GB2256534A

GB2256534A - Coaxial-waveguide converter.

Info

Publication number: GB2256534A
Application number: GB9208946A
Authority: GB
Inventors: Nobutaka Inoue
Original assignee: Maspro Denkoh Corp
Current assignee: Maspro Denkoh Corp
Priority date: 1991-04-26
Filing date: 1992-04-24
Publication date: 1992-12-09
Anticipated expiration: 2012-04-24
Also published as: FR2677176A1; JP3101930B2; GB2256534B; DE4213539A1; GB9208946D0; JPH04328901A

Description

COAXIAL-WAVEGUIDE CONVERTER

Background of the Invention

1. Field of the Invention

This invention relates a coaxial-wave guide converter wherein waveguidemode vertically polarized and horizontally polarized electromagnetic waves are converted to respective coaxial-mode electric signals and vice versa.

2. Description of the Prior Art

A coaxial-waveguide converter is conventionally known which has the construction as shown in Fig. 11. A circular waveguide 10g is formed, at one end thereof, with an opening 11g and is closed. at the other end thereof, by a shortcircuiting wall 12g. Two probes 17g and 18g to obtain respective coaxial-mode electric signals from vertically polarized and horizontally polarized waves introduced into the waveguide 10g are disposed in the the waveguide 10g at an interval along the axial line of the waveguide.

In this conventional coaxial-waveguide converter, a distance X equal to a quarter of a wavelength in a treated frequency band is necessary between the probe 17g close to the front side namely to the opening 11g and the probe 18g at the rear side. Moreover, a distance Y as long as X is necessary between the probe 18g at the rear side and the short- - 11% 11 circuiting wall 12g. Thus the distance between the location of the probe 17g at the front side and to the location of the short-circuiting wall 12 amounts to a half of the wavelength and the circular waveguide log has to be considerably long in its longitudinal direction. Accordingly, there is a problem that the converter is large-sized. If the distance between the probes and that between the probe at the rear side and the shortcircuiting wall are reduced for the purpose of miniaturizing the converter, there appear another problem that electric characteristics such as insertion loss and crossing polarized waves discriminating ratio are deteriorated.

Summary of the Invention

This invention has been made in order to solve the above mentioned problems in the prior art (technical subjects) and an object of it is to provide a coaxial -wave guide converter which is miniaturized by mounting a conducting rod on a short circuiting wall and by disposing two probes on a plane perpendicular to the axial line of a circular waveguide and can exhibit superior electric properties despite such miniaturizing.

According to the present invention, when waveguide-mode vertically polarized and horizontally polarized electromagnetic waves come into a circular waveguide, each of the two probes can separately convert each of the waves into a coaxial-mode signal and pick up the signal.

In the coaxial -wavegui de converter according to the present invention, the conducting rod is attached to the short-circuiting wall of the circular waveguide and disposed along the axial line of the circular waveguide. The two probes are disposed on a plane perpendicular to the axial lone of the circular waveguide so that the axes of the probes may intersect at right angles on the axial line of the circular waveguide. Accordingly, the present invention has a feature that a small distance between the short-circuiting wall and each of the probes (such as about one sixth to one ninth of a wavelength in a treated frequency band) is sufficient. This means that the distance from the location of the probe to the location of the short-circuiting wall can be small and leads to an advantage that the converter can be miniaturized.

Furthermore, since the converter capable of being thus miniaturized has the above mentioned construction, each of the probes can pick up its electric signal with various better electric characteristics from each of the waveguide-mode vertically polarized and horizontally polarized waves which have come into the circular waveguide.

Brief Description of the Drawings

Fig. 1 is a longitudinal section of a converter-fitted - A - primary radiator:

Fig. 2 is a section taken along a line II-II in Fig. 1; Fig. 3 is a bottom view of the primary radiator; Fig. 4 is a left side elevation of the primary radiator; Fig. 5 is a graph showing characteristics of insertion loss; Fig. 6 is a graph showing characteristics of crossing polarized waves discriminating ratio; Fig. 7 is a graph showing characteristics of return loss; Fig. 8 is a fragmental longitudinal section showing a different embodiment; Fig. 9 is a longitudinal section showing a still different embodiment:

Fig. 10 is a left side elevation of the embodiment in Fig. 9 and Fig. 11 is a schematic perspective view showing a prior art embodiment.

Description of the Preferred Embodiments

Embodiments of the present invention are explained in reference with the drawings. A converter-fitted primary radiator in a parabola antenna is shown by a reference numeral 1. The converter-fitted primary radiator 1 consists of a primary radiator 2, circuit basal plates 3 and 4 at- f r_ 1 tached to the radiator 2, a cap 5 to cover an opening of the primary radiator 2 and a cover 6 to protect the circuit basal plates 3 and 4. The primary radiator 2 is first explained. Reference numerals 8 and 9 show a coaxial-waveguide converter and a horn, respectively. Both members are integrally formed as shown in the figures. The coaxial-waveguide converter 8 is explained. A circular waveguide 10 is made of an electrically well-conducting metal such as aluminum. The inner diameter D of the waveguide 10 is set equal to, for example, 15.74 mm which is a length suitable for the satisfactory propagation of waves in a treated frequency band such as 11.7-12.2 GHz. A reference numeral 11 shows an opening formed at one end of the circular waveguide 10. A shortcircuiting wall 12 is adapted to close the other end of the circular waveguide 10 and is formed integrally with the waveguide 10. A conducting rod 14 made of an electrically well-conducting metal is formed on the short-circuiting wall 12 so that the rod 14 may disposed along the axial line 10a of the circular waveguide 10. The rod 14 is formed integrally with the short-circuiting wall 12 in the present embodiment but may be formed separately and then mounted on the short-circuiting wall 12. The separate conducting rod 14 may be mounted in an arbitrary manner so long as the conducting rod 14 and the shortcircuiting wall 12 form a short circuit for waves in the treated frequency band. Accordingly, the conducting rod 14 may be mounted on the short-circuiting wall 12 either 6. - directly or with a thin dielectric film sandwiched therebet ween. The conducting rod 14 is a circular rod in the present embodiment but may be an elliptic or square rod.

Next in Fig. 2, reference numerals 17 and 18 show probes. The probes 17 and 18 are used for the purpose of receiving, for example, vertically polarized and horizontally polarized waves, respectively. Each of these probes 17 and 18 is made of an electrically well-conducting material and is mounted through an insulator 20 inserted in a through hole 19 formed in the wall of the circular waveguide 10. Both probes 17 and 18 are disposed on a plane perpendicular to the axial line 10a of the circular waveguide 10 as is clear from their relationship shown in Figs. 1 and 2. Furthermore, the probes 17 and 18 are disposed so that the axial lines of them intersect at right angles on the axial line 10a of the circular waveguide 10 as shown in Fig. 2. Inside protrusions 17a and 18a of the probes 17 and 18. respectively are extending into the circular waveguide 10 and adapted to pick up electric signals from the waves in the waveguide. Outside protrusions 17b and 18b extending into the outside of the circular waveguide 10 are adapted to function as connectors to the circuit basal plates. Reference numerals 17c and 18c are connecting portions to connect the inside protrusions to the outside ones.

In the next place, a circuit basal plate mount 22 is provided on the outer circumferential surface of the circular 7 waveguide 10. The mount 22 is formed with a flat surface. This flat surface intersects each of the planes of polarization of the two waves introduced into the circular waveguide 10 at an angle of 450. As is clearly seen from Fig. 1, the mount 22 has such a sufficient length that the mount reaches a part of the external circumferential surface of the horn 9. A reference numeral 24 shows a cover mount formed integrally with the circular waveguide 10.

In the next place, the horn 9 is well known one for introduction and radiation of electromagnetic waves and is formed. on the inner circumferential surface thereof, with well known plural steps 25, 26, 27 and 28. A reference numeral 29 shows a cap holder of the horn 9 and the aforementioned cap 5 is secured at this holder.

In the next place, the circuit basal plates 3 and 4 are both printed basal plates, on which various electronic components 32 and 34 are mounted and a well known converter circuit is formed. The circuit basal plate 3 of these circuit basal plates 3 and 4 is put closely to and secured on the circuit basal mount 22. In this situation of the circuit basal plate 3, the outside protrusions 17b and 18b of the aforementioned probes 17 and 18 are connected with solder to terminals provided on the circuit basal plate 3. On the other hand, the circuit basal plate 4 is mounted, by a well known mounting means, on a mount (not shown) provided on the outer circumferential surface of the aforementioned primary - p - radiator 2.

In the next place. the aforementioned cover 6 is put as shown in Figs. 1 and 2 and is secured on the cover mount 24 by a fastening screw 35. To the splicing surfaces 36 of the cover 6 and the cap 5 is applied a sealing material to make the inside of the cover waterproof.

Now the operation of the converterfitted primary radiator 1 is explained. Two waveguide-mode vertically polarized and horizontally polarized waves come into of the primary radiator 1. Namely. these waves are introduced through the horn 9 into the circular waveguide 10 in the coaxialwaveguide converter 8. Then a coaxial-mode electric signal is obtained in the inside protrusion 17a of the probe 17 from the waveguide-mode vertically polarized wave of these two waves. The signal reaches the outside protrusion 17b through the connecting portion 17c. On the other hand, another coaxial-mode electric signal is obtained in the inside protrusion 18a of the probe 18 from the waveguidemode horizontally polarized wave of those two waves. The signal reaches the outside protrusion 18b through the connecting portion 18c. Each of the signals reaching respective outside protrusion 17b or 18b is sent to the circuit basal plate 3, where the frequency conversion and other processings of the signals are performed in a well known manner. Output signals are obtained from output terminals (not shown) in the converter-fitted primary radiator 1.

When the coaxial-mode signals are obtained by the coaxial -waveguide converter 8 from the vertically polarized and horizontally polarized waves, respectively in the above mentioned operation, the converter 8 of the present embodiment has the following advantages. Namely, the converter 8 of the present embodiment is provided with the conducting rod 14 and besides the probes 17 and 18 are disposed in the above mentioned manner. Consequently, the electric signals can be obtained, with less insertion loss, in the outside protrusions 17b and 18b of the probes 17 and 18. Furthermore, the signal in each of the outside protrusions 17b and 18b of the probes 17 and 18 can be obtained with higher crossing polarized waves discriminating ratio.

The above mentioned coaxial-waveguide converter may be one for transmitting purpose. In this case, coaxial-mode signals are given to the probes 17 and 18. Then these signals are converted into waveguide-mode vertically polarized and horizontally, polarized waves, respectively and the waves are radiated from the opening 11 through the horn 9 into the space in front of the horn.

In the next place, are explained the dimensions of the conducting rod 14, the lengths of the inside protrusions 17a and 18a of the probes 17 and 18 and the setting of the distance between the protrusions and the shortcircuiting wall 12. First, the length of the inside protrusions 17a and 18a of the probes 17 and 18 is set equal to, for example, about - 1 n, one fifth of the free-space wavelength. of a wave in the treated frequency band. This length can be set equal to an arbitrary value between one sixth and one fourth of the wavelength 1 by selecting either a larger or a smaller diameter of the inside protrusions 17a and 18a. On the other hand, the diameter d of the conducting rod 14 is selected to be equal to, for example, one fourth of the inner diameter D of the circular waveguide 10 so that the impedance at the side of the circular waveguide 10 may well match the impedance at the side of the probes 17 and 18. This diameter d may be made either smaller or larger so long as the conducting rod 14 does not contact the probes 17 and 18. After the diameter d of the conducting rod 14 is determined in the above mentioned manner, the distance L1 between the probes 17 and 18 and the shortcircuiting wall 12 is set. When the diameter d of the conducting rod 14 is one fourth of the inner diameter of the circular waveguide 10, one sixth of the wavelength _ is selected as a standard of the length Ll. However, when the diameter d is larger, the distance L1 can be decreased up to a value as small as, for example, about one ninth of the wavelength. On the other hand, when the diameter d is smaller, the distance L1 can be increased up to a value as large as about one third of the wavelength A. After the distance L1 is set in the above mentioned manner, the length L2 of the conducting rod 14 is set. This length L2 is selected so that the distance L3 between the end of the v conducting rod 14 at the side of the opening 11 and the intersection of the axial line of the conducting rod 14 and the plane including the axial lines of the probes 17 and 18 may be one fourth of the wavelength.. Namely, the length L3 is set equal to the sum of the distance L1 and one fourth of the wavelength;,.

In the next place, several definite examples with different values of the above mentioned dimensions are given in Table 1 and the insertion loss characteristics, the charac teristics of crossing polarized waves discriminating ratio and the return loss characteristics in these examples are shown in Figs. 5, 6 and 7, respectively.

Table 1 definite examples d (mm) L1 (mm) L3 (mm) 3.04 5.41 /4.6) 6, 60 ( /3. 8)1 2 3.95 4.16 /6.0) 6. 61 ( /3. 8)i 3 4.76 3.40 /7.4) 6. 60 ( /3. 8)! 3.95 4.16 /6.0) 13. 00 ( /2. 0)l 3.95 4,16 /6.0) 19.28 (, /1.3) 4 5 In Fig. 5, the standard value of insertion loss for the judgment of acceptance or rejection as products is, for example, 0.4 dB and the smaller insertion losses in the definite examples 1, 2 and 3 satisfy the standard value. In - -19 - Fig. 6, the standard value of the crossing polarized waves discriminating ratio for the judgment is, for example, 20 dB and the larger ratios in the definite examples 1, 2, 3 and 5 satisfy the standard value. In Fig. 7, the standard value of return loss for the judgment is, for example, 17 dB and the larger losses in the definite examples 1, 2 and 3 satisfy the standard value.

In the next place, Fig. 8 shows a different embodiment of the present invention i.e. an embodiment in which an conducting rod 14e is formed with an integral conical matching member 37. When the matching member of this type is provided, the efficiency of conversion from the waveguide- mode to the coaxial-mode is raised in the case of reception of waves. Moreover, the efficiency of conversion from the coaxial-mode to the wavegui de -mode is raised in the case of transmission of waves. Members which are considered same as or constructionally equivalent to the members in the foregoing figures are given the reference numerals same as those in the foregoing figures but with an affixed alphabet e and the explanation of the members is not repeated. (Members of this type in the following figures are similarly given reference numerals with an affixed alphabet f and the explanation of the members is not repeated.) In the next place, Figs. 9 and 10 show an embodiment in which a circularlylinearly polarized waves converter 38 is connected to the front side of a coaxial -wave guide converter 8f so that a circularly polarized wave may be received. The converter 38 includes a waveguide 40 formed integrally with a circular waveguide 10f in a converter 8f. A phase difference plate 41 is provided inside the waveguide 40. While the circularly polarized wave is passing through the waveguide 40, a phase difference appears between those components of the circularly polarized wave whose planes of polarization are perpendicular to and parallel to the phase difference plate 41. The length of the phase difference plate 41 (the length in the axial direction of the waveguide 40) is set equal to a value such as to make the phase difference 900. The phase difference plate 41 secured at both edges thereof which are fitted in slits 42 and 42 formed in the wall of the waveguide 40.

In the converter constructed in this manner, a righthanded circularly polarized wave directed towards the converter 38 is converted into a vertically polarized wave while the circularly polarized wave is passing through the converter 38. This wave enters the coaxial-waveguide converter 8f and an electric signal is picked up by a probe 17f. On the other hand, a left-handed circularly polarized wave entering the converter 38 is converted into a horizontally polarized wave. This wave enters the converter 8f and an electric signal is picked up by a probe 18f.

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Claims

1. A coaxial-waveguide converter comprising a circular waveguide formed, at one end thereof, with an opening for the introduction of electromagnetic waves and closed, at the other end thereof. by a shortcircuiting wall. and two probes adapted to pick up respective coaxialmode electric signals from vertically polarized and horizontally polarized waves respectively which have been introduced into the waveguide, wherein a conducting rod is attached, at one end thereof to said short-circuiting wall so that said rod may be disposed along the axial line of said circular waveguide, and said two probes are disposed on a plane perpendicular to the axial line of the circular waveguide so that the axial lines of the respective probes may intersect at right angles on the axial line of said circular waveguide.

2. A coaxial -waveguide converter as set forth in claim 1 wherein a conical matching member is attached to the other end of said conducting rod.

3. A coax i al -waveguide converter as set forth in claim 1 wherein said circular waveguide is formed, on the outer circumferential surface thereof, with that flat mount for a circuit basal plate which intersects each of the planes of polarization of the vertically polarized and horizontally polarized waves at an angle of 45

4. All coaxial-waveguide converter substantially as hereinbef-ore described with reference to the drawings and/or as sho%r. in figures 1 to 5,0r figure 8, or figures 9 and 10 of the drawings.

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