RU2380801C2 - Design of wideband receiving ferrite antenna with improved screening - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: antenna design is proposed, which is simpler compared to available antennas of similar type. Simplicity of proposed technical solution is provided by double application of one and the same elements of antenna design: internal walls, base and cover. On one side, they produce cradle for ferrite rods together with external wall, and on the other side, they are simultaneously elements of electric screen.

EFFECT: reduced perception of wideband ferrite antenna to electric component of electromagnetic field.

3 cl, 8 dwg

Description

The invention relates to radio technology and can be used in the field of radio communications, radio navigation or direction finding.

Broadband (non-adjustable) receiving magnetic antennas (MA) with ferrite cores have several advantages over electric type antennas [1, 2, 3]. In particular, due to ferrites, such antennas are small in size, they are less susceptible to the strong electrical component of the interference field from nearby sources. These antennas have a selective radiation pattern in the form of a figure of eight, which determines their use for navigation and direction finding.

However, the effective height of magnetic antennas is usually very small and is often calculated literally in millimeters. To obtain an acceptable antenna sensitivity across the field, the sensitivity of the signal amplifiers induced in the frame (winding) should be extremely high. Under these conditions, without taking special protective measures, a noticeable level of interference from the electric component of the field can be induced to the winding and to the input of the amplifier, which leads to an increase in the susceptibility of the antenna to interference from nearby sources of interference, to a distortion of its radiation pattern and, as a result, to a decrease in the real antenna sensitivity and direction finding accuracy [4]. The use of special technical solutions to eliminate the influence of the electric component of the field often leads to a significant complication of the antenna or to a decrease in its sensitivity.

The purpose of the invention is to reduce the susceptibility of a broadband ferrite antenna to the electrical component of the electromagnetic field using the most simple technical solution.

Ferrite antennas are known [1, 5], in which the windings on a ferrite rod are placed in an electric shield. In the broadband version of the antenna, its windings will be connected to a broadband amplifier, which will also need to be shielded. It is necessary to shield the connecting line between the amplifier and the winding. The design turns out to be quite complex, given that for direction finding or omnidirectional reception, it is necessary to use two orthogonal ferrite rods.

A known ferrite antenna with a cross-shaped arrangement of ferrite rods [6], in which the windings on each rod are made symmetrically relative to its center, and their outputs are connected to the input of the differential amplifier. Such symmetrization allows sufficiently effectively suppressing the in-phase component of the electric field. However, with the cruciform shape of the ferrite core, the volume is irrationally used, in which there is no room for a convenient symmetrical arrangement of the amplifier boards near the windings. The maximum for which there is room is for small balancing transformers. Removal of amplifiers from the windings leads to lengthening of the connecting lines and, as a rule, to a deterioration of the antenna parameters, in particular, to a decrease in its broadband and an increase in the interference to the connecting lines from the electric component of the field.

Ferrite antennas are known [7, 8], in which ferrite cores are arranged in a square (in the form of a frame). They use volume more rationally, and a place appears in the central part of the ferrite square to accommodate amplifiers and other necessary electronics. But in this design, each pair of opposite rods with windings is quite far apart from each other and form a dipole, which can induce a noticeable voltage level from the electric component of the field. These antennas are highly susceptible to the common-mode electric field component and require more careful shielding. Therefore, in [8], the top cover of the antenna is made of conductive material and, together with the base, acts as an electric screen.

The closest in its technical essence device (prototype) is a ferrite antenna [9], containing four ferrite cores with windings, located in the form of a square on a conductive base, a top cover of conductive material with a size equal to the base, and amplifier boards in a separate screen, placed inside a ferrite square. The outer walls of the antenna are made of radiolucent (dielectric) material. Above the amplifier screen inside the ferrite square there is a cross-board designed for high-frequency connections between antenna elements. This antenna design has a fairly high degree of shielding from the electrical component of the electromagnetic field, but it is very complex and cumbersome. In addition, ferrite rods with high brittleness are fixed at individual points, which does not allow for sufficient strength of the product with respect to vibration and shock, especially when using large rods (length up to 0.5-1 m).

To simplify the design while maintaining a high degree of shielding, it is proposed to install vertical walls of conductive material on the basis of the antenna, forming an inner square. The space bounded by these inner walls, outer radiolucent walls and the base forms a lodgement in which ferrite rods with windings are placed and fixed. The rods are fixed by filling the free space between the walls of the lodgement and the rods with rubber-like radiolucent material (compound, sealant, etc.). An amplifier is placed in the inner square opposite each ferrite core, with the input of the winding of the corresponding rod connected via the shortest path through the holes in the wall of the inner square.

In the proposed design, an enclosed, well-shielded space is formed inside the antenna, bounded by a base, a lid and internal walls, in which amplifiers, the most sensitive to interference elements, are located. In this case, the inner walls should have good electrical contact at the ends, both between themselves and between the base and the cover along the entire perimeter. The connecting lines between the windings of the rods and the inputs of the amplifiers have a minimum length and do not require a special cross-board. In addition, ferrite rods with windings also appear in a semi-closed screen formed by the protruding parts of the base and cover, as well as the outer sides of the walls of the inner square.

Thus, in the proposed design of the antenna, the shielding of all its elements, the most susceptible to the effects of an electric field, is achieved by a simpler technical solution than in the prototype. This simplification is achieved due to the double use of the same structural elements: internal walls, base and cover. On the one hand, together with the outer wall they form a lodgement for ferrite rods, and, on the other hand, are simultaneously elements of an electric screen. The presence of double walls (internal conductive and external radiolucent) significantly increases the mechanical resistance of the antenna body to bending, which is important when using long rods made of such a brittle material as ferrite. Fastening ferrite rods by pouring it with rubber-like material in the tool tray provides impact resistance of the structure.

In the central part of the antenna can be placed an auxiliary board (control, summation of signals, RF junctions, etc.) and an external connector. The construction is strictly symmetric. Symmetry helps to achieve the identity of the electrical parameters of the frames, which improves the direction-finding parameters of the antenna.

Figure 1 shows the appearance of the antenna housing assembly, figure 2 is a view of the housing without a top cover and outer side walls, figure 3 is a top view of the antenna without a top cover with stacked ferrite cores and boards, figure 4 - section of antenna AA with the top cover. In the drawings are indicated by numbers:

1 - top cover;

2 - external walls;

3 - housing base;

4 - inner walls;

5 - ferrite rods;

6 - filling with rubber-like material;

7 - windings;

8 - amplifier boards;

9 - an auxiliary payment;

10 - external connector.

The screen around the ferrite rods cannot be closed, since in this case the antenna becomes inoperative. That is why the side walls must be made of a dielectric radio-transparent material. Arrows E in Fig. 4 show the lines of force of the electric component of the field acting on the antenna. It can be seen that the cover prevents the penetration of the field E both inside the case and to the windings.

The presence of conductive surfaces (screens) near the ferrite rod reduces the effective height of the antenna [10, 11], which leads to a decrease in its sensitivity. Therefore, to reduce the influence of the screen on the sensitivity of the antenna, it is proposed that the angular parts of the lid located above the ends of the ferrite rods be made of radiolucent material. In Fig. 5, one of the corners of the lid with the radiolucent part 1a is highlighted by hatching. Removing the screen from the ends of the ferrite rods from above can improve the sensitivity of the antenna up to 20%. The lid can be made entirely of radiolucent material, and metallization is performed, for example, by gluing a sheet of foil of the corresponding shape from below. It is important that the metallization has good electrical contact with the ends of the vertical walls of the inner square of the housing around the perimeter.

Under conditions of an increased level of electrical interference, it is proposed to further improve the shielding of the windings of ferrite rods by introducing additional external vertical conductive shielding walls 11 opposite the windings (highlighted by shading in Figures 6, 7, 8) with a width equal to or slightly greater than the width of the windings. Each shielding wall can be mounted on the cover, Fig.6, or on the base, Fig.7. It can consist of two halves, which are attached to the base and cover, Fig. 8. Shielding walls can be mounted directly on the side radiolucent wall. In the latter case, it is necessary to ensure electrical contact with the base or cover. It is important to leave an electric gap between the cover and the base to prevent the formation of a closed screen around the ferrite core. The introduction of an additional screening wall leads to some decrease in the effective height of the antenna. The degree of reduction increases with increasing width of the winding.

The conductive parts of the housing can be made of aluminum alloys, and the side walls of PCB (fiberglass).

Using the proposed technical solution allows us to simplify the design of the antenna, improve its overall dimensions and reduce cost while maintaining high protection from the effects of the electrical component of the signal field and interference.

LITERATURE

1. Khomich V.I. Ferrite antennas. Mass radio library. Issue 721.-M.: Energy, 1969 - 96 p.

2. Vershkov M.V. Calculation and design of ship radio communication antennas. - L .: Sea transport, 1963 - 148 p.

3. Bobkov A.M. Real selectivity of radio channels in a complex jamming environment. - St. Petersburg, Abris, 2001 .-- 216 p.

4. Kukes I.S., Old man M.E. Basics of direction finding. - M .: Owls. Radio, 1964 .-- 640 s.

5. US patent No. 2981950, NKI 343-788, 1959

6. US patent No. 6570543 B1, MKI H01Q 7/04, 2003

7. US patent No. 6014111, MKI H01Q 7/08, 2000

8. US patent No. 3495264, MKI H01Q 7/08, 1970

9. US patent No. 3721989, MKI H01Q 7/08, 1971

10. Mikheev A.F. The electrical parameters of the loop antenna with or without a ferrite core near the conductive surface // Radio Engineering, 1985, No. 10, - p. 64-67.

11. Dodonov A.V., Mikheev A.F. Underwater Radio - M.: Military Publishing House, 1996. - 190 p.

Claims (3)

1. A broadband ferrite antenna containing four ferrite rods with windings arranged in a square on a conductive base, a top cover of a conductive material of a size equal to the base, outer walls made of radiolucent material, and amplifier boards placed inside the ferrite square, characterized in that on the base of the antenna there are installed vertical walls of conductive material forming an inner square, while the space bounded by the outer sides of the walls is formed about the square, with the inner sides of the radiolucent outer walls and the base, forms a lodgement in which ferrite rods with windings are placed and fixed by filling with rubber-like radiolucent transparent material, and an amplifier is placed in the inner square opposite each ferrite core, with its input connected through openings in the wall of the inner square conclusions of the winding of the corresponding rod. 2. The device according to claim 1, characterized in that the corners of the top cover are made of radiolucent material. 3. The device according to claim 1, characterized in that it contains additional external vertical conductive walls with a width equal to or greater than the width of the windings, which are in electrical contact with either the base or the top cover.

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