JP5340015B2 - Waveguide bandpass filter - Google Patents

Description

  The present invention relates to a waveguide bandpass filter used in a fixed wireless device, a microwave communication device, and the like, and more particularly to a waveguide bandpass filter having a notch portion.

  Waveguide bandpass filter that can be used for wireless subscriber data communication services (using three frequency bands of 22 GHz, 26 GHz, and 38 GHz and capable of high-speed communication data of several Mbps to several tens of Mbps) Therefore, there is a need for a small filter having a low loss and a steep out-of-band attenuation characteristic.

  As such a filter, for example, a waveguide bandpass filter provided with a notch described in JP-A-2003-163507 is known.

  FIG. 1 is a perspective view of this conventional waveguide bandpass filter. In the waveguide 10, a plurality of coupling windows 12 are provided to form a band pass filtering portion 14, and notch portions 16 and 18 are provided close to the outermost coupling window of the band pass filtering portion 14. ing.

  The band pass filtering unit 14 determines a pass band of a signal passing through the waveguide 10. The notches 16 and 18 attenuate the set frequency components outside the passband.

  According to this conventional waveguide bandpass filter, it is possible to obtain a steeper attenuation pole and a large amount of attenuation outside the passband without causing an increase in insertion loss and deterioration of reflection characteristics in the passband. .

JP 2003-163507 A

  In a conventional waveguide bandpass filter having a notch, in order to make the attenuation pole steep and as close to the passband as possible, the notch and the bandpass filter are brought close to the bandpass filter. It is necessary to strengthen the electromagnetic field coupling.

  However, it is difficult to bring the notch portion very close to the bandpass filtering portion due to the physical constraints of the structure. For this reason, in the conventional structure, the electromagnetic field coupling between the bandpass filtering part and the notch part could not be strengthened.

  An object of the present invention is to provide a waveguide bandpass filter having attenuation characteristics due to a band-pass filtering portion and a notch portion having strong electromagnetic field coupling.

  The present invention relates to a waveguide bandpass filter composed of a conductor case and a conductor lid, and includes a band-pass filtering unit including a plurality of stages of cavity resonators and a first-stage cavity resonance of the band-pass filtering unit. A first cavity that is electromagnetically coupled to the vessel via a coupling window, a first notch portion that is electromagnetically coupled to the first cavity via a first coupling window, and a bandpass filtering unit A second cavity that is electromagnetically coupled to the last-stage cavity resonator through a coupling window, and a second notch portion that is electromagnetically coupled to the second cavity via a second coupling window A first electromagnetic field coupling strengthening portion that is provided in the first cavity and that strengthens electromagnetic field coupling between the first notch portion and the first-stage cavity resonator, and is provided in the second cavity. And a second electromagnetic field coupling reinforcing part for strengthening electromagnetic field coupling between the second notch part and the final cavity resonator is formed in the conductor case. To.

  According to the waveguide bandpass filter of the present invention, the electromagnetic coupling between the band-pass filtering portion and the notch portion can be strengthened. Therefore, the attenuation pole due to the notch can be brought close to the band pass region.

  In addition, compared with the conventional waveguide bandpass filter, the waveguide bandpass filter of the type in which the conductor case and the conductor lid of the present invention are closely fixed is provided between the bandpass filter portion and the notch portion. This makes it easy to design the band-pass filtering part and the notch part.

It is a figure which shows the conventional waveguide band pass filter. It is a figure which shows the conductor case of the waveguide band pass filter which is the 1st Example of this invention, (A) is a perspective view, (B) is a top view. It is a figure for demonstrating an example of the dimension of the structure of the conductor case of the waveguide band pass filter of a 1st Example. It is a figure which shows the structure for sealing a conductor case with a conductor cover, (A) is a perspective view of a conductor case, (B) is a perspective view after sealing. It is a figure for demonstrating the change of Q value of each part in the waveguide band pass filter of a 1st Example. It is a figure which shows the reflection characteristic and the transmission characteristic of the waveguide band pass filter of 1st Example of a 38 GHz band. It is a figure which shows the conductor case of the waveguide band pass filter which is the 2nd Example of this invention, (A) is a perspective view, (B) is a top view.

  Hereinafter, embodiments of the waveguide bandpass filter of the present invention will be described with reference to the drawings.

  The waveguide band-pass filter of the present invention is of a type in which a conductor case and a conductor lid mainly made of aluminum or brass are closely fixed. Such a conductor case and a conductor lid can be produced by molding or cutting. Alternatively, a molded resin obtained by plating a metal may be used.

  2A and 2B are diagrams showing a conductor case of the waveguide bandpass filter according to the first embodiment of the present invention, where FIG. 2A is a perspective view and FIG. 2B is a plan view.

  The conductor case 20 is formed with five-stage cavity resonators 22, 24, 26, 28, 30 arranged in a straight line. The cavity resonator 22 constitutes a first-stage cavity resonator, and the cavity resonator 30 constitutes a final-stage cavity resonator. Adjacent cavity resonators are electromagnetically coupled via a coupling window 32. These cavity resonators 22 to 30 constitute a band pass filtering unit 34.

  The first-stage cavity resonator 22 is electromagnetically coupled to a cavity (acting as a cavity resonator) 38 through a coupling window 36. On the other hand, the cavity resonator 30 at the final stage is electromagnetically coupled to a cavity (acting as a cavity resonator) 42 through a coupling window 40.

  The cavity 38 is connected to the input-side line 44, and the cavity 42 is connected to the output-side line 46.

  A notch 48 is provided close to the input-side cavity 38, and the notch 48 is electromagnetically coupled to the cavity 38 via a coupling window 50. On the other hand, a notch portion 52 is provided close to the output-side cavity 42, and the notch portion 52 is electromagnetically coupled to the cavity 42 via a coupling window 54.

  The notch part attenuates a set frequency component outside the pass band to form a steep attenuation pole (notch), and is also called a notch resonator.

  A post (in this embodiment, a prism) 60 protruding from the wall surface is provided on the wall of the cavity 38 facing the coupling window 50 of the notch 48 on the input side. On the other hand, a post (in this embodiment, a prism) 62 protruding from the wall surface is provided on the wall portion of the cavity 42 facing the coupling window 54 of the notch portion 52 on the output side.

  These posts 60 and 62 are for strengthening electromagnetic field coupling between the notch portions 48 and 52 and the bandpass filtering portion 34. That is, the post 60 strengthens the electromagnetic field coupling between the notch portion 48 and the first-stage cavity resonator 22, and the post 62 strengthens the electromagnetic field coupling between the notch portion 52 and the last-stage cavity resonator 30.

  The shape of the post is not limited to a prism, and may be other shapes such as a cylinder. By setting the protruding length and width from the wall portion of the post, the strength of the electromagnetic field coupling between the notch portions 48 and 52 and the bandpass filtering portion 34 can be adjusted.

  FIG. 3 is a diagram for explaining an example of the structural dimensions of the waveguide bandpass filter of the present embodiment.

  In FIG. 3, the line width is a, the protruding length of the post 60 from the wall is b, the width of the post 60 is c, the width of the coupling window 50 of the notch 48 is d, the post 60 and the first-stage cavity resonator 22. The distance from the coupling window 36 is e.

  The protruding length b of the post 60 is preferably 1/3 to 1/2 of the line width a. The width c of the post 60 is preferably narrow, but is preferably smaller than the width d of the coupling window 50 of the notch 48. The distance e between the post 60 and the coupling window 36 of the first-stage cavity resonator 22 is preferably about 0.8λg in the case of a 38 GHz band filter. Note that λg is the wavelength of the signal propagating through the waveguide (in-tube wavelength).

  The conductor case of the above-described embodiment is hermetically sealed with a conductor lid to constitute a waveguide bandpass filter. 4A and 4B are diagrams showing a structure for sealing the conductor case 70 with the conductor lid 72. FIG. 4A is a perspective view of the conductor case, and FIG. 4B is a perspective view after sealing.

  A conductor case 70 shown in FIG. 4A is obtained by providing a plurality of screw holes 74 in the conductor case 20 shown in FIG. The conductor lid 72 is formed with insertion holes (not shown) corresponding to the plurality of screw holes 74 of the conductor case 70.

  The conductor lid 72 is positioned and placed on the conductor case 70, and the screw 76 is passed through the insertion hole of the conductor lid 72 and fastened to the screw hole 74 of the conductor case 70. Thereby, the conductor lid 72 is tightly fixed to the conductor case 70.

  FIG. 5 is a diagram for explaining a change in the Q value of each part in the waveguide bandpass filter of this embodiment. In designing the filter, it is required to consider the Q value as follows. . The Q value is a value representing the sharpness of the resonance peak.

  The band-pass filtering unit 34 composed of the five-stage cavity resonators 22, 24, 26, 28, and 30 has a large Q value and requires frequency adjustment.

  Since the cavities 38 and 42 located on both sides of the bandpass filtering unit 34 have a small Q value and a wide frequency band, it is not necessary to adjust the frequency.

  The notch portions 48 and 52 have a large Q value and need to be adjusted in frequency.

  FIG. 6 is a diagram showing the reflection characteristic (S11) and the transmission characteristic (S21) of the waveguide bandpass filter of the present embodiment of the 38 GHz band. It can be seen that a steeper attenuation pole is obtained at a specific frequency near the pass band without increasing the insertion loss and deteriorating the reflection characteristics.

  The reason why the attenuation pole approaches the pass band is that the posts 60 and 62 strengthen the electromagnetic field coupling between the notches 48 and 52 and the band pass filtering unit 34.

  7A and 7B are diagrams showing a conductor case of a waveguide bandpass filter according to a second embodiment of the present invention, where FIG. 7A is a perspective view and FIG. 7B is a plan view.

  The difference from the waveguide bandpass filter of the first embodiment is that the electromagnetic field coupling strengthening portion is a post provided apart from the cavity wall surface. Since other structures are the same as those of the first embodiment, the same components as those in FIG. 2 are denoted by the same reference numerals.

  A post (in this embodiment, a cylinder) 80 is provided apart from the wall surface of the cavity 38 facing the coupling window 50 of the notch 48, while the wall 42 of the cavity 42 facing the coupling window 54 of the notch 52. In addition, a post (in this embodiment, a cylinder) 82 is provided apart from the wall surface. By adjusting the size and the separation distance of each post 80, 82, the electromagnetic coupling strength between the notch 48 and the first-stage cavity resonator 22 can be adjusted, and the notch 52 and the last-stage cavity can be adjusted. The electromagnetic field coupling strength with the resonator 30 can be adjusted.

  The shape of the post is not limited to a cylinder, and may be other shapes such as a prism. By setting the distance from the wall of the post and the size of the post, it is possible to adjust the strength of the electromagnetic field coupling between the notch portions 48 and 52 and the bandpass filtering portion 34.

  Also in the second embodiment, similarly to the first embodiment, the attenuation pole by the notch portion can be brought close to the band pass region.

20, 70 Conductor case 22, 24, 26, 28, 30 Cavity resonator 32, 36, 40, 50, 54 Coupling window 34 Passband filtering section 38, 42 Cavity 44, 46 Line 48, 52 Notch section 60 , 62 Post 72 Conductor lid 74 Screw hole 76 Screw 80, 82 Post

Claims (4)

A waveguide bandpass filter composed of a conductor case and a conductor lid,
A band-pass filtering unit composed of a multi-stage cavity resonator;
A first cavity that is electromagnetically coupled to a first-stage cavity resonator of the band-pass filtering unit via a first-stage coupling window;
A first notch portion which is electromagnetically coupled through said first coupling window to the first cavity,
A second cavity electromagnetically coupled to a final cavity resonator of the bandpass filtering unit via a final coupling window;
A second notch portion which is electromagnetically coupled through said second coupling window to the second cavity,
A first electromagnetic field coupling enhancement which is provided in the first cavity so as to face the first notch portion and strengthens the electromagnetic field coupling between the first notch portion and the first-stage cavity resonator. And
The second electromagnetic coupling is provided in the second cavity so as to oppose the second notch portion, and strengthens the electromagnetic coupling between the second notch portion and the final cavity resonator. Strengthening department,
A waveguide bandpass filter formed in the conductor case. The first electromagnetic coupling reinforcement portion is a first post which is provided in contact with the wall of the first cavity opposite to said first coupling window,
2. The guide according to claim 1, wherein the second electromagnetic field coupling strengthening portion is a second post provided in contact with a wall portion of the second cavity facing the second coupling window. Wave tube bandpass filter. The first electromagnetic coupling reinforcement portion is a first post which is spaced apart from the wall of the first cavity opposite to said first coupling window,
2. The guide according to claim 1, wherein the second electromagnetic field coupling strengthening portion is a second post provided to be separated from a wall portion of the second cavity facing the second coupling window. Wave tube bandpass filter.   The waveguide band-pass filter according to claim 1, wherein the conductor lid is fixed to the conductor case with a screw.

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