Circularly polarized wave-linearly polarized wave transducer

Abstract: The invention presents a circularly polarized wave-linearly polarized wave transducer using a waveguide characterized by expanding the inner wall of the section vertical to the tube axis of the waveguide in a taper form having a gradient in the tube axial direction, setting the taper gradient in the tube axial direction differently at plural parts in the circumferential direction of the inner wall, thereby producing a difference in the propagation constant of two modes orthogonal at the microwave frequency being used, and determining the taper gradient and overall length of the waveguide so that the phase difference of the two modes may be π/4 at both ends of the waveguide, and the circularly polarized wavelinearly polarized wave transducer operating securely can be realized in a simple constitution in which the slide core of die in the die-casting process can be drawn out from one direction only by expanding the shape of the section of the waveguide in a taper form with a gradient in the tube axial direction.

Description: BACKGROUND OF THE INVENTION The present invention relates to a circularly polarized wave-linearly polarized wave transducer using a waveguide operated at microwave frequency. Hitherto, as the circularly polarized wave-linearly polarized wave transducer using a waveguide operated at microwave frequency, as shown in a side view and a front sectional view in Fig. 2 (a), (b), a dielectric plate 12 was inserted in a tube of a circular waveguide 11 for transmitting TE11 mode at the operating frequency; as shown in a side view and a front sectional view in Fig. 3 (a), (b), a trapezoidal ridge metal piece 14 was placed in the tube axial direction of a circular waveguide on the inner wall of a circular waveguide 13 for transmitting TE11 mode at the operating frequency; or as shown in a side view and a front sectional view in Fig. 4 (a), (b), the sectional shape of a circular waveguide 15 for transmitting TE11 mode at the operating frequency was deformed in steps by a metal piece 16. However, the circularly polarized wave-linearly polarized wave transducers of the prior arts individually had the following problems. In Fig. 2, the dielectric 12 was needed, and it also required means for holding the dielectric 12 within the tube of the circular waveguide 11 in order to inscribe the dielectric 12 in the inner wall of the circular waveguide 11, while a strict relative precision was also demanded. In Fig. 3. although the dielectric was not necessary, when manufacturing the circular waveguide 13 integrating the ridge metal piece 14 by die casing process, it vas required to divide the slide core of the die into two sections due to shape restriction of the ridge metal piece 14 to draw out from both sides in the tube axial direction of the circular waveguide 13. In Fig. 4, since the sectional shape is charged largely in steps by the metal piece 16, discontinuity of impedance was caused, and sufficient performance could not be obtained. JP-A-01097001 discloses a phase shifter which may be used as a transducer between linear and circular polarisation. Here, a generally circular waveguide has a narrow central portion having an elliptic cross section which gradually changes towards both ends of the waveguide. This "two-way tapered structure" again requires two die sections for its manufacture and therefore does not lend itself readily to mass production. DE-A-3613474 discloses a polarised wave transducer in which the waveguide has a sloping step between a first diameter portion and a second diamter portion. This structure suffers from the same disadvantages as those discussed in relation to Fig 4 above in that the discontinuity caused by the step is detrimental to overall performance. The "Design of a Superelliptic Waveguide Polarizer" was discussed at the 16th European Microwave Conference, 8-12 September 1986 at Dublin, Ireland, by Ladanyi-Turoczy, recorded at pages 441-446. This design has the waveguide cross section changing gradually from circular to elliptical and back again, and suffers from the manufacturing disadvantages discussed above. SUMMARY OF THE INVENTION It is hence an object of the invention to present a circularly polarized wave-linearly polarized wave transducer using a circular waveguide, without using dielectric, capable of drawing out a slide core of a die from one side only when manufacturing by die-casting process, and not causing discontinuity of impedance. The invention presents a circularly polarized wave-linearly polarized wave transducer using a circular waveguide characterized by expanding the inner wall of the section vertical to the tube axis of the circular waveguide in a taper form having a gradient in the tube axial direction, setting the taper gradient in the tube axial direction differently at plural parts in the circumferential direction of the inner wall, thereby producing a difference in the propagation constant of two modes orthogonal at the microwave frequency being used, and determining the taper gradient and overall length of the circular waveguide so that the phase difference of the two modes may be π/4 at both ends of the circular waveguide. The invention as set forth in claim 1 is a circularly polarized wave-linearly polarized wave transducer comprising a circular waveguide having an inner wall characterized by a plurality of curved portions, each portion having a different position about the circumference of the circular waveguide, the diameter of the inner wall in a first one of said plurality of curved portions being tapered with a first constant gradient from one end of the waveguide to the other in the axial direction, the diameter of the inner wall in a second one of said plurality of curved portions being tapered with a second constant gradient from one end of the waveguide to the other in the axial direction, said second constant gradient being different from said first constant gradient, whereby when a circularly polarized wave enters from one end, a linearly polarized wave is delivered from the other end. Thus, (1) the material cost and assembling and manufacturing cost are saved because dielectric is not used. and thereby the yield is enhanced, (2) according to the die-cast process capable of drawing out the slide core of the die from one side only of the tube axis of the circular waveguide, the die manufacturing and process manufacturing control process are saved, and the yield is enhanced and the cost is also curtailed, and (3) the diameter of the inner wall at a section vertical to the tube axis of the circular waveguide is expanded in a taper form having a gradient in the tube axial direction, and hence the impedance is not discontinuous, performance is enhanced, and also circularly polarized wave-linearly polarized wave transformation by circular waveguide is achieved. The above advantages are preferably acheived by constructing the waveguide according to claim 2. The invention as set forth in claim 3 is a circularly polarized wave-linearly polarized rave transducer characterized by the constitution for transforming from circularly polarized wave to linearly polarized wave most efficiently when a phase difference of π/4 is produced between mode 1 for propagating a circular waveguide A and mode 2 for propagating a circular waveguide B. The preferred circularly polarized wave-linearly polarized wave transducer, according to the invention is composed of a waveguide having one end of which inner wall section is circular, and other end of which inner wall section is a shape divided by a circle of an inner diameter different in the right angle direction, in which the input of circularly polarized wave is a circular section, and the circular section of the section of output portion of linearly polarized wave having a different inner diameter in the right angle direction is divided and arranged in the circumferential direction, and thereby an efficient transformation of circularly polarized wave and linearly polarized wave is realized. The circularly polarized wave-linearly polarized wave transducer of the invention brings about the following effects. The material cost and assembling and manufacturing cost are saved because dielectric is not used, and thereby the yield is enhanced. According to the die-cast process capable of drawing out the slide core of the die from one side only of the tube axis of the circular waveguide, the die manufacturing and process manufacturing control process are saved, and the yield is enhanced and the cost is also curtailed. The diameter of the section vertical to the tube axis of the waveguide is expanded in a taper gradient in the tube axial direction and hence the impedance is not discontinuous, performance is enhanced. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 (a) is a front view of a circularly polarized wave-linearly polarized wave transducer in an embodiment of the invention: Fig. 1 (b) is a side sectional view along cut-off line P-P' in Fig. 1 (a): Fig. 1 (c) is a side sectional view along cut-off line Q-Q' in Fig. 1 (a): Fig. 2 (a) is a side view of a circularly polarized wave-linearly polarized wave transducer in a conventional embodiment; Fig. 2 (b) is a front view of Fig. 2 (a); Fig. 3 (a) is a side view of a circularly polarized wave-linearly polarized wave transducer in other conventional embodiment: Fig. 3 (b) is a front view of Fig. 3 (a) ; Fig. 4 (a) is a side view of a circularly polarized wave-linearly polarized wave transducer in a different conventional embodiment; and Fig. 4 (b) is a front view of Fig. 4 (a). DESCRIPTION OF THE PREFERRED EMBODIMENT Fig. 1 (a), Fig. 1 (b), and Fig. 1 (c) refer to an embodiment of the invention, respectively showing a front view of a circular waveguide manufactured by die-casting process from aluminum or the like, a side sectional view along cut-off line P-P' in Fig. 1 (a), and a side sectional view along cut-off line Q-Q' in Fig. 1 (a). Fig. 1 (a) is a front view as seen from the direction of a tube axis 2 of a circular waveguide 1, or, in other words. a front view as seen from the direction of drawing out the slide core of the die in the die-casting process. In Fig. 1 (a), (b), (c), the circular waveguide 1 has its inner wall at a section vertical to the tube axis 2 of the circular waveguide 1 expanded in a taper having a gradient in the tube axial direction, and the taper gradient in the tube axial direction is different in plural portions in the circumferential direction of the inner wall. One end of the circular waveguide 1 is a circle of which diameter 5 of inner wall is A. The diameter of inner wall (corresponding to curvature) of the circular waveguide 1 is expanded in a taper gradient in the direction of tube axis 2, that is, in the tube axis direction of the circular waveguide 1. This taper gradient is a first gradient 3 (1) in the side sectional view in Fig. 1 (b), and is a second gradient 4 (2) different from gradient 3 in the side sectional view in Fig. 1 (c). Herein, 1 is smaller than 2. Therefore, at the other end of the circular waveguide 1, the diameter of inner wall (corresponding to curvature) of the circular waveguide 1 in the side sectional view in Fig. 1 (b) and side sectional view in Fig. 1 (c) is respectively first diameter 6 (A1) and second diameter 7 (A2), and the first diameter A1 is smaller than the second diameter A2. The taper shape shown in side sectional view in Fig. 1 (b) and side sectional view in Fig. 1 (c) is formed in the arc portion of a corresponding quarter of a circle in the circumferential direction of the circular waveguide 1. That is, in the front view in Fig. 1 (a), the portion forming the taper with gradient 3 is formed at a position indicated by angle 8, and the portion forming the taper with gradient 4 is formed at a position indicated by angle 9. Both angle 8 and angle 9 are 90 degrees. In the circular TE11 mode in which the maximum electric field vector is orthogonal to start point and end point of a confronting arc within angle 8 in the diagram, that is, in the circular TE11 mode in which the maximum electric field vector coincides with line segment P-P' in the diagram (hereinafter called mode 1). the circular waveguide 1 may be equivalently regarded as a tapered elliptical waveguide. Similarly, in the circular TE11 mode in which the maximum electric field vector is orthogonal to start point and end point of a confronting arc within angle 9 in the diagram, that is, in the circular TE11 mode in which the maximum electric field vector coincides with line segment Q-Q' in the diagram (hereinafter called mode 2), the circular waveguide 1 may be equivalently regarded as a tapered elliptical waveguide. That is, in the circular waveguide 1, the elliptical waveguide corresponding to mode 1 and the elliptical waveguide corresponding to mode 2 are disposed at positions indicated by angle 8 and angle 9, respectively. The taper gradient 3 (1) of the elliptical waveguide corresponding to mode 1 is smaller than the taper gradient 4 (2) of the elliptical waveguide corresponding to mode 2, and therefore the wavelength in tube (λg) in mode 2 is longer than the wavelength in tube in mode 1 (the propagation constant refers to 2π/λg). The gradient 3 (1), gradient 4 (2), and overall length (L) of circular waveguide can be experimentally determined in the relation of (2π/λg)L=π/4 at the operating frequency, and a phase difference of π/4 occurs between the two modes. Therefore, the circularly polarized wave entering from one end in the tube axial direction of the circular waveguide 1 propagates in the circular waveguide 1 as two circular TE11 modes (mode 1 and mode 2) with a phase difference of π/4, and at the other end these two modes 1 and 2 are in phase and transformed into a linearly polarized wave. Incidentally, the taper of the inner wall of the circular waveguide 1 is not limited to linear taper, but it may be also a curved taper or a taper including a discontinuous step portion so far as discontinuity of impedance may not be caused. The phase difference π/4 may be (N+1/4)π (N is an integer). In the embodiment, the diameter of inner wall (corresponding to curvature) of the circular waveguide 1 in Fig. 1 (a) is a combination of two circles of first diameter of a circle coinciding with line segment P-P'. and second diameter of a circle coinciding with line segment Q-Q', but, of course, same effects are obtained by the inner wall section of elliptical shape having first and second diameter approximately.

Claims: A circularly polarized wave-linearly polarized wave transducer comprising a circular waveguide (1) having an inner wall characterized by a plurality of curved portions, each portion having a different position about the circumference of the circular waveguide, the diameter of the inner wall in a first one of said plurality of curved portions being tapered with a first constant gradient (3) from one end of the waveguide to the other in the axial direction (2), the diameter of the inner wall in a second one of said plurality of curved portions being tapered with a second constant gradient (4) from one end of the waveguide to the other in the axial direction, said second constant gradient being different from said first constant gradient, whereby when a circularly polarized wave enters from one end, a linearly polarized wave is delivered from the other end. A circularly polarized wave-linearly polarized wave transducer as claimed in claim 1, wherein the first one of the plurality of curved portions of the circular waveguide is formed by a first pair of curved portions at opposite positions on the inner wall of the circular waveguide, each having the first constant gradient in the axial direction, and the second one of the plurality of curved portions of the circular wave guide is formed by a second pair of curved portions at opposite positions on the inner wall of the circular waveguide, each having the second constant gradient in the axial direction, wherein each one of the first pair of curved portions alternates with a respective one of the second pair of curved portions. A circularly polarized wave-linearly polarized wave transducer as claimed in claim 1, wherein a phase difference of π/4 is generated between a first mode propagating in said first one of said plurality of portions of the circular waveguide and a second mode propagating in said second one of said plurality of portions of the circular waveguide. A circularly polarized wave-linearly polarized wave transducer of claim 1, further comprising: a first end; a second end; wherein said first constant gradient and said second constant gradient extend from the first end to the second end and along the inner wall of the circular waveguide, and a circularly polarized wave enters from the first end of the circular waveguide, and a linearly polarized wave is generated and output at the second end of the circular waveguide.

Inventors: YOSHIMURA YOSHIKAZA, YOSHIMURA, YOSHIKAZA
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1996
Main classification: H01P1
IPC codes: H01P1, H01P5