JPH0697703A - Strip line dual mode filter - Google Patents

Abstract

(57) [Abstract] [Purpose] A stripline dual-mode filter used in high-frequency band filters used in various electrical equipment. , A high-performance stripline dual-mode filter. [Structure] A one-wavelength strip line loop resonator 101 having a uniform line width has a parallel coupling line, and the mutual positional relationship is such that they are symmetrical with respect to a center line parallel to the parallel coupling line. By providing terminals A and B for connecting the input and output capacitors 102a and 102b at positions 90 ° apart from each other, the strip line dual mode filter operates as a strip line dual mode filter, and the strip line dual mode is arranged at the line spacing of the parallel coupled lines. -The bandwidth of the filter can be controlled, and a high-performance wideband stripline dual-mode filter can be realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compact and low-cost stripline dual mode filter used for communication devices and measuring instruments in the UHF to SHF band.

[0002]

2. Description of the Related Art A stripline filter usually uses a one-wavelength stripline ring resonator or the like in order to reduce the radiation loss, but it has a drawback that it has a large shape although the loss is small. In order to solve the drawback of this one-wavelength stripline ring resonator filter, a dual-mode filter that excites two quadrature modes in one resonator has also been proposed, but has not been put into practical use.

A conventional stripline dual mode filter will be described below. FIG. 7 is a block diagram of a conventional stripline dual mode filter. This is 1991 IEEE International Microwave Symposium Dig by JACurtis et al.
est, pp.443-446 (N-1) (I-E-E International Microwave Symposium Digest).

In FIG. 7, 201 is a strip line ring resonator of one wavelength (electrical length of 360 °), 202a,
Reference numeral 202b is an input / output capacitor, 203a and 203b are input / output lines, and 204 is a strip line stub with an open tip.
The strip line ring resonator 201 is arranged so that the angle between the input and output lines is 90 °, and the strip line stub 204 with the tip open and the centers of the input and output lines 203a and 203b are 135 °.

The operation of the stripline dual mode filter having the above-described structure will be qualitatively described below with the concept of a traveling wave. First input line 2
The traveling wave propagating from 03a is field-coupled to the one-wavelength stripline ring resonator via the input / output capacitor 202a, and a strong electric field is generated in the vicinity of the input line. This electric field propagates in the clockwise and counterclockwise directions as a traveling wave. First, consider the counterclockwise traveling wave. This traveling wave undergoes a 90 ° phase change and reaches the vicinity of the output line, but since the electric field is 0 here, it does not couple to the output line 203b. When the position is further advanced 135 °, the position of the stripline stub 204 with the open end is reached. Here, since the line has a discontinuous portion, a part thereof becomes a reflected wave, and the rest propagates to the vicinity of the input line and is coupled to the input line 203a via the gap capacitance 202a. The reflected wave at the open-ended strip line stub 204 recedes 135 ° and reaches the vicinity of the output line. However, since the phase difference is 270 ° for the round trip, the electric field is maximized here and electric field coupling occurs to cause the output line 20.
The traveling wave propagates to 3b. Similarly, as for the traveling wave in the clockwise direction, only the reflected wave at the stripline stub 204 having the open tip is propagated to the output line 203b. Since the magnitude of the reflection is remarkable when the discontinuity is large, the magnitude of the traveling wave propagating can be controlled by the line length of the stripline stub 204 having the open tip. Considering this operation as a resonator, in the case of the configuration of FIG. 7, there are two orthogonal modes in the resonator, and the degree of coupling between the two resonance modes can be controlled by the structure of the stripline stub 204 with an open tip. Mean a thing. That is, it can be considered that the resonator operates as a dual-mode filter and has a function corresponding to a two-stage filter with one resonator, which can be said to contribute to downsizing.

[0006]

However, in the above configuration, the coupling degree, that is, the pass band width as a filter is adjusted only by the strip line stub having an open tip, and the pass band cannot be made large, so that the application area of the filter is limited. There is a problem that it is difficult to construct a multistage filter.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a strip line dual mode filter having a wide band and a multistage filter having a simple structure.

[0008]

In order to achieve this object, a stripline dual mode filter according to the present invention has a uniform stripline loop resonator, in which discontinuities such as stubs are not provided in the stripline. It is composed of lines and has a parallel coupling part, and the pass bandwidth can be controlled by the line spacing or the feedback capacitance.

[0009]

[Function] With this configuration, the two orthogonal
Since the resonator can be excited in one mode, a dual mode filter using one and a plurality of stripline loop resonators can be realized. Further, since the coupling degree can be easily controlled also by the feedback capacitance, the pass bandwidth can be controlled even when the shape is limited.

[0010]

(Embodiment 1) A first embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, 101 is a stripline loop resonator of one wavelength, 102a and 102b are input / output capacitors, and the input / output capacitors 102a and 102b are positions in the stripline loop resonator 101 separated by an electrical length of 90 °. And are connected at symmetrical positions A and B on the parallel line. That is, the strip line loop resonator 10
In No. 1, the X portions facing each other form a parallel coupling line portion, and the overall shape is line-symmetric with respect to the YY line.
Reference numerals 103a and 103b are input / output lines. The stripline loop resonator 101 may be a rectangular stripline loop resonator 104 as shown in FIG.

The operation of the strip line dual mode filter having the above structure will be described.

First, the traveling wave propagating through the input line 103a is coupled to the inside of the strip line loop resonator 101 via the input capacitor 102a. The signal propagated to the strip line loop resonator 101 is distributed clockwise and counterclockwise, but when reaching the terminal B, the electrical length is 90 ° or 27.
Since it is at a position advanced by 0 ° and the electric field becomes 0, the output line 10
It is not directly output to 3b. However, since the stripline loop resonator 101 has a parallel coupling line having a line width W and a line spacing S, it is electromagnetically coupled, and the mode in which the electric field is maximum at the position of the terminal B is caused by the electromagnetic field coupling. It occurs both clockwise and counterclockwise and operates as a stripline dual mode filter.

FIG. 3 shows the frequency characteristic of the strip line dual mode filter according to this embodiment. FIG. 3 shows a pass characteristic with respect to frequency as a result of circuit analysis when the dielectric constant and the line width W / H are constant.

As is apparent from FIG. 3, the stripline dual-mode filter according to the present embodiment has a passband width of 0.02 to 0.1 in terms of a specific bandwidth normalized by the center frequency due to the line spacing S / H. An excellent effect is obtained in that it can be controlled within a certain range.

As described above, according to this embodiment, in the one-wavelength loop resonator having the parallel coupling line, the electric length is 9
By providing input / output terminals at positions 0 ° apart and symmetrical with respect to the center line parallel to the parallel coupled line, it is possible to operate as a dual-mode filter and to achieve high performance and high productivity. A mode filter can be realized.

(Second Embodiment) A second embodiment of the present invention will be described below with reference to the drawings.

In FIG. 3, 101 is a one-wavelength strip line loop resonator, 102a and 102b are input / output capacitors, and 103a and 103b are input / output lines. The input / output capacitors 102a and 102b are connected to terminals A and B, which are arranged at positions separated by an electrical length of 90 ° and are located symmetrically on the parallel line. The above is the same as the configuration of FIG.
The difference from the configuration of FIG. 1 is that terminals C and D are provided at positions 90 degrees away from terminals A and B in terms of electrical length, respectively, and feedback capacitance 10
5 is connected.

The operation of the stripline dual mode filter having the above structure will be described below.

Similar to the first embodiment shown in FIG. 1, the traveling wave propagating through the input line 103a is converted into the input capacitance 102a.
Through the strip line loop resonator 101. The signal propagated to the strip line loop resonator 101 is distributed clockwise and counterclockwise, but when it reaches the terminal B, it is at a position advanced by 90 ° or 270 ° in terms of electrical length, and the electric field becomes 0. It is not directly output to the line 103b. However, the stripline loop resonator 10
Since 1 has a parallel coupling line having a line width W and a line spacing S, it is electromagnetically coupled, and the mode in which the electric field is maximum at the position of terminal B due to the influence of the electromagnetic coupling is clockwise or counterclockwise. Each occurs and acts as a dual mode filter. Further, since the electric field is maximized at the terminal C, the signal is propagated to the terminal D by coupling with the feedback capacitor 105, and the electrical length is 180
A signal is output by being connected to the terminal B located at a position apart from each other.

As described above, the feedback capacitor 1 is added to the first embodiment.
By connecting 05, there are two excitation conditions,
Even if the line spacing and line width are fixed, the feedback capacitance 105
The pass bandwidth can be controlled by controlling

The frequency characteristics of the strip line dual mode filter according to this embodiment are shown in FIG. FIG. 5 shows a pass characteristic with respect to frequency as a result of circuit analysis when the dielectric constant, the line width W / H, and the line interval S / H are constant.

(Embodiment 3) A third embodiment of the present invention will be described below with reference to the drawings.

In FIG. 6, the structure of the first embodiment is connected in cascade by interstage coupling capacitors 106a and 106b and interstage connecting line 107. Here, the case where the cascade connection of the first embodiment is used is described as the embodiment, but it goes without saying that the second embodiment may be connected in cascade.

By cascade-connecting the first embodiment or the second embodiment as in this embodiment, a multistage strip line dual mode filter can be easily realized.

In the first to third embodiments, the strip line dual mode filter has been shown, but the line used is a microstrip line or a line having a laminated structure such as a triplate structure and incorporated therein. May be configured by.

[0027]

As described above, according to the present invention, by having the parallel coupling portion in the one-wavelength strip line loop resonator having the terminals for connecting the input and output capacitances, which are arranged at the electrical distance of 90 °. Orthogonal resonance modes are available,
By controlling the line spacing, the passband width can be controlled, and when the line spacing is determined, it is possible to realize a high-performance and wideband excellent stripline dual-mode filter that can also control the passband width with the feedback capacitance. It is a thing.
Moreover, since the structure is simple, a low-cost and highly productive stripline dual-mode filter can be realized.

[Brief description of drawings]

FIG. 1 is a plan view of a stripline dual mode filter according to a first embodiment of the present invention.

FIG. 2 is a plan view of another main part of the stripline dual mode filter in the same embodiment.

FIG. 3 is a characteristic diagram showing frequency characteristics of a stripline dual mode filter in the same embodiment.

FIG. 4 is a plan view of a stripline dual mode filter according to a second embodiment of the present invention.

FIG. 5 is a characteristic diagram showing frequency characteristics of a stripline dual mode filter in the same example.

FIG. 6 is a plan view of a stripline dual mode filter according to a third embodiment of the present invention.

FIG. 7 is a plan view of a conventional stripline dual mode filter.

[Explanation of symbols]

 101, 104 One-wavelength strip line loop resonator 102a, 102b Input / output capacitance 103a, 103b Input / output line 105 Feedback capacitance 106 Interstage coupling capacitance 107 Interstage connection line

Claims (4)

[Claims] 1. A strip-line one-wavelength loop resonator having a parallel coupled line, an electrical length of the line of which is approximately 360 °, and a line width of which is uniform, and two terminals for connecting an input / output capacitance with an electrical length. A stripline dual-mode filter, characterized in that the terminals are provided at 90 ° apart and the terminals are symmetrical with respect to a center line parallel to the parallel coupled line. 2. A strip-line one-wavelength loop resonator having a parallel coupled line, an electrical length of the line of which is approximately 360 °, and a line width of which is uniform, and two terminals for connecting an input / output capacitance with an electrical length. The terminals are provided at positions separated by 90 °, the terminals are provided at positions symmetrical with respect to the center line parallel to the parallel coupled line, and the terminals are separated by an electrical length of 90 ° from the two terminals on the parallel coupled line. A stripline dual-mode filter characterized in that two more terminals are provided at positions on the parallel coupled line, and a capacitor is connected to the terminals. 3. A stripline one-wavelength loop resonator having a parallel coupled line, an electrical length of the line of which is about 360 °, and a line width of which is uniform, is rectangular in shape.
Alternatively, the stripline dual-mode filter described in 2. 4. A stripline dual mode filter comprising a plurality of stripline dual mode filters according to claim 1, 2 or 3 connected in cascade.