JPS616810A - High-frequency impedance transformer - Google Patents

Abstract

PURPOSE:To provide a miniaturized and low-cost impedance transformer by a method wherein the length of coaxial lines is selected so as to correspond to one fourth wave length of an operating cener frequency, and outside conductors of the plural numbers of coaxial lines which have the same characteristic impedance are grounded and their core conductors are connected in parallel at each end thereof and is designated as an input-output terminal. CONSTITUTION:Coaxial lines 31, 32, 33 have the same impedance ZT respectively and line length corresponds to one fourth wave length of operating central frequency. If impedance, whose reference impedance is Zo, is connected to an input terminal 34 and impedance looked from output terminal 35 is Zout, Zout=ZTE<2>/Zo=Zr<2>/9Zo. Zo is an impedance in a measurement device and is normally 50OMEGA. ZT is 75OMEGA, 50OMEGA, 25OMEGA, etc. which is able to obtain easily as standard products and also is very low-cost. If Zo=50OMEGA is designated and is selected either one of 75OMEGA, 50OMEGAm 25OMEGA as a coaxial line, Zout becomes 12.5OMEGA, 5.56OMEGA, 1.39OMEGA and a transformer which is high impedance transformation ratio can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a high frequency impedance transformer used in low impedance measurement circuits, matching circuits, etc.

Conventional Structures and Their Problems Recently, high-power semiconductor devices for high frequencies have been widely used, but as the output increases, both their input and output impedances have become several ohms or 1 ohm or less. However, most measurement systems for high frequency circuits are usually 50Ω, 2
The standard is 5Ω or 75Ω, making it extremely difficult to measure impedance levels that are extremely different, and the accuracy is poor.

Conventionally, in order to perform highly accurate measurements, an innovinidance transformer has been used to lower the impedance of the measurement system.

This transformer uses a quarter-wave transmission line, and a coaxial type. Figures 1a and 1b show such coaxial lines, which are composed of an outer conductor 11, an inner conductor 12, and a low-loss dielectric 13 filled between the inner and outer conductors 11 and 12. A reference impedance Zo is connected to the input end 23 of the quarter-wavelength transformer 21, and the impedance seen from the output end is Zout. Broken transformer 21
If the line impedance of is ZT, then Zout =
It becomes ZT2/20. Zo = 50Ω, 25Ω, Z
If T-2oΩ, Zout = 8Ω, 50
Ω is converted to 8Ω.

By the way, the line impedance is defined as the coaxial inner conductor radius a
, the inner diameter of the outer conductor is 81, and the dielectric constant is 81.
ZT-(eo/to) 6n (b/a) is given by. Coaxial lines that are commercially available and put into practical use often use a material such as polyethylene with εr=2.0 as a dielectric material. At this time, the 50Ω line is b/a==s, 2
s, i, 20Ω line becomes b/a-1, 50Ω, 25. Assuming that the radius of the coaxial outer conductor is 1.0 mm, in the case of 50Ω, the center conductor radius is 0.307 mm and the dielectric thickness is 0.693 mm, whereas in the case of 20Ω line, it is 0.6251N117, respectively. It becomes 0.375mm. In this way, the lower the impedance and the smaller the diameter of the outer conductor, the thinner the dielectric cylinder becomes.
Manufacturing is difficult because coaxial centers tend to shift. In addition, the diameter of the medium conductor becomes large and it loses its flexibility, making it inconvenient to handle as a line.Therefore, there are few commercially available low impedance lines, and they are expensive.

On the other hand, although it is not impossible to realize a low impedance line using a strip line, it is not practical because the number of knob conductors in the line increases rapidly as the impedance becomes lower.

As mentioned above, lines for impedance transformers have disadvantages such as the lower the impedance, the more difficult it is to realize them, and even if they can be realized, they will be expensive.

OBJECTS OF THE INVENTION An object of the present invention is to provide a small and inexpensive impedance transformer using a commercially available standard product and inexpensive coaxial line.

This is an inexpensive impedance transformer constructed according to the invention, and also has the feature that the transformation ratio can be freely selected by combining coaxial lines with different impedances.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 shows the wiring of a high frequency impedance transformer in one embodiment of the present invention. In Figure 3, 3
Coaxial lines 1, 32, and 33 each have the same impedance Z, and the line length is a quarter wavelength at the center frequency used.

All of these outer conductors are grounded, and the center conductors are connected to each other at their tips to form an input terminal 34 and an output terminal 35.

By connecting the coaxial cable as described above, the effective impedance ZTE of the line becomes ZT/3. Now, if we connect the impedance that is the reference impedance ZO to the input terminal 35, and let the impedance visible from the output terminal 35 be Zout. ,Zout2ZTX/Zo-ZT2/
It becomes 9Zo. ZO is the impedance of the measurement system,
Usually 50Ω. In addition, the two guns are 75Ω, 5Ω as standard products.
There are 0Ω, 25Ω, etc., which are easily available and extremely inexpensive. 1Zo-50Ω, and 75Ω as a coaxial line.
Ω, 50Ω.

When selecting either 25Ω, Zout is 12
．． 5Ω, 6.56Ω, and 1.39Ω, and a transformer with a high impedance transformation ratio can be easily realized.

In the case of FIG. 3, three coaxial lines are selected, but any number may be used. stomach! , N impedances ZT
When using a coaxial line of , the effective line impedance ZT
, : ZT/N, output impedance ZOut
It is obvious that 2ZTE2/ZO-ZT2/(N2ZO).

The same line impedance was chosen to simplify the explanation, but there is no problem even if they are different. For example, characteristic impedance ZTI+ZT2, Zr
L (≧0) for each of the three types of lines in 2.

In the case of the selected combination of M (Q≧○) and N (≧0),
Zrw ” 1 / (L/ ZT1+ M/ZT2
+N/ZT5). From this, the choice of impedance transformer is extremely flexible.

Note that even if the characteristic impedance of the line is different, the line length must be selected so that there is a quarter-wave diversion at the center frequency, but in practice it is preferable to keep it constant. Therefore, the dielectric AA ratio of the coaxial line must be the same.At this time, the propagation speed of the line will be the same, and even if the line impedance is different, the wavelength will be the same.

FIG. 4 shows a second embodiment of the invention.

In order to widen the band of the transformer, the transformer 1g is configured in multiple stages.

In FIG. 4, the lines 41, 42 constitute a first transformer, the lines 43, 44, 45, 46, 47 constitute a second transformer, which are connected in series and connected to the first transformer. An input terminal 46 is provided, while an output terminal 47 is provided on the second transformer.

The input terminal 46 is on the high impedance side, and the output terminal 47 is on the low impedance side. If the line impedance is constant, the number of lines for the first transformer is small and the number of lines for the second transformer is large. In general, lines can be used in combination, and the role condition is that the output impedance Zout+ of the first transformer must be selected to be larger than the effective line impedance ZTE2 of the second transformer. Just choose a combination below. Although examples of two-stage configurations have been described above, it is clear that these can also be applied to transformers with three or more stages. By using a multi-stage configuration, a broadband high-frequency transformer with a large impedance transformation ratio can be realized.

FIG. 5 ← 1 This is an embodiment showing a method of connecting the coaxial lines shown in FIGS. 3 and 4. At line connections, inductance tends to occur, circuit matching tends to change, and lances tend to occur between single lines. In Fig. 5, 51 is a coaxial line, 52, 53 is a center conductor of the coaxial line, 54 is a dielectric substrate, 55 is a dielectric J, 1 plate, 6 plates, 4 upper body putter/, 56 is a center W This is a through hole for inserting the body 62, 53 and the conductor wire for input/output coupling. By using this through hole 56 and fixing it mechanically and electrically with solder etc., the connection length of the line can be minimized and the connection part of each line can be made constant. It is possible to reduce stray components in the line, maintain balance between lines, and improve electrical characteristics.

Effects of the Invention As described above, the present invention makes it possible to realize a low-impedance, compact, and low-loss impedance transformer by using a plurality of commercially available and easily available inexpensive coaxial lines. At the same time, it expands the flexibility in selecting transformation ratios, and also enables broadband configuration with a multi-stage configuration.It can be applied to the measurement of high-frequency, high-output half-core devices, or the impedance matching of such devices. The industrial value is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a conventional coaxial line, FIG. 2 is a schematic diagram of a conventional impedance transformer using a coaxial line, and FIG. 3 is a wiring diagram of a high frequency impedance generator in an embodiment of the present invention. FIG. 4 is a wiring diagram of a high frequency impedance transformer in the second embodiment of the present invention, FIG.
FIG. 5 is a perspective view showing a method of connecting the lines in FIG. 4; 31 ~ 33. 41 ~ 4 ends, 51... Quarter wavelength coaxial line, 34. 41 - Input terminal, 35, 4 ends... - Output terminal, 54... Dielectric substrate for line connection, 55...・
・Copper body pattern, 66...Through hole. Name of agent Toshio Nakao, lawyer and 1 other person 1st
Figure (Mountain, (b) 1? Figure 2 Figure 3 Figure 4 Figure 5 ◇ Guko

Claims (5)

[Claims] (1) The length is selected to be a quarter wavelength of the operating center frequency, and the outer conductor is grounded using multiple coaxial lines with equal characteristic impedance, and the center conductors are connected in parallel at both ends for input/output. A high frequency impedance transformer characterized by having terminals. (2) Characteristic impedance is 75Ω, 50Ω, 25Ω
Claim 1 characterized in that it is any one of
The high frequency impedance transformer described in Section 1. (3) High-frequency impedance transformation according to claim 1, characterized in that it is constructed by selecting one or more coaxial lines of two or more types each having the same propagation velocity and different characteristic impedances and combining a plurality of them. vessel. (4) The high frequency impedance transformer according to claim 3, characterized in that two or three types of coaxial lines having a characteristic impedance of 75Ω, 50Ω, or 25Ω are combined. (5) Claim 1, characterized in that it has a line connection section configured by inserting and connecting center conductors of a plurality of coaxial lines into a plurality of through holes provided in a double-sided conductor-covered dielectric substrate. The high frequency impedance transformer described in Section 1.