Primary radiator in which the total length of dielectric feeder is reduced

Abstract: Disclosed is a primary radiator of the type in which a dielectric feeder is held at an open end of a wave guide, wherein the total length of the dielectric feeder is reduced. In a primary radiator in which a dielectric feeder is held at an open end of a wave guide, the dielectric feeder (5) includes a holding portion (5a) forced into the interior of the open end portion of the wave guide, and a radiation portion (5b) protruding outwardly from the open end of the wave guide (1), a recess (6) being formed in an end surface of the holding portion. The recess consists of a stepped hole composed of a large diameter cylindrical hole (6a) and a small diameter cylindrical hole (6b) connected to the bottom surface thereof, the depth of each cylindrical hole being approximately 1/4 of the wavelength λε of the radio wave propagated through the dielectric feeder (5).

Description: The present invention relates to a primary radiator provided in a satellite receiving reflective antenna or the like and, in particular, to a primary radiator using a dielectric feeder. Fig. 6 is a sectional view of a conventional primary radiator using a dielectric feeder. This primary radiator comprises a wave guide 1 one end of which is open and the other end of which is formed as a closed surface 1a, and a dielectric feeder 2 held at the open end of the wave guide 1. Inside the wave guide 1, a first probe 3 and a second probe 4 are installed so as to be orthogonal to each other, the distance between the probes 3 and 4 and the closed surface 1a corresponding to approximately 1/4 of the guide wavelength. The dielectric feeder 2 is formed of a dielectric material, such as polyethylene. A holding portion 2a is formed in the middle of the dielectric feeder 2, and a radiation portion 2b and a conversion portion 2c are formed on either side of it. The outer diameter of the holding portion 2a is substantially the same as the inner diameter of the wave guide 1. By forcing the holding portion 2a into the open end portion of the wave guide 1, the dielectric feeder 2 is secured to the wave guide 1. Both the radiation portion 2b and the conversion portion 2c have a conical configuration, and the radiation portion 2b protrudes to the exterior from the open end of the wave guide 1, the conversion portion 2c extending into the interior of the wave guide 1. The primary radiator, constructed as described above, is installed at the focal position of the reflecting mirror of a satellite receiving reflective antenna. A radio wave transmitted from the satellite converges at the dielectric feeder 2 and undergoes impedance matching before entering the wave guide 1. And, of the linearly polarized wave input to the wave guide 1, consisting of horizontally polarized wave and vertically polarized wave, the horizontally polarized wave is received by the first probe 3, and the vertically polarized wave is received by the second probe 4, the reception signal being frequency-converted into an IF frequency signal by a converter circuit (not shown) before being output. Compared with a conical horn type primary radiator having a wave guide whose open end portion is flared, the conventional primary radiator using a dielectric feeder, constructed as described above, is advantageous in that a reduction in radial dimension can be achieved. However, due to the radiation portion 2b and the conversion portion 2c formed at either end of the dielectric feeder 2 and having a conical configuration, the total length of the dielectric feeder 2 is rather large. In particular, the conversion portion 2c extending in the wave guide 1 must be.formed as a long cone in order to secure a satisfactory impedance matching with the wave guide 1. Further, the holding portion 2a forced into the wave guide 1 must be long enough to stabilize the attitude of the dielectric feeder 2, with the result that a reduction in the size of the primary radiator is prevented. US-A-5,907,309 discloses a primary radiator comprising a wave guide and a dielectric feeder, which comprises a radiation portion, a holding portion and a recess in the holding portion. In accordance with the present invention, there is formed at the end surface of the holding portion secured to the inner surface of the wave guide a recess extending in the axial direction of the wave guide or a protrusion having a height corresponding to approximately 1/4 of the wavelength of the radio wave. In this construction, the recess or the protrusion formed at the end surface of the holding portion functions as an impedance conversion portion, so that, in spite of the fact that a sufficient length is secured for the holding portion to stabilize the attitude of the dielectric feeder, it is possible to reduce the total length of the dielectric feeder, making it possible to achieve a reduction in the size of the primary radiator. In accordance with the present invention, there is provided a primary radiator comprising a wave guide having at one end an opening for introducing a radio wave, and a dielectric feeder held at the open end of the wave guide, wherein the dielectric feeder comprises a radiation portion protruding from the open end of the wave guide and a holding portion secured to the inner surface of the wave guide, a recess extending in the axial direction of the wave guide being formed at the end surface of the holding portion. It is possible to reduce the length of the radiation portion and further reduce the size of the primary radiator when there are formed at the end surface of the radiation portion a plurality of annular grooves having a depth corresponding to approximately 1/4 of the wavelength of the radio wave. In this construction, the impedance matching of the wave guide and the dielectric feeder is effected in the recess extending inwardly from the end surface of the holding portion, so that it is possible to secure a sufficient length for the holding portion to stabilize the attitude of the dielectric feeder, and reduce the total length of the dielectric feeder to achieve a reduction in the size of the primary feeder. In the above construction, the recess may have a conical or a pyramid-like configuration tapering off toward the interior of the dielectric feeder. To reduce the depth of the recess, however, it is desirable to form it as a cylindrical hole having a depth corresponding to approximately 1/4 of the wavelength of radio wave, or a stepped hole consisting of a plurality of continuously formed cylindrical holes having different diameters, the depth of each cylindrical hole corresponding to approximately 1/4 of the wavelength of radio wave. In this case, in each cylindrical hole, the phase of the radio wave reflected at the bottom surface and the open end of the cylindrical hole is reversed to be canceled, so that it is possible to substantially reduce the reflection component of the radio wave, and the impedance matching with the wave guide is effected satisfactorily. There is no particular restriction to the number of recesses. However, when forming a single recess at the end surface of the holding portion, it is desirable for the recess to be matched with the position of the axial center of the wave guide. On the other hand, when forming a plurality of recesses at the end surface of he holding portion, it is desirable to provide the recesses in an annular arrangement around the axis of the wave guide, or provide the recesses symmetrically with respect to the axis of the wave guide. In accordance with the present invention, there is further provided a primary radiator comprising a wave guide having at one end an opening for introducing radio wave, and a dielectric feeder held at the open end of the wave guide, wherein the dielectric feeder includes a radiation portion protruding from the open end of the wave guide and a holding portion forced into the interior of the wave guide, a protrusion having a height corresponding to approximately 1/4 of radio wave being formed at the end surface of the holding portion. In this construction, the phase of the radio wave reflected at the protruding surface of the protrusion and the bottom surface is reversed to be canceled, so that the reflection component of the radio wave is substantially reduced and a satisfactory impedance matching with the wave guide is ensured, whereby it is possible to restrain the protruding amount of the protrusion functioning as the impedance conversion portion to reduce the total length of the dielectric feeder, thereby achieving a reduction in the size of the primary radiator. In the above construction, there is no particular restriction to the number of protrusions. However, when forming a single protrusion at the end surface of the holding portion, it is desirable to match this protrusion with the position of the axis of this wave guide. On the other hand, when forming a plurality of protrusions at the end surface of the holding portion, a stepped protrusion consisting of a plurality of continuously formed cylindrical portions having different diameters is formed, the height of each cylindrical portion corresponding to approximately 1/4 of the wavelength of radio wave. Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a sectional view of a primary radiator according to a first embodiment of the present invention; Fig. 2 is a right-hand side view of a dielectric feeder provided in the primary radiator; Fig. 3 is a left-hand side view of the dielectric feeder; Fig. 4 is a schematic diagram illustrating the dielectric feeder; Fig. 5 is a sectional view of a primary radiator according to a second embodiment of the present invention; and Fig. 6 is a sectional view of a conventional primary radiator. As shown in these drawings, the primary radiator of this embodiment comprises a circular-sectioned wave guide 1 one end of which is open and the other end of which is formed as a closed surface 1a, and a dielectric feeder held at the open end of the wave guide 1, a first probe 3 and a second probe 4 being installed inside the wave guide 1 so as to be orthogonal to each other. The distance between these probes 3, 4 and the closed surface 1a corresponds to approximately 1/4 of the guide wavelength λg, the probes 3 and 4 being connected to a converter circuit (not shown). The dielectric feeder 5 is formed of a dielectric material having a low dielectric loss tangent. In this embodiment, polyethylene (dielectric constant ε = 2.25), which is inexpensive, is used in view of the price. The dielectric feeder 5 comprises a holding portion 5a having a recess 6 at one end, and a radiation portion 5b flared at the other end of the holding portion 5a, a plurality of annular grooves 7 being formed in the end surface of the radiation portion 5b. The outer diameter of the holding portion 5a is substantially the same as the inner diameter of the wave guide 1. By forcing the holding portion 5a into the open end of the wave guide 1, the dielectric feeder 5 is secured to the wave guide 1. The recess 6 is a stepped hole consisting of a cylindrical portion 6a having a relatively large diameter and a cylindrical portion 6b continuously formed at the bottom of the cylindrical portion 6a, the depth of the cylindrical portions 6a and 6b being approximately 1/4 of the wavelength λε of the radio wave propagated in the dielectric feeder 5. The radiation portion 5b of the dielectric feeder 5 protrudes outwardly from the open end of the wave guide 1, and this radiation portion 5b is flared so as to make an angle  with respect to the peripheral surface of the holding portion 5a. The annular grooves 7 are concentrically formed in the end surface of the radiation portion 5b, and the depth of the annular grooves 7 is approximately 1/4 of the wavelength λ 0 of radio wave propagated through the air. The radiation portion 5b is a receiver of the radio wave reflected by the reflective mirror. To receive the radio wave efficiently, a predetermined directional angle is necessary for the radiation pattern of the radiation portion 5b. This radiation pattern is determined by the diameter D of the end surface of the radiation portion 5b and the length L of the radiation portion 5b. Assuming that the directional angle of the radiation pattern is fixed, the angle , the diameter D and the length L are closely related to each other. The larger the angle , the larger the diameter D of the end surface of the radiation portion 5b, and the length L of the radiation portion 5b can be reduced. When the angle 0 exceeds a critical angle, the radio wave entering through the end surface of the radiation portion 5b is allowed to be transmitted through the peripheral surface of the radiation portion 5b. Taking these facts into consideration, the range of the angle 0 is set as follows: 0 <  < sin -1 (1/ ε ) In this embodiment, polyethylene is used as the material of the dielectric feeder 5, and its dielectric constant ε is 2.25. By substituting the value of ε = 2.25 into formula (1), the following range of the angle  is obtained: 0° <  < 43.5°. Thus, by making the angle  as large as possible within this range, it is possible to reduce the length L of the radiation portion 5b. Next, the operation of this primary radiator, constructed as described above, will be described. The radio wave transmitted from the satellite is collected by the reflective mirror of the antenna to reach the primary radiator. It enters the dielectric feeder 5 through the radiation portion 5b and converges. A plurality of annular grooves 7 are formed in the end surface of the radiation portion 5b, and the depth of the annular grooves 7 is approximately 1/4 of the wavelength λ 0 of the radio wave propagated through the air, so that the phase of the radio wave reflected by the end surface of the radiation portion 5b and the bottom surface of the annular grooves 7 is reversed to be canceled, whereby there is practically no reflection component of radio wave directed to the radiation portion 5b, thereby making it possible to converge the radio wave efficiently on the dielectric feeder 5. The radio wave entering through the radiation portion 5b is propagated through the dielectric feeder 5 and undergoes impedance matching with the wave guide 1 at the end surface of the holding portion 5a. In the end surface of the holding portion 5a, there is formed a recess 6 consisting of two cylindrical holes 6a and 6b continuously formed in a step-like fashion, and the depth of the cylindrical holes 6a and 6b is approximately 1/4 of the wavelength λε of the radio wave propagated through the dielectric feeder 5, so that the radio wave reflected by the end surface of the holding portion 5a and the bottom surface of the small-diameter cylindrical hole 6b and the radio wave reflected by the bottom surface of the large-diameter cylindrical hole 6a undergo phase reversal to be canceled, whereby there is practically no reflection component of radio wave propagated through the dielectric feeder 5 and directed toward the interior of the wave guide 1, thereby making the impedance matching of the wave guide 1 and the dielectric feeder 5 satisfactory. And, of the linearly polarized wave consisting of a horizontally polarized wave and vertically polarized wave input to the wave guide 1, the horizontally polarized wave is received by the first probe 3 and the vertically polarized wave is received by the second probe 4, the reception signal being frequency-converted to an IF frequency signal by a converter circuit (not shown) and output. In the first embodiment described above, the recess 6 formed in the end surface of the holding portion 5 functions as the impedance conversion portion, so that it is possible to reduce the total length of the dielectric feeder 5, making it possible to achieve a reduction in the size of the primary radiator. Further, the total length of the dielectric feeder 5 is not increased if a sufficient length is secured for the holding portion 5a, so that it is possible to stabilize the attitude of the dielectric feeder 5. Further, the recess 6 consists of a stepped hole composed of two cylindrical holes 6a and 6b continuously formed in a step-like fashion, and the depth of the cylindrical holes 6a and 6b is approximately 1/4 of the wavelength λε of the radio wave propagated through the dielectric feeder 5, so that the radio wave reflected by the bottom surfaces of the cylindrical holes 6a and 6b and by the open end undergoes phase reversal to be canceled, whereby the impedance matching of the wave guide 1 and the dielectric feeder 5 is satisfactory. Fig. 5 is a sectional view of a primary radiator according to a second embodiment of the present invention, and the components corresponding to those of Fig. 1 are indicated by the same reference numerals. The second embodiment differs from the first embodiment in that a protrusion 8 is formed on the end surface of the holding portion 5a instead of the recess. Apart from that, it has the same basic construction as the first embodiment. The protrusion 8 is a reversal of the recess 6, that is, it consists of a stepped protrusion composed of a large-diameter cylindrical portion 8a and a small-diameter cylindrical portion 8b protruding from the end surface of the large-diameter cylindrical portion 8a, and the height of the cylindrical portions 8a and 8b is approximately 1/4 of the wave length λε of the radio wave propagated through the dielectric feeder 5. Thus, of the radio wave propagated through the dielectric feeder 5 and directed toward the end surface of the holding portion 5a, the radio wave reflected by the end surfaces of the cylindrical portions 8a and 8b and the bottom surface undergoes phase reversal to be canceled, so that there is practically no reflection component of radio wave propagated through the dielectric feeder 5, and the impedance matching of the wave guide 1 and the dielectric feeder 5 is satisfactory. In the primary radiator, constructed as described above, the protrusion 8 formed on the end surface of the holding portion 5a functions as the impedance conversion portion, so that, although the effect is somewhat less remarkable than that of the first embodiment, it is possible to reduce the total length of the dielectric feeder 5 as compared to the prior art, making it possible to achieve a reduction in the size of the primary radiator. The primary radiator of the present invention is not restricted to the above embodiments, and various modifications are possible. For example, it is possible to appropriately increase or decrease the number of steps of the recess or protrusion formed at the end surface of the dielectric feeder, to concentrically arrange the plurality of annularly formed recesses, or to scatter the plurality of recesses while maintaining the symmetricalness. Further, it is possible to change the configuration of the recesses to a conical or pyramid-like one, to change the sectional configuration of the recess or the protrusion to one other than circular, for example, a polygonal one, such as triangular or square, or to change the sectional configuration of the wave guide 1 and the holding portion 5a of the dielectric feeder 5 from the circular one to a rectangular one. The present invention, described above, provides the following advantage. In a primary radiator holding a dielectric feeder at the open end of a wave guide, when there is formed at the end surface of the holding portion secured to the inner surface of the wave guide a recess or a protrusion which extends in the axial direction of the wave guide and whose depth or height corresponds to approximately 1/4 of the wavelength of radio wave, the recess or the protrusion functions as the impedance conversion portion, so that, although a sufficient length is secured for the holding portion to stabilize the attitude of the dielectric feeder, it is possible to reduce the total length of the dielectric feeder, making it possible to achieve a reduction in the size of a primary radiator.

Claims: A primary radiator comprising a wave guide (1) having at one end an opening for introducing a radio wave, and a dielectric feeder held at the open end of the wave guide, wherein the dielectric feeder comprises a radiation portion (5b) protruding from the open end of the wave guide and a holding portion (5a) secured to the inner surface of the wave guide, a recess (6) extending in the axial direction of the wave guide being formed at the end surface of the holding portion, characterized in that a plurality of annular grooves (7) having a depth corresponding to approximately 1/4 of the wavelength of the radio wave are formed at the end surface of the radiation portion. A primary radiator according to Claim 1, wherein the recess has a conical or a pyramid-like configuration tapering off toward the interior of the dielectric feeder. A primary radiator according to Claim 1, wherein the recess (6) is formed as a cylindrical hole having a depth corresponding to approximately 1/4 of the wavelength of radio wave. A primary radiator according to Claim 1, wherein the recess is a stepped hole consisting of a plurality of continuously formed cylindrical holes (6a, 6b) having different diameters, the depth of each cylindrical hole corresponding to approximately 1/4 of the wavelength of radio wave. A primary radiator according to any preceding claim, wherein the number of said recesses is one, the recess being provided at the axial position of the wave guide. A primary radiator according to any Claim 1 to 4, wherein a plurality of said recesses are provided annularly around the axis of the wave guide. A primary radiator according to any Claim 1 to 4, wherein a plurality of said recesses are provided symmetrically with respect to the axis of the wave guide.

Inventors: YUANZHU DOU, YUANZHU, DOU
Applicants: ALPS ELECTRIC CO LTD, ALPS ELECTRIC CO., LTD.
Application year: 2000
Main classification: H01Q13
IPC codes: H01Q13, H01Q19