JPH0320162B2 - - Google Patents

Description

[Detailed Description of the Invention] "Object of the Invention" (Industrial Application Field) The present invention relates to a distributed constant coupled line used in a high frequency band higher than the UHF band, and particularly relates to a microwave circuit suitable for widening the band. It is something.

(Prior Art/Problems to be Solved by the Invention) There is a strong demand for widening the band of microstrip coupling lines widely used in filters and directional couplers.

In order to widen the band of this microstrip coupled line, the mode impedance ratio (m) =
It is necessary to increase the EVEN mode impedance (Z _0e )/ODD mode impedance (Z ₀₀ ).

The above reason will be briefly explained next.

For example, the image impedance Z _I in the case of a bandpass filter as shown in Fig. 9 is Z _I =√(Z _0e −Z ₀₀ ) ² −(Z _0e +Z ₀₀ ) ² cos ² θ/2 _SIN θ…
…(1).

Here, Z _0e is EVEN mode impedance Z ₀₀ is ODD mode impedance θ is electrical length.

The image impedance Z _I is expressed as shown in FIG. 10, but if the image impedance Z _I is "Z _I = 0"
To find the cutoff frequency θ _c , (Z _0e −Z ₀₀ ) ² −(Z _0e +Z ₀₀ ) ² cos ² θ=0 …(2) ∴cosθ _c =±Z _0e −Z ₀₀ /Z _0e +Z ₀₀ =±m-1/m+1...
...(3) In the above equation (3), m=Z _0e /Z ₀₀ .

Therefore, the cutoff frequencies θ _c1 and θ _c2 are becomes.

Here, the fractional bandwidth W _r is W _r =θ _c2 −θ _c1 /π/2=2/π(π−2cos ⁻¹
m-1/m+1) = 2-4/πcos ^-1 m-1/m+1...
...(5) As is clear from the above equation (5), it can be seen that the larger the mode impedance ratio m becomes, the closer the fractional bandwidth W _r becomes to "W _r =2", resulting in a wider band.

Also, from this, the EVEN mode impedance Z _0e should be set high and the ODD mode impedance
It can be seen that a wider band can be achieved by lowering Z ₀₀ .

Furthermore, even in the case of multi-stage filters, broadband filters have high EVEN mode impedance Z _0e ,
Since a low ODD mode impedance Z ₀₀ is required, it is necessary to increase the mode impedance ratio m in order to achieve a wide band.

Further, the degree of coupling C is expressed as "C=m-1/m+1", and it can be seen that the larger the mode impedance ratio m is, the better for tight coupling.

Next, a conventional microstrip two-wire coupled line will be briefly explained based on FIGS. 11 to 13.

First, the microstrip two-line coupled line shown in FIG.
Two signal line conductors 2 and 3 having a width W are arranged with a distance S between them. Further, a ground conductor 4 is arranged on the lower surface of the dielectric substrate 1. In the microstrip two-wire coupled line shown in FIG. 11, the signal line conductors 2 and 3 are arranged on the same plane of the dielectric substrate 1, so in order to widen the band, it is necessary to It was necessary to narrow the interval S between the conductors 2 and 3, and there was a limit to widening the band due to problems with manufacturing accuracy.

In order to solve the above-mentioned problems, a microstrip two-wire coupled line shown in FIGS. 12 and 13 was proposed.

FIG. 12 shows that two signal line conductors 2 and 3 having a width W are arranged on the upper surface of a dielectric substrate 1 having a thickness h, with a distance S between them, and the two signal line conductors 2 and 3 are covered. A dielectric 5 is provided on the top surface of the dielectric 5, and a non-grounded conductor 6 is disposed on the upper surface of the dielectric 5. Further, a ground conductor 4 is arranged on the lower surface of the dielectric substrate 1. The microstrip two-wire coupled line shown in FIG. 12 is called an overlay structure, and is a method for lowering the ODD mode impedance _Z00 . However, with this overlay structure, the ODD mode impedance Z ₀₀ changes greatly due to changes in the dielectric constant and thickness, and if the thickness is not increased, the ODD mode impedance Z ₀₀
The dielectric material becomes too low, and if the thickness is increased, the material for the dielectric part is expensive, resulting in high costs.

In addition, the microstrip two-line coupled line shown in FIG. 13 has two signal lines 2 and 3 having a width W arranged at a distance S on the upper surface of a dielectric substrate 1 having a thickness h, and On the lower surface of the dielectric substrate 1, a non-conductor portion 7 is provided at a position corresponding to the two signal lines 2 and 3, and a ground conductor 4 is provided at the other portion.

In the above configuration, when excited in the same phase,
The EVEN mode impedance Z _0e can be made high because the distance between the signal line conductors 2 and 3 and the ground conductor 4 is wide, and the fractional bandwidth W _r can be made large.

As mentioned above, in the microstrip two-wire coupled line shown in FIGS. 12 and 13, any means can only be applied to either the ODD mode impedance Z ₀₀ or the EVEN mode impedance Z _0e . There is a drawback that no effect can be obtained, and each method has a drawback that it cannot be easily designed because the electric field distribution is complicated.

The present invention has been made in view of the above-mentioned points, and its purpose is to allow both the EVEN mode impedance Z _0e and the ODD mode impedance Z ₀₀ to vary significantly, and to
It is an object of the present invention to provide a microwave circuit that can set mode impedance Z _0e high and ODD mode impedance Z ₀₀ low, and can achieve a wide band.

"Structure of the Invention" (Means for Solving the Problems) A microwave circuit according to the present invention includes a two-wire coupled line disposed at opposing positions on the front and back sides of a dielectric substrate, and both sides of the two-line coupled line. ground conductors arranged at intervals, and conductive means for electrically connecting the signal line conductors constituting the two-wire coupled line arranged at opposite positions on the front and back sides of the dielectric substrate. We are trying to solve the problem by being prepared.

(Function) Ground conductors are arranged at intervals on both sides of the two-wire coupled line, and two ground conductors are placed at opposing positions on the front and back sides of the dielectric substrate.
Since the linear coupled line is arranged and a conductive means is provided between the signal line conductors constituting the two-wire coupled line, the EVEN mode impedance Z _0e becomes a high impedance almost equal to the characteristic impedance of the conventional coplanar coupled line. , ODD mode impedance Z ₀₀ is achieved by parallelizing the circuits by means of conductive means provided between the signal line conductors, and can obtain an extremely low impedance. Therefore, the EVEN mode impedance Z _0e is high;
The ODD mode impedance Z ₀₀ can be set extremely low, the mode impedance ratio m can be increased, and a wide band can be achieved.

(Example) An example of a microwave circuit according to the present invention will be described based on FIGS. 1 to 8.

First, a first embodiment of the microwave circuit according to the present invention shown in FIGS. 1 and 2 will be described. FIG. 1 is a sectional view, and FIG. 2 is a plan view of FIG. 1.

In the figure, 11 is a dielectric substrate with a thickness h, 12, 13
is a two-wire coupled line arranged on a dielectric substrate 11 with a spacing S ₁ , and signal line conductors 12a, 12b and 13 are placed on the dielectric substrate 11 at opposing positions.
a and 13b are arranged to form a distributed constant coupled line. Reference numeral 14 denotes a ground conductor, which is arranged on the common plane of the dielectric substrate 11 on which the two-wire coupled lines 12 and 13 are arranged, with a spacing S ₂ on both sides. Reference numeral 15 denotes a signal line conductor 12 constituting the two-wire coupled lines 12 and 13 disposed on opposite sides of the dielectric substrate 11.
Conductive means for electrically connecting between signal line conductors 12a and 12b and between 13a and 13b, respectively.
A plurality of through holes penetrating the dielectric substrate 11 are formed between b. There is no particular relationship between the diameter of the through hose and the width of the line conductor. Further, the diameter of the through hole may be larger than the width of the conductor.

By configuring as above, EVEN
The mode impedance Z _0e has a distribution state in which most of the electric field is in the air, and can exhibit a high impedance state approximately equal to the characteristic impedance of a conventional coplanar coupled line.

By the way, the conventional coplanar coupled line originally has a structure in which it is difficult to obtain low impedance, and conversely, high impedance can be easily obtained by widening the interval _S2 .

Therefore, the EVEN mode impedance Z _0e is
Two-wire coupled line 12 (or 13) and ground conductor 1
A high impedance can be easily obtained by widening _the distance _S2 .

On the other hand, since the ODD mode impedance Z ₀₀ is such that most of the electric field is distributed within the dielectric substrate 11, a low impedance approximately equal to the characteristic impedance of a conventional microstrip coupled line can be obtained. Furthermore, in addition to the above-described operation, the signal line conductors 12a and 12b constituting the two-wire coupled lines 12 and 13 and between the signal line conductors 13a and 1
Since a plurality of through holes constituting the conductive means 15 are formed between the two wire coupling lines 12 and 3b,
13 circuits can be parallelized, and an extremely low impedance of approximately half the characteristic impedance of a conventional microstrip coupled line can be obtained.

Therefore, the embodiment shown in FIGS. 1 and 2 described above operates the high impedance characteristic of the coplanar coupled line as the EVEN mode impedance Z _0e , and also operates the low impedance characteristic of the microstrip coupled line. The low impedance characteristic based on the parallelization of the circuits by the through holes of the conductive means 15, which is added as an effect superimposed on the low impedance characteristic, can be realized as the ODD mode impedance Z ₀₀ . Therefore, "mode impedance ratio (m) =
EVEN mode impedance (Z _0e )/ODD mode impedance (Z ₀₀ ) can be made large, making it possible to achieve a wide band.

3 and 4 show an example in which the first embodiment described above is applied to a directional coupler.
The figure is a front view, and FIG. 4 is a back view.

This directional coupler has a relative dielectric constant ε _r =4.5, a dielectric substrate thickness h = 1 mm, and signal line conductors 12a, 1
Width W of 2b and 13a, 13b = 2 mm, signal line conductor 12a, 13a (and 12b, 13b)
When the distance between the ground conductor 14 and each signal line conductor (12a, 12b, 13a, 13b) S ₁ = 0.2 mm, and the distance S ₂ between the ground conductor 14 and each signal line conductor (12a, 12b, 13a, 13b) = 1.5 mm, EVEN mode impedance Z _0e ≒ 120Ω ODD mode impedance Z ₀₀ It became ≒20Ω. Therefore, it was possible to increase the mode impedance ratio m, and it was possible to achieve a wide band.

Next, in a second embodiment of the microwave circuit according to the present invention shown in FIGS. 5 and 6, two parallel through holes 16a and 16b formed in a dielectric substrate 11 are used as conductive means. At the same time, conductors 17a and 1 are inserted into the respective through holes 16a and 16b.
7b are fitted together. Note that the conductors 17a, 17b are the signal line conductors 12a, 12
b, 13a, and 13b.

Further, the conductors 17a and 17b may be plate-shaped or rod-shaped, or may be formed by providing a long hole in a ceramic substrate, pouring a conductive paste into the hole, drying it, and firing it.

By configuring as above, EVEN
The mode impedance Z _0e can be obtained as high impedance by the same operation as in the first embodiment described above. On the other hand, ODD mode impedance Z ₀₀ is surface coupling, so
Very deep connections can be achieved. Therefore, a very low ODD mode impedance Z ₀₀ is obtained. Therefore, a large mode impedance ratio m can be obtained, and a wide band can be achieved.

FIG. 7 shows the third part of the microwave circuit according to the present invention.
This is an example of the following.

In this third embodiment, a signal line conductor 12 constituting two wire coupled lines 12 and 13 is used as a conductive means.
A, 12b and a part of 13a, 13b are buried in the dielectric substrate 11, respectively, and a through hole 18 is formed in the dielectric substrate 11 in the buried portion.
was formed. Note that the relationship between the through hole diameter and the line conductor width is not particularly determined. Also,
The diameter of the through hole may be larger than the width of the conductor.

By configuring as described above, the relationship between the conductivity of the dielectric substrate 11 and the conductor spacing S can be adjusted appropriately.
This is suitable for obtaining the ODD mode impedance Z ₀₀ , and is also effective when the signal line conductor 12a etc. cannot be buried very deeply.

FIG. 8 shows the fourth part of the microwave circuit according to the present invention.
This is an example of the following.

In this fourth embodiment, as a conductive means, signal line conductors 12a, 12b and 13a, 13b constituting a two-wire coupled line are deeply embedded in a dielectric substrate 11, leaving a part of them, and the opposing signal line The conductors 12a and 12b and the signal line conductors 13a and 13b are formed close to each other.

The above configuration is effective when the dielectric substrate 11 has a large relative dielectric constant ε _r and a thick thickness h.

In the case of the third and fourth embodiments shown in FIG. 7 and FIG. Signal line conductors 12a, 12b
and 13a, 13b, it is possible to obtain a distributed constant coupled line with low manufacturing cost and high performance.

"Effects of the Invention" According to the microwave circuit according to the present invention, the EVEN mode impedance Z _0e can be set high and the ODD mode impedance Z ₀₀ can be set low, regardless of manufacturing accuracy, so that the mode impedance ratio m can be set high. It is possible to increase the bandwidth and achieve a wide band. In addition, it has excellent features such as being able to easily design because there are few design parameters, and being able to obtain a distributed constant coupled line with low manufacturing cost.

[Brief explanation of the drawing]

1 to 8 show an embodiment of the microwave circuit according to the present invention, in which FIG. 1 is a sectional view, FIG. 2 is a plan view of FIG. 1, and FIG. 3 is a surface view.
Figure 4 is a back view, Figure 5 is a sectional view, Figure 6 is a
The plan view and FIGS. 7 and 8 are cross-sectional views. 9 to 13 show conventional examples, in which FIG. 9 is an explanatory schematic diagram showing an example of a bandpass filter, FIG. 10 is a characteristic diagram of FIG. 9,
FIGS. 11, 12 and 13 are cross-sectional views. 11; dielectric substrate; 12, 13; two-wire coupled line; 12a, 12b, 13a, 13b; signal line conductor; 14; ground conductor; 15; conductive means.

Claims (1)

[Scope of Claims] 1. A two-wire coupled line arranged at opposing positions on the front and back sides of a dielectric substrate, a ground conductor arranged at intervals on both sides of the two-line coupled line, and a 1. A microwave circuit comprising conductive means for electrically connecting signal line conductors constituting a two-wire coupled line disposed at opposite positions on the front and back sides. 2. The microwave circuit according to claim 1, wherein a plurality of through holes are formed as the conductive means. 3. The microwave circuit according to claim 1, wherein conductors are fitted into two parallel through holes formed in the dielectric substrate as the conductive means to operate as a coupled line. 4. As the conductive means, a portion of the signal line conductor constituting the two-wire coupled line is embedded in a dielectric substrate, and a through hole is formed in the dielectric substrate at the embedded portion.
Microwave circuit described in section. 5. Claim No. 5, in which the signal line conductors constituting the two-wire coupled line are deeply buried in a dielectric substrate having a high relative dielectric constant as conductive means, leaving a part of the signal line conductors remaining, and opposing signal line conductors are brought close to each other. The microwave circuit according to item 1.