RU2293408C1 - Mirror antenna feed - Google Patents

Abstract

FIELD: antenna engineering.

SUBSTANCE: novelty is that conductor with inductive character of conductivity is secured in mirror antenna feed that has waveguide and reflector on protective dielectric shell installed outside waveguide coaxially with respect to the latter; this conductor functions to match shell and aperture of waveguide at a time and can be made, for instance, in the form of flat or wire ring, or in the form of a few thin-wire turns.

EFFECT: ability of matching high-quality feed in broad frequency band, enhanced antenna gain and polarization isolation.

3 cl, 12 dwg

Description

The invention relates to radio engineering and can be used in antenna technology, in particular in communications and satellite television.

Known irradiator mirror antenna, consisting of a waveguide, a reflector and a protective dielectric plate located in the aperture of the reflector [1, p. 544, 535, Fig. 10-22a]. The matching of the feed is based on the compensation of waves reflected from the neck of the reflector and the dielectric plate. The disadvantage of this irradiator is matching in a narrow frequency range due to the fact that the distance between the neck of the reflector and the plate is significant.

A coordinated support in a circular waveguide is also known, consisting of a dielectric thin disk and two coaxial ring flat conductors located on its surfaces with an inductive character of conductivity [2]. A thin dielectric disk is a capacitive type conductivity. This conductivity is compensated by the inductive conductivity of the rings located on the dielectric disk. Due to this, the washer is consistent in a wide range of frequencies. The disadvantage of this matched washer is that when it is installed in the aperture as a protective dielectric cover, compensation for the jump in the wave resistance of the waveguide and free space does not occur, which leads to a deterioration in the matching of the irradiator.

Also known is an irradiator for a symmetrical parabolic antenna, containing a round waveguide protruding above a ribbed reflector with rectangular grooves, a dielectric ring and a radiolucent dielectric film to exclude the influence of climatic factors [3]. The matching of the irradiator is based on the use of a thin dielectric film having radiolucent properties. The disadvantage of this irradiator is the presence of a thin film that does not provide sufficient strength during operation. In particular, such a film can be easily torn by the beaks of the raven.

Also known is an irradiator of a mirror antenna containing a waveguide, a reflector and a protective dielectric casing mounted on a reflector [1, p. 535, Fig. 10-22b]. The casing is designed to protect the irradiator from atmospheric conditions. The casing is located behind the opening of the reflector. The matching of the irradiator is based on the compensation of waves reflected from the aperture of the irradiator and the dielectric casing. The disadvantage of this irradiator is matching in a narrow frequency range due to the fact that the distance between the aperture of the irradiator and the dielectric casing is significant. This mirror antenna feed is selected as a prototype.

The present invention is based on the task of creating a reflector antenna reflector with matching in a wide frequency range.

The problem is solved in that in the irradiator of a mirror antenna containing a waveguide, a reflector and a protective dielectric casing mounted outside the waveguide, a conductor with an inductive nature of conductivity is fixed on it. Additionally, a conductor with an inductive nature of conductivity is made in the form of a flat or wire ring. Additionally, the wire ring is made in the form of several turns of thin wire.

This embodiment of the reflector antenna illuminator makes it possible to match the illuminator with good quality in a wide frequency range, increase the antenna gain and polarization isolation.

The invention is illustrated by drawings, where

- figure 1 shows a variant of the irradiator for an axisymmetric reflector antenna;

- figure 2 shows a variant of the irradiator for offset mirror antenna;

- figure 3 shows embodiments of the inductive conductor;

- figure 4 shows the curves of the reflection coefficient of the irradiator with an inductive ring and without it.

The irradiator for an axisymmetric mirror antenna is shown in Fig. 1 and consists of, for example, a circular waveguide 1, a flange 2, a waveguide transition 3 of an oval cross-section, a reflector 4 and a protective dielectric casing 5, mounted in the waveguide 1. Inside the waveguide 1, a dielectric a polarizer plate 6, designed to form a circular polarization field and oriented at an angle of 45 degrees to the plane E of the waveguide transition 3. The reflector 4 is made according to any known scheme and serves to framing the corresponding wide radiation pattern. The plane 7 of the dielectric casing 5 is located at a distance of 0.125λ, where λ is the working wavelength from the aperture 8 of the waveguide 1. On the inner plane 7 of the dielectric casing 5 there is a conductor with an inductive nature of conductivity, made, for example, in the form of a flat ring 9. Ring 9 is installed coaxially with the waveguide 1. The reflector 4 is connected to the waveguide 1 using a screw 10.

The irradiator for the offset mirror antenna is shown in FIG. 2 and consists of, for example, a circular waveguide 11, a flange 12, an oval cross-sectional waveguide transition 13, a reflector 14 and a protective dielectric casing 15 mounted on the reflector 14. A polarizer dielectric plate 16 may be disposed inside the waveguide 11 to form a circular field polarization and oriented at an angle of 45 degrees to the plane E of the waveguide transition 13. The reflector 14 forms a narrower radiation pattern designed to irradiate the offset mirror. The plane 17 of the protective dielectric casing 15 is also located at a distance of 0.125λ from the aperture 18 of the waveguide 11. In this case, on the inner plane 17 of the dielectric casing 15 there is a conductor with an inductive nature of conductivity, made, for example, in the form of a flat ring 19. Ring 19 is mounted coaxially with the waveguide 11. The reflector 14 is mounted on the waveguide 1 using a screw 20.

Consider the principle of operation of the irradiator mirror antenna. The reflection of the wave in the aperture of the waveguide occurs due to a jump in wave impedances of the waveguide and free space. The frequency dependence of the reflection coefficient of a circular waveguide is decreasing [4, p. 241, 242]. The reflection coefficient for a circular waveguide varies in the frequency range from 0.3 to 0.15. There are two possibilities for matching the waveguide aperture with additional conductivity in accordance with the Volpert-Smith diagram. The first possibility is to set the capacitive type conductivity inside the waveguide at a distance of 0.125λg, where λg is the wavelength in the waveguide. The second possibility is to install inductive conductivity outside the waveguide at a distance of 0.125λ from the aperture of the waveguide. As is known, the magnitude of inductive conductivity decreases with increasing frequency, that is, the reflection from it is of a decreasing nature, as well as for the reflection coefficient from the aperture of the waveguide. Therefore, for broadband matching, the second option is more preferable, providing compensation for waves of approximately the same amplitude in the operating frequency range. In this case, the inductive type conductivity should also compensate for the capacitive conductivity of the dielectric casing on which it is located. Thus, the protective dielectric casing should also be located at a distance of 0.125λ. For waves with circular polarization of the field, it is advisable to perform the inductive conductor in the form of a ring having axial symmetry. This inductive ring will provide the radio transparency of the protective dielectric casing and broadband matching of the irradiator. Since the inductive ring is a weakly excited element, since the reflection from it is comparable with the reflection from the aperture of the waveguide, it practically does not affect the radiation pattern of the irradiator.

Inductive conductivity can also be implemented on the basis of other structures. The conductivity of a rectilinear conductor depends on its length. A rectilinear conductor oriented along the lines of the electric field and not having electrical contact with the waveguide wall has a capacitive type conductivity with a conductor length of less than λ / 2. In this case, the conductor fully reflects the wave at a length of λ / 2 (resonance phenomenon). To ensure the inductive nature of the conductivity, the length of the rectilinear conductor must be selected in the range from λ / 2 to λ (and so on, taking into account the periodicity). When the length of the conductor is equal to λ, there is no reflection from it, since the half-waves of the current on the conductor are the same and opposite. In practice, it is advisable to use long curved conductors to realize inductive conductivity and place it on the surface of the casing. The frequency dependence of the reflection coefficient of a curved conductor is determined by the total length of the conductor and the ratio of the part of the conductor parallel to the electric field and the part perpendicular to it. The design of inductive conductors may be different. They can be made on the basis of wire structures or flat conductors on a dielectric substrate, can be made in the form of spirals or repeatedly bent at right angles to conductors. The choice of the optimal design of the inductive conductor is determined by the design of the irradiator, the influence of the reflector and the type of polarization. Figure 3 shows embodiments of the inductive conductor. For a linearly polarized wave, it is sufficient to apply a long curved conductor elongated along the direction of polarization of the wave (along the electric field vector E). The shape of a long conductor can be made in the form of a spiral 21, a meander 22 or a snake 23. The frequency dependence of the reflection coefficient of a curved conductor depends on its parameters (number of turns, length of the conductor, step), and the reflection coefficient decreases with decreasing step of the curved conductor. The geometric dimensions of the conductors are selected from the conditions for matching the irradiator. In Fig. 3d, the inductive conductor is made in the form of two arcs 24 of conductors. The electric field vector E is directed along the ends of the arcs. At the ends of arcs 24, the conduction currents are zero, so the two arcs act as a continuous inductive ring.

For a wave of circular polarization, it is advisable to perform an inductive conductor in the form of a ring. Ring 25 can be made of wire, the ends of which are soldered, fig.3d. The flat ring 26 in FIG. 3e can be cut out of metal foil and glued onto the plane of the casing, etched on a photo mask on a thin foil-coated dielectric film or sprayed onto the plane of the casing. Another embodiment of ring 27 is a few turns of thin wire of FIG. Due to several turns, a wire break is insignificant for a circularly polarized wave; therefore, a multi-turn ring acts as a continuous one. The manufacture of such a ring does not require the use of complex technologies and devices. The coils are wound on a round blank of the desired radius, and then the ring is glued to the plane of the dielectric casing.

Figure 4 presents the experimental curves of the dependence of the reflection coefficient. Curve 28 corresponds to the initial reflection coefficient from the aperture of the offset irradiator of FIG. 2 with a protective dielectric casing 15 with a thickness of 0.02λ. The reflection coefficient reaches a value of 0.3 at the lower end of the range. Curve 29 corresponds to the reflection coefficient from the aperture of the offset irradiator with a protective dielectric casing 15, on the surface of which an inductive ring 19 is located. Ring 19 provides good matching of the irradiator in the frequency range up to 20 percent. The inner radius of the ring 19 is equal to 0.3λ, the width of the ring is 0.04λ. These results are also confirmed by calculations based on the electrodynamic modeling program.

The advantage of the proposed solution is the matching of the irradiator in a wide range of frequencies. In this case, the reflection loss is reduced by 0.2 dB. In addition, the proposed solution leads to an improvement in polarization isolation in the case of a circularly polarized wave, since the wave reflected from the aperture of the waveguide directly contributes to the cross-polarization component. The assessment shows that a decrease in the reflection coefficient from the irradiator aperture from 0.21 to 0.05 leads to an increase in the polarization isolation of the irradiator by 13 dB. Thus, the proposed irradiator provides an increase in the gain of the mirror antenna due to a decrease in reflection losses and an increase in the level of polarization matching.

Information sources

1. Zhuk M.S., Molochkov Yu.B. Design of antenna-feeder devices. - M. - L .: "Energy", 1966.

2. RF patent No. 2038660, H 01 P 1/00, 1992.

3. USSR patent No. 1794266, H 01 Q 13/02, 1990.

4. Eisenberg G.Z., Yampolsky V.G., Tereshin O.N., Antennas for VHF. - Part 1. M .: "Communication", 1977.

Claims (3)

1. A mirror antenna irradiator comprising a waveguide, a reflector and a protective dielectric casing mounted outside the waveguide, characterized in that a conductor with an inductive conductivity is attached to the casing coaxially to the waveguide, matching the casing and the aperture of the waveguide. 2. The irradiator according to claim 1, characterized in that the conductor with an inductive nature of conductivity is made in the form of a flat or wire ring. 3. The irradiator according to claim 2, characterized in that the wire ring is made in the form of several turns of thin wire.

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