JPS5811049Y2 - Isolator - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a unidirectional attenuator, that is, an isolator, which allows microwaves to pass in one direction and not in the opposite direction.

Depending on the type of propagation line, this type of circuit is considered to be a waveguide type, coaxial type, strip line type (including microstrip type), etc., but here we will focus on small size and compatibility with microwave IC circuits. For this reason, we devised a stripline directional attenuator.

Conventional stripline directional attenuators are shown in Fig. 1 a, l.
), a branch line 4 is attached to the main line 1a, lb of the strip line constructed on the dielectric substrate 2, and an auxiliary branch line 5 is provided for the purpose of canceling the reflection caused by attaching the branch line 4. It has a structure in which a ferrimagnetic material 6 such as ferrite or garnet is attached near the connection point, and a magnetic field IDC that just causes magnetic resonance absorption is applied from the outside to the ferrimagnetic material 6. Ta.

In order to generate circularly polarized waves at the connection part, the length of the branch line 4 is set to one wavelength, and the reflection of the branch line 4 is canceled out by 8.
1. The length of the auxiliary branch line 5 was selected to be i wavelength.

Therefore, in this structure, when the frequency becomes low, the branch line 4
The disadvantage is that the length becomes long and the shape becomes large, making it impractical.

The operation of a conventional isolator will be explained with reference to FIGS. 1a and 1).

Since the branch line 4 is a one-wavelength line with an open end, the impedance seen from the connection point of the main lines 1a and lb toward the open end operates as an inductive reactance.

Let the inductive reactance be jX.

The main lines 1a and lb have a characteristic impedance Z of normal lines.

terminated with a load equal to

Therefore, when the voltage at the connection point (2) is applied, the current Im flowing along the main lines 1a, 1b in the vicinity of the connection point becomes.

On the other hand, if the current flowing into the branch line 4 at the connection point is Is, then the following equation is obtained.

Therefore, Is becomes a current whose phase lags Im by 90°,
Furthermore, since these currents spatially form an angle of 90°, in the case of Zo2X, a circularly polarized magnetic field is generated at the connection point.

Since the direction of rotation of this circularly polarized magnetic field is reversed depending on the direction of the radio waves propagating through the main lines 1a and lb, the ferrimagnetic material (gyromagnetic diagonal material) 6 placed near this connection point
When a magnetic field Hoc is applied from a direction perpendicular to the surface of the ground conductor 3, resonance absorption occurs only when the high frequency circularly polarized magnetic field is clockwise when looking at the direction of this magnetic field.

A unidirectional attenuator is then possible.

However, when the branch line 4 is attached to the main lines 1a and lb,
Since impedance discontinuity occurs at the connection point, radio waves are reflected there, making it impractical.

Therefore, in order to eliminate the reflection, a reactance having a value of -iX may be connected in parallel to the branch line 4.

■・ This is realized by the auxiliary branch line 5 of wavelength g.

When considering the above operation, the circuits a and l) in FIG. 1 can be represented by any number of circuits such as the one shown in FIG.

Focusing on this point, this invention is characterized by using lumped constant elements instead of using distributed constant lines such as branch line 4 and auxiliary branch line 5 to obtain the same operation.

An embodiment of this invention will be described below with reference to FIGS. 3 and 4.

In FIG. 3, the branch line 4 in FIG. 1 is replaced with an inductance 7 such as a coil, and the auxiliary branch line 5 is replaced with a capacitor 8.

FIG. 4 shows that main lines 1a, lb, inductance 7, and capacitor 8 are formed as conductor patterns on the surface of a dielectric substrate 2 with a ferrimagnetic material 6 embedded therein by using vapor deposition, plating, etching, or printing technology. This is what I did.

When manufactured using printing technology or the like, conductive patterns having the same shape can be accurately formed, which is effective in stabilizing the characteristics of the isolator, and can reduce the cost of the device.

Note that the ferrimagnetic material 6 has a size that occupies an area equal to or larger than that of the joint, and by using the ferrimagnetic material 6 of such a size, the lumped constant element 7,
8 can both contribute to the formation of a circularly polarized rotating magnetic field.

In conventional isolators using distributed constant lines,
It is necessary to manufacture branch lines with dimensions according to the frequency.
Therefore, as the frequency decreases, the dimensions become larger, but with this invention, there are no such dimensional restrictions, so even low frequency products can be made compact, and the frequency characteristics are improved as follows. It will also improve.

That is, in order to improve the performance of the isolator, it is desired that the microwave rotating magnetic field at the joint where the ferrite is mounted be as circularly polarized as possible.

However, even if such a design is made at the center frequency, the circularly polarized wave will be distorted if the frequency changes.

The magnitude of the microwave magnetic field depends on the current.

Considering that a constant voltage is applied to the junction, the current flowing in each branch is determined by the impedance seen from the junction to each line, so a change in the size of the microwave magnetic field is a change in impedance. It can be evaluated by

As shown in equation (1) above, the current Im flowing through the main line
is the characteristic impedance Z.

does not have frequency characteristics, so it does not change even if the frequency changes.

However, the branch line 4 and the auxiliary branch line 5 are reactance elements whose magnitude changes with frequency.

This causes the wave to deviate from the circularly polarized state.

Therefore, it is preferable to keep the frequency dependence of the reactance element as small as possible.

By the way, the impedance of the distributed constant type reactance element as shown in FIG. 1 is expressed as Z=-jZoCOtβl (3).

Here, Zo is the characteristic impedance of the branch line 4 and the auxiliary branch line 5, and is selected to be equal to that of the main line.

β is the phase constant, l is the line length, and is selected to be one wavelength in the branch line 4 and one wavelength in the auxiliary branch line 5. It is a function.

(β=ωgrbu). Therefore, at the center frequency f,
The impedances of the branch line 4 and the auxiliary branch line 5 are JZo and JZo, respectively, which are equal in magnitude to the impedance of the main line but differ in phase by 90 degrees, so that a circularly polarized rotating magnetic field is created.

On the other hand, when replacing it with a lumped constant element according to this invention, the impedance is Z=jwL, 7. = −j −8−・・・・・・(4
), so the center frequency f.

The values of L and C are determined so that 1Zl=Z.

In the conventional isolator and the isolator of this invention designed in this way, when the frequency is moved from the center, the branch line composed of branch constant lines, as shown in the following table,
The auxiliary branch line exhibits a considerably greater frequency dependence than that of the lumped element.

As can be seen from this result, when using lumped elements and satisfying the isolator conditions, the change in impeller lath due to frequency change is small, and both elements 7 and 8 change in a well-balanced manner, and the isolator frequency The characteristics will be significantly improved.

3 and 4 show an example in which a ferrimagnetic material 6 is embedded in a dielectric substrate 2, but the dielectric substrate and the ferrimagnetic material may be replaced with a single ferrimagnetic substrate. All of the above applies not only to the microstrip type but also to the triplate type strip line.

Furthermore, there are various types of inductances and capacitors, and it goes without saying that any convenient configuration can be adopted, and the present invention is not limited to the above-mentioned embodiments.

[Brief explanation of drawings]

Fig. 1a is a plan view of a conventional unidirectional attenuator with the magnet removed, Fig. 1 is a sectional view taken along line A-A in Fig. 1a, and Fig. 2 is a sectional view of Fig. 1a, l). Electrical equivalent circuit, Figure 3 is part 1 of this idea.
FIG. 4A is a perspective view showing an embodiment, FIG. 4A is a plan view showing another embodiment of the invention, and FIG. In the figure, 1a and lb are main lines, 2 is a dielectric substrate, 3 is a ground conductor, 6 is a ferrimagnetic material, 7 and 8 are lumped constant elements, and 9 is a ground wire.

Claims (1)

[Scope of utility model registration request] It has a main line constituted by a strip line, and includes both or one of an actance element for generating a circularly polarized magnetic field in the electromagnetic waves propagating on the main line and a reactance element for matching the reflection caused by the reactance element. Consisting of a lumped constant element, the element is connected between the main line and the ground conductor, and a junction equivalent to a junction is placed at or near the connection point of the reactance element and the main line to generate a circularly polarized magnetic field. Or an isolator formed by inserting a ferrimagnetic material occupying a larger area and applying a magnetic DC bias to the ferrimagnetic material from the outside.