accordingly, it is to be appreciated that an improved antenna has been described, comprising means for providing selected combinations of polarization and beam patterns.

Although the invention has been illustrated and described 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. An antenna comprising an apertured waveguide having two sets of perpendicularly-oriented apertures, the apertures of the first set coacting with the apertures of the second set to form aperture-pairs; means for producing a standing-wave in said waveguide, and causing energy to escape from said aperture-pairs in an ellipticallypolarized manner; and

voltage-sensitive means for selectively changing said standing-wave to effect a selected ellipticity of said escaping energy.

2. An antenna comprising an apertured waveguide having a first set of inclined slots, and a second set of inclined slots;

switchable waveguide impedance means for establishing a standing-wave operative to couple to an alternate one of said first and second sets of inclined slots for causing an alternate one of said sets of inclined slots to be associated with a corresponding one of a first and second beam-pattern.

3. An antenna comprising an apertured Waveguide having a first set of inclined slots, a second set of inclined slots, and a third set of inclined slots;

first means for establishing a standing-wave capable of coupling to said first set of inclined slots, and causing said first set of inclined slots to be associated with a beam of a first beam-pattern; second means for establishing a standing-wave capable of coupling to said second set of inclined slots, and causing said second set of inclined slots to be associated with a beam of a second beam-pattern; and

third means for establishing a standing-Wave capable of coupling to said third set of inclined slots, and causing said third set of inclined slots to be associated with a beam of a third beam-pattern.

4. An antenna comprising an apertured Waveguide having a first set of inclined slots, a second set of inclined slots, and a third set of inclined slots;

first means for establishing a stand-wave capable of coupling to said first set of inclined slots, and causing said first set of inclined slots to be associated with a beam of a first beam-pattern;

second means for establishing a standing-wave capable of coupling to said second set of inclined slots, and causing said second set of inclined slots to be associated with a beam of a second beam-pattern; and

third means for establishing a stand-Wave capable of coupling to said third set of inclined slots, and causing said third set of inclined slots to be associated with a beam of a third beam-pattern;

a magic-tee; and

means for coupling one port of said magic-tee with the set of slots associated with one of said beam patterns, and for coupling another port of said magictee with the sets of slots associated with the other two beam-patterns.

5. In a time-shared, single channel microwave monopulse receiving antenna the combination comprising A microwave feed having a first and second slotted array,

Said first slotted array being responsive to an even distribution of received energy corresponding to a monopulse sum signal;

Said second slotted array being responsive to an odd distribution of received energy corresponding to a monopulse difierence signal;

Voltage-sensitive impedance coupling means adapted to be connected to a source of a switching signal for alternately coupling said first and second arrays to said microwave feed.

6. In a duplexing microwave antenna for transmitting and receiving radar energy the combination comprising A four-port microwave hybrid tee,

A first and second port of said tee adapted to be connected to a radar transmitter and receiver respectively;

microwave-Wave feed means having A first and second slotted array adapted for generating a monopulse sum and difierence a11- tenna pattern respectively, said microwave feed means comprising a first and second waveguide section coupled to a third and fourth port respectively of said hybrid tee;

variable microwave impedance means for alternatively coupling each of said arrays to said microwave feed, whereby said antenna is enabled to provide alternatively .a monopulse sum pattern in response to transmitted energy applied to said first port of said hybrid tee and a monopulse sum pattern in response to a received energy output occurring at said second port of said hybrid tee.

7. A cross-polarized linear array microwave energy antenna including,

a rectangular waveguide including means for applying microwave energy thereto,

means for providing a standing wave pattern within said waveguide having the maximum transverse current amplitudes occurring at position of minimum longitudinal current amplitudes,

14 at least one series slot in said waveguide and positioned substantially /2 guide wavelength points of said standing wave pattern, developed by said means for providing, at least one shunt slot in said waveguide and positioned substantially at /2 guide wavelength points of said standing wave pattern, developed by said means for providing, and

means for selectively shifting the standing wave pattern by an amount equal to an odd number of quarter of guide wavelengths of the energy in said waveguide.

8. A microwave antenna providing selected combinations of polarization and beamwidth of an emergent beam and having a microwave feed and comprising At least two slotted array-s fed at one extremity thereof by said feed; and

Voltage-sensitive microwave impedance means coupling said arrays to said feed, and comprising passive microwave shorting means beyond a second extremity of said arrays and spaced apart therefrom and voltage sensitive microwave phase-shifit means interposed between said second extremity of said arrays and said passive shorting means.

9. A linear array microwave energy antenna including, a waveguide including means for applying microwave energy thereto; means for providing a standing wave pattern within said waveguide having the maximum transverse current amplitudes occurring at positions of minimum longitudinal current amplitudes;

at least one series slot in said waveguide and positioned substantially at /2 guide wavelength points of said standing wave pattern, developed by said means for providing;

at least one shunt slot in said waveguide and positioned substantially at /2 guide wavelength points of said standing wave pattern, developed by said means for providing; and

means for selectively shifting the standing Wave pattern by an amount equal to an odd number of quarter of guide wave-lengths of the energy in said waveguide.

References Cited UNITED STATES PATENTS 2,479,209 8/ 1949 Chu 343771 2,679,590 5/ 1954 Riblet 343771 2,764,756 9/ 1956 Zaleski 3437 7 1 2,771,605 11/1956 Kirkman 343-771 2,982,960 5/196 1 Shanks 34*376 7 6,005,984 10/1961 Winder et M. i 3437'71 FOREIGN PATENTS 760,388 10/ 1956 Great Britain.

HER-MAN KARL SAALBACH, Primary Examiner.

-E-LI LIEBERMAN, Examiner.

M. NUSSBAUM, Assistant Examiner.

Claims

2. AN ANTENNA COMPRISING AN APERTURED WAVEGUIDE HAVING A FIRST SET OF INCLINED SLOTS, AND A SECOND SET OF INCLINED SLOTS; SWITCHABLE WAVEGUIDE IMPEDANCE MEANS FOR ESTABLISHING A STANDING-WAVE OPERATIVE TO COUPLE TO AN ALTERNATE ONE OF SAID FIRST AND SECOND SETS OF INCLINED SLOTS FOR CAUSING AN ALTERNATE ONE OF SAID SETS OF INCLINED SLOTS TO BE ASSOCIATED WITH A CORRESPONDING ONE OF A FIRST AND SECOND BEAM-PATTERN.