JPS59125102A - Radio wave filter device for high frequency - Google Patents

Abstract

PURPOSE:To miniaturize a radio wave filter device for high frequency which uses a microstrip line by having the discontinuous characteristic impedance for a secondary transmission line and setting the ratio of the characteristic impedance at a level larger than 1. CONSTITUTION:The tip of a secondary transmission line 2 is substantially opened or short-circuited to secure the discontinuous characteristic impedance. Such a line 2 is branched from a microstrip main transmission line 1. The discontinuous lengths l1 and l2 are set smaller than 1/4 effective wavelength for the characteristic impedance of the line 2. When the tip of the line 2 is opened in terms of high frequency, the characteristic impedance Z01 of the start terminal side is set larger than the characteristic impedance Z02 of the tip side. While Z01 is set smaller than Z02 when the tip of the line 2 is short-circuited in terms of high frequency. Either one or all of the line width (a), the gap (b) and the dielectric constant epsilon are changed in order to have the discontinuous characteristic impedance.

Description

[Detailed Description of the Invention] Industrial Field of Application The present invention relates to a high frequency radio wave filter device using a Micros (IJ) tubular line, and in particular provides a configuration for making the radio wave filter compact. .

Conventional Structure and Problems There are many examples of this type of filter, and a representative example is Japanese Patent Publication No. 6-39666. FIG. 1 shows the configuration of a conventional example. In the figure, the arrow 1 direction is the main transmission line 1, the y direction is the sub transmission line 2, and a plurality of them are arranged in the X direction to obtain the filter characteristics of the desired frequency band. This is another conventional example, and is a microstrip line for matching of a microwave transistor amplifier. A length of 20EF (E (high frequency choke)) with one end short-circuited with a capacitor is connected to the main line 3.

This RFC supplies DC power from terminal B, and
By increasing the impedance at the operating frequency when looking at the sub line 4 from , the sub line 4 is provided so that the operation at high frequencies is the same as when the sub line 4 is not connected.

These radio wave filters using microstrip lines have a simple structure, have no moving parts, and have a high Q, so they have many applications.

The principle of the filter will be explained using the circuit shown in FIG.

In a zero-distribution constant line system, which shows an equivalent circuit when a load impedance 6 ZR is connected to the tip of the characteristic impedance sub-line 4 extending in the y direction, the impedance zB seen from the B end is converted according to the following equation.

However, β: effective phase constant (β=]) In the case of the conventional example shown in Fig. 1, the tip A is open (η = 8 - ■), so the above equation becomes 0, and in the case of Fig. 2, the tip A is High frequency short circuit (
1 = o) Note' 2 formulas are ZB (SH) = Z□ j ta
n99°.

The value of Therefore, the load impedance 6J is reversed at the B end. This state is well known as impedance inversion as a special example of impedance conversion. This is the principle of

-1- Contrary to the advantages of the prior art, the problem with the prior art is that for impedance inversion, the dimensional variation cannot be made less than one-fourth of the effective wavelength λeff. Therefore, for relatively low frequencies, the filter becomes large.

OBJECTS OF THE INVENTION The present invention solves the above-mentioned conventional problems, and aims to reduce the size of the filter.

Structure of the Invention FIG. 4 shows an equivalent circuit for explaining the invention in detail.

A feature of the present invention is that the characteristic impedance of the sub-transmission line is made discontinuous.

The operation will be explained in case 22 when the load end is short-circuited. The impedance zT at the terminal T when looking at the load side is 7, T=j Zo2 tanβ2''2.

The impedance ZB seen from terminal B is 1-A1tan/Jeltan/j%2.

Therefore, 1 = K1tanβJ4 ・tanβ2
It will be understood that if Q2 is satisfied, the short circuit state of the load impedance can be reversed to the open state at the B terminal. Note that the conventional example corresponds to 1-1. 1 to the ratio of characteristic impedance
If you make it thicker than 1, then (tanβ, 4 x
The value of tanβ222) can be reduced by that amount. In the range where the dimensions Qj + "2 are each smaller than a quarter of the effective wavelength, there is a positive correlation with tanβ111.tanβ2"2, so it can be concluded that the dimension Huff 22 can be shortened by increasing the Klcl) value by 1. means.

Frequency: 2450 MHz, effective wavelength: λeff+λ1. λ
2 is the wavelength of free space, and 1 is the ratio of the characteristic impedance.
An example when is set to 2 is shown below.〇The same holds true when the load end is opened (zp-■).

Therefore, 1 (−K2 tanβ+R+ ” ta
Impedance can be reversed if nβ222 is satisfied. The explanation for reducing the size by increasing the value of 2 to the ratio of characteristic impedances by more than 1 is the same as the above explanation regarding the short circuit state.

As is clear from the above explanation, if the characteristic impedance is made discontinuous in both cases where the load impedance is short-circuited and open, and the ratio of the characteristic impedances is increased by more than 1, the improvement will be made that much compared to the conventional example. You can understand that the dimensions can be compressed.

Next, the microstrip line (hereinafter abbreviated as M-3 line)
is shown in Figure 6. In the M-5 line, a strip conductor 6 having a line width a and a conductor substrate 7 are opposed to each other with a gap therebetween, and are attached to a dielectric material 8 made of dielectric material 8 from both sides. M-3
The radio wave propagation mode of the line is quasi-TEM wave, and its characteristic impedance is ε. ff: Effective dielectric constant. Characteristic impedance Z for coarse accuracy.

Therefore, it can be understood that in order to make the characteristic impedance discontinuous, it is sufficient to change any or all of the line width a1 gap 1 dielectric constant ε in the propagation direction.

DESCRIPTION OF EMBODIMENTS FIGS. 6 and 7 show embodiments of the present invention. Fig. 6 shows the case where the tip 2a of the sub-transmission line 2 is open, and Fig. 7 shows the case where the tip A is open, and the line width is 82(OP)〉al(loP)a.
By setting + (sH) > a2 (SH), the characteristic impedance ratio becomes 2. 1 is also thicker than 1.

FIG. 8 shows an example in which filters with open tips A are provided in multiple stages.

Although the above-mentioned embodiments have shown a two-part string of characteristics and one-beam dance, it goes without saying that the present invention includes more than two-part strings.

Effect of the invention (1) A compact radio wave filter can be constructed.

(2) The ratio of characteristic impedances is an important parameter. Desired filter characteristics can be obtained simply by controlling the ratio of each dimension and dielectric constant, as well as the absolute value dimension.

(3) As can be seen from the comparison of Figures 1 and 8, not only can the line configuration be made more compact, but also the amount of metal used for the IJ tube conductor can be reduced (4) Conventionally, due to the long wavelength The M-8 line radio wave filter can now be applied to frequency bands that were previously unavailable.

[Brief explanation of the drawing]

1 and 2 are block diagrams of a conventional radio wave filter device, FIG. 3 is an equivalent circuit diagram of FIGS. 1 and 2, FIG. 4 is an equivalent circuit diagram for explaining the present invention, and FIG. The figure is a schematic diagram of the same microstrip and power line, and Figures 6, 7, and 8 are configuration diagrams of a radio wave filter device that is an embodiment of the present invention.・・・・・・Subtransmission line, A end・
・ ・Short-circuited end of the sub-transmission line, B-terminal --- Starting end of the sub-transmission line 0 Name of agent Patent attorney Satoshi Nakao 5th man and 1 other person Figure 1 f Figure 2 C Figure 3 m =〉χ @4 Figures Figure 5 Figure 8

Claims (4)

[Claims] (1) A sub-transmission line is provided that branches off from the main microstrip transmission line and the tip is substantially open or short-circuited, and the characteristic impedance of the sub-transmission line is made discontinuous.The length of the sub-transmission line is less than a quarter wavelength. radio wave filter device. (2) The radio wave filter device for high frequencies according to claim 1, wherein when the tip of the sub-transmission line is opened in terms of high frequency, the characteristic impedance at the starting end side of the sub-transmission line is larger than that at the tip. (3) When the tip of the sub-transmission line is short-circuited at high frequency, the characteristic impedance at the starting end side of the sub-transmission line is smaller than that at the tip. . (4) The high-frequency radio wave filter according to claim 1, in which either the line width 1 gap of the IJ tube line, the relative dielectric constant, or a combination thereof is changed (to make the characteristic impedance discontinuous) Device.