US 2982960 A
Description (OCR text may contain errors)
`Maly 2, 1961 H. E. sHANKs 2,982,960
ARBITRARILY POLARIZED sLoT RADIATOR Fi1ed Aug. 29, 1958 www Vthe 'two modes and so disturbs the pattern.
United States Patent 1@` aan ii-iii 2,982,960 1 ARBITRARILY PoLAiuzED ysLornAinAroR Howard E. Shanks, South Pasadena, Calif., assignor to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware I Filed Aug. 29, 19,58., Ser. No.,758,021"
5 Claims. (Cl. 343-767) The present invention relates to a slot radiator and more particularly to yan arbitrarily polarized slot radiator. 1
Electronically controlled beam formation has been simplified by the development of xed position antenna arrays providing variable polarization of radiating elements to establish the desired patterns. One system coinprises a section of rectangular waveguide having a plurality of normally non-radiating slots with associated internally mounted adjustable irises. By suitable control of the transverse position of the irises the current distribution within the waveguide is distorted so that the slots radiate and, by separate control of the phase and amplitude of radiation from the rpective slots, linear polarization results to provide desired scanningv patterns. This type antenna array is readily adapted for electrical control by including ferrite materials as the inductive elements of the irises with electrical control `of the magnetization of such elements to vary the polarizationr'of radiation from the slots.
Another type of antenna arrayfor obtaining similar results has been developed, but requires moving parts to accomplish variable polarization. In brief, this type of antenna comprises a rectangular waveguide having a plurality of spaced-apart inclined slots in a narrow wall which normally radiate and a transversely disposed parallel-plate transmission line into which the waveguide feeds energy.
The excitation of the transmission line is in two modes, namely, two linearly polarized modes, and the combination of the two modes at the output of the transmission line establishes the polarization. Since'each mode is propagated with a different phase velocity within the transmission line,rthe distance between the feed and the output provides a means of varying polarization over the length of the output and thereby the pattern of radiation. `Thus, the position of the rectangular waveguide within the parallel-plate transmission line' is made physically variable with respect to the output. To maintain a specilic pattern of radiation with this type antenna requires an extremely stable source of microwave energy, particularly with respect to frequency, as a'ny change in the excitation aliecting the phase velocity of the modes results in diiferent changes in the respective value for Fine mechanical adjustments are then required to overcome such phase velocity sensitivity and these adjustments decrease the scope of utility of the antenna where the environment precludesv .the opportunity or desirability of correcting the resultantpattern of radiation.
The present invention comprises, in brief, a square waveguide having at least one pair of transversely crossed slots for propagating microwave energy in two independentl space-orthogonal modes. The two modes are the same and have the same frequency so that each mode is propagated with the rsame phase velocity as the other and phase velocity insensitivity results. Variable polarization of radiation from the pair of crossed slots is obslot. mode 16 of energy in waveguide 11, it is seen that one slot 2 Y tained by control of the relative phase andramplitude of the two space-orthogonal modes.
It is therefore an object to provide a new improved arbitrarily polarized slot radiator. v
AnotherV object is to -provide a slot radiator excited by two space-orthogonalpmodes of microwave energy having same phase velocity. A g
Still another object is to provide an arbitrarily polarized slot radiator excited by twospace-orthogonal modes of microwave energy having the same phase velocity with the relative phase `and amplitude of the modes being variable.
A further object is to provide an antenna array having 'a plurality of spaced-apart radiating elements with arbitrary polarization.v
Other objects and advantages of the invention will be apparent from the following description and claims considered together with the accompanying drawing in which:
Figure 1 is a schematic perspective View of an arbi-V trarily polarized slot radiator with current patterns shown for the modes of excitation;
Figure'Z is a series of vectors indicating polarization for various phase relationships of mode excitations as shown in Figure l; and
Figure 3 is a perspective view of an antenna array having a plurality of slot radiators in accordance with Figure l. n Referring to Figure 1 in detail, there is schematically shown a section of rectangular waveguide 11 having symmetrically related crossed slots 12 and 13 through one wall 14 thereof. One slot 12 is disposed along the longitudinal centerline of the wall 14 and the other slot 13 is .transversely disposed'with respect to this wa'll with both slots having the same center. For simplicity of description'and illustration both slots 12 `and 13 are dimensioned for resonance at the frequency of microwave energy propagated through waveguidell, however, this is not an absolute requirement for operation, as will be set forth hereinafter. l
In accordance with the present invention, two independent space-orthogonal dominant TEM modes of microwave energy, as represented by current distribution patterns 16 and-17, respectively, are suitably coupled to one end of waveguide 11 for propagation thereby. As is well known a slot in ia ywaveguide wall does not couple energy from the waveguide unless a component of the current distribution is transverse to the narrow dimension of the Thus, considering the current distribution of one 12 will Vradiate While the other slot 13 will not radiate.
In further detail,.it is ,to be noted that the current flowof mode 16. is transversely from side to side of wall 14 so that current components are principally perpendicular to slot` 12 across the narrow dimension while being principally parallel to the longitudinal dimension of slot 13.
Now, `considerin'g the current distribution of the other Y radiate.
The resultant radiation from crossed slots -12 and 13 is then a vectoral .sum of electrical elds in the slots and several representative relationships are shown in YFigure Z. Using mode 16 as a reference and with the two rnodes adjusted-to provide equal values of maximum Aelectrical field at the respective slots 12 and 13, then Figure 2a illustrates the orthogonal condition of the elec- 3 c i trical fields, E12 and E13, established at the slots. When' the two modes 16 and 17 are in phase, the resultant radiation is linearly polarized and lies along the 45 degree vector ER, as shown in Figure 2b. For the condition where the two modes are exactly out of phase,fthe re sultant polarization is again linear and rotated by `90 degrees 1with respect to the in-phase condition, as indicated by vector ER in Figure 2c. The final representative condition is obtained when the two modes have a phase difference of 90 degrees and circular polarization results, as indicated by the vector ER and the curved arrow 21 of Figure 2d.
For phase differences of the modes 16 and 17, which lie between those illustrated above, elliptical polarization of the resultant radiation occurs. Thus, an arbitrarily polarized slot radiator is provided and, since the wave guide 11 is square, both modes 16 and 17 are propagated with the same phase velocity to obviate any inherent sensitivity to such factor. While symmetrically crossede slots 12 and 13 have been illustrated and described, it is to be noted that a'similarly located circular aperture 18 will operate in the same manner to achieve arbitrary `polarization of radiation. Also, with respect to the foregoing description, it was stated that the two` modes 16 and 17 were adjusted to provide equal maximum values of electrical field at the crossed slots 12 and 13 for purposes of simplicity and it will now be readily apparent that variations in linear polarization occur for a condition of fixed phase relationship, but with changes in the relative amplitude of the two modes.
In operation one end of waveguide 11 is suitably coupled to a conventional source of microwave energy (not shown), or to two sources suitably synchronized to operate at the same frequency, to excite two independent space-orthogonal modes for propagation by the waveguide. One mode 16 excites the longitudinally extended slot 12 and the other mode 17 excites the transversely extended slot 13. The excited electrical fields at the two crossed slots 12 and 13 then combine to provide radiation which is polarized in accordance with the relative phase and amplitude of the two modes.
A single pair of crossed slots 12 and v13 in the wall of square waveguide l11 may readily be used as a variable 'mode-transition coupler between two sections of waveguide and, also, may serve as one element of an antenna array. With respect to the latter, reference is made to the perspective view of an antenna array as illustrated in Figure 3. Thus, a section of square waveguide 31 has a plurality of spaced-apart pairs of symmetrically crossed transverse slots 32-38 along the center line ofone wall 39 of the waveguide. To excite oneof the two spaceorthogonal modes, as indicated by the electrical field vector l41, a section of rectangular waveguide.42 is mounted transversely from wall 39 of waveguide 31 with the broad walls thereof extended across wall 39. By suitably connecting a conventional source of microwave energy to port 43 of waveguide 42, such energy is propagated in the dominant TEM mode, as indicated by electrical field arrow 44, to square waveguide 31.
Similarly, to excite the other orthogonal mode, as
indicated by electrical field arrow 46, a second section of rectangular waveguide 47 is mounted transversely from wall 48, which is adjacent to the first referenced wall 39 with the broad walls thereof extended acrosswall 48. Thus, with port 49 of waveguide 47 suitably connected to the previously-mentioned conventional source, or to a second source synchronized for the same frequency, energy is propagated in the dominant TEm mode, as indicated by` electrical field vector 5 1, to square waveguide i of the summation of radiation from the independently eX- cited series of crossed slots 32-38. Now, by varying the relative phase or amplitude of the two modes of the energy source, different patterns of radiation, both linearly polarized and circularly polarized, are obtained. Suitable programming of the aforementioned variations then provides a variable polarized beam and such programming may be readily accomplished by electronic means, such as well-known computers of various types. Since the phase velocity for both modes is the same, the frequency of the source may also be altered within the values which the waveguides 31, 42, and 47 support, wthout further adjustments.
For some patterns of radiation it may be desirable to build into the array a specific variation in amplitude from end to end. This is readily accomplished by cutting the slots larger at one end than the other with graded slot dimensions between the two extremes. It will also be apparent that three-dimensional beam formation can be obtained by mounting several radiator arrays as described in the foregoing in parallel relationship and suitably controlling the polarization of each array to obtain such type of operation.
While the salient features of the present invention have been described with respect to a particular embodiment, it will be readily apparent that numerous modifications may be made Within the spirit and scope of the invention and it is therefore not desired to limit the invention to the exact details shown except insofar as they may be set forth in the following claims.
What is claimed is:
1. 1u an arbitrarily polarized radiator, the combination comprising a section of square waveguide for propagating 4two independent spaceorthogonal modes of microwave energy, means coupled to said waveguide for exciting said two modes, and at least one pair of symmetrically crossed transverse slots in a wall of said waveguide, said crossed slots having a common center with one slot cxtending along the center line of such wall for separatev excitation by said modes, whereby polarization of radiation from said slots depends upon the relative phase and amplitude of said modes of energy.
2. In an arbitrarily polarized radiator, the combination comprising a section of square waveguide for propagating two independent space-orthogonal modes of microwave energy, a pair of rectangular waveguides for propagating microwave energy in the dominant mode mounted transversely on said square waveguide to respectively excite said two space-orthogonal modes, and at least one pair of symmetrically crossed transverse slots in a wall of said waveguide, said crossed slots having a common center with one slot extending along the center line of such wall for separate excitation by said modes, whereby polarization of radiation from said slots depends upon the relative phase and amplitude of said modes of energy.
Y3. In an arbitrarily polarized radiator, the combination comprising a section of square waveguide for propagating two independent space-orthogonal modes of microwave energy at the same frequency, a first section of rectangular waveguide coupled to said square waveguide to excite one of said two modes for propagation thereby, a second sec tion of rectangular waveguide coupled to said square waveguide to excite the other of said two modes for propagation thereby, and at least one pair of symmetrically crossed transverse slots in a wall of said waveguide, said crossed slots having a common center with one slot extending along the center line of such wall for separate excitation by said modes, whereby polarization of radiation from said slots depends upon the relative phase and amplitude of said modes of energy. i
4. In an arbitrarily polarized radiator, the combination comprising a section of square waveguide for propagating two independent space-orthogonal T1301 modes of microwave energy at the same frequency, a first section of rectangular waveguide mounted transversely on one wall of said `square waveguide with the broad walls extended across said one Wall for propagating energy in a TEM mode to excite one of said two modes in said square waveguide, a second section of rectangular waveguide mounted transversely on a second wall of said square waveguide adjacent said one wall for propagating energy in a TEM mode to excite the other of said two modes in said square waveguide, and at least one pair of symmetrically crossed transverse slots in a wall of said waveguide, said crossed slots having a common center with one slot extending along the center line of such slotted wall for separate excitation by said modes, whereby circular or linear polarization of radiation from said slots is obtained dependent upon the relative phase and amplitude of Said modes of energy.
5. In an arbitrarily polarized radiator, the combination comprising a section of square waveguide for propagating two independent space-orthogonal TEM modes of microwave energy at the same frequency, a rst section of rectangular wave guide mounted tarnsversely on one wall of said square waveguide with the broadwalls extended across said one wall for propagating energy in a TEM mode to excite one of said two modes in said square waveguide, a second section of rectangular waveguide mounted transversely on a second wall of said square waveguide adjawith one slot of each pair extending along the center line of such wall, whereby the center-line slots of each pair are excited by one of said modes and the transverse slots are excited by the other of said modes to provide a beam polarized in accordance with the relative phase and amplitude of said two modes of energy.
References Cited in the file of this patent UNITED STATES PATENTS 2,557,951 De Rose et al. June 26, 1951 2,629,052 Iams Feb. 17, 1953 2,679,590 Riblet May 25, 1954 2,825,031 Parisi Feb. 25, 1958 2,851,681 Cohn Sept. 9, 1959 2,908,906 Kurtz Oct. 13, 1959 FOREIGN PATENTS p 140,425 Australia Mar. 12, 1951