Ultrawide-band linear-circular polarization converter

Abstract

In an ultrawide-band linear-circular polarization converter, in a noncircular waveguide which has negative-phase characteristics in which a phase gradually decreases in accordance with an increase in a frequency over an ultrawide-band frequency range, a dielectric structure which has positive-phase characteristics, in which a phase gradually increases in accordance with an increase in a frequency, having a complementary relationship with the negative-phase characteristics in the ultrawide-band frequency range is provided.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to ultrawide-band linear-circular polarization converters, and more particularly relates to an ultrawide-band linear-circular polarization converter which has a noncircular waveguide including a dielectric structure and which is set so that frequency-versus-phase characteristics of the noncircular waveguide and those of the dielectric structure complement each other in a range of the ultrawide-band.

[0003] 2. Description of the Related Art

[0004] Hitherto, in a transmitter-receiver which transmits or receives a satellite broadcasting having a dual-band or an ultrawide-band circularly polarized signal, an ultrawide-band or wide-band linear-circular polarization converter has been used to convert a circularly polarized signal into a linearly polarized signal, and vice versa.

[0005] In this case, the dual-band has two frequency bands among satellite broadcasting frequency band at several giga-hertz, such as a frequency band of 12.2 GHz to 12.7 GHz and a frequency band of 19.7 GHz to 20.2 GHz. The wide-band is a frequency band of, for example, 10.7 GHz to 12.75 GHz among the satellite broadcasting frequency band of the above several giga-hertz.

[0006] FIGS. 5A and 5B are cross-sectional views showing a first construction example of a known linear-circular polarization converter, in which FIG. 5A is a cross-sectional view perpendicular to the longitudinal direction and FIG. 5B is a cross-sectional view in the longitudinal direction.

[0007] As shown in FIGS. 5A and 5B, in the first construction example of a known linear-circular polarization converter, a circular waveguide 51 has a planar dielectric structure 52 provided so as to be along the direction of one diameter thereof. In this case, the planar dielectric structure 52 is provided so as to be along the direction of one diameter of the circular waveguide 51 which is sloped at approximately 45 degrees to the direction of the internal electric field E of the circular waveguide 51. Both side faces extending in the longitudinal direction of the dielectric structure 52 are cut inwardly in a generally triangular shape.

[0008] FIGS. 6A and 6B are cross-sectional views showing a second construction example of a known linear-circular polarization converter, in which FIG. 6A is a cross-sectional view perpendicular to the longitudinal direction and FIG. 6B is a cross-sectional view in the longitudinal direction.

[0009] As shown in FIGS. 6A and 6B, in the second construction example of a known linear-circular polarization converter, a ridged conductor structure 62 is provided at a part of the inner wall of a circular waveguide 61. In this case, the ridged conductor structure 62 is provided at a position of the inner wall of the circular waveguide 61 which is sloped at approximately 45 degrees to the direction of the internal electric field E of the circular waveguide 61. In the ridged conductor structure 62, the height of an edge part in the longitudinal direction is lower than that of a central part.

[0010] In these linear-circular polarization converters, when a linearly polarized signal is input to an input terminal thereof, a circularly polarized signal can be output from an output terminal thereof, and vice versa.

[0011] Generally, linear-circular polarization converters can perform a predetermined linear-circular polarization conversion on a polarized signal propagating through the waveguide in a frequency band which causes the phase difference |φ| (=|φV−φH|) between the vertical-polarization phase φV of the polarized signal and the horizontal-polarization phase φH thereof to be maintained within a range of 90°±10°.

[0012] Since the frequency bands of known linear-circular polarization converters causing the phase difference |φ| to be maintained within the range of 90°±10° are relatively narrow frequency ranges, known linear-circular polarization converters cannot be used as wide-band linear-circular polarization converters or ultrawide-band linear-circular polarization converters which activate in a broader frequency range than that of the wide-band linear-circular polarization converters.

[0013] Since known linear-circular polarization converters only have a relative frequency band of several percent, favorable conversion characteristics cannot be obtained throughout a relative frequency band of the order of ten percent or a relative frequency band of several tens of percent.

SUMMARY OF THE INVENTION

[0014] Accordingly, the present invention is made considering such a technical background. It is an object of the present invention to provide an ultrawide-band linear-circular polarization converter for capable of offering favorable frequency-versus-phase characteristics as a linear-circular polarization converter in a frequency range of an ultrawide-band.

[0015] To this end, according to a first aspect of the present invention, there is provided an ultrawide-band linear-circular polarization converter in which, in a noncircular waveguide which has negative-phase characteristics in which a phase gradually decreases in accordance with an increase in a frequency over an ultrawide-band frequency range, a dielectric structure which has positive-phase characteristics, in which a phase gradually increases in accordance with an increase in a frequency, having a complementary relationship with the negative-phase characteristics in the ultrawide-band frequency range is provided.

[0016] In the ultrawide-band linear-circular polarization converter, the noncircular waveguide may be an elliptic waveguide.

[0017] In the ultrawide-band linear-circular polarization converter, the dielectric structure may be provided in the direction of the minor axis of the elliptic waveguide, and the dielectric structure may have edge parts which are thin in the thickness direction and a central part which is thick in the thickness direction.

[0018] As described above, according to the present invention, by combining the noncircular waveguide having negative-phase characteristics and the dielectric structure having positive-phase characteristics which complement the negative-phase characteristics, the following advantages are obtained: the ultrawide-band linear-circular polarization converter can be caused to have generally flat frequency-versus-phase characteristics which enable favorable linear-circular polarization conversion to be performed in the ultrawide-band frequency range; and the ultrawide-band linear-circular polarization converter can be obtained, having a simple construction, without causing an increase in manufacturing cost or the like.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIGS. 1A, 1B, and 1C are diagrams showing the construction of an ultrawide-band linear-circular polarization converter according to one embodiment of the present invention;

[0020] FIGS. 2A, 2B, and 2C are graphs showing frequency-versus-phase characteristics of the ultrawide-band linear-circular polarization converter, a noncircular waveguide, and a dielectric structure, shown in FIGS. 1A, 1B, and 1C;

[0021] FIGS. 3A, 3B, 3C, and 3D are cross-sectional views showing the constructions of other noncircular waveguides in which positive-phase characteristics can be obtained in an ultrawide-band frequency range;

[0022] FIGS. 4A, 4B, 4C, and 4D are cross-sectional views showing the constructions of other planar dielectric structures in which negative-phase characteristics can be obtained in the ultrawide-band frequency range;

[0023] FIGS. 5A and 5B are cross-sectional views showing the construction of a first known linear-circular polarization converter; and

[0024] FIGS. 6A and 6B are cross-sectional views showing the construction of a second known linear-circular polarization converter.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Embodiments of the present invention are described with reference to the accompanying drawings.

[0026] FIGS. 1A, 1B, and 1C show the construction of an ultrawide-band linear-circular polarization converter according to one embodiment of the present invention; FIG. 1A is a cross-sectional view perpendicular to the longitudinal direction; FIG. 1B is a cross-sectional view in the longitudinal direction; and FIG. 1C is a lateral sectional view in the longitudinal direction.

[0027] As shown in FIG. 1A to FIG. 1C, the ultrawide-band linear-circular polarization converter according to the present embodiment has an elliptical waveguide 1 (noncircular) and a planar dielectric structure 2 provided along the minor-axis diameter of the elliptical waveguide 1 (noncircular). In this case, the planar dielectric structure 2 in which the plate thickness is thin at edges 21 and thick at a middle 22 is constructed. The planar dielectric structure 2 may have another configuration as long as the planar dielectric structure 2 has low reflection characteristics.

[0028] FIG. 2A is a graph showing frequency-versus-phase characteristics of the ultrawide-band linear-circular polarization converter shown in FIGS. 1A to 1C; FIG. 2B is a graph showing frequency-versus-phase characteristics of the noncircular waveguide 1; and FIG. 2C is a graph showing frequency-versus-phase characteristics of the planar dielectric structure 2.

[0029] In FIGS. 2A to 2C, the axis of the abscissa represents working frequencies f and the axis of the ordinate represents phase differences |φ| (=|φV−φH|) in degrees.

[0030] As described above, φV is the vertical-polarization phase of the polarized signal propagating through the waveguide, and the φV is the horizontal-polarization phase of the polarized signal propagating through the waveguide.

[0031] Operations of the ultrawide-band dielectric linear-circular polarization converter shown in FIGS. 1A to 1C are described with reference to FIGS. 2A to 2C.

[0032] Frequency-versus-phase characteristics of the noncircular waveguide 1 alone are as shown in FIG. 2B. In the frequency range of an ultrawide-band between a frequency fC and a frequency 2fC, as a frequency f increases from the frequency fC toward the frequency 2fC, the phase difference |φ| drops comparatively rapidly in the proximity of the frequency fC. In a subsequent frequency range, the phase difference |φ| drops slowly and becomes less than ninety degrees while dropping. Subsequently, the phase difference |φ| continues to drop at the same rate. In this case, a frequency range BW1 in which the phase difference |φ| is maintained within a range of 90°±10° is limited to a very small part of the frequency range between the frequency fC and the frequency 2fC.

[0033] Frequency-versus-phase characteristics of the dielectric structure 2 alone are as shown in FIG. 2C. In the frequency range of the ultrawide-band between the frequency fC and the frequency 2fC, as the frequency f increases from the frequency fC toward the frequency 2fC, the phase difference |φ| rapidly drops in the proximity of the frequency fC, After the phase difference |φ| drops below ninety degrees, the phase difference |φ| starts to gradually increase. When the phase difference |φ| exceeds ninety degrees and reaches a frequency range which is in the proximity of the frequency 2fC, the phase difference |φ| increases comparatively rapidly. In this case as well, a frequency range BW2 in which the phase difference |φ| is maintained within the range of 90°±10° is limited to a very small part of the frequency range of the ultrawide-band between the frequency fC and the frequency 2fC.

[0034] As shown in FIG. 2A, frequency-versus-phase characteristics of an ultrawide band linear-circular polarization converter constructed by combining the noncircular waveguide 1 and the dielectric structure 2 have phase characteristics obtained by combining negative-phase characteristics in which, as shown in FIG. 2B, the phase difference gradually decreases in accordance with an increase in the frequency in the noncircular waveguide 1, and positive-phase characteristics in which, as show in FIG. 2C, the phase difference gradually increases in accordance with an increase of the frequency in the dielectric structure 2. By constructing the noncircular waveguide 1 and the dielectric structure 2 so that the above negative-phase characteristics and the above positive-phase characteristics are complementary in an ultrawide-band frequency range BW between the proximity of the frequency fC and that of the frequency 2fC, substantially flat phase characteristics can be obtained. To be concrete, the phase difference |φ| is maintained within the range of 90°±10°. As a result of this, this ultrawide-band linear-circular polarization converter enables favorable conversion characteristics to be achieved over the ultrawide-band frequency range BW.

[0035] When a linearly polarized signal is input to an input terminal of this ultrawide-band frequency linear-circular polarization converter, a circularly polarized signal is output from an output terminal of the ultrawide-band frequency linear-circular polarization converter where the linearly polarized signal is converted into the circular polarized signal, and vice versa. A predetermined linear-circular polarization conversion can be applied to a polarized signal over the ultrawide band frequency range BW.

[0036] FIGS. 3A, 3B, 3C, and 3D are cross-sectional views showing construction examples of other noncircular waveguides in which the above negative-phase characteristics can be obtained over the ultrawide band frequency range BW.

[0037] In this case, a noncircular waveguide 11 shown in FIGS. 3A and 3B is constructed by providing a ridged conductor structure 12 at the inner wall thereof.

[0038] A noncircular waveguide 13 shown in FIGS. 3C and 3D is constructed by providing ridged conductor structures 14 and 15 at parts of the inner wall thereof which face each other.

[0039] Instead of using the elliptic (noncircular) waveguide 1 as shown in FIG. 1A, by using the noncircular waveguide 11 or 13 having the construction shown in FIG. 3A or 3C, the negative-phase characteristics shown in FIG. 2B may be also obtained over the ultrawide band frequency range BW.

[0040] FIGS. 4A, 4B, 4C, and 4D are cross-sectional views showing construction examples of other planar dielectric structures in which the above positive-phase characteristics can be obtained over the ultrawide band frequency range BW.

[0041] In this case, a planar dielectric structure 16 shown in FIG. 4A, which is identical to the planar dielectric structure 52 shown in FIG. 5B, has both side faces thereof extending in the longitudinal direction cut inwardly in a generally triangular shape.

[0042] A planar dielectric structure 17 shown in FIG. 4B has both side faces thereof extending in the longitudinal direction cut inwardly in a generally rectangular shape.

[0043] A planar dielectric structure 18 shown in FIG. 4C is provided at one side of the inner wall of a waveguide, and the height of the dielectric structure 18 in the longitudinal direction thereof is varied in a circular manner.

[0044] A planar dielectric structure 19 shown in FIG. 4D is provided at one side of the inner wall of a waveguide, and the height of the dielectric structure 18 in the longitudinal direction thereof is varied in a triangular manner.

[0045] Instead of using the planar dielectric structure 2 in FIGS. 1B and 1C, by using the planar dielectric structure 16, 17, 18, or 19 having the construction shown in FIG. 4A, 4B, 4C, or 4D, the positive-phase characteristics shown in FIG. 2C may be also obtained in the ultrawide band frequency range BW.

[0046] In each embodiment described above, the examples in which the elliptic waveguides 1, 11, and 13 are employed as a waveguide for obtaining the negative-phase characteristics as shown in FIG. 2B over the ultrawide-band frequency range BW are described. However, in the present invention, waveguides enabling the above negative-phase characteristics to be obtained are not limited to those elliptic waveguides. Noncircular waveguides apart from elliptic waveguides, such as rectangular waveguides or their analog, may obtain such negative-phase characteristics.

[0047] As described above, according to the present invention, by combining the noncircular waveguide having negative-phase characteristics and the dielectric structure having positive-phase characteristics which complement the negative-phase characteristics, the following advantages are obtained: the ultrawide-band linear-circular polarization converter can be caused to have generally flat frequency-versus-phase characteristics which enable favorable linear-circular polarization conversion to be performed in the ultrawide-band frequency range; and the ultrawide-band linear-circular polarization converter can be obtained, having a simple construction, without causing an increase in manufacturing cost or the like.

Claims

1. An ultrawide-band linear-circular polarization converter, wherein, in a noncircular waveguide which has negative-phase characteristics in which a phase gradually decreases in accordance with an increase in a frequency over an ultrawide-band frequency range, a dielectric structure which has positive-phase characteristics, in which a phase gradually increases in accordance with an increase in a frequency, having a complementary relationship with said negative-phase characteristics in said ultrawide-band frequency range is provided.

2. An ultrawide-band linear-circular polarization converter according to claim 1, wherein said noncircular waveguide is an elliptic waveguide.

3. An ultrawide-band linear-circular polarization converter according to claim 2, wherein: said dielectric structure is provided in the direction of the minor axis of said elliptic waveguide; and wherein said dielectric structure has edge parts which are thin in the thickness direction and a central part which is thick in the thickness direction.