RU2578729C1 - Microwave attenuator - Google Patents

Abstract

FIELD: instrument engineering.

SUBSTANCE: invention relates to use of attenuator with fixed attenuation when taking measurements in waveguide channels with high power level. This invention consists in the fact that microwave attenuator consists of metal rectangular waveguide, absorber and screen, the waveguide is made with height b narrow wall and width and wide wall, in which there are two interconnected identical smooth transitions of length L and variable height decreasing to b₂, absorbing surface of each transition is aligned with absorbing surface of absorber width s located on one of the wide walls of waveguide and the reflecting surface transition is located on the opposite wide wall, if s<a, α=arctg((b-b₂)/L), where α is the angle of inclination of transition.

EFFECT: reducing standing-wave ratio and non-uniformity of the transmission coefficient in frequency band of the waveguide, smooth change of electric strength and adjustment of attenuation in small range at structural and process simplification.

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Description

The invention relates to microwave technology and can be used as an attenuator with fixed attenuation when measured in waveguide paths with a high power level.

Fixed absorbing attenuators are known [1] for waveguides with volumetric absorbing resistance. The attenuator represents a segment of the waveguide tube with flanges, within which an absorbing resistance is installed.

The disadvantages of their design are:

- a complex form of the absorber, requiring for its manufacture no less complex mandrel, which leads to an increase in the cost of its production;

- the presence of glue or air gaps between the absorber and the waveguide, increasing the transitional thermal resistance;

- unspecified electrical characteristics: VSWR and uneven transmission coefficient in the frequency range of the waveguide.

Closest to the claimed technical solution is the waveguide attenuator [2], adopted for the prototype, containing a segment of a rectangular waveguide and volumetric absorption resistance, characterized in that the volumetric absorption resistance is made in the form of a main rectangular prism, the base plane of which is conjugated with the plane of one of the wide walls rectangular waveguide, the width of the base is equal to the width of the rectangular waveguide, and the height is less than the height of the rectangular waveguide, while the main prism is at least on one side parallel to the cross section of a rectangular waveguide, it is conjugated with a matching element in the form of an additional rectangular prism structurally combined with the main prism and made of the material of the main prism, while the base plane of the additional prism coincides with the interface plane of the main prism with the waveguide, the width of the base equal to the width of the rectangular waveguide, and the height of the additional prism is less than the height of the main prism.

The disadvantages of this design are:

- technological difficulties in the manufacture of the profile of the absorber;

- the need for additional processing of the absorber when setting to a fixed attenuation.

The technical result of the inventive microwave attenuator is to reduce the VSWR and the uneven transmission coefficient in the frequency band of the waveguide, a smooth change in dielectric strength, as well as the ability to adjust attenuation to a small extent with structural and technological simplification.

The technical result is achieved in that the microwave attenuator contains a rectangular metal waveguide, an absorber and a screen. The waveguide is made with a height b of a narrow wall and a width a of a wide wall, in which two identical smooth transitions are formed, interconnected with each other, of length L of variable height, decreasing to b ₂ . The absorbing surface of each transition is combined with the absorbing surface of the absorber of width s located on one of the wide walls of the waveguide, and the reflecting surface of the transition is located on the opposite wide wall, provided s <a, α = arctan ((bb ₂ ) / L), where α transition angle The absorbing surface of the absorber can be made in the form of a rectangle, and its width s is in the range 0.6a≤s≤0.7a.

To reduce the VSWR, all the walls of one of the smooth transitions can be metallized, but the length of the attenuator topology will double.

Two identical smooth transitions allow you to smoothly change the electric strength of the attenuator and simplify its manufacture.

The height b of ₂ smooth transitions determines the initial attenuator attenuation before tuning.

When attenuation is adjusted, the junction of the smooth transitions is milled, increasing the height b ₂ , which reduces the initial attenuation to the required one.

The angle of inclination α = arctan ((bb ₂ ) / L) of the transition affects the VSWR of the attenuator. To obtain VSWR <1.1, the angle α can be in the range 0 ° ≤α≤6 °. At α = 0 °, the inclined surface of the transition becomes flat, and the transition itself degenerates into a rectangular waveguide.

For ease of manufacture, the absorbing transition surface is located on a flat wide wall of the waveguide and combined with the absorbing surface of the absorber, which allows the use of a simple absorber: a rectangular parallelogram, and choosing the width s of the absorber without rigid reference to the width a of the wide waveguide wall.

In order to obtain the minimum non-uniformity of the transmission coefficient and uniform distribution of microwave energy in the absorber volume, the width s of the absorber surface of the absorber should be within 0.6a≤s≤0.7a depending on the parameters of the absorber material: dielectric constant ε and dielectric loss tangent tanδ.

The proposed design of the microwave attenuator is illustrated by drawings.

In FIG. 1 shows the design of the proposed microwave attenuator, where: a metal waveguide - 1, an absorber - 2, a screen - 3, a smooth transition - 4.

In FIG. 2 shows the design of the proposed microwave attenuator according to claim 3.

In FIG. 3 shows optimized topologies of 10 dB microwave attenuators with a fixed absorber length: a - construction of FIG. 1b - construction of FIG. 2.

In FIG. 4 shows graphs of VSWR in the frequency range 26-40 GHz for the topologies of FIG. 3.

In FIG. 5 shows plots of the transmission coefficient S21 in the frequency range 26-40 GHz for the topologies of FIG. 3.

In FIG. 6 shows the dependences of the transmission coefficient S21 on the smooth transition height b ₂ at a frequency of 35 GHz for the topologies of FIG. 3.

Example

The waveguide 1 is made of copper rectangular. The waveguide housing 1 is made of two parts, separated by a wide wall and connected by screws. The height of the narrow wall b = 3.4 mm, the width of the wide wall a = 7.2 mm. Two identical smooth transitions 4 connected to each other are made in the housing. Each smooth transition 4 has a length L = 17 mm, the height decreases to b ₂ = 2.26 mm, and the angle of inclination is α≈3.8 °. The absorber 2 is located on the flat wide wall of the transition so that its absorbing surface is aligned with the plane of the wide wall. The absorber 2 is made in the form of a rectangular parallelogram from a corundum-titanate ceramic plate KT-30 with a length of 2L = 34 mm and a height of 2 mm. The width of the absorbing surface of the absorber is 2 s = 4.5 mm. The absorber 2 is placed in a screen 3 made of copper, and is fixed in it by an electrically conductive adhesive or soldering. An example corresponds to the topology of FIG. 3a.

The proposed microwave attenuator operates as follows.

An electromagnetic wave propagating in a rectangular waveguide 1 enters the channel of the first smooth transition 4 of variable height. Falling on the absorbing surface of the absorber 2, the electromagnetic wave attenuates, being converted into thermal energy, which is removed through the screen 3 to the cooling system. The non-absorbed part of the energy of the electromagnetic wave enters the channel of the second smooth transition 4 of variable height, where the process of its absorption and conversion into thermal energy with heat removal occurs in the same way as in the first transition 4.

The feasibility of the invention is verified by calculation on the topologies of the microwave attenuators shown in FIG. 3, with a fixed length L and width s of the absorber.

The VSWR plots (FIG. 4) of the microwave attenuator topologies show that the design of FIG. 3b has better matching (VSWR <1.02) compared with the design of FIG. 3a, but this result is achieved with twice the length of the attenuator topology. However, increasing the length of the attenuator may be convenient for mounting an overall cooling system.

The graphs of the transmission coefficient S21 (Fig. 5) of the microwave attenuator topologies show a low level of its non-uniformity (ΔS21 = 0.15 ... 0.2 dB) in the waveguide frequency band, which indicates the attenuator broadband.

Graphs of the dependence of the transmission coefficient S21 on the height b2 of a smooth transition at a frequency of 35 GHz (Fig. 6) show the possibility of tuning S21 in the range of more than 10 dB.

Experimental 10-dB microwave attenuators with a waveguide channel [7.2 × 3.4] with a total length of 5 cm, in which a KT-30 corundum-titanate ceramic plate with a height of 2 mm was used as an absorber, made it possible to obtain an VSWR of less than 1.1.

Using absorbers made of other absorbing materials and adjusting the width s of the absorbing surface of the absorber and the transition height b2, it is possible to use a microwave attenuator at low, medium, and high power levels.

Information sources

1. I.P. Bushminsky. Production of microwave structural elements. Waveguides and waveguide devices. - M .: Higher school, 1974, p. 182, fig. 3.6.

2. Application No. 2012147432/08 of the Russian Federation, IPC Н01Р 1/26. Waveguide attenuator. - Declared. 11/07/12; publ. 05/20/14, Bull. Number 14.

Claims (3)

1. A microwave attenuator comprising a rectangular metal waveguide, an absorber and a shield, characterized in that the waveguide is made with a height b of a narrow wall and a width a of a wide wall, in which two identical smooth transitions are formed, interconnected with each other, of length L of variable height, decreasing to ₂ b, the absorbent surface of each transition is aligned with the absorbing surface of the absorbent width s, situated on one of the broad walls of the waveguide, and the transition of the reflecting surface located on the opposite broad wall , Provided that s <a, α = arctg ( (bb ₂₎ / L), where α - angle of inclination of the transition. 2. The microwave attenuator according to claim 1, characterized in that the absorbing surface of the absorber is made in the form of a rectangle, and its width s is in the range 0.6a≤s≤0.7a. 3. The microwave attenuator according to claim 1, characterized in that all the walls of one of the smooth transitions are metallized.

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