Polarization transformation circuit

An apparatus adapted for easily performing polarization switching is disclosed. Within a second waveguide connected to a first waveguide, there is embedded a polarization transformation circuit in the state rotated relative to the second waveguide at an angle set, based on a reflection characteristic indicating a characteristic of a reflection coefficient with respect to a polarization frequency.

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2006-252679 filed on Sep. 19, 2006, the content of which is incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a waveguide apparatus used for an antenna for transmitting and receiving microwave and milliwave signals, and more particularly, to a waveguide apparatus including a polarization transformation circuit for switching between a horizontally polarized wave and a vertically polarized wave in a linear polarized wave.

2. Description of the Related Art

In conventional waveguide apparatuses in which plural waveguides are connected, a polarization transformation circuit is used in order to connect plural waveguides. This polarization transformation circuit is a circuit for performing an impedance matching between the output impedance of one waveguide and the input impedance of another waveguide connected to the waveguide.

Referring toFIG. 1, there is illustrated a waveguide apparatus comprising waveguides1001,1002, and polarization transformation circuits1003,1004. By polarization transformation circuits1003,1004, matching between output impedance of waveguide1001and input impedance of waveguide1002is performed. In this example, since waveguides1001and1002are disposed so that the vibration directions of polarized waves that passed through respective waveguides1001and1002are horizontal to each other, no impedance miss-matching between the output impedance of waveguide1001and the input impedance of waveguide1002occurs. Accordingly, in order to perform impedance matching between the output impedance of waveguide1001and the input impedance of waveguide1002, it is not necessary to rotate polarization transformation circuits1003,1004.

Referring toFIG. 2, similarly to the waveguide apparatus shown inFIG. 1, there is illustrated a waveguide apparatus comprising waveguides1001,1002, and polarization transformation circuits1003,1004. Impedance matching between the output impedance of waveguide1001and the input impedance of waveguide1002is performed using polarization transformation circuits1003,1004. In this example, since waveguides1001and1002are disposed so that the vibration directions of polarized waves that passed through respective waveguides1001and1002that are perpendicular to each other, impedance miss-matching between the output impedance of waveguide1001and the input impedance of waveguide1002will occur. For this reason, every time polarization wave switching is performed, in order to perform impedance matching between the output impedance of waveguide1001and the input impedance of waveguide1002, it is necessary to respectively rotate respective polarization transformation circuits1003,1004by suitable angles.

Moreover, a technology capable of performing, in a manner integral with the waveguide, polarization wave switching in the case where the vibration directions of input/output polarized waves of the waveguides are perpendicular to each other is disclosed in the JP2004-363764A.

However, in the case where plural waveguides are disposed so that vibration directions of input/output polarized waves of the waveguides are perpendicular to each other, it is necessary to perform impedance matching between respective waveguides. Further, in order to ensure that those waveguides have sufficient characteristics, there is the problem that it is necessary to have polarization transformation circuitry comprising two or more parts to perform impedance matching between both waveguides. Moreover, the problem that the plural parts that constitute the polarization transformation circuitry need to rotate, at a suitable angle, each time polarization wave switching is performed occurs.

In addition, in the technology disclosed in the above-mentioned patent document, there is the problem that since a fixed structure is employed only in the case where the vibration directions of input/output polarized waves of the waveguides are perpendicular to each other, such technology cannot be utilized as it is in the case where the vibration directions of input/output polarized waves of the waveguides are horizontal to each other.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a waveguide apparatus capable of easily performing polarization switching.

In the present invention as constituted above, the polarization transformation circuit is embedded within the second waveguide connected to the first waveguide in a state rotated relative to the second waveguide at an angle that is set, based on a reflection characteristic indicating a characteristic of a reflection coefficient with respect to a waveguide polarization frequency.

Thus, the number of parts resulting from integration of parts can be reduced, and polarization wave switching work can be facilitated. Further, it is possible to easily perform polarization wave switching.

The above and other objects, features, and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings which illustrate an example of the present invention.

EXEMPLARY EMBODIMENT

Referring toFIG. 3, there is illustrated waveguide apparatus comprising waveguide101serving as a first waveguide, waveguide102serving as a second waveguide, and polarization transformation circuit103. Moreover, polarization transformation circuit1021is embedded within waveguide102. In this case, waveguides101and102are disposed so that the vibration directions of polarized waves that passed through the respective waveguides are horizontal to each other, and respective waveguides101and102are connected through polarization transformation circuit103.

Referring toFIG. 4, there is illustrated the waveguide apparatus, which has a configuration similar to theFIG. 3, and which comprises waveguide101serving as the first waveguide, waveguide102serving as the second waveguide, and polarization transformation circuit103. Moreover, polarization transformation circuit1021is embedded within waveguide102. In this case, waveguides101and102are disposed so that the vibration directions of polarized waves that passed through respective waveguides101and102are perpendicular to each other, and the respective waveguides are connected through polarization transformation circuit103.

Polarization transformation circuit1021shown inFIGS. 3 and 4is embedded within waveguide102in the state rotated in advance at a suitable angle where impedance matching between waveguides101and102can be performed only by rotating polarization transformation circuit103at a suitable angle. The angle where polarization transformation circuit1021is rotated in advance is based on the reflection coefficients of waveguides101and102. Thus, even in the case where waveguides101and102as shown inFIG. 3are disposed so that the vibration directions of polarized waves that passed through respective waveguides101and102are horizontal to each other, it is possible to perform impedance matching between waveguides101and102. Moreover, even in the case where waveguides101and102as shown inFIG. 4are disposed so that the vibration directions of polarized waves that passed through the respective waveguides are perpendicular to each other, it is possible to perform impedance matching between waveguides101and102. Namely, as a result of the fact that polarization transformation circuit1021is embedded within waveguide102in the state rotated in advance at a suitable angle, this is sufficient for performing impedance matching in an electric field horizontally polarized wave and in an electric field vertically polarized wave in order to only rotate polarization transformation circuit103.

In this example, the lengths of polarization transformation circuit103and polarization transformation circuit1021are set in advance to ¼ of the waveguide wavelength. Thus, the phase difference at reflection becomes equal to 180 degrees so that the reflection characteristic becomes satisfactory. Moreover, even in the case where the length of polarization transformation circuit103is set to ¼ of the waveguide wavelength and the length of polarization transformation circuit1021is set to ¾ of the waveguide wavelength, phase difference at reflection becomes equal to 180 degrees so that the reflection characteristic becomes satisfactory. Further, even in the case where the lengths of polarization transformation circuit103and polarization transformation circuit1021are set to ¾ of the waveguide wavelength, phase difference at reflection becomes equal to 180 degrees so that the reflection characteristic becomes satisfactory.

An angle rotated when polarization transformation circuit1021shown inFIGS. 3 and 4is embedded within waveguide102will now be described.

As shown inFIG. 5, when the waveguide apparatus of the present invention shown inFIG. 3is viewed from the direction of A, polarization transformation circuit1021is embedded within waveguide102in the state rotated at an angle θ1relative to waveguide101, polarization transformation circuit103and waveguide102.

As shown inFIG. 6, when the waveguide apparatus of the present invention shown inFIG. 4is viewed from the direction of B, polarization transformation circuit1021is embedded in the state rotated at an angle of θ1relative to waveguide102. Moreover, an angle that polarization transformation circuit1021and polarization transformation circuit103form is assumed to be θ2. Further, polarization transformation circuit103is rotated at an angle θ3relative to waveguide101.

InFIGS. 5 and 6, respective angles θ1to θ3are set based on the reflection characteristic which will be described later. As an angle for obtaining reflection characteristic which will be described later,
θ3:θ2:θ1=1:√2:1
is mentioned as an example. In this case, θ1=about 26°, θ2=about 38° and θ3=about 26° are respectively optimum angles.

In the reflection characteristics of the electric field horizontally polarized wave in an exemplary embodiment shown inFIG. 3, as shown inFIG. 7, within the range from 0.95 f0to 1.05 f0in which the frequency band has a relative bandwidth 10% of polarization frequency f0, the reflection coefficient is below −30 dB which is the target value in the present invention. From this result, it is seen that sufficient reflection characteristics can be obtained in the electric field horizontally polarized wave. In this example, angle θ1shown inFIG. 5is set to about 26°. In this case, the abscissa indicates the frequency (GHz) of the polarized wave, and the ordinate indicates the reflection coefficient (dB).

In the reflection characteristic of the electric field vertically polarized wave in an exemplary embodiment shown inFIG. 4, as shown inFIG. 8, within the range from 0.95 f0to 1.05 f0in which the frequency band has a relative bandwidth 10% of the polarization frequency f0, the reflection coefficient is below −30 dB which is the target value in the present invention. From this result, it is seen that sufficient reflection characteristics can be obtained also in the electric field vertically polarized wave. In this example, angles θ1, θ2and θ3shown inFIG. 6are respectively set to about 26°, about 38° and about 26°. In this case, the abscissa indicates the frequency (GHz) of the polarized wave, and the ordinate indicates the reflection coefficient (dB).

It is to be noted that the relative bandwidth which is the range for determining whether or not the reflection coefficient is suitable can be expanded depending upon the conditions such as the frequency used and the lengths of waveguides101,102, etc. For this reason, the above-described suitable angles also vary in accordance with such conditions. Namely, it is necessary to set, as an optimum angle, angles in which the reflection coefficient in the relative bandwidth that correspond to the use condition of the waveguide apparatus at that time is suitable.

As explained above, in the present invention, from among two polarization transformation circuits103,1021which connect waveguides101and102, polarization transformation circuit1021is embedded within waveguide102in the state rotated at an angle set, based on the reflection coefficient within the waveguide. For this reason, in the case where the vibration direction of a polarized wave that passed through waveguide101and the vibration direction of a polarized wave that passed through waveguide102are horizontal to each other, it is possible to perform impedance matching between waveguides101and102just by rotating polarization transformation circuit103by a suitable angle. Moreover, also in the case where the vibration direction of a polarized wave that passed through waveguide101and the vibration direction of a polarized wave that passed through waveguide102are perpendicular to each other, it is possible to perform impedance matching between waveguides101and102just by rotating polarization transformation circuit103by a suitable angle. Thus, the number of parts can be reduced through the integration of parts and polarization wave switching work can be facilitated.

Moreover, any other polarization transformation circuit may be disposed between waveguides101and102.

Further, a polarization transformation circuit whose length is set to the length of ¼ of each waveguide wavelength of waveguides101and102may be embedded within waveguide102, and the length of the other polarization transformation circuit may be set to ¼ of each waveguide wavelength of waveguides101and102.

Further, a polarization transformation circuit whose length is set to the length of ¾ of each waveguide wavelength of waveguides101and102may be embedded within waveguide102, and the length of the other polarization transformation circuit may be set to ¼ of each waveguide wavelength of waveguides101and102.

In addition, a polarization transformation circuit whose length is set to the length of ¾ of each waveguide wavelength of waveguides101and102may be embedded within waveguide102, and the length of the other polarization transformation circuit may be set to ¾ of each waveguide wavelength of waveguides101and102.

While an exemplary embodiment of the present invention has been described in specific terms, such description is for illustrative purpose only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.