RU2484559C2 - Printed board with suspended substrate - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: proposed is a printed board containing planar impedance conductors on a multilayered dielectric substrate with a metal screen; the dielectric substrate includes at least three layers, the thickness of each of the equal to a quarter of the operating wave length; the layers are made of a material with varied dielectric permeability and are positioned with linear decrease of the layers wave-pattern resistances from the screen plane towards that of impedance conductors. The printed board may be equipped with an additional multilayered dielectric screen positioned on the opposite side of the planar impedance conductors; the screen includes at least three layers, the thickness of each of the equal to a quarter of the operating wave length; the layers are made of a material with varied dielectric permeability and are positioned with linear increase of the layers wave-pattern resistances from the impedance conductors plane.

EFFECT: ensuring adaptation of the board dielectric layers to each other with linear decrease of their wave-pattern resistances from the screen plane towards that of impedance conductor which enables prevention of reflected wave occurrence in the cross section as well as ensuring the impedance conductors adaptation to the ambient air space.

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Description

The invention relates to microstrip technology and can be used to create highly efficient microwave devices and antennas.

Known single-sided, double-sided or multi-layer printed circuit boards made on a rigid or flexible base [Medvedev A.M. Printed circuit boards. Constructions and materials. - M .: Technosphere, 2005. - S.22-25]. A multilayer printed circuit board contains alternating layers of thin insulating substrates with conductive patterns deposited on them, physically connected to one multilayer base. Each of the inner layers can be a single-sided or double-sided board with interlayer transitions. In this case, the main direction of development of these printed circuit boards is to increase the precision and density of the layout of a highly integrated element base, and the properties and parameters of insulating substrates are not given due attention, which does not allow the efficient use of such printed circuit boards in the microwave range.

Closest to the proposed invention are printed circuit boards with suspended substrates, used for various microwave devices and strip antennas [Electrodynamic calculation of the characteristics of strip antennas / B. A. Panchenko, S. T. Knyazev et al. - M .: Radio and communication, 2002 . - S.75-93]. Such printed circuit boards contain a suspended substrate consisting of a dielectric base with a high value of relative permittivity, on one side of which conductive elements are located, and an air gap separating the metal screen located on the other side. The disadvantage of such printed circuit boards is the lack of coordination of wave impedances of the dielectric base of the substrate and the air gap, which leads to the appearance of a reflected wave in the cross section of the board.

The technical problem to which this invention is directed is the creation of a printed circuit board with a suspended substrate, in the cross section of which a reflected wave does not occur, since the dielectric layers of the substrate are matched to each other, and their wave resistance decreases linearly from the plane of the screen to the plane of the impedance conductors. In addition, when using a printed circuit board for microstrip antennas and emitters, it is necessary to match the impedance conductors with external air space, which is ensured by a multilayer dielectric screen with wave impedance linearly increasing from the plane of the impedance conductors.

The technical problem is solved by the fact that in a printed circuit board containing planar impedance conductors located on a dielectric substrate with a metal screen, according to the invention, the dielectric substrate is multilayer and includes at least three layers, each of which is equal to a quarter of the working wavelength, the layers are made of a material with different dielectric constants and placed with a linear decrease in the wave impedances of the layers from the plane of the screen to the plane of the impedance conductor ov. In addition, the printed circuit board is equipped with an additional multilayer dielectric screen placed on the opposite side of the planar impedance conductors, the multilayer dielectric screen includes at least three layers, each of which is equal to a quarter of the working wavelength, the layers are made of material with different dielectric constants and placed with a linear increase in the wave impedances of the layers from the plane of the impedance conductors.

The technical result achieved in the implementation of the totality of the claimed essential features is to ensure matching of the dielectric layers of the board with each other with a linear decrease in their wave impedance from the plane of the screen to the plane of the impedance conductors, which avoids the occurrence of a reflected wave in the cross section, as well as ensuring the coordination of impedance conductors with external airspace, which is achieved by a multilayer dielectric screen with linearly waving wave resistance.

The invention is illustrated by drawings, where

figure 1 presents a cross section of a board with a suspended three-layer substrate of thickness d,

figure 2 presents a cross section of a board with a suspended three-layer substrate of thickness d ₁ and a three-layer matching dielectric shield of thickness d ₂ .

figure 3 presents graphs of the dependence of the modulus of the reflection coefficient on the number of layers for a three-layer substrate with ε ₁ = 9.8; ε ₂ = 5.6; ε ₃ = 2.4 and a suspended substrate with an air gap at ε ₁ = 9.8; ε ₂ = 1.0.

The relative permittivities of the layers of the substrate and the dielectric screen linearly decrease with increasing layer number.

, где µ, ε - относительные магнитная и диэлектрическая проницаемости слоя соответственно. Для воздушного зазора эта величина равна 120π≈377 Ом [Григорьев А.Д. Электродинамика и техника СВЧ. - М.: Высшая школа, 1990. - С.26-27]. В большинстве случаев практического применения волновое сопротивление отрезка линии передачи СВЧ должно составлять 50 или 75 Ом. При этом в поперечном сечении платы - прототипа - наблюдается резкий скачок волнового сопротивления, приводящий к сильному отражению волны от границы раздела диэлектрического слоя с воздушным зазором.The operation of the printed circuit board with a suspended substrate is as follows. It is known that the wave (characteristic) resistance of the dielectric layer is determined by the formula $$Z=\sqrt{\frac{\mu }{\epsilon }}$$

where μ, ε are the relative magnetic and dielectric constant of the layer, respectively. For the air gap, this value is 120π≈377 Ohm [Grigoryev A.D. Electrodynamics and microwave technology. - M.: Higher School, 1990. - P.26-27]. In most practical applications, the impedance of the microwave transmission line segment should be 50 or 75 ohms. Moreover, in the cross section of the board - the prototype - there is a sharp jump in wave resistance, leading to strong reflection of the wave from the interface of the dielectric layer with the air gap.

In the proposed embodiment of the printed circuit board (figure 1), the substrate is made of a three-layer with a uniform decrease in the value of wave resistance from the plane of the screen to the plane of the impedance conductors. If the thickness of each layer of a quarter of the working wavelength is equal, for a microwave device made on such a board in its cross section, the amplitude of the reflected wave is very small, which leads to a decrease in losses and an increase in the efficiency of its operation.

When using the proposed printed circuit board to create microstrip antennas and emitters, their impedance conductors, which in most cases have impedance of tens of ohms, must be coordinated with an external air space having a resistance of 377 ohms. For this, a multilayer dielectric screen with a wave impedance linearly increasing from the plane of the impedance conductors is introduced into the board design (Fig. 2). With the number of layers of the matching screen not less than three and the thickness of each layer equal to a quarter of the working wavelength, equalization of the jump in the wave resistance is achieved, which provides an increase in the emissivity and the expansion of the radiation pattern of antennas and radiators.

The ability to achieve this goal is confirmed by the results of the calculation and analysis of the dependences of the module of the reflection coefficient on a multilayer dielectric medium with a linearly and abruptly changing value of the relative permittivity. The coefficient of reflection coefficient | G | for two layers of dielectric with numbers 1 and 2 can be calculated by the formula

$$\left|G\right|=\left|\frac{Z_2-Z_{\mathrm{one}}}{{\mathrm{<figure-callout\; id="2"\; label="Z"\; filenames="00000005.png"\; state="\{\{state\}\}">Z</figure-callout>}}_2+Z_{\mathrm{one}}}\right|=\left|\frac{\sqrt{{\epsilon }_{\mathrm{one}}}-\sqrt{{\mathrm{<figure-callout\; id="2"\; label="\epsilon "\; filenames="00000005.png"\; state="\{\{state\}\}">\epsilon </figure-callout>}}_2}}{\sqrt{{\epsilon }_{\mathrm{one}}}+\sqrt{{\mathrm{<figure-callout\; id="2"\; label="\epsilon "\; filenames="00000005.png"\; state="\{\{state\}\}">\epsilon </figure-callout>}}_2}}\right|$$

and similarly obtained for any number of layers. Figure 2 shows the dependence | G | of the number of layers N for a three-layer model of a printed circuit board with a linear change in the relative dielectric constant (ε ₁ = 9.8; ε ₂ = 5.6; ε ₃ = 2.4) and a two-layer model of a circuit board - a prototype with an air gap in which the resistance changes abruptly (ε ₁ = 9.8; ε ₂ = 1.0). From the graphs obtained, it can be seen that the three-layer model differs from the prototype in almost half the module of reflection coefficient, which is almost uniform in cross section of the printed circuit board.

The advantage of the proposed printed circuit board with a suspended substrate and matching multi-layer dielectric screen is the ability to achieve a more uniform change in wave impedance in the cross section with less loss and criticality of changes in the relative dielectric constant of the substrate compared to the prototype.

Claims (2)

1. A printed circuit board containing planar impedance conductors located on a dielectric substrate with a metal screen, characterized in that the dielectric substrate is multilayer and includes at least three layers, each of which is equal to a quarter of the working wavelength, the layers are made of material with different permittivity and placed with a linear decrease in wave impedances of the layers from the plane of the screen to the plane of the impedance conductors. 2. The printed circuit board according to claim 1, characterized in that it is equipped with an additional multilayer dielectric screen placed on the opposite side of the planar impedance conductors, the multilayer dielectric screen includes at least three layers, each of which is equal to a quarter of the operating wavelength, layers made of a material with different dielectric constants and placed with a linear increase in the wave impedances of the layers from the plane of the impedance conductors.

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