JP4565145B2 - Ultra-wideband bandpass filter - Google Patents

Description

  The present invention relates to an ultra-wideband bandpass filter whose specific band exceeds 20%.

  It is predicted that a UWB (Ultra Wide Band) wireless system capable of high-speed communication of large-capacity information such as moving images without requiring wiring will rapidly spread to network applications. In the UWB wireless system, each communication apparatus communicates using a very wide frequency band, so a wider ultra-wide bandpass filter is required.

  In order to clarify the wideband characteristics of the filter, the ratio band = (passband width) / (passband center frequency) is used.

  In Patent Document 1, a first band-shaped resonance conductor film that is electromagnetically coupled to each other between the same dielectric layers of a dielectric substrate formed by laminating a plurality of dielectric layers, and a second band-shaped band constituting a resonance circuit. A resonance conductor film is provided in parallel, and a back surface ground conductor film facing each band-shaped resonance conductor film is disposed on the back surface of the multilayer substrate, and a second band-shaped resonance conductor film is formed on the surface of the multilayer substrate. A high-frequency filter having a surface ground conductor film disposed so as to face each other is described.

  Further, Patent Document 2 includes a resonator using a coplanar structure transmission path constituted by a metal conductor formed on one main surface of a substrate, and crosses the resonator and electromagnetic waves. A high frequency filter is described in which input / output signal lines to be coupled are provided on the other main surface of the substrate.

  Patent Document 3 discloses a dielectric substrate, a plurality of stripline resonators formed on the dielectric substrate in a state where both ends are open and electromagnetically coupled to each other, and an external circuit formed on the dielectric substrate. Two transmission lines for connection, and at least one of the stripline resonators is bent at the center in the longitudinal direction, thereby reducing electromagnetic coupling between every other line and reducing the passband. A band-pass filter that is flat and has a steep skirt characteristic in a frequency band lower than the pass band is described.

  Patent Document 4 discloses a four-terminal directional coupler using a microstrip line. In particular, FIG. 4D shows broadband coupling characteristics.

  However, in the above example, in Patent Documents 1 to 3, the UWB wireless system does not have a filtering characteristic having a sufficiently wide bandwidth, and in Patent Document 4, insertion loss occurs when used as a filter. There was a problem of being big.

JP 2002-198202 A JP 2003-115701 A JP 2004-104588 A JP 03-296304 A

"MICROSTRIP FILTERS for RF / MICROWAVE APPLICATIONS", Wiley Series In Microwave And Optical Engineering, pp.278-279.

  In a UWB wireless communication system, a bandpass filter having a specific band characteristic of 20 to 100% or more, a small insertion loss, and a good group delay characteristic is realized.

  According to the present invention, a specific bandwidth of 100% or more and an out-of-band attenuation characteristic required for the UWB wireless communication standard can be simultaneously realized by one pan path filter. This has been difficult to achieve in the past.

  In the ultra-wideband bandpass filter according to the present invention, as shown in FIG. 1, a conductor connected to a waveguide extending from the first input end and having a shorted end with an open end or a ground conductor is connected to the output. A conductor connected to a waveguide and a coupling conductor having an open end or a short-circuited end to the ground conductor are arranged opposite to each other with air or a dielectric interposed therebetween, and a ground conductor is disposed near the coupling conductor or waveguide. Provided. This structure operates as a bandpass filter through electromagnetic coupling between the coupling conductors. An example of the pass characteristic is shown in FIG.

Here, when the electromagnetic coupling between the respective coupling conductors is strengthened, as shown in FIG. 1C, a flat characteristic is exhibited in the vicinity of the frequency f ₀ where the passing intensity is maximum. The present invention positively realizes such a flat characteristic, and uses broadside coupling in order to realize strong electromagnetic coupling in a high frequency region.

  In order to effectively transmit a high-frequency signal, a waveguide such as a microstrip line or a coplanar waveguide is used. When the two waveguides are close together, electromagnetic coupling occurs between the waveguides. Depending on the difference in the positional relationship between the two electromagnetically coupled waveguides, the site of electromagnetic coupling differs, and it can be divided into broad side coupling and edge coupling.

  Edge coupling is configured by arranging two (or a plurality) of planar transmission lines in parallel on the same plane. Since electromagnetic energy mainly depends on the capacitance between the edges that are close to each other, the smaller the distance between the edges, the stronger the coupling. However, due to physical limitations such as processing accuracy, it is difficult to obtain a strong bond above a certain level. Also, in order to achieve impedance matching with the transmission line connected to the coupling portion, it must be slightly smaller than the transmission line.

  Broadside coupling is configured by arranging conductors on two or more parallel planes that are flat but different. Since a large electromagnetic coupling can be obtained with the wide surfaces facing each other, a large coupling can be easily obtained in principle as compared with the edge coupling structure. Although it is not as simple as the case of using edge coupling in terms of manufacturing, the structure is suitable for obtaining a strong coupling because it is not limited by the machining accuracy as in the case of the edge structure. In addition, the coupling portion of the broadside coupling structure is structurally characterized in that the line width is larger than that of the waveguide in order to achieve impedance matching with the waveguide.

  Some examples illustrating the broadside coupling of the present invention have a shape similar to a capacitor made on a substrate. Further, since the input / output terminals are independent conductors via a dielectric, there is necessarily a capacitance. Thus, the path from the input end to the output end looks like a circuit coupled by a capacitor. However, the present invention includes a waveguide in addition to the broad-side coupling structure, and the waveguide has a ground conductor. Furthermore, the propagating signal exists as a traveling wave. As described above, the operating principle is different from that of a simple capacitor, and the constituent elements are also different in that a waveguide and a ground conductor are provided.

For this reason, the ultra-wideband bandpass filter of the present invention has one or a plurality of pairs of broad-side coupled conductors, a waveguide connecting the coupling conductors in the case of a plurality of pairs, a ground conductor and a conductor. An input-side waveguide comprising a wave conductor and inputting an electric signal to one of the coupling conductors; and an output-side waveguide comprising a ground conductor and a waveguide conductor and outputting an electric signal from the other one of the coupling conductors; The width of the coupling conductor connected to the input-side waveguide is larger than the width of the waveguide conductor of the input-side waveguide, and the width of the coupling conductor connected to the output-side waveguide is The coupling conductor connected to the input-side waveguide and the coupling conductor connected to the output-side waveguide are planar conductors that are larger than the width of the waveguide conductor of the side waveguide, and the length of each of the coupling conductors Circumference corresponding to approximately equal half-wavelength It is to use a phenomenon that attenuation pole occurs in several.

  Further, the coupling conductor connected to the input-side waveguide and the coupling conductor connected to the output-side waveguide can both be configured to have an open end.

  The coupling conductor connected to the input-side waveguide and the coupling conductor connected to the output-side waveguide can both be configured to have a short-circuited end.

  The width of the coupling conductor connected to the input-side waveguide is larger than the width of the waveguide conductor of the input-side waveguide, and the width of the coupling conductor connected to the output-side waveguide is the output-side waveguide. The impedance is matched by making it larger than the width of the waveguide conductor.

  The input-side waveguide or the output-side waveguide constitutes a microstrip line or a coplanar waveguide. That is, a combination in which the waveguide on the input side is a microstrip line and the waveguide on the output side is a coplanar waveguide, a combination in which both the waveguide on the input side and the waveguide on the output side are microstrip lines, or the input This is a combination in which both the side waveguide and the output side waveguide are coplanar waveguides.

In the ultra-wideband bandpass filter of the present invention, the first waveguide conductor of the waveguide constituting the microstrip line and the coupling conductor connected to the first waveguide conductor are provided on the first surface,
A ground conductor associated with the first waveguide, a second waveguide conductor of the waveguide constituting the coplanar waveguide, a coupling conductor connected to the second waveguide conductor, and a ground conductor of the second waveguide On the second surface,
The first and second surfaces are arranged in parallel.

The input-side waveguide and the output-side waveguide are coplanar waveguides each composed of a waveguide conductor and a ground conductor,
A waveguide conductor and a ground conductor constituting the input-side waveguide, and a coupling conductor connected to the waveguide conductor constituting the input-side waveguide are provided on the first surface,
A waveguide conductor and a ground conductor constituting the output-side waveguide, and a coupling conductor connected to the waveguide conductor constituting the output-side waveguide are provided on the second surface.

  In addition, the pair of coupled conductors that are broad-side coupled is constituted by a single-layer or multi-layered electric insulator, a gas body, or conductors that are parallel to each other across a vacuum.

The above ultra-wideband bandpass filter is connected in series,
Two pairs of coupling conductors constituting two broadside couplings are arranged by assigning two coupling conductors to each surface of a pair of surfaces;
Two coupling conductors arranged on one side are connected via a waveguide conductor,
Two coupling conductors arranged on the other surface are connected to the waveguide conductor of the input-side waveguide or the waveguide conductor of the output-side waveguide.

  Further, it is arranged on at least two parallel surfaces, and includes at least two or more ultra-wideband bandpass filters as described above, and a plurality of coupling conductors constituting the plurality of ultra-wideband bandpass filters are used for waveguide Use a conductor to connect in series, parallel, or any series-parallel.

  Or it comprises using the 1st surface and 2nd surface which were chosen from the 1st, 2nd, and 3rd electric conductor surface parallel in order, The 1st in any one of Claims 1-8 A waveguide conductor connecting the respective coupling conductors formed on the second surface of the ultra-wideband bandpass filter and the second ultra-wideband bandpass filter configured using the second surface and the third surface. And connected in series, and a ground conductor is provided on any of the first, second, and third surfaces.

  Of the first, second, third, and fourth surfaces that are parallel to each other, a ground conductor region is provided on the first or fourth surface, and the above-described ultra-wideband bandpass is formed on the second and third surfaces. A filter is provided.

  In addition, the above-mentioned plurality of ultra-wideband bandpass filters having different passband characteristics are connected in series, in parallel, or in series-parallel.

A plurality of the above ultra-wideband bandpass filters having different passband characteristics are connected in series, parallel, or series-parallel,
The passband characteristics are set by changing the distance between two waveguide conductors that perform input and output.

  The plurality of ultra-wideband bandpass filters and a lowpass filter having a cutoff frequency higher than that of the ultra-wideband bandpass filter are connected in series.

  The coupling conductor connected to the waveguide conductor of the input-side waveguide is separated from the coupling conductor connected to the waveguide conductor of the output-side waveguide, and the distance is between the coupling conductors that are broad-side coupled. Not more than 3 times the distance.

  Embodiments of the present invention will be described below in detail with reference to the drawings. In the following description, devices having the same function or similar functions are denoted by the same reference numerals unless there is a special reason.

  An example of the ultra wideband bandpass filter of the present invention will be described first with reference to FIG. The input section is composed of a ground conductor 3 and a microstrip line type waveguide 1 facing it. One end of the coupling conductor 10 is connected to the waveguide 1 and the other end is an open end. The output portion is generally opposite to the structure from the waveguide 1 to the coupling conductor 10 and is composed of the coupling conductor 11 continuous with the waveguide 2. The waveguide 2 is a CPW (coplanar waveguide), and the side close to the input end is an open end. The coupling conductors 10 and 11 are opposed to each other with a gas body such as air or carbon tetrachloride or an insulating film including a dielectric film interposed therebetween, and are broadside coupled. In this example, the input side and the output side are line symmetric, but function as an ultra-wideband bandpass filter even if they are out of line symmetry. Further, when the length (L) in the traveling direction of the signal at the broadside coupling portion is approximately half of the signal wavelength, an attenuation pole (pole) is generated in the high frequency side pass characteristic. That is, the pass bandwidth is half proportional to L. Further, FIG. 2 shows a case where the coupling conductor is rectangular, but it is possible to avoid electric field concentration by chamfering the corners of the four corners of the rectangle. In general, the shape does not need to be rectangular, and any shape that does not reflect traveling waves can be used.

FIG. 3 shows a measurement example of the passband characteristic of the broadside coupling in FIG. The coupling conductor is provided with a substrate having a relative dielectric constant of 9.6 and a thickness of 0.254 mm, and is a rectangle having a width of 1.6 mm and a length of 3.5 mm. The specific bandwidth obtained from this figure is about 170%.

  FIG. 4 shows an example of an ultra-wideband bandpass filter using broadside coupling having a short-circuited end with respect to the ground conductor. The input end is connected to the broadside coupling conductor 11a by a coplanar waveguide 2a. The opposite side of the coupling conductor 11a to the waveguide 2a is a short-circuited end, and is connected to the ground conductor 3a. The coupling conductor 11b facing the coupling conductor 11a is also a short-circuited end and is connected to the ground conductor 3b. The output part is composed of a coupling conductor 11b and a coplanar waveguide 2b continuous to the coupling conductor 11b. Also in this case, the coupling conductors 11a and 11b are opposed to each other with a gas body such as air or carbon tetrachloride or an insulating film including a dielectric film interposed therebetween, and are broadside coupled. Although FIG. 4 shows the case where the coupling conductor is rectangular, it is possible to avoid electric field concentration by chamfering two corners of the rectangle that is not short-circuited to the ground conductor. Further, it is not necessary to have a rectangular shape, and any shape that does not reflect traveling waves can be used as in the case of the open end.

FIG. 5 shows an example of measurement of the passband characteristics of the ultra wideband bandpass filter using the short-side broadside coupling shown in FIG. The coupling conductor is provided with a substrate having a relative dielectric constant of 2.17 and a thickness of 0.508 mm, and is a rectangle having a width of 3.8 mm and a length of 7.0 mm. The specific bandwidth in this case is about 120%.

FIG. 6 shows the configuration of FIG. 2 connected in series at a coplanar portion. The distance between the conductor 10a and the conductor 10b is represented by a gap G. Here, FIG. 8 shows measured values of pass characteristics when the configuration of FIG. 6 is connected in series in three stages. The size used in this measurement is shown in FIG. It can be seen from the S ₂₁ characteristic of FIG. 8 that a good ultra-wideband bandpass filter that passes from 3.00 GHz to 10.63 GHz is formed. This ratio band is about 110%.

FIG. 9 shows a change in pass characteristics when L is changed under the condition of G = 1.5 mm. FIG. 10 shows the relationship between the resonance frequency obtained from this result and the ratio L / λ _g (where λ _g = λ ₀ / ε _r , ε _r is the relative dielectric constant of the substance between the conductors). Yes. From FIG. 7, it can be seen that the proportionality constant is 0.47, which is almost ½. Using this relationship, the pass characteristic can be designed freely.

  FIG. 11 shows the result of changing G under L = 7 mm. FIG. 19 shows the relationship between the gap and the resonance frequency. As can be seen from this figure, the attenuation pole on the high frequency side can be linearly controlled by changing the gap to about 1.6 mm at the maximum. This corresponds to about three times the thickness of the dielectric between the coupling conductors.

  FIG. 12 shows an ultra-wideband bandpass filter using broadside coupling between coupled conductors, each connected to a microstripline waveguide.

  FIG. 13 also shows an ultra-wideband bandpass filter using broadside coupling between conductors each continuous in a coplanar waveguide. The feature of this example is that the input side and the output side are targets.

  FIG. 14 shows an ultra-wideband bandpass filter using broadside coupling between conductors that are sandwiched from above and below by a shield layer and each continuous to a coplanar waveguide. The feature of this example is that there is little radiation loss and it is less likely to pick up external noise.

  FIG. 15 shows a microstrip line type ultra-wideband bandpass filter and a coplanar type ultrawideband bandpass filter connected in series. An input waveguide conductor, an output waveguide conductor, Is formed on another surface. Furthermore, multistage connection in series is also possible. This can be formed by further laminating a number of conductor layers that form waveguide conductors and coupling conductors and dielectric layers. Alternatively, it can be formed by inputting from the upper layer and connecting in series with the conductor of the lower conductor layer, and again connecting in series with the conductor of the upper conductor layer.

  FIG. 16 shows an embodiment in which an ultra-wideband bandpass filter and a lowpass filter are connected in series. The low-pass filter has the same effect on both the input side and the output side. The low pass filter 15 is for limiting the periodic pass characteristic of the ultra wide band pass filter to the pass band of the lowest frequency.

  FIG. 17 shows the use of a series connection in order to realize the pass characteristics of a single ultra-wideband bandpass filter with the rising characteristics and the falling characteristics different from the pass characteristics of a single filter. FIG. 16 shows a microstrip line type ultra-wideband bandpass filter connected in series. FIG. 17 shows an example in which the broad side coupling portions having different lengths, La and Lb, are connected in series. Furthermore, the gaps Ga and Gb between the conductors are also different.

  In FIG. 18, microstrip line type ultra-wideband bandpass filters having different pass characteristics are connected in parallel, and signals of different bands are filtered and separated into outputs 1 or 2. In FIG. 18, the lengths La and Lb of the broadside coupling portion are the same, and the intervals Ga and Gb of the microstrip line type conductors are different. Furthermore, as shown in FIG. 19, it is easy to make the passband characteristics slightly different by adjusting this interval.

  FIG. 20 shows an example in which radiation other than UWB is suppressed by using the above ultra-wideband bandpass filter in a UWB transmitter. The present invention can be applied to a UWB communication device as in the case of using a narrowband bandpass filter for a narrowband communication device.

  Similar to the case of forming a trap circuit using a conventional bandpass filter, the trap circuit can be formed using the ultra-wideband bandpass filter of the present invention. Moreover, the ultra-wideband bandpass filter of the present invention can be used particularly for pulse waveform shaping because of its wide bandwidth.

It is a figure which shows the principle of this invention. It is a figure which shows the basic form of the ultra-wideband band pass filter using the broad side coupling | bonding of an open end. It is a figure which shows the example of a pass-band characteristic of the ultra wideband band pass filter of FIG. It is a figure which shows the basic form of the ultra-wideband band pass filter using the broad side coupling | bonding of a short circuit end. It is a figure which shows the example of a pass-band characteristic of the ultra wideband band pass filter of FIG. It is a figure which shows the ultra wideband band pass filter using the broad side coupling | bonding connected in two steps | paragraphs in series, (a) is a bird's-eye view, (b) shows a top view. It is a figure which shows the specific example of the ultra-wideband band pass filter using broadside coupling. It is a figure which shows the example of a characteristic of the ultra wideband band pass filter using broadside coupling. It is a figure which shows the example of a characteristic of the ultra-wideband band pass filter depending on the size of the conductor which carries out broad side coupling | bonding. It is a figure which shows ratio by the size of the conductor which carries out the broad side coupling | bonding divided | segmented with the wavelength. It is a figure which shows the example of a characteristic of the ultra wideband band pass filter depending on a gap space | interval. It is a figure which shows the example of the ultra wideband band pass filter using the broad side coupling which used the microstrip waveguide for both poles. It is a figure which shows the example of the ultra wideband band pass filter using the broad side coupling which used the coplanar waveguide for both poles. It is a figure which shows the example of the ultra-wideband band pass filter using the broad side coupling which provided the shield layer up and down. It is a figure which shows the example of the ultra-wideband band pass filter using the broad side coupling | bonding which comprised two in series over three conductor layers. It is a figure which shows the example of the ultra-wideband band pass filter using the broad side coupling connected in series with the low pass filter. It is a figure which shows the example of the ultra-wideband band pass filter using the broadside coupling connected in series. It is a figure which shows the example input simultaneously to the ultra wideband band pass filter using two different broad side coupling | bondings. It is a figure which shows the example of a relationship between a gap space | interval and a resonant frequency. It is a block diagram which shows a transmitter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Microstrip waveguide 2 Coplanar waveguide 3 Ground conductor 4 Space, gas body, or insulator 5 Waveguide part 6 Broadside coupling part 7 Waveguide part 8 Gap 10, 10a, 10b Coupling conductor 11, 11a, 11b Coupling Conductor 12 Waveguide conductor 13, 13a, 13b Ground conductor 14 Coupling conductor and waveguide conductor 15 Low-pass filter

Claims (15)

A plurality of coupling conductors that are broad-side coupled, an input-side waveguide that inputs an electric signal to one of the coupling conductors, and another one of the coupling conductors that includes a grounding conductor and a waveguide conductor. And an output-side waveguide that outputs an electrical signal from
The width of the coupling conductor connected to the input-side waveguide is larger than the width of the waveguide conductor of the input-side waveguide, and the width of the coupling conductor connected to the output-side waveguide is equal to that of the output-side waveguide. Larger than the width of the wave conductor,
The coupling conductor connected to the input-side waveguide and the coupling conductor connected to the output-side waveguide are planar conductors, and an attenuation pole is generated at a frequency corresponding to a half wavelength substantially equal to the length of each of the coupling conductors. An ultra-wideband bandpass filter characterized by using a phenomenon .   The ultra-wideband bandpass filter according to claim 1, wherein both the coupling conductor connected to the input-side waveguide and the coupling conductor connected to the output-side waveguide have open ends.   The ultra-wideband bandpass filter according to claim 1, wherein both the coupling conductor connected to the input-side waveguide and the coupling conductor connected to the output-side waveguide have a short-circuited end.   4. The ultra-wideband bandpass filter according to claim 1, wherein the input-side waveguide or the output-side waveguide constitutes a microstrip line or a coplanar waveguide. A first waveguide conductor of a waveguide constituting the microstrip line and a coupling conductor connected to the first waveguide conductor are provided on the first surface;
A ground conductor associated with the first waveguide, a second waveguide conductor of the waveguide constituting the coplanar waveguide, a coupling conductor connected to the second waveguide conductor, and a ground conductor of the second waveguide On the second surface,
The ultra-wideband bandpass filter according to claim 4, wherein the first and second surfaces are arranged in parallel. The input-side waveguide and the output-side waveguide are coplanar waveguides each composed of a waveguide conductor and a ground conductor,
A waveguide conductor and a ground conductor constituting the input-side waveguide, and a coupling conductor connected to the waveguide conductor constituting the input-side waveguide are provided on the first surface,
The waveguide conductor and ground conductor constituting the output-side waveguide, and the coupling conductor connected to the waveguide conductor constituting the output-side waveguide are provided on the second surface. 4. The ultra-wideband bandpass filter according to any one of 3.   7. The pair of coupling conductors that are broadside coupled is constituted by an electric insulator having a single layer or a multilayer structure, a gas body, or a conductor that is arranged in parallel with a vacuum interposed therebetween. The ultra-wideband bandpass filter described in 1. The ultra-wideband bandpass filter according to claim 1 is connected in series,
Two pairs of coupling conductors constituting two broadside couplings are arranged by assigning two coupling conductors to each surface of a pair of surfaces;
Two coupling conductors arranged on one side are connected via a waveguide conductor,
An ultra-wideband bandpass filter characterized in that two coupling conductors arranged on the other surface are connected to a waveguide conductor of an input side waveguide or a waveguide conductor of an output side waveguide. Comprising at least two ultra-wideband bandpass filters according to any one of claims 1 to 8 arranged on at least two or more parallel surfaces;
An ultra-wideband bandpass filter characterized in that a plurality of coupling conductors constituting a plurality of ultrawideband bandpass filters are connected in series, in parallel, or in arbitrary series-parallel using a waveguide conductor. The first ultra-wideband bandpass filter according to any one of claims 1 to 7, comprising a first surface and a second surface selected from first, second, and third electric conductor surfaces that are parallel in order. And a second ultra-wideband bandpass filter according to any one of claims 1 to 8 configured by using the second surface and the third surface, and connecting each coupling conductor formed on the second surface. It is connected in series using a waveguide conductor,
An ultra-wideband bandpass filter characterized in that a ground conductor is provided on any of the first, second, or third surfaces. Of the first, second, third, and fourth surfaces parallel in order, a ground conductor region is provided on the first or fourth surface,
An ultra-wideband bandpass filter according to any one of claims 1 to 9, provided on the second and third surfaces.   An ultra-wideband bandpass filter comprising a plurality of ultrawideband bandpass filters according to any one of claims 1 to 9 having different passband characteristics, connected in series, in parallel, or in series-parallel. A plurality of ultra-wideband bandpass filters according to claim 8 having different passband characteristics, connected in series, in parallel, or in series-parallel,
An ultra-wideband bandpass filter characterized in that the passband characteristic is set by changing the distance between two waveguide conductors for input and output.   An ultra-wideband bandpass filter according to any one of claims 1 to 13 and a lowpass filter having a cutoff frequency higher than that of the ultra-wideband bandpass filter are connected in series. Wideband bandpass filter.   The coupling conductor connected to the waveguide conductor of the input-side waveguide is separated from the coupling conductor connected to the waveguide conductor of the output-side waveguide, and the distance is the distance between the coupling conductors that are broad-side coupled. The ultra-wideband bandpass filter according to claim 8, which is three times or less.

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