RU2459323C1 - Radome wall - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: radome wall has dielectric layers which are thin compared to the wavelength and an array with inductive susceptance, which consists of a set of metal wires lying in parallel in a periodic order and placed in parallel to the electric field vector of the incident electromagnetic wave. The wires in the array have periodic curvatures along their length, which increase the length of a wire by at least double, wherein the period of the curvatures is at least three-times smaller than the period of the array, and the period of the array is less than half the minimum working wavelength of the object.

EFFECT: use of the disclosed wall enables to increase inductance of the array without using wires with microscopic thickness in said wall, which enables to compensate for reflection from thin dielectric layers and reduce coefficient of reflection from the radome wall.

5 cl, 10 dwg

Description

The invention relates to radio engineering and can be used to create objects using radiotransparent shelters (RPU) - walls of antenna radomes and radiotransparent shelters of antennas with dielectric layers thin relative to the working wavelength (λ ₀ ). Particularly effective may be the use of this invention for radio-technical enlightenment of the walls of the RPU, designed to work in the decimeter and long wavelengths of the centimeter wavelength ranges.

To create RPU objects operating in the decimeter and long wavelengths of the centimeter wavelength range, use a wall consisting of dielectric layers thin relative to the wavelength (λ ₀ ). Such a wall has a capacitive character of reflection, the level of which may not be low enough to provide the necessary radio technical characteristics of the system “shelter object - RPU”. It is known that such a wall can be clarified using an inductive type grating (from wires), i.e. provide compensation for waves reflected from thin dielectric layers of the wall. As a result, in a certain frequency range, the reflection level of the incident electromagnetic wave can be reduced.

It is known that to protect the RPU from icing, static electricity (lightning protection), and also to provide lighting, a wire grating is used, the inductive conductivity of which is partially compensated by the capacitive conductivity of the vibrator grating (US patent 2007252775 (A1) "Radome with detuned elements and continuous wires ", published 2007.11.01). The introduction of additional elements with a capacitive nature of the reflection can be ineffective and lead to a narrowing of the frequency range and the sector of the angle of incidence of the wave, in which the shelter wall has a low level of reflection.

Known RPU wall for antenna fairings and protective shelters of antennas of aiming stations and target tracking systems (RF patent No. 2168816. “Radiolucent wall of the fairing”, published June 10, 2001), consisting of dielectric layers and metal elements in the form of gratings with inductive conductivity made of a set of periodically arranged metal wires. The specified wall can be used to create RPU products (antennas) operating in the millimeter range and the shortwave part of the centimeter range of wavelengths.

In the case of using such walls to create RPU objects operating in the decimeter range or in the long wavelength part of the centimeter wavelength range, the drawback is that either a wall with an unacceptably large thickness or a wire thickness in the grating should be unacceptably small.

Closest to the proposed wall is the wall of the RPU - a cowl that protects microwave sensors in a car, described in patent No. EP 2151889 ("Radome for radar sensor in a motor vehicle", published 2010.02.01), including at least a dielectric layer, the thickness of which is multiple λ _0/2, with a layer of paint, which can be considered as a thin dielectric layer with respect to λ ₀ and an inductive type array consisting of a set of periodically spaced lines or a wavy metal wires. The wires in the grating are parallel to the electric field vector of the incident electromagnetic wave. The lattice in this invention serves to compensate for the effect of the paintwork on the radio-technical qualities of the fairing wall for microwave sensors, that is, to reduce the reflection level of the fairing. Since microwave sensors in cars, as indicated in the patent, operate in the millimeter wavelength range, this method of compensation can be effective. If it is necessary to compensate for the reflection of the incident wave from thin dielectric layers in the decimeter range and in the long wavelength part of the centimeter wavelength range, it is necessary to use a lattice with very thin wires to manufacture this wall, which is associated with technological difficulties.

The present invention solves the problem of creating radiotransparent shelters with walls consisting of dielectric layers thin with respect to λ ₀ for objects operating in the decimeter range and the long-wavelength part of the centimeter wavelength range.

The technical result of the invention is to improve the radio characteristics of the RPU wall, namely, to reduce the reflection coefficient without using wires with a microscopic thickness in the lattice that is part of this wall.

The essence of the invention lies in the fact that in the wall of a radiotransparent shelter, including dielectric layers thin with respect to λ ₀ and an inductive type grating, consisting of a set of metal wires parallel to each other arranged in a periodic order, installed parallel to the electric field vector of the incident electromagnetic wave, the grating is made of a set of wires with periodic curvatures along the length of the wire, increasing the length of the wire by at least two times, while the period of curvature is less e not less than three times the lattice period, and the lattice period is less than half the minimum working wavelength (λ _min / 2).

In addition, the invention lies in the fact that the set of wires in the lattice is a system made of at least two mutually perpendicular sets of parallel wires with periodic bends without electrical contact between these sets.

In addition, the essence of the invention lies in the fact that the lattice is made of a set of wires with periodic curvatures in the form of a meander.

In addition, the invention lies in the fact that the lattice is made of a set of wires with periodic curvatures in the form of a solenoid.

In addition, the essence of the invention lies in the fact that the grating is installed in front of, behind or between the dielectric layers.

As is known, to calculate the radio-technical characteristics of a wall using equivalent circuits, the dielectric layer with a grating can be represented by a circuit in which the action of the grating is taken into account by the reactance Z _q shunting the stepped transmission line. The value of Z _q (or the value of the input conductivity of the lattice) can ultimately be expressed in terms of the inductance of the lattice L, which depends on the parameters of the lattice, layer, parameters and structure of the wires.

The use of a lattice of wires bent along their length with a curvature period of at least three times the lattice period, and the curvature should increase the length of the wire by at least two times, and the lattice period should be less than λ _min / 2, allows you to further increase the inductance of the grating without using wires with a microscopic thickness in it and without increasing the period of the grating. As a result, with an increase in the inductance of the grating, a deeper compensation of reflections from dielectric layers can be achieved, i.e. reduce the reflection coefficient of the wall of the RPU.

Performing curvature of wires with a curvature period of at least three times the lattice period will allow you to get additional lattice inductance with sufficiently large values. Performing curvature of wires with a curvature period equal to or greater than the lattice period will not allow obtaining an additional inductance that significantly increases the inductance of the lattice, since the additional inductance is the sum of the specific inductances of each curvature along the length of one lattice period.

Curvature of the grating wires, increasing the length of the wires by less than two times, will not allow to obtain additional inductance, which significantly increases the inductance of the grating, since the electrodynamic effect of the wires with each other leads to the fact that, at small curvatures, the specific inductance of each curvature has very small values.

The implementation of the lattice with a period greater than λ _min / 2 will lead to the appearance of Floquet harmonics in the scattered field of the lattice, which will degrade the radio technical properties of the RPU wall, which is manifested in a strong distortion of the radiation pattern of the “covered object - RPU” system. In addition, gratings made with a period close to λ _min / 2 have an inductance that strongly depends on the angle of incidence of the electromagnetic wave, which leads to an increase in the reflection coefficient from the RPU wall with an inclined incidence of the electromagnetic wave.

The use of curved wires in the form of a meander allows you to obtain significant values of the additional inductance necessary to ensure a decrease in the reflection coefficient of the lattice, while the lattice can be printed.

The use of wire bends in the form of a solenoid allows one to obtain very large values of the additional inductance in the grating, while the grating elements will have small dimensions in the direction perpendicular to the electric field vector of the incident electromagnetic wave.

The implementation of a set of wires in the array of at least two mutually perpendicular sets of parallel-mounted wires with periodic curvature without electrical contact between these sets will allow you to get a lattice with radio engineering properties that are not dependent on the polarization of the incident electromagnetic wave, while eliminating spurious resonances that are observed when the presence of electrical contact between these systems with an oblique fall on the grating parallel to the polarized electromagnetic wave ln, which sharply worsens the radio technical properties of the walls of the RPU.

Placing the lattice in front of or behind the dielectric layers allows the RPU wall to be made in a rather simple way using conventional technologies for the production of RPU from dielectrics. Placing the lattice between the dielectric layers allows the RPU wall to be made with much better radio-technical characteristics, but the production of such walls is substantially complicated.

The invention is illustrated by drawings, in which Fig. 1 shows the structure of the RPU wall with a lattice of twisted wires, Fig. 2 is a diagram of the curvature of wires in the form of a meander, Fig. 3 is a diagram of the curvature of wires in the form of a solenoid, Fig. 4 is two mutually perpendicular sets of wires with periodic curvatures, FIG. 5 is an equivalent diagram of a long line for a dielectric wall with a grid of curved wires, FIG. 6 is a dependence of the additional inductance of the grid on the extension of the wire when the wire is curved in the form of a meander, FIG. 7 is a frequency the dependence of the reflection coefficient from the RPU wall for normal incidence of an electromagnetic wave, Fig. 8 is the frequency dependence of the reflection coefficient from the RPU wall for a perpendicularly polarized electromagnetic wave at an angle of incidence of 50 °, Fig. 9 is the frequency dependence of the reflection coefficient from the RPU wall for a parallel polarized electromagnetic wave when the angle of incidence is 50 °, figure 10 is the frequency dependence of the reflection coefficient from the wall of the RPU with normal incidence of an electromagnetic wave.

The RPU wall includes (Fig. 1) at least one dielectric layer 1 thin with respect to λ ₀ and an inductive conductivity grating 2, consisting of a set of metal wires arranged in a periodic order 3. In this case, the wires 3 of the grating 2 are parallel to the vector 4 the electric field of the incident electromagnetic wave in front of or behind the dielectric layer 1 or between the layers 1. The wires 3 in the lattice 2 are made with periodic curvature 5 along the length 8 of the wire 3 with a curvature period of not less than three times and period 7 of lattice 2. Curvature 5 of wire 3 with the specified period 6 should increase the length 8 of wire 3 by at least two times, and period 7 of lattice 3 should be less than λ _min / 2 of object 9.

The curvature of 5 wires 3 in the form of a meander 10 (figure 2) will allow you to make the lattice 2 in a printed manner. In addition, the curvature of 5 wires 3 in the form of a meander 10 will allow to obtain sufficiently large values of the additional inductance 12 in the lattice 2, since each element 11 of the meander 10 has a sufficiently large specific inductance. Additional inductance 12, obtained due to the curvature of 5 wires 3 in the form of a meander 10, can be approximately calculated by the method of sections according to the formula:

Where:

- количество элементов 11 меандра 10 на расстоянии одного периода T_X 7;

где n≠m,

- the number of elements 11 meander 10 at a distance of one period T _X 7;

where n ≠ m,

L is the intrinsic inductance of the element 11 of the meander 10,

M _nm is the mutual inductance between the elements 11 n and m.

N is the number of elements considered 11 meander 10.

where l _M is the length 13 of the element 11 of the meander 10,

d _P - width 14 of the wire 3.

where S _nm = | nm | S is the distance between the mth and nth elements of the meander,

S - period of 6 curvatures 5.

The curvature of 5 wires 3 in the form of a solenoid 15 (Fig. 3) will allow to obtain large values of the additional inductance 12 of the grating 2, while the size of the 16 elements 17 of the solenoid 15 in the perpendicular direction to the electric field strength vector 4 is quite small compared to the incident wavelength, so as each element 17 of the solenoid 15 has a much larger specific inductance than the element 11 of the meander 10. The additional inductance 12, obtained by bending 5 wires 3 in the form of solenoid 15, can be calculated method m portions by the formula:

where d _c is the diameter of the solenoid 18,

- количество элементов 17 соленоида 15 в одном периоде 7 решетки 2,

- the number of elements 17 of the solenoid 15 in one period 7 of the lattice 2,

T _x - period 7 of the lattice 2,

S - period 6 of curvature 5.

A set of wires 3 in the lattice 2 can be made in the form of a system 19 made of at least two mutually perpendicular sets of parallel-mounted wires 3 with periodic curvatures without electrical contact 20 between these sets (Fig. 4).

Thin dielectric layers 1 can be made of any low-loss dielectric material, such as fiberglass, fluoroplastics, ceramics, etc. The metal wires 3 with inductive conductivity can be made of metals with low resistivities, such as gold, silver, copper, steel, aluminum, etc.

The proposed wall of the RPU works as follows. When an electromagnetic wave is incident on thin dielectric layers, 1 part of it is reflected, and the reflection of the electromagnetic wave is capacitive in nature. When an electromagnetic wave is incident on a grating 2 with inductive conductivity, part of it is reflected, and the reflection of the electromagnetic wave is inductive. The reflected fields from thin dielectric layers 1 and from the grating 2 partially cancel each other, thereby reducing the level of reflection from the wall as a whole. Optimal compensation is achieved when the amplitude of the reflected field from the thin dielectric layers 1 is equal to the amplitude of the reflected field from the grating 2, and the phases of these fields are shifted by 180 °. Approximately this condition is achieved when the following equality holds:

Where

ω is the circular frequency

ε ₀ - dielectric constant of free space,

d _i - the thickness of the i-th thin dielectric layer 1 in the wall of the RPU,

ε _i - the relative permeability of the i-th thin dielectric layer 1 in the wall of the RPU,

L is the inductance of the grating 2.

In the decimeter range and in the long-wavelength part of the centimeter wavelength range, in order to achieve condition (4), it is necessary to increase the inductance of the grating 2. Also, the increase in the inductance of the grating 2 is achieved by periodically bending 5 wires 3 included in it with a period of 6 bendings, not less than three times smaller than the period 7 of the lattice 2, while the period of the lattice 2 remains less than λ _min / 2.

A more accurate idea of the operation of the RPU wall can be obtained on the basis of the theory of the equivalent long line of the layered dielectric structure. Thin dielectric layers located in front of and behind the grating are quadripoles with transmission matrices 21 and 22, which depend on the parameters of the layers 1, the angle of incidence, and the polarization of the incident wave, in the equivalent long line (Fig. 5). The lattice 2 of the straight wires 3 can be described in the equivalent long line with some inductance 23, which determines the inductance of the lattice 2 of the straight wires 3 and can be calculated by the formula:

(β принимает значение М или Е);Where

(β takes the value M or E);

(для перпендикулярной поляризации),

(for perpendicular polarization),

(для параллельной поляризации);

(for parallel polarization);

и

вычисляются как входные сопротивления 24 и 25 эквивалентной длинной линии (фиг.5);

and

calculated as input impedances 24 and 25 of the equivalent long line (figure 5);

T _x - period 7 of the lattice 2;

d _P - width 14 of the flat wire 3 lattice 2;

(m - целое число);

(m is an integer);

χ ₂ = k ₀ sinθ; k ₀ is the wave number;

θ is the angle of incidence of the wave.

To reduce the reflection coefficient, it is necessary that the resistance 26 from the input side of a long line taking into account the inductance 23 is equal to the wave resistance of the free space 27. For many cases, the inductance 23 without increasing the period 7 of the grating 2 is not enough. The bending of 5 wires 3 in the lattice 2 is equivalent to sequentially connecting an additional inductance 12 with an inductance 23. In addition, with an increase in the angle of incidence of the electromagnetic wave, the value of the inductance 23 can change significantly, which can lead to an increase in the reflection coefficient when the electromagnetic wave is incident on the RPU wall. The value of the additional inductance 12 practically does not depend on the angle of incidence of the electromagnetic wave.

The invention is illustrated by the following examples.

Example 1. The example shows the dependence of the additional inductance of the grating, which is used as part of the RPU wall for an object operating at a frequency of 5.0 GHz. Additional inductance was obtained due to the curvature of the wires in the form of a meander 10. The example illustrates the low efficiency of slight elongation due to the curvature of the wires of the grating.

At a frequency of 5.0 GHz, the dependence of the additional inductance 12 of the lattice 2 on the relative elongation of 30 wires 3 of the lattice 2, obtained by curving 5 wires 2 in the form of a meander 10, was calculated.

An RPU wall is considered, containing a grating 2 made with a period of 7 equal to 20.0 mm, which is 0.3 wavelengths, of flat wires 3 with a thickness of 14 equal to 0.313 mm, with distortions 5 of wire 3 in the form of a meander 10 with a period 6, curvature 5 of wire 3, equal to 1.25 mm, which is 0.0625 of period 7 of lattice 2, i.e. less than twelve times the lattice period. Figure 6 shows the dependences 28 and 29 of the additional inductance 12, measured in nH per square versus the relative elongation of the wire 30. Dependence 28 is calculated by the method of sections, and dependence 29 is calculated by the method of integral equations, which gives more accurate results. It can be noted that the extension of the wire by less than half gives small values of the additional inductance 12 of the grating 2. The inductance 23 of the grating 2 with the same period 7 of the straight wires 3 with the same thickness 14 is 15.5 nH per square. To double this value without decreasing the period 7 of the grating 2, it is necessary to reduce the thickness 14 of the wire 3 to approximately 10 μm. Curvature 5 of wire 3 in the form of a meander 10 with a relative elongation of 30 wires 3 four and a half times allows you to achieve the same result without changing the thickness of the wire and the use of wires with microscopic thickness.

Example 2. In a numerical example, the RPU wall is presented for operation in the frequency range from 1.0 GHz to 1.4 GHz. The wall reflection coefficient should not exceed -20 dB at incidence angles from 0 to 50 degrees.

The considered wall of the RPU consists of three dielectric layers 1 and a lattice 2 of wires 3, curved in the form of a meander 10. The thickness of the dielectric layers 1: 1.25 mm; 20.0 mm vs 1.25 mm. Relative permittivity of the layers 1: 4.3; 1.1; 4.3. The lattice 2 consists of flat wires 3 with a thickness of 14 equal to 0.625 mm, curved in the form of a meander 10 with a relative elongation of 30 equal to fourteen. Lattice 2 has a period of 7 equal to 40 mm, which is 0.19 λ _min in the frequency range under consideration. Period 6 of curvature 5 is 2.5 mm, which is 0.0625 of period 7 of lattice 2. Such lattice 2 has an inductance of 194 nH per square. The wires 3 in the lattice 2 are parallel to the vector 4 of the electric field of the incident electromagnetic wave. No wires with microscopic thickness were used in the grating.

Figures 7, 8, 9 show the calculated frequency dependences of the reflection coefficients on the RPU wall for three cases: at normal incidence, at a 50 ° angle of incidence for perpendicular polarization, and at a 50 ° angle of incidence for parallel polarization, respectively. Dependence 31 refers to the case of an RPU wall without a lattice 2 (first option). Dependence 32 refers to the wall of the RPU with a lattice 2 mounted on the surface of the wall in front of or behind the dielectric layers 1 (second option). Dependence 33 refers to the RPU wall with a grating 2 installed in the center of the wall between the dielectric layers (third option). As can be seen from the graphs, the third option is the best, but it is quite complicated for implementation. The second option allows you to get a reflection coefficient from the RPU wall of no higher than -20 dB in the frequency band from 1.0 to 1.4 GHz for angles of incidence from 0 to 50 ° for any polarization of the incident wave field. The first version of the wall does not allow to achieve the desired result (maximum reflection coefficient is -14 dB).

Example. 3. In an experimental example, the RPU wall is considered for operation in the frequency range from 1.0 GHz to 2.0 GHz.

The RPU wall includes three dielectric layers 1. The thickness of the dielectric layers 1: 0.6 mm; 13.0 mm; 0.9 mm. The relative dielectric constant of the layers 1: 3,7; 1.1; 3.7. To reduce the reflection coefficient of such a wall, we used a grating 2 with a period of 7 equal to 20 mm, which is 0.19 λ _min , of round wires 3 with a wire diameter of 0.5 mm, twisted in the form of a solenoid 15 with a period of 6 curvature 5, equal to 1 , 18 mm, which is 0.059 of the lattice period. The diameter of the solenoid 18 is 4.5 mm. The wires in the lattice are lengthened due to twisting twelve times. Such a grid 2 has an inductance of 299 nH per square. The grating 2 was mounted on the wall surface in front of the dielectric layer 1 with a thickness of 0.9 mm. Figure 10 presents the calculated and measured frequency dependence of the reflection coefficient with normal incidence of an electromagnetic wave on the wall of the RPU. Dependencies 34 and 35 relate to the case of RPU walls without grating 2, measured and calculated, respectively. Dependencies 36 and 37 relate to the case of RPU walls with a lattice 2, measured and calculated, respectively. From a comparison of dependence 36 with dependence 34 and from a comparison of dependence 37 with dependence 35, it can be concluded that the use of such a lattice 2 of wires 3 bent in the form of a solenoid 10 leads to a significant decrease in the reflection coefficient (see Fig. 10) from the wall in frequency range under consideration. The minimum reflection coefficient is observed at a frequency of 1.25 GHz. No wires with microscopic thickness were used in the grating.

As follows from the foregoing and as follows from the examples, the use of the invention allows the creation of RPU walls with high radio technical characteristics, namely with a low reflection coefficient (an additional decrease in reflection coefficient of at least 10 dB) for objects operating in the decimeter and in the long-wavelength part of the centimeter wavelength ranges. The manufacture of such walls with gratings is also simplified, since it becomes possible not to use wires with microscopic thickness in the gratings.

Claims (5)

1. The wall of the radiotransparent shelter, including dielectric layers thin with respect to the length of the incident electromagnetic wave, and an inductive type grating, consisting of a set of metal wires parallel to each other arranged in a periodic order, installed parallel to the incident electric wave vector of the electric field, characterized in that the grating is made of a set of wires with periodic curvatures along the length of the wire, increasing the length of the wire by at least two times, while the period of claim ivleny less is not less than three times the grating period and the grating period less than half the minimum operating wavelength. 2. The wall according to claim 1, characterized in that the set of wires in the lattice is a system made of at least two mutually perpendicular sets of parallel wires with periodic curvatures without electrical contact between these sets. 3. The wall according to claim 1, characterized in that the lattice is made of a set of wires with periodic curvatures in the form of a meander. 4. The wall according to claim 1, characterized in that the lattice is made of a set of wires with periodic curvatures in the form of a solenoid. 5. The wall according to claim 1, characterized in that the lattice is installed in front of, behind or between the dielectric layers.

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