Waveguide coaxial converter

Abstract: Disclosed is a waveguide coaxial converter which has a waveguide which is in the form of a bottomed rectangle and in which a high-frequency signal propagates; at least two means for regulating a capacitive susceptance which are provided with having a predetermined angle to an axis line of the waveguide at a predetermined position on a wide face of the waveguide and are respectively disposed at an interval of one eighth of a guide wavelength λg in the direction of the axis line; and at least a pair of step portions for stepwise narrowing the width between both internal sidewalls of the waveguide, each of the step portions being provided on the internal sidewalls respectively, wherein the step portions are placed with a distance of one eighth of the guide wavelength in the direction of the axis line.

Description: This invention relates to a waveguide coaxial converter for a microwave circuit, and more particularly to, waveguide coaxial converter having a regulating means of load impedance. A waveguide coaxial converter is in general used for the conversion of the propagation form of a high-frequency signal between a waveguide and a coaxial line. In such waveguide coaxial converter, the impedance matching between a waveguide and a coaxial line and the biasing to a detector etc. provided with the coaxial line is desired to be effectively achieved. JP-U-61-27203 discloses one type of a waveguide coaxial converter in which an insulating portion is provided at the connecting part between a ridge portion and an internal wall of the waveguide and a connecting conductor from the ridge portion is disposed through a small hole provided with the wall of the waveguide and the connecting conductor is used as a biasing terminal. JP-A-63-187707 discloses a waveguide coaxial converter in which a ridge waveguide band cross section is strictly calculated such that a cut-off frequency is brought outside a operating frequency, thereby obtaining the operating frequency more than one octave, and a dielectric, by the layer number of which impedance matching is realized, is provided at the opening of the waveguide. Further, JP-U-57-36006 discloses a waveguide matching circuit in which a plurality of screws are deposited at intervals of λg/4 (λ:guide wavelength) on the feeding portion of the waveguide. However, in the above conventional waveguide coaxial converter, the matching range does not cover both a capacitive region and an inductive region, i.e., it is limited to the capacitive region. Further, since the conventional waveguide coaxial converter is in general separated from a regulating means of load impedance, there is a disadvantage that the scale must become large after it is connected with a waveguide with the regulating means of load impedance. EP-A-0 247 794 discloses a matching technique for step discontinuities in waveguides which uses two capacitive elements spaced less than a quarter of a guide wavelength apart. Accordingly, it is an object of the invention to provide a waveguide coaxial converter in which the matching range of susceptance can be extended over both a capacitive region and an inductive region. It is a further object of the invention to provide a waveguide matching circuit in which the matching range of susceptance can be extended over both a capacitive region and an inductive region. These objects are achieved with the features of the claims. In the waveguide coaxial converter according to the invention, an inductive susceptance at the side of a load is increased by the step portions where the internal sidewalls are stepwise narrowed. However, due to the capacitive susceptance regulating means, the capacitive susceptance can be regulated. As a result, the impedance matching can be carried out over the wide range from an inductive region to a capacitive region. Furthermore, due to the capacitive susceptance regulating means, which are provided with having a predetermined angle to an axis line of the waveguide at a predetermined position on a wide face of the waveguide and are respectively disposed at an interval of one eighth of a guide wavelength λg in the direction of the axis line, the size in the direction of the axis line can be significantly decreased. Moreover, the increase of the cut-off frequency caused by the step portions can be suppressed by a ridge portion with a proper shape. In the waveguide matching circuit according to the invention, an inductive susceptance at the side of a load is increased by inductive materials. However, due to the capacitive susceptance regulating means, the capacitive susceptance can be regulated. As a result, the impedance matching can be carried out over the wide range from an inductive region to a capacitive region. Furthermore, due to the capacitive susceptance regulating means, which are provided with having a predetermined angle to an axis line of the waveguide at a predetermined position on a wide face of the waveguide and are respectively disposed at an interval of one eighth of a guide wavelength λg in the direction of the axis line, the size in the direction of the axis line can be significantly decreased. The invention will be explained in more detail in conjunction with the appended drawings, wherein: FIG.1A is a partially broken plan view showing a conventional waveguide coaxial converter as well as a separated waveguide, FIG.1B is a partially broken side view of FIG.1A, FIG.2A is a cross sectional view showing a waveguide coaxial converter in a preferred embodiment according to the invention, FIG.2B is a cross sectional view cut along the line A-A in FIG.2A, and FIG.3 is a cross sectional view showing a waveguide matching circuit in a preferred embodiment according to the invention. Before explaining a waveguide coaxial converter in the preferred embodiment, the aforementioned conventional waveguide coaxial converter will be explained in FIGS. 1A and 1B. FIGS.1A and 1B show a conventional waveguide coaxial converter in which three screws 32 for adjusting the amount of insertion vertical to the longitudinal axis thereof are disposed at respective intervals of λg/4 on the top of a waveguide 30. When regulating the impedance, a capacitive susceptance can be changed according to the respective amount of insertion of the screws 32. Therefore, the matching of impedance can be performed in a practical range, though it is not all range. When the waveguide coaxial converter comprises a waveguide 30 with such regulation mechanism of the impedance, a waveguide coaxial converter 33 which serves as an interface to a coaxial line is, as shown in FIG.1A or 1B, attached to an opened end of the waveguide 30. Next, a waveguide coaxial converter in a preferred embodiment will be explained in FIGS.2A and 2B. The waveguide coaxial converter 10 comprises step portions 11a, 11b, screws 12 for regulating a capacitive susceptance, a connector 13 for connecting the converter 10 with a coaxial line, a center conductor 14 in the connector 13 and a ridge portion 15. As shown in FIG.2A, the internal sidewalls and internal wide faces in the waveguide coaxial converter 10 are formed tapered with being gradually narrowed from an opened end to a bottom portion. The step portions 11a and 11b formed at both inside walls are disposed at an interval of λg/8. The respective faces for forming the step portions 11a and 11b are parallel to the face on the opening of the waveguide coaxial converter 10. A pair of screws (means for regulating a capacitive susceptance) 12 so that the amount of insertion in the direction of the internal wide face can be optionally regulated are disposed at predetermined positions on the internal wide face which respectively correspond to the positions of the step portions 11a, 11b. Furthermore, to correct the increase of the cut-off frequency caused by the step portions 11a, 11b, a ridge portion 15 is formed in nearly the center of the internal wide face. The ridge portion 15 is, as shown in FIG.2B, provided with a tapered face by which the thickness is gradually increased in the direction of the bottom portion, and a flat face extending from the tapered face to the bottom portion. A center conductor 14 is attached to the flat face of the ridge portion 15. In the waveguide coaxial converter 10 with such structure, according as the amount of insertion of the screws 12 is changed, the damping amount of a high-frequency signal is changed. Namely, by making the amount of insertion of the screws 12 variable, the load impedance can be varied. Hereon, when the amount of insertion of the screws 12 is minimized, i.e., in the case of substantially making no use of the screws 12, an inductive susceptance becomes predominant as a whole due to the step portions 11a, 11b formed on the internal sidewall. Therefore, regulating the capacitive susceptance by the amount of insertion of the screws 12 makes it possible that the regulation of the impedance as a whole is performed over the range from an inductive region to an capacitive region. As a result, the frequency range where the matching of impedance can be carried out is significantly enlarged. On the other hand, since the ridge portion 15 for originally reducing the cut-off frequency is formed as shown in FIG.2B, it can be also used for the impedance conversion between the waveguide and the coaxial line to provide an interface for the coaxial line. Thereby, the total scale can be reduced. Moreover, such structure for the impedance conversion between the waveguide and the coaxial line in this embodiment is suitable for casting and does not need a supporting material such as Teflon® for the center conductor 14. Therefore, a waveguide coaxial converter for high power can be easily made to reduce the manufacturing cost. FIG.3 shows a waveguide matching circuit in a preferred embodiment of the invention. The waveguide matching circuit 20 comprises inductive rods 21a, 21b and screws 22 for regulating a capacitive susceptance. As shown in FIG.3, the waveguide matching circuit 20 has the inductive rods 21a and 21b which are disposed at an interval of λg/8 on the internal sidewall, replacing the step portions 11a, 11b in the waveguide coaxial converter 10 as mentioned above. Further, a pair of screws 22 are disposed on the same planes as the respective inductive rods 21a, 21b. The screws 22 are the same ones as the screws 12 in the waveguide coaxial converter as mentioned above. In operation, when the amount of insertion of the screws 22 is minimized, i.e., in the case of substantially making no use of the screws 22, an inductive susceptance becomes predominant as a whole due to the inductive rods 21a, 21b. Therefore, regulating the capacitive susceptance by the amount of insertion of the screws 22 makes it possible that the regulation of the impedance as a whole is performed over the range from an inductive region to an capacitive region. As a result, the frequency range where the matching of impedance can be carried out is significantly enlarged. Meanwhile, the number of the step portions 11a, 11b or the inductive rods 21a, 21b is not limited to two.

Claims: A waveguide coaxial converter (10), comprising: a waveguide which is in the form of a bottomed rectangle and in which a high-frequency signal propagates; at least two means (12) for regulating a capacitive susceptance which are provided along a line having a predetermined angle to an axis line of said waveguide at a predetermined position on a wide face of said waveguide and are respectively disposed at an interval of one eighth of a guide wavelength λg in the direction of said axis line; and at least a pair of step portions (11a,11b) for stepwise narrowing the width between both internal sidewalls of said waveguide, each of said step portions being provided on said internal sidewalls respectively, wherein said step portions are placed with a distance of one eighth of said guide wavelength in the direction of said axis line. A waveguide coaxial converter, according to claim 1, wherein: said waveguide is provided with a ridge portion which includes a tapered face by which a thickness of said ridge portion is gradually increased in the direction from an opening to a bottom of said waveguide and a flat face extending from said tapered face to said bottom, said flat face of said ridge portion being connected with a center conductor of an coaxial line. A waveguide coaxial converter, according to claim 2, wherein: said ridge portion has a shape by which an increase of a cut-off frequency caused by said step portions is suppressed. A waveguide matching circuit (20), comprising: a waveguide for propagating a high-frequency signal in which means for regulating an impedance is provided; wherein said impedance regulating means comprises: at least two means (22) for regulating a capacitive susceptance which are provided along a line having a predetermined angle to an axis line of said waveguide at a predetermined position on a wide face of said waveguide and are respectively disposed at an interval of one eighth of a guide wavelength λg in the direction of said axis line; and at least two inductive materials (21a,21b) which are disposed on an internal sidewall of said waveguide in parallel with and at the same interval of said capacitive susceptance regulating means. A waveguide matching circuit, according to claim 4, wherein: said capacitive susceptance regulating means and said inductive materials are placed in a face in parallel with an opening face of said waveguide.

Inventors: UMEZU KEIICHI, UMEZU, KEIICHI, Umezu, Keiichi, c/o NEC Engineering, Ltd.
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1995
Main classification: H01P5
IPC codes: H01P5