DE1038623B - Directional damping line, consisting of a waveguide with a strip-shaped damping element - Google Patents

Description

The invention is concerned with the compensation of the temperature response of direction-dependent damping arrangements for the microwave area.

To achieve a direction-dependent damping effect in microwaves, plate-shaped ferrites are placed in a waveguide in a well-known manner and exposed to a transverse magnetic constant field that is perpendicular to the direction of propagation of the electromagnetic waves in the waveguide. If the field strength of the constant field is chosen so that gyromagnetic resonance occurs, an electromagnetic wave is maximal in one direction of propagation - z. B. by 20 db ■ - ■ and minimal in the opposite direction of propagation - z. B. by 0.5 db - attenuated. The energy absorbed by the waveguide shaft is converted into heat in the ferrite itself. The process of gyromagnetic resonance in ferromagnetic materials can be explained by the magnetic effects of the precession of electrons with spin around the direction of an applied magnetic field. It is well known that ferrites usually have a considerable temperature drift _{, ie the gyromagnetic resonance condition ω = γH 1} changes as a function of the temperature. Here, ω means the angular frequency, γ the gyromagnetic ratio (magnetic moment of the electron spin divided by the circular moment) and H _{ the static magnetic field strength. This phenomenon shows in particular those ferrites that are suitable for the lower part of the microwave region, that is for frequencies up to 4000 MHz. Materials with a relatively low Curie point are used for such ferrites in order to achieve the greatest possible forward-backward damping ratio.

To eliminate the temperature dependency one can use the magnetic ferrites Constant field also give a temperature response in such a way that this is the temperature dependence of the Ferrite just compensated.

Such temperature compensations are known. They are based on the fact that one to the largely temperature constants Permanent magnets a temperature-dependent ferromagnetic material in suitable Way connected in parallel or in series. In this way, the field strength of the constant field is built in one or more temperature-dependent resistors regulated. These compensation arrangements however, they are very complex and therefore expensive.

Tests have now shown that these extremely complicated known compensation arrangements are not necessary to compensate for the temperature drift of the attenuator if you use the attenuator performs according to the invention.

Directional damping line,

consisting of a waveguide
with strip-shaped attenuator

Applicant:

Telefunken G. mb H.,
Berlin NW 87, Sickingenstr. 71

Dipl.-Phys. Rudolf Steinhart, Backnang (Württ),
has been named as the inventor

In a direction-dependent attenuation line, which consists of a waveguide in which a strip-shaped Attenuator or strip-shaped «attenuator (Ferrite strips) are attached, there is a transverse to the direction of propagation of the waves static magnetic field, suitable for generating gyromagnetic resonance in these attenuators. The aspect ratio of this strip or these strips is selected according to the invention so that that a compensation of the temperature response of the gyromagnetic resonance occurs.

The subject matter of the invention is intended in an exemplary embodiment with reference to the figure are explained in more detail.

In a waveguide 1, a ferrite strip 3 is attached as a direction-dependent attenuator. A magnet system 2 generates a constant field for generating deir gyromagnetic resonance in this ferrite strip 3. The field strength H _{a of} this field runs perpendicular to the direction of propagation of electromagnetic waves that pass through the rectangular waveguide. The ferrite strip 3 also has a rectangular cross-section in the exemplary embodiment. The strip height is designated by h and the thickness of the strip by d .

The testing of such an arrangement has now shown that, surprisingly, a temperature compensation of the gyromagnetic effect occurs when the ratio of height h and thickness d of the relatively long ferrite strip 3 had a very specific value. None of the known compensation circuits were used here, ie self-compensation is possible with a very specific shape of the ferrite strip.

An explanation for this unexpected behavior is given below. In the figure, the middle

809 637/359

point of the cross-sectional area of the strip 3 as the starting point of a coordinate system whose axes are denoted by N _x , N _y and N ₂ and which are intended to represent the direction of the demagnetization factors of the ferrite strip according to its geometric dimensions.

The resonance frequency can be changed after replacing the ferrite plate by an ellipsoid with the same semi-axes taking into account the demagnetization factors according to the well-known Kittel equation determine:

N _x = 4π

h + d

= 4π

h + d

ω = γ \ (H _a +

ρ-1

4nM _s ) (H _a -

«5 M ₃
If one carries out the differentiation, one obtains

Η _α (9-2) = 2 ^ -4πΜ ₃

(4)

Equation (4) is inserted into equation (1) and transformed

conditional changes in the saturation magnetization M _s independently. Given the assumptions made, the dimensioning required for temperature compensation can accordingly be estimated with sufficient accuracy.

If, for example, a ferrite, which is used to achieve the gyromagnetic resonance at a frequency of 4000 MHz, has a saturation magnetization of M _s = - ^ · 2000 Gauss, then according to equation (6) a

ω = 71 / Wa + (N _x - N _z ) M ₃ ] [H _a + (N, - N _Z ) M _S ] (1)

Here, ω denotes the angular frequency, N _x , N _y , N ₂ the demagnetization factors, H _a the externally applied DC field strength, γ the gyromagnetic ratio, M _s the saturation magnetization.

According to the practical application, the expansion of the ferrite strip in the 3 ' direction is assumed to be very large compared to the dimension in in the x and ^ directions. This means that N _y f ^ Q. With this approximation, it follows from the relationship for the demagnetization factors given in the journal Physical Review, June 1945 (see p. 352, equations 2.14 to 2.16):

(2)

To simplify matters, one writes for -j- = ρ and

if the transformed values for N _x and N _{2 are inserted} into equation (1), one obtains

35

It is now required that the resonance frequency ω in equation (3) remains constant when the temperature changes. As already mentioned, the external field is practically independent of temperature, and the same naturally also applies to the demagnetization factors and thus also to the ratio ρ. However, the saturation magnetization M _s is strongly temperature-dependent in the case of ferromagnetic substances. The stated requirement is therefore:

45

(5)

The temperature compensation takes place when equation (4) and equation (5) are satisfied at the same time. So (4) is used in (5) with the elimination of H _a . You then get

ρ y Q - 1
(ρ + ΙΗρ
where for abbreviation

(6)

is set.

If the ratio g = - ^ - of equation (6) is sufficient, the resonance frequency ω of temperature ₇ / νοη2π · 2.8 = 2π · 2.8 · 1ι
Oe

ft) 2π 4000- ΙΟ ⁵

-sec

- -ΙΟ- "= 0.715

γ4π M _s 2π x 2.8 x 2000

From equation (6) then follows for the aspect ratio ρ = 3.88. Inserting this value into equation (3), (4) or (5) then results in a resonance field strength of H _a = 1250 Oe.

As can be seen from equation (6), there is exactly one real solution for ρ, which, however, is always in the range ρ> 2, which means that this simple temperature compensation for insulators of the so-called Ε-type (here the broad side of the Ferrite strip arranged parallel to the electrical vector of the H ₁₀ -WeIIe) is possible.

If the aspect ratio calculated according to equation (6) does not meet the ρ necessary or desirable to achieve a favorable damping ratio, a ferrite with changed saturation magnetization M _s can be used according to equation (4). The advantages of the invention are in this case that, when choosing a suitable saturation magnetization, the Curie point of the material from which the attenuator is made does not have to be taken into account, as long as it is possible to provide the external constant field with the necessary strength.

The temperature compensation by appropriate selection of the aspect ratio φ can of course also be used for directional lines with a dielectric.

Claims (3)

Patent claims. 1. Direction-dependent attenuation line, consisting of a preferably rectangular one Waveguide in which a strip-shaped attenuator or strip-shaped attenuators are arranged, in particular ferrite strips, with a transverse to the direction of propagation electromagnetic waves in the waveguide there is a constant magnetic field, which is dimensioned in such a way that gyromagnetic resonance is generated in these attenuators, characterized in that the aspect ratio of the strip or strips is in such a manner it is chosen that a temperature compensation of the gyromagnetic resonance occurs. 2. Arrangement according to claim 1, characterized in that the strip dimension in the direction of propagation of the electromagnetic waves is much larger than the width and height of the strip and that the ratio (ρ) of Stripe height Qi) for the stripe thickness (d) the following equation is sufficient: e Ve-i (Q + 1) (e where for the abbreviation R = - j —— y 4t π μ. ₃ here ω means the angular frequency, γ the gyro- is set; magnetic ratio, M _s the saturation magnetization. 3. Arrangement according to claim 1 or 2, characterized in that the saturation magnetization (Mj) is chosen so that an aspect ratio (ρ) suitable for temperature compensation results, which has a favorable damping ratio. 1 sheet of drawings