US 3089102 A
Description (OCR text may contain errors)
May 7, 1963 H. RowLAND 3,089,102
DUAL-POLARIZED HORN Filed April 25, 1960 2 Sheets-Sheet 1 FIG.;
Fl G 3 FIG. 4
BY Howard 7.- 17o w/ana' farla, am@ M ATTORNEYS May 7 1963 H. J. RowLAND 3,089,102
DUAL POLARIZED HORN Filed April 25. 196C 2 sheets-sheet 2 BY /vowara'fow/and @2; ma M ATTORNEYS United States Patent O v 3,089,102 DUAL POLARIZED HORN Howard J. Rowland, Egypt, Mass., assignor to Electronic Specialty Co., a corporation of California Filed Apr. 25, 1960, Ser. No. 24,425 6 Claims. (Cl. 333-6) This invention relates generally to antennas and more particularly concerns antenna systems operating with radio waves of complementary polarizations.
For many years heretofore, there has been considerable effort devoted to the development and improvement of diversity communication systems and tropospheric scatter communication sys-tems, both within the ambit of military communication requirements and the requirements of the commercial field. These efforts have caused scientists working in the U.H.F. (ultra high frequency) and V.H.F. (very high frequency) areas of electromagnetic propagation to re-focus their thinking upon one of the more difficult and, until now, unsatisfactorily solved difficulties relating to the propagation and reception of energy of different frequencies land different polarizations using the same basic radiation structure.
Dual polarization antennas capable of operating at a plurality of frequencies generally are not new in the Iantenna. field. The art discloses that horn-type antennas have been used to receive or transmit dual polarized signal waves in separated lfrequency bands. This has been accomplished in the prior art by employing energizing antennas, or pick-up means, depending upon whether the horn is used for transmission or reception, judiciously positioned near the end of a flared waveguide. The two signals of different frequency are radiated or received with their polarizations crossed in order to eliminate interaction. The horn-like structure is common to both energizing lantennas or pick-up means. It is not uncommon that the horn-like structure will respond differently to the two frequency bands. When this is the case, it means that for one frequency band the radiation pattern will have Ia given shape yand for the other frequency band the radiation pattern will be different, sharper or broader, than the pattern of the first signal due to la difference in the frequency response of the horn. 'Ihis is a decided disadvantage in `certain communication systems and particularly in certain radio diversity systems where it is desired to have the signals of the two polarizations and therefore the two frequencies correspond yas closely as possible in their radiation patterns so that substantially the same area is covered by each signal. Furthermore, placing the dipole radiating elements in the mouth of the horn presents a difficult mounting problem; once mounted, these elements are flimsy and definitely limited in powerhandling capacity compared to the radiation from the waveguide.
Perhaps the most elementary of the proposals made for simultaneously transmitting or receiving radio waves of different electric-vector polarizations is the use of a plurality of dipole or other linear antennas, one oriented along each direction of polarization. To generate or receive cross polarized waves, v-two adjacent perpendicularly oriented antennas have been employed. But, because of the physical juxtaposition of such antennas, a certain amount of cross polarization reception or transmission will occur. Some of the horizontally polarized energy, as an illustration, may induce a voltage in the vertically polarized antenna and vice versa. This is particularly true in the ultra high frequency and microwave ranges where even the thickness dimension of an antenna may be an appreciable portion of the wave length `and thus capable of intercepting cross polarization energy. Cross coupling is also increased in a case where 3,089,102 Patented May 7, 1963 ICC a common transmission system is employed and especially in waveguide microwave systems where the cross coupling could exist due to inadvertently generated higher order modes.
While this is tolerable in some systems, there are other occasions where it is entirely undesirable. For example, it may be necessary to receive in a radio receiver a weak polarized radio wave signal in the presence of a strong transmitted differently polarized signal. Attempts, therefore, must be made to minimize cross polarization effects and feedback through careful construction, orientation and symmetry of the -antenna parts of a system. The conventional horn design techniques have not solved the problem in cases where there are very stringent system requirements as to the amount of ,allowable cross coupling, such as where the coupled transmitted signal is of the order of magnitude of the amplitude or greater than the amplitude of the received signal itself. Of course, the horn is only part of the system-in conjunction with duplexer elements-which provide for signal separation; but a well designed horn can provide nearly half of the required separation.
An object of the present invention, accordingly, is to provide a new and improved antenna `system in which cross polarization effects are minimized.
An additional object of the invention is lto dispense with discontinuities in the horn which are presented by dipole elements in many conventional units.
Another object of the invention is to provide a dual polarization antenna having radiation patterns for each polarization which have coincident focusing points.
Still another object of the invention is to provide a dual polarized horn which can carry maximum power in both polarizations.
A furthe-r object of this invention is to provide a dual polarization antenna which is structurally simple and rigid, and in which the close tolerance elements are physically integrated with the rigid physical structure of a waveguide antenna system.
Basically, the present invention employs two lengths of rectangular waveguide, one oriented horizontally, the other oriented vertically 4along their elongated axes meeting angularly in a V and Working into a section of waveguide which is essentially square, having approximately the larger dimension of the guides on each of the four sides. The square waveguide thus is capable of propagating torthogonally polarized energy from either rectangular waveguide. From the intersection of the V section segment, which has at the outer face thereof a square configuration, there extends a length of waveguide connected -to the outer face `and having the same square configuration; to this length of `square waveguide is connected in turn `a horn or comparable radiating structure associated with the wavegiide system.
More specifically, two sections of rectangular waveguide are caused to lintersect in a V, each length of guide being 4oriented in a horizontal and vertical position respectively; that is, a broad wall of a vertically oriented section intersects a narrow wall of Isimilar waveguide, both sections being on substantially the same plane, thus forming `a V-shaped unit. The angular intersection and termination of the two guides is carried into a square section of waveguide, the dimension of which is a function of the highest frequency 'to be propagated.
The angle 0 at which the horizontally oriented section of waveguide intersects the vertically oriented section is the angle at which the projected opening of the former in the latter is exactly one-half the dimension of a side of the square interface at the interconnection. For example, with standard RETMA, VVR-designation waveguide, the narrow dimension is exactly half the broad, critical dimension. If the broad dimension equals the dimension of the side of the square, then the angle betwen the two lengths of waveguide required to create the square is precisely 30 displaced from a right angle intersection of the two lengths.
The lengths of the horizontal, vertical and square sections are uncritical except in so far as impedance matching for low standing wave ratios over the operating band requires the placement of matching probes at certain distances from the intersection face.
The energy propagated from associated transmitters through either the horizontal or vertical waveguide will be coupled to a tapered horn or comparable element through the square section of waveguide. Feedback between vertical and horizontal sections has been found to be no less than 30 db down and is more generally in an order of magntude of 50-60 db down. It should be noted that the power output from either polarization is not limited by dipoles mounted in the horn. Moreover, signicantly greater band widths at lower voltage standing wave ratios (VSWRs) can be readily achieved through judicious placement of matching probes within the three sections.
Other objects as well as features of the invention will be more clearly understood from the detailed discussion which follows in which:
FIG. 1 is a top plan view of a dual polarized unit ernbodying the features of this invention;
FIG. 2 is a side elevation view of the device of FIG. 1;
FIG. 3 is an end view of the device looking toward a disk which forms the horn element;
FIG. 4 is a detail in perspective taken on the line 4 4 of FIG. 2;
FIG. 5 is a top plan view of an alternative embodiment of the invention before matching elements and coupling members are assembled;
FIG. 6 is a side elevation view of the device shown in FIG. 5;
FIG. 7 is an end view of the waveguide section shown in FIG. 5 looking toward the radiating end of the antenna;
FIG. 8 is a detail in perspective taken on the line 8 8 of FIG. 6.
Referring to FIGS. 1-3, the structure embodying this invention is generally designated at 8. In its basic embodiment, it comprises two lengths of angularly connected waveguide, 10 and 12, which form a V, and a third waveguide 14 which is connected to the V to form a non-symmetrical Y. The two waveguide lengths 10 and 12 intersect with their axes of propagation in a common plane but with waveguide 10 oriented to propagate a horizontally polarized wave while waveguide 12 is rotated 90 relative thereto for propagating a vertically polarized wave.
As shown in FIG. 1, the length of rectangular waveguide 10 diverges at 16 along its non-critical, narrow dimension 18 into an opening at 20. The length 22 of this divergence 16 has a dimension comparable to the broad, critical width 24 of the waveguide section 12. The surface 26 of the diverging narrow wall 28 has a rectangular aperture 30 therein at which the other section 12 of the waveguide is secured by welding or any other suitable means to form the non-symmetrical V. FIGS. 3 and 4 in particular show the complementary axial displacement of the two sections 10 and 12 at their intersection 20.
Referring to FIG. 4 particularly, it will be noted that the intersection is substantially square. The dimension 32 of the square waveguide section 14 is a function of the highest frequency at which it is desired to operate; the dimension of the diagonal of the square 20 must be, in terms of wave lengths, substantially equal to or less than the wavelength of the highest frequency which it is proposed to pass through the network 8.
One consideration which experiments have indicated to be of some importance is the need for close tolerances in the precise angular displacement of the two waveguide sections 10 and 12. For optimum results, the 90 relationship between the two waveguides 10 and 12 should be held within 030 of arc. Similar close tolerances are important in the location of the rectangular opening 20 and in the mounting of waveguide section 12 in that opening. Here, tolerances of .015 are sought for the precise location of the waveguides in respect to each other. Both of these purely physical and mechanical requirements bear on the critical necessity that the electric fields within the two waveguide lengths 10 and 12 must be disposed in substantially perpendicular alignment. It should be clearly emphasized, however, that once these mechanical tolerances are satisfied by careful alignment and construction, the unit 8 is mechanically extremely rugged; when it is integrated with an antenna and other associated waveguides, the entire structure is rigid and considerably less susceptible to disorder in actual use than any dual polarization units known.
A more extensive discussion is in order regarding the angle at which the vertically oriented waveguide 10 and the horizontally oriented waveguide 12 intersect. Irrespective of the size of waveguide employed, the angle 0 of divergence of the broad surface 32 and narrow surface 26 of waveguide section 10 into an open face 20 is that angle which causes the interface 20 to be a square. As shown in FIG. l, angle 0 must be such that dimension B equals dimension A. Standard WR designation RETMA waveguide has narrow walls which are one-half the dimension of the broad walls. If the square section has the same dimension as the broad wall of standard waveguide, then the angle of divergence 6 is 30. Experimental results have shown that this angle of intersection 0 is applicable to all of the various standard RETMA rectangular waveguide designations.
In the embodiment illustrated in FIGS. 1-4, the proposed application required a band width of 730 Mc.1000 Mc. The cutoff frequency of WR 975 standard rectangular waveguide being well below 730 Mc., this size would be suitable. As already noted, however, the square interface 20 at the intersection of waveguides 10 and 12 must have a diagonal which does not exceed the wave length of the highest frequency to be propagated, in this case, 1000 Mc. 0:30 cm.). Thus the diagonal of the square 20 may equal but not exceed 30 cm. or 11.8. Therefore, the dimension of a side of square 20 must not exceed 8.35. The broad dimension 24 of waveguide 10 accordingly tapers from the standard 9.75 at 34 to 8.3" at 20. This taper is indicated generally at 16 in FIG. 2. Similarly, the narrow face 28 tapers, as indicated in FIG. 1 at 36 so that standard WR 975 waveguide can be used for section 12. In this embodiment shown in FIGS. 1-4, for the projected opening B to equal A the angle 0 is required to be approximately 25.
It is well understood by those skilled in this art that any discontinuity'or intersection such as is involved in Y-connection of this invention requires impedance matching consideration. Therefore, capacitive matching stubs 38 are provided in waveguide sections 10, 12 and 14. The physical length of each of these sections is not critical except Ifor the proper location of the stubs 38 in respect to the interconnection junction of the three sections.
As is well known, the need for impedance matching is directly related to the broad band width requirements of this application. Except for properly locating the matching stubs 38, the three elements 10, 12 and 14 of the Y unit 8 can be of any length required by the particular application.
With the unit 8 oriented as shown, it is adapted to transmit or receive radio waves of complementary polarization. Appropriate receiving or transmitting apparatus, not shown, may be connected to the waveguide sections 10 and 12 in a conventional manner to launch or absorb electromagnetic energy, for example, in the TEM mode.
The manner in which this construction substantially eliminates cross-polarization effects between radio waves of electric-vector polarization normal to the respective perpendicularly oriented broad waveguide walls will now be explained. Radio energy in the horizontally oriented section 12 which is polarized parallel to the axis of the narrow walls is directed toward the intersection 20 of the square waveguide section 14 and the vertically oriented section 10. With two paths available, the route into the vertically oriented section is seen to have an impedance considerably higher for the vertically polarized energy than the route through the square waveguide section 14. The vertical waveguide section 10 presents its narrow dimension 18 to the electric waves launched from the horizontal section 12. The dimension 18 is well below cutoff at the propagated frequency. On the other hand, the dimension 32 of the square waveguide 14 toward the radiating end 40 of the unit 8 is comparable with the propagating dimension 24 of the horizontal waveguide section 12. The isolation of the vertical section has been found to be no less than 30 db and generally in an order of 50-60 db.
Turning now to FIGS. 5 and 8, there will be seen another embodiment of the invention using a larger waveguide. The primed numerals designating the various elements correspond with the numerals of FIGS. 1-4. In this unit 8', standard RETMA WR-2100 waveguide is employed. The upper frequency of the required operating band width is such that the broad dimension 24 of the standard guide is the same as the side of the square section. No taper is required, therefore.
In this larger size embodiment of the invention, it is a simple matter of mechanical convenience to Abring the vertically oriented section 10 around in a short bend 42 adjacent the horizontal section 12'; but the operation of this horn 8 is substantially identical with that described previously.
Clearly, the principles of this invention may be applied to any size of waveguide in a manner explained in the foregoing description. While it has been convenient to describe the interconnections as a V or a Y, it is evident that the arms of the Y may be bent as required providing the criteria of interconnection are preserved.
Undoubtedly other variations of the preferred embodiment will occur to those skilled in this art, and it is intended, therefore, that the invention be contemplated within the spirit and ambit of the claims rather than the specific examples described.
1. Apparatus for passing complementarily polarized electromagnetic waves, said apparatus comprising first and second lengths of rectangular waveguide having broad walls and narrow walls and a common connection, one
of said broad walls of said first length diverging from the opposite substantially straight broad wall at an angle to form a substantially square open face, said diverging broad wall having a centrally located rectangular aperture the narrow dimension of which is centered in said diverging broad wall for connecting an end of said second length of waveguide to said diverging portion whereby said first and second lengths of waveguide form a V connection, the `cross-sections of said first and second lengths being disposed at a right angle.
2. Apparatus as defined in claim l, the diagonal dimension of said square face being equal to or less than the wave length of the highest frequency to be passed and with the sides of said square longer than the cutoff dimension for the lowest frequency to be passed.
3. Apparatus as defined in claim 1, further including a length of square waveguide having one end connected to said square face and the other end supporting a fiat conductive disc.
4. Apparatus as defined in claim l, said angle of divergence being that which makes the projection of said aperture into said square section be equal to one-half the side dimension of said square.
5. Apparatus for passing complementarily polarized electromagnetic waves comprising first and second rectangular waveguides having axes of propagation parallel and with their cross-sections at right angles, the narrow wall of said first waveguide being substantially centered along the broad Wall of said second waveguide and both of said waveguides terminating at a common reference plane, a section of square waveguide having dimensions substantially equal to the edge dimension of said broad wall and positioned with the edge of one wall centered relative to and coinciding with the edge of the narrow wall of said first waveguide in said plane, and a transition section between said square section and said first and second waveguides comprising extensions of the other three walls of said square section to join the three walls of said second waveguide and conductive members extending in said reference plane from the broad walls of said first waveguide to intersect said extensions of said walls which are normal to said plane.
6. Apparatus according to claim 5 in which said rectangular waveguides and said square section are angularly arranged so that the broad dimension of said first waveguide in said reference plane projected into said square section equals one-half the edge dimension of said square section.
References Cited in the le of this patent UNITED STATES PATENTS l 2,364,371 Karan Dec. 5, 1944