JP7496953B1 - Polarization separation circuit and antenna - Google Patents

Abstract

The polarization separation circuit includes a conversion waveguide (1) having one circular terminal (1A) whose cross section perpendicular to the tube axis direction is circular and two rectangular terminals (1Ba, 1Bb) whose cross section perpendicular to the tube axis direction is rectangular, and a shape obtained by converting the cross section perpendicular to the tube axis direction from the circular cross section to the cross sections of the two rectangular terminals, and a septum phase plate (2; 2M) having a plurality of step noses (7a to 7d) and arranged inside the conversion waveguide, wherein the septum phase plate has a shape in which the width of the septum phase plate in the short side direction narrows in a stepped manner, and is arranged inside the conversion waveguide so that the tip of the septum phase plate formed to be tapered in a stepped manner is located on the circular terminal side of the conversion waveguide.

Description

This disclosure relates to polarization separation circuits primarily used in the VHF, UHF, microwave and millimeter wave bands.

A polarization separation circuit that inserts a septum phase plate into a square waveguide is known as a circuit that separates two orthogonal circularly polarized signals (right-handed, left-handed) or two orthogonal linearly polarized signals (vertical, horizontal) (see, for example, Figure 5 of Non-Patent Document 1).

A conventional polarization splitter circuit includes a square waveguide and a septum phase plate, where the square waveguide has one square waveguide terminal and two rectangular waveguide terminals. The septum phase plate is inserted into the square waveguide so that two rectangular waveguides are formed, and is formed so that it tapers in a stepped manner from the rectangular waveguide terminal to the square waveguide terminal.

In such a polarization splitting circuit, when a circularly polarized signal is input from the square waveguide terminal, a signal is output from a different rectangular waveguide terminal depending on whether the input signal is right-handed or left-handed. When a linearly polarized signal is input from the square waveguide terminal, the two rectangular waveguide terminals output signals with the same electric field direction for linearly polarized signals perpendicular to the septum phase plate, and the two rectangular waveguide terminals output signals with opposing electric field directions for linearly polarized signals horizontal to the septum phase plate.

In such a polarization separation circuit, the polarization separation characteristics are determined by the dimensions or thickness of the step portion of the septum phase plate.

In addition, the polarization splitter is generally used in connection with a horn antenna having a circular waveguide terminal. For this reason, a converter is provided between the horn antenna and the polarization splitter to connect the circular waveguide terminal of the horn antenna to the square waveguide terminal of the polarization splitter (for example, the circular to rectangular transition in Figure 11 of Non-Patent Document 1).

“X-Band Choked Horn Antenna for On-Board TTC Downlink of Deep Space Satellite Applications,” 2017 IEEE International Conference on Antenna Innovations & Modern Technologies for Ground, Aircraft and Satellite Applications

Conventional polarization splitting circuits with square waveguide terminals require a converter when used in connection with a horn antenna with a circular waveguide terminal, which creates the problem that the axis of an antenna constructed using a polarization splitting circuit becomes longer by the length of the converter.

This disclosure has been made to solve such problems, and aims to provide a polarization separation circuit that makes it possible to shorten the axis of the antenna.

A polarization splitting circuit according to an embodiment of the present disclosure comprises a conversion waveguide having one circular terminal and two rectangular terminals each having a circular cross section perpendicular to the tube axis direction, the cross section perpendicular to the tube axis direction being transformed from the circular cross section to the cross section of the two rectangular terminals, and a septum phase plate having multiple step nosings and disposed inside the conversion waveguide, the septum phase plate having a shape in which the width of the septum phase plate in the short side direction tapers in a stepped manner, and the tip of the septum phase plate formed in a stepped manner is disposed inside the conversion waveguide so as to be positioned on the circular terminal side of the conversion waveguide.

The polarization separation circuit according to the embodiment of the present disclosure makes it possible to shorten the axis of the antenna.

1 is a perspective view of a polarization splitter circuit for explaining a configuration of the polarization splitter circuit according to a first embodiment; 1 is a plan view of a polarization separation circuit according to a first embodiment; 1 is a side view of a polarization separation circuit according to a first embodiment. 1 is a perspective view of a conversion waveguide according to a first embodiment; FIG. 2 is a perspective view of a septum phase plate according to the first embodiment. FIG. 2 is a plan view of a septum phase plate according to the first embodiment. FIG. 2 is a side view of the septum phase plate according to the first embodiment. FIG. 1 is a plan view of a square waveguide for comparison, the outer wall of which has a uniform square shape. 8B is an explanatory diagram for explaining the cross-sectional shape of the septum phase plate at positions A and B in FIG. 8A. FIG. 13 is a plan view of a comparative conversion waveguide in which the shape of the outer wall is converted from circular to square and the septum phase plate nosing is at a right angle. 9B is an explanatory diagram for explaining the cross-sectional shape of the septum phase plate at positions A and B in FIG. 9A. FIG. 1 is a plan view of a conversion waveguide in which the shape of the outer wall is converted from circular to square and the nosing of the septum phase plate is acute, according to the first embodiment. 10B is an explanatory diagram for explaining the cross-sectional shape of the septum phase plate at positions A and B in FIG. 10A. FIG. 11 is a perspective view of a polarization splitter circuit for explaining the configuration of the polarization splitter circuit according to the second embodiment. FIG. 11 is a side view of a polarization separation circuit according to a second embodiment. FIG. 11 is a perspective view of a septum phase plate according to a second embodiment. FIG. 11 is a side view of a septum phase plate according to a second embodiment. FIG. 11 is a perspective view of a polarization splitter circuit for explaining the configuration of the polarization splitter circuit according to the third embodiment. FIG. 11 is a perspective view of a conversion waveguide according to a third embodiment. FIG. 2 is a diagram showing an antenna configuration including a polarization splitter circuit, a horn antenna, and a filter according to an embodiment.

Various embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. Note that components with the same or similar reference numerals in the drawings have the same or similar configurations or functions, and redundant descriptions of such components will be omitted.

Embodiment 1.
<Configuration>
Fig. 1 is a perspective view of a polarization splitting circuit for explaining the configuration of the polarization splitting circuit according to the first embodiment of the present disclosure. In Fig. 1, 1 is a conversion waveguide, 2 is a septum phase plate, 3 is a circular waveguide, 4 is a circular waveguide terminal, 5 is a rectangular waveguide, and 6 is a rectangular waveguide terminal. Fig. 2 shows a plan view of the polarization splitting circuit (viewed from a direction perpendicular to the septum phase plate), Fig. 3 shows a side view of the polarization splitting circuit (viewed from a direction parallel to the septum phase plate), Fig. 4 shows a perspective view of the conversion waveguide, Fig. 5 shows a perspective view of the septum phase plate, Fig. 6 shows a plan view of the septum phase plate (viewed from a direction perpendicular to the septum phase plate), and Fig. 7 shows a side view of the septum phase plate (viewed from a direction parallel to the septum phase plate). In Figs. 5 and 6, 7 is a nosing of the septum phase plate.

(Circular Waveguide)
As shown in Fig. 1, the circular waveguide 3 has a generally cylindrical shape and has circular waveguide terminals, which are circular openings, at both ends. In Fig. 1, one of the two circular waveguide terminals is illustrated as circular waveguide terminal 4.

(Rectangular Waveguide)
The rectangular waveguides 5a and 5b are waveguides having substantially the same shape. Except when it is necessary to distinguish between them, the rectangular waveguides 5a and 5b are hereinafter collectively referred to as the rectangular waveguide 5. As shown in FIG. 1, the rectangular waveguide 5 has an overall rectangular cross-section, and has rectangular waveguide terminals at both ends, which are rectangular openings. The rectangular waveguide terminals have a cross section corresponding to the cross section of one of the two rectangular terminals 1B (1Ba, 1Bb) of the conversion waveguide 1. In FIG. 1, one of the rectangular waveguide terminals at both ends is illustrated as a rectangular waveguide terminal 6. That is, the rectangular waveguide terminal 6a of the rectangular waveguide 5a and the rectangular waveguide terminal 6b of the rectangular waveguide 5b are illustrated.

(Conversion Waveguide)
As shown in Fig. 4, the conversion waveguide 1 is a waveguide having one circular terminal 1A whose cross section perpendicular to the tube axis direction is circular and two rectangular terminals 1Ba and 1Bb whose cross section perpendicular to the tube axis direction is rectangular, and has a shape in which the cross section of the conversion waveguide 1 perpendicular to the tube axis direction is converted from a circular cross section to the cross sections of the two rectangular terminals 1Ba and 1Bb. A septum phase plate 2 is disposed inside the conversion waveguide 1. The two rectangular terminals 1Ba and 1Bb are positioned adjacent to each other with the septum phase plate 2 sandwiched between them, so that the two rectangular terminals 1Ba and 1Bb form a single virtual end face that is generally substantially square. The two rectangular terminals 1Ba and 1Bb may be collectively referred to simply as rectangular terminal 1B.

As an example, as shown in FIG. 1, the circular terminal 1A of the conversion waveguide 1 is connected to the circular waveguide terminal of the circular waveguide 3, and the two rectangular terminals 1Ba and 1Bb of the conversion waveguide 1 are connected to the two rectangular waveguide terminals of the rectangular waveguides 5a and 5b, respectively.

(Septum phase plate)
As shown in Fig. 5 or 6, the septum phase plate 2 has a shape in which the width in the short side direction of the septum phase plate 2 narrows in a step-like manner. As shown in Fig. 1, the septum phase plate 2 having such a shape is disposed inside the conversion waveguide 1 so that the tip of the septum phase plate 2 formed to be narrow in a step-like manner is located on the circular terminal 1A side of the conversion waveguide 1 and the septum phase plate 2 equally divides the internal space of the septum phase plate 2. As an example, the septum phase plate 2 may be disposed inside the conversion waveguide 1 by insertion. As another example, the septum phase plate 2 and the conversion waveguide 1 may be integrally formed by a 3D printer, and the septum phase plate 2 may be disposed inside the conversion waveguide 1.

In addition, the nosings 7a, 7b, 7c, and 7d of the septum phase plate 2, which are the areas surrounded by circles in Fig. 5, form acute angles when the septum phase plate 2 is viewed in a plane, as shown in Fig. 6. More specifically, the nosing 7a is formed so that a line extending from the side of the septum phase plate 2 in the short direction of the septum phase plate 2 and a line along the length of the septum phase plate 2 form an acute angle in a plane view. Similarly, the nosings 7b to 7d are formed so that a line extending from the side of the septum phase plate 2 in the short direction of the septum phase plate 2 and a line along the length of the septum phase plate 2 form an acute angle in a plane view. It is not necessary for all the nosings to be acute angles, and at least one nosing may be an acute angle.

<Operation>
When a circularly polarized signal is input from the circular waveguide terminal 4, the signal is output from one of the different rectangular waveguide terminals 6a and 6b depending on whether the signal is right-handed or left-handed. When a linearly polarized signal is input from the circular waveguide terminal 4, the two rectangular waveguide terminals 6 output signals with the same electric field direction for linearly polarized signals perpendicular to the septum phase plate 2, and the two rectangular waveguide terminals 6 output signals with opposing electric field directions for linearly polarized signals horizontal to the septum phase plate 2. The dimensions of the septum phase plate 2 are adjusted to achieve good polarization separation.

Here, the operation of this embodiment will be described in more detail by comparing a configuration consisting of a typical square waveguide, a configuration in which the outer wall is converted from a circular waveguide to a square waveguide and the septum phase plate has a right-angled nosing, and a configuration in which the outer wall is converted from a circular waveguide to a square waveguide and the septum phase plate has an acute-angled nosing.

8A shows a plan view (viewed from a direction perpendicular to the septum phase plate) of a square waveguide as a comparison object in which the outer wall shape is uniform and square, and FIG. 8B shows an explanatory diagram for explaining the cross-sectional shape of the septum phase plate at positions A and B in FIG. 8A. FIG. 9A shows a plan view (viewed from a direction perpendicular to the septum phase plate) of a conversion waveguide as a comparison object in which the outer wall shape is converted from a circle to a square and the nose of the septum phase plate is a right angle, and FIG. 9B shows an explanatory diagram for explaining the cross-sectional shape of the septum phase plate at positions A and B in FIG. 9A. FIG. 10A shows a plan view (viewed from a direction perpendicular to the septum phase plate) of a conversion waveguide 1 in which the outer wall shape according to embodiment 1 is converted from a circle to a square and the noses 7a to 7d of the septum phase plate 2 are acute angles, and FIG. 10B shows an explanatory diagram for explaining the cross-sectional shape of the septum phase plate 2 at positions A and B in FIG. 10A.

In the configuration consisting of a typical square waveguide as shown in Figure 8A, the shape of the outer wall is uniform in the tube axial direction, so that the cross-sectional shape is the same at position A and position B as shown in Figure 8B, and the phase constant of the signal propagating through the region between position A and position B is constant. Similarly, the phase constant of the signal propagating through the region between position B and position C, position C and position D, and position D and position E is constant. Adjusting the dimensions of the septum phase plate under such conditions is relatively easy, and good polarization separation characteristics can be easily obtained.

On the other hand, as shown in Figure 9A, in a configuration in which the shape of the outer wall of the conversion waveguide is converted from a circle to a square and the nose of the septum phase plate is at a right angle, the shape of the outer wall changes along the tube axis direction, so that the position of the septum phase plate is the same at positions A and B, but the cross-sectional shape is different, as shown in Figure 9B. In the conversion from a circular waveguide to a square waveguide shown in Figure 9A, the cutoff frequency shifts to a lower range at position B compared to position A, and the phase constant of the signal propagating in the region between positions A and B is no longer constant. The same is true between positions B and C, between positions C and D, and between positions D and E. This makes it difficult to adjust the dimensions of the septum phase plate, making it difficult to obtain good polarization separation characteristics.

Compared to the configuration shown in FIG. 9A, in the configuration of FIG. 10A according to the present embodiment 1, the noses 7a to 7d (see FIG. 5) of the septum phase plate 2 are acute angles, so that the position of the septum phase plate 2 differs in the cross sections at positions A and B, as shown in FIG. 10B. In FIG. 10B, the position difference is shown as ΔS. When viewed in cross section, the septum phase plate 2 functions as a ridge, and as the height of the ridge decreases, the cutoff frequency shifts to a higher frequency. Therefore, at position B, the shift to a lower frequency due to the change in the shape of the outer wall is compensated, and the change in the phase constant of the signal propagating through the region between positions A and B is reduced compared to the configuration of FIG. 9A, and approaches the configuration of FIG. 8A. Therefore, as in the case of the configuration of FIG. 8A, it is relatively easy to adjust the dimensions of the septum phase plate 2, and good polarization separation characteristics can be easily obtained.

As described above, in a configuration in which the outer wall of the conversion waveguide 1 is formed so as to convert from a circle to a square, the influence of the outer wall is compensated for and good polarization separation characteristics are obtained by making the nosings 7a-7d of the septum phase plate 2 acute angles. In addition, in a configuration in which the outer wall is formed so as to convert from a circle to a square, a circular waveguide terminal is provided, so when used in connection with a horn antenna having a circular waveguide terminal, a converter between a circular waveguide and a square waveguide is not required and the axis is shortened. Therefore, when used in connection with a horn antenna having a circular waveguide terminal, the effect of achieving both a short axis and good polarization separation characteristics can be obtained.

Embodiment 2.
Next, a polarization splitter circuit according to a second embodiment of the present disclosure will be described with reference to Fig. 11 to Fig. 14. Fig. 11 is a perspective view of the polarization splitter circuit for explaining the configuration of the polarization splitter circuit according to the second embodiment. Fig. 12 is a side view of the polarization splitter circuit (viewed from a direction parallel to the septum phase plate), Fig. 13 is a perspective view of the septum phase plate 2M, and Fig. 14 is a side view of the septum phase plate 2M (viewed from a direction parallel to the septum phase plate). In Figs. 11 to 13, the members indicated by reference numbers 1 and 3 to 7 are the same as the members indicated by those reference numbers in Figs. 1 and 5. The septum phase plate 2M in Figures 11 to 14 differs from the septum phase plate 2 in Figures 1 and 5 in that the shape of the side of the septum phase plate 2M (the surface viewed from a direction parallel to the septum phase plate 2M) is trapezoidal, i.e., the thickness of the septum phase plate 2M changes in a trapezoidal shape along the tube axis direction.

The polarization separation circuit of this embodiment 2 also has the effect of obtaining good polarization separation characteristics, similar to the polarization separation circuit of embodiment 1.

Furthermore, since changes in the shape of the side of the septum phase plate 2M have a greater effect on the reflection characteristics than on the effect on changes in the phase constant, the effect of improving the reflection characteristics can be obtained by using the shape of the side of the septum phase plate 2M as a design parameter.

Embodiment 3.
Next, a polarization splitter circuit according to the third embodiment of the present disclosure will be described with reference to Figs. 15 and 16. Fig. 15 is a perspective view of the polarization splitter circuit for explaining the configuration of the polarization splitter circuit according to the third embodiment. Fig. 16 is a perspective view of the converted waveguide 1M. In Figs. 15 and 16, the members indicated by reference numbers 2 to 4 are the same as the members indicated by those reference numbers in Fig. 1. The converted waveguide 1M in Figs. 15 and 16 differs from the converted waveguide 1 in Fig. 1 in that a corner R8A is provided at the rectangular terminal 1B of the converted waveguide 1M. Note that in Fig. 16, in order to emphasize the corner R8A, the end face of the converted waveguide 1M is simply drawn as if it were one square terminal, but the converted waveguide 1M actually has two rectangular terminals formed thereon as in Fig. 4. Therefore, more specifically, corners R8A are provided at the four corners of each of the two rectangular terminals of the converted waveguide 1M. Correspondingly, corners R8B are provided at the corners of the rectangular waveguide terminals of the rectangular waveguides 5Ma and 5Mb.

The polarization separation circuit of this embodiment also has the effect of providing good polarization separation characteristics, similar to the polarization separation circuit of embodiment 1.

Furthermore, since the change in shape of the outer wall of the conversion waveguide 1M is more gradual than when it is converted to a square, the effect of the change in the outer wall is reduced, resulting in even better polarization separation characteristics.

In addition, when connecting another waveguide component that is manufactured by cutting and has corners with R, there is no discontinuity and good reflection characteristics are obtained.

In addition, since no flat ceiling is formed in any of the first, second, and third embodiments, it is possible to manufacture the polarization separation circuit by stacking in the tube axis direction using a 3D printer. Stacking a circular waveguide in the tube axis direction improves the roundness, and it also has the advantage of providing better polarization separation characteristics than when manufactured in an oblique direction.

Furthermore, an antenna may be constructed by connecting a horn antenna 9 having a circular waveguide terminal to the polarization separation circuit. The horn antenna 9 is connected to the conversion waveguide 1 for a polarization separation circuit that does not have a circular waveguide 3, and to the circular waveguide 3 for a polarization separation circuit that does not have a circular waveguide 3. An antenna having such a horn antenna 9 has the advantage that it can be manufactured by a 3D printer. As shown in FIG. 17, an antenna in which the circular waveguide terminal of the horn antenna 9 is connected to the circular waveguide terminal 4 of the polarization separation circuit can be manufactured by a 3D printer. In FIG. 17, a form in which the horn antenna 9 is connected to the polarization separation circuit of the first embodiment is shown, but the polarization separation circuit of the second or third embodiment may be connected to the horn antenna 9.

Furthermore, such an antenna may further include at least one filter. The filter can filter signals in a desired frequency band. An antenna including the filter 10a or 10b has the advantage that it can be manufactured using a 3D printer. As shown in FIG. 17, an antenna in which the filters 10a and 10b are connected to the rectangular waveguide terminals 6a and 6b of the polarization splitter circuit, respectively, can be manufactured using a 3D printer. FIG. 17 shows a form in which the filters 10a and 10b are connected to the polarization splitter circuit of the first embodiment, but the polarization splitter circuit of the second or third embodiment may also be connected to the filters 10a and 10b.

<Additional Notes>
Certain aspects of the various embodiments described above are summarized below.

(Appendix 1)
The polarization separation circuit of Appendix 1 includes a conversion waveguide (1; 1M) having one circular terminal (1A) whose cross section perpendicular to the tube axis direction is circular and two rectangular terminals (1Ba, 1Bb) whose cross section perpendicular to the tube axis direction is rectangular, and a septum phase plate (2; 2M) having a plurality of step noses (7a to 7d) and disposed inside the conversion waveguide, the septum phase plate having a shape in which the width of the septum phase plate in the short side direction becomes narrower in a stepped manner, and the septum phase plate is disposed inside the conversion waveguide so that the tip of the septum phase plate formed to be narrower in a stepped manner is located on the circular terminal side of the conversion waveguide.

(Appendix 2)
The polarization splitter circuit of Supplementary Note 2 is the polarization splitter circuit described in Supplementary Note 1, wherein at least one of the plurality of nosings has an acute angle in a plan view.

(Appendix 3)
The polarization separation circuit of supplementary note 3 is the polarization separation circuit of supplementary note 1 or 2, wherein the septum phase plate (2M) is trapezoidal in side view.

(Appendix 4)
The polarization splitter circuit of Supplementary Note 4 is the polarization splitter circuit according to any one of Supplementary Notes 1 to 3, wherein the two rectangular terminals have corners R(8A).

(Appendix 5)
The polarization splitting circuit of Supplementary Note 5 is the polarization splitting circuit described in any one of Supplementary Notes 1 to 4, further comprising a circular waveguide (3) having a circular cross section perpendicular to the tube axis direction and connected to the circular terminal.

(Appendix 6)
The antenna of Supplementary Note 6 comprises a polarization splitter circuit according to any one of Supplements 1 to 4, and a horn antenna (9) connected to the circular terminal of the conversion waveguide.

(Appendix 7)
The antenna of Supplementary Note 7 comprises the polarization splitter circuit described in Supplementary Note 5 and a horn antenna (9) connected to the circular waveguide.

(Appendix 8)
The antenna of Supplementary Note 8 is the antenna of Supplementary Note 6, further comprising two rectangular waveguides (5a, 5b) each having a cross-section corresponding to a cross-section of one of said two rectangular terminals and connected respectively to said two rectangular terminals.

(Appendix 9)
The antenna of Supplementary Note 9 is the antenna of Supplementary Note 7, further comprising two rectangular waveguides (5a, 5b) each having a cross-section corresponding to a cross-section of one of said two rectangular terminals and connected respectively to said two rectangular terminals.

(Appendix 10)
The antenna of claim 10 is the antenna of claim 8, wherein the rectangular waveguide has a corner R(8B).

(Appendix 11)
The antenna of claim 11 is the antenna of claim 9, wherein the rectangular waveguide has a corner R(8B).

(Appendix 12)
The antenna of Supplementary Note 12 is any one of the antennas of Supplementary Notes 8 to 11, further comprising two filters (10a, 10b) connected to the two rectangular waveguides.

It is possible to combine embodiments, or modify or omit each embodiment as appropriate.

The polarization splitting circuit disclosed herein can be connected to a horn antenna having a circular waveguide terminal and used as an antenna.

1 (1M) conversion waveguide, 1A circular terminal, 1B square terminal, 2 (2M) septum phase plate, 3 circular waveguide, 4 circular waveguide terminal, 5 (5Ma, 5Mb, 5a, 5b) rectangular waveguide, 6 (6a, 6b) rectangular waveguide terminal, 7 (7a-7d) step nosing, 8 (8A, 8B) corner R, 9 horn antenna, 10 (10a, 10b) filter.

Claims (14)

a conversion waveguide having one circular terminal and two rectangular terminals each having a circular cross section perpendicular to the tube axis direction, the cross section perpendicular to the tube axis direction being converted from the circular cross section to the cross sections of the two rectangular terminals;
a septum phase plate having a plurality of nosings and disposed within the conversion waveguide;
Equipped with
the septum phase plate has a shape in which the width in a short side direction of the septum phase plate narrows in a stepped manner, and is disposed inside the conversion waveguide such that a tip of the septum phase plate formed in a stepped manner is located on a circular terminal side of the conversion waveguide ,
At least one of the plurality of nosings has an acute angle in a plan view.
Polarization separation circuit. 2. The polarization splitter circuit according to claim 1 , wherein the septum phase plate is trapezoidal in side view. 3. The polarization splitter circuit according to claim 2 , wherein said two rectangular terminals have rounded corners. 4. The polarization splitter circuit according to claim 3 , further comprising a circular waveguide having a circular cross section perpendicular to the tube axis direction, the circular waveguide being connected to the circular terminal. A polarization splitter circuit according to any one of claims 1 to 3 ,
a horn antenna connected to the circular terminal of the conversion waveguide;
An antenna comprising: A polarization splitter circuit according to claim 4 ;
a horn antenna connected to the circular waveguide;
An antenna comprising: 6. The antenna of claim 5 , further comprising two rectangular waveguides each having a cross section corresponding to a cross section of one of said two rectangular terminals and connected to said two rectangular terminals, respectively. 7. The antenna of claim 6 , further comprising two rectangular waveguides each having a cross section corresponding to a cross section of one of said two rectangular terminals and connected to said two rectangular terminals, respectively. 8. The antenna of claim 7 , wherein said rectangular waveguide has radiused corners. 9. The antenna of claim 8 , wherein said rectangular waveguide has radiused corners. 8. The antenna of claim 7 , further comprising two filters connected to the two rectangular waveguides. 9. The antenna of claim 8 , further comprising two filters connected to the two rectangular waveguides. 10. The antenna of claim 9 , further comprising two filters connected to the two rectangular waveguides. 11. The antenna of claim 10 , further comprising two filters connected to the two rectangular waveguides.

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