JPS62247601A - Fixed resistance attenuator - Google Patents

Abstract

PURPOSE:To obtain a fixed resistance attenuator having comparatively satisfactory frequency characteristics by inserting a transmission line having a characteristic impedance lower than that of other two transmission lines and the electrical length of 1/4 wavelength compared with the using frequency in series between said two transmission lines via resistors. CONSTITUTION:A transmission line 31 having an impedance lower than those of both transmission lines 30 and 32 is inserted between these two lines 30 and 32. These lines 30-32 are connected with each other by the 1st and 2nd resistors 33 and 34. In this case, the electrical length of the 2nd transmission line 31 is set at 1/4 using frequency so that the impedances are equal to pure resistance in terms of both resisters 33 and 34. For instance, the impedances of both lines 30 and 32 are set at 50OMEGA together with the resistance values of resistors 33 and 34 set at 25OMEGA and the impedance of the line 31 set at 43.3OMEGA respectively. Under such conditions, a 4-6GHz using frequency band is secured with 5dB insertion loss and 20dB reflection loss respectively.

Description

[Detailed Description of the Invention] [Summary] In a fixed resistance attenuator, a first transmission line and a second transmission line, and a second transmission line and a third transmission line are connected to the first and second resistors, respectively. and the second transmission line is connected so that the distance between the positions where the impedance of the first and second resistors appears to be pure resistance at a predetermined frequency is λg/4 (λg is the shortened wavelength). By having a long electrical length and a characteristic impedance lower than that of the first and third transmission lines, relatively good frequency characteristics can be obtained at a low cost.

[Industrial application field]

The present invention relates to improvements in fixed resistance attenuators, particularly fixed resistance attenuators used in the microwave band.

Fixed resistance attenuators are used in almost all microwave circuits, for example, and are required to be inexpensive and have relatively good frequency characteristics.

[Conventional technology]

FIG. 3 is a block diagram of a conventional example, FIG. 4 is a block diagram of another conventional example, and FIG. 5 is a block diagram of still another conventional example. Below, the third
The structure of a conventional example of a fixed resistance attenuator will be explained with reference to FIGS.

FIG. 3 (al is a plan view, and FIG. 3(b) is a cross-sectional view taken along line A-A in FIG. 3(a). As shown in FIG. 3, the ground conductor 5
The strip line 1 is cut by a resistive film 2 formed on an alumina substrate 4 fixed thereon, and both ends of this resistive film are grounded via grounding fittings 3.3''. Fixed resistance attenuators can be used from DC to about 10 GHz, and are also used in measuring instruments, etc. However, they use an alumina substrate, are expensive because the resistive film must be adjusted to a specified value, and require no grounding fittings. It becomes necessary.

FIG. 4 shows a π-type fixed resistance attenuator (Al is formed of thin film resistors 6, 7.8 on an alumina substrate, and one end of this resistor 7.8 is connected to a λg/4 oven stub 9. 10. Such a configuration can be used without problems regarding attenuation, characteristic impedance, etc. in a band where one end of the resistor is considered to be short-circuited. Note that 1 is a strip line.

Figure 4(b) shows a chip resistor 13.14°15 connected to a strip line 11.12 formed on a flow glass substrate or an epoxy substrate (lower price than an alumina substrate). It is a π-type fixed resistance attenuator like the one in Figure (a). Note that one end of the chip resistor 13.15 is grounded through the through hole 16.16'', but since chip resistors are inexpensive and can be connected by soldering, it is possible to connect at several 100 MHz to 2 GHz. It can be used to some extent.

Figure 5(a) and Figure 5(b) are shown in Figure 4(a) and Figure 4(
Instead of the π-type fixed resistance attenuator in bl, it is configured with a T-type, and 16, 17, and 18 are thin film resistors, and 19 is a λg/4
Open stub, 20~22 is strip line, 23~
25 is a chip resistor, and the usable frequency range is the same as above. Figure 5 (C) shows that the grounding is not done through the 16° flexible through hole in Figure 5 (bl), but is grounded at a high frequency using a λg/4 oven stub. However, if the operating frequency is 4 GHz or higher, Depending on the dimensions of the resistor, an imaginary part appears outside the resistive film, causing the attenuation amount and characteristic impedance to deteriorate from desired values.

[Problem that the invention seeks to solve]

As explained above, fixed resistance attenuators with good frequency characteristics are expensive, low-priced ones have poor frequency characteristics, and it is difficult to obtain fixed resistance attenuators with relatively good frequency characteristics at a low price. There is a problem with this.

[Means for solving problems]

The above problem is caused by the first transmission line 30 as shown in FIG.
and the second transmission line 31, the second transmission line and the third transmission line 32, and the first resistor 33 and the second resistor 34.
The second transmission line 31 has an electrical length such that the distance between the positions where the impedance of the first and second resistors appears to be pure resistance at a predetermined frequency is λg/4. This problem is solved by the fixed resistance attenuator of the present invention having a characteristic impedance set lower than the characteristic impedance of the first and third transmission lines 30, 32.

[Effect]

In the present invention, the electrical length of the second transmission line is determined by resistors 33 and 34.
The distance between the positions where the impedance seen as a pure resistance at the required frequency is λg/4, and the resistance value RI of the resistor 33 + the impedance Z+ of the second transmission line, the resistance value R2+ of the resistor 34, and the load. Attenuation characteristics were obtained by performing voltage distribution with impedance ZL.

In other words, as the frequency increases, the phase difference (deviation in electrical length) that appears to be pure resistance due to the dimensions of the resistor increases, deteriorating the frequency characteristics. This can be solved by placing it. However, since the above configuration cannot be achieved when the dimensions of the resistors 33 and 34 are combined at a frequency of λg/4 or more, the frequency is limited to the following.

As a result, a fixed resistance attenuator with relatively good frequency characteristics can be obtained at a low cost and with a simple configuration.

〔Example〕

Calculated and measured loss values are shown.

First, when an equivalent circuit of the embodiment of the present invention shown in FIG. 1 is obtained, it becomes as shown in FIG. 2 (al).

Here, R,, R2 are the resistance values of the resistors 33 and 34, z,
is the impedance of the second transmission line, and Z, , Z, is the load.

The signal source impedance is shown respectively.

The characteristics of the circuit shown in FIG. 2 (al) can be easily determined by using the F matrix as is well known.

and At the center frequency is required.

However, although the calculated value is calculated using only the resistor, in reality, an imaginary part is included due to the phase shift due to the dimensions of the chip resistor and the frequency characteristics of λg, so the characteristics will change as you move away from the center frequency. .

For example, negative values are obtained for R, = R, = 25 Ω, the impedance of the second transmission line is 43.3 Ω, and the signal source impedance Zs, and the spacing is λg/4 at 5 GHz, so the reflection loss is If the frequency becomes very large, the reflected power will be small (that is, the transmitted power will be large), but if the frequency deviates beyond this value, an imaginary part will occur and the reflection loss will deteriorate. Furthermore, when the insertion loss is actually measured from 4 to 4, a value like the solid line is obtained, and at about 4 to 6 GH2, a reflection loss of about 20 dB or more and an insertion loss of about 5 dB are obtained, which is 4 in Figure 5 fc) above.
It is sufficiently usable even at a frequency of about 6 GHz, which is higher than about GHz, and is inexpensive because a chip resistor is used as the resistor and a flow glass substrate is used as the dielectric substrate.

〔Effect of the invention〕

As explained in detail above, the present invention has the advantage that a fixed resistance attenuator with relatively good frequency characteristics can be obtained at a low cost by using a chip resistor and, for example, a flow glass substrate.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention, Figure 2 is the attenuation characteristic diagram of Figure 1, Figure 3 is a configuration diagram of the conventional example. FIG. 4 is a configuration diagram of another conventional example, FIG. 5 shows a configuration diagram of yet another conventional example. In the figure, 30 is a first transmission line; 31 is a second transmission line; 32 is the third transmission line, 33 is the first resistor; 34 indicates a second resistor. Non-meeting old month 0 arrest 3 shoes example aTIt doorguji]%-tD Un　2　■ (C) History (-man i)'s unheard 0) Sueo 1 fall 5 mouths early

Claims (1)

[Claims] The first transmission line (30) and the second transmission line (31), and the two transmission lines and the third transmission line (32) are connected to the first transmission line (30) and the second transmission line (31).
is connected through a resistor (33) and a second resistor (34), and the second transmission line (31) has an impedance looking at the first and second resistors at a predetermined frequency. It is characterized by having an electrical length such that the distance between the positions that appear to be pure resistance is λg/4, and having a characteristic impedance set lower than the characteristic impedance of the first and third transmission lines (30, 32). Fixed resistance attenuator.