RU2745734C1 - Antenna device for mono-pulse radar system - Google Patents

Abstract

FIELD: antennas.

SUBSTANCE: invention relates to antenna technology, in particular, to antennas for a monopulse radar system on an unmanned aerial vehicle. The technical result is achieved in that the antenna device of a monopulse radar system containing a sum-difference converter connected to a feed, a movable reflector with an antenna drive and a fixed counterreflector, differs from the prototype in that the movable reflector is made in the form of a paraboloid with a cut off upper segment, a fixed counterreflector is made in the form of a plate, the projection of which on the vertical plane of symmetry of the antenna device is located obliquely, at an angle of 22.5° to the projection on the same plane of the movable reflector in its neutral position, the four-channel feed connected to the sum-difference converter is installed in the segment of the movable reflector that's freed after the cut, is bent towards the fixed counter-reflector with the center of its front end located at the focal point of the movable parabolic reflector in its neutral position and consists of the rear and front end four-channel two-channel sections and a straight connecting two-channel section, which is docked with the above-mentioned lower and upper final four-channel sections by means of two four-channel sections rotatable at an angle of 22.5° in the form of sectors of a toroidal waveguide, and to compensate for the difference in the length of the outer and inner pair of channels of the rotating sections of the feed between internal pairs of channels of the first and second rotary four-channel sections, symmetrically relative to the plane of symmetry of the feed, two compensation sections are inserted, while the counter-reflector plate is made of radio-transparent material, on which a linear polarization selector is applied, reflecting electromagnetic waves with vertical polarization and transmitting electromagnetic waves with horizontal polarization, the movable reflector is made with an element for transforming the polarization of the reflected signal into the perpendicular direction of polarization, which is made in the form of a linear polarization selector rotated at an angle of 45° to the direction of both horizontal and vertical polarization, and located at a distance of one quarter of the wavelength of the radio signal from the short-circuit reflective layer.

EFFECT: said invention is aimed at providing the maximum possible antenna gain with a limited diameter of the reflector, turning in two mutually perpendicular directions relative to the longitudinal axis of the antenna, as well as expanding the operating frequency band of the antenna to increase the noise immunity of the radar.

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Description

The invention relates to antenna technology and, in particular, to antennas for a monopulse radar system on an unmanned aerial vehicle.

Reflector antennas [1] with a parabolic mirror and a point feed located at the focus of the parabola are widely used among antennas. The spherical wave of the radio signal emanating from the feed is converted after reflection from the mirror into a plane wave propagating in the direction of the positive axis of the paraboloid.

The disadvantage of such antennas is the large distance from the feed to the mirror, which makes it impossible to use them on an unmanned aerial vehicle due to severe restrictions in terms of weight and size characteristics.

To reduce the weight and size parameters, two-mirror Cassegrain antennas are used, which are widely used in radar to form monopulse radiation patterns [2]. The antenna consists of a parabolic main mirror (reflector) and a hyperbolic additional mirror (counter-reflector). The irradiator is located on the center line connecting the centers of the counter-reflector and the reflector, in which a special hole is made for the irradiator. The spherical waves emitted by the irradiator, after being reflected from the counterreflector, propagate towards the reflector, and at the same time remain spherical, as if emanating from the imaginary focus of the counterreflector located behind the counterreflector. The reflector converts spherical waves into plane waves propagating in the direction of the antenna axis.

The overall dimensions of such an antenna are reduced in the direction of the center line due to the use of a counter-reflector. At the same time, the diametrical parameters of such an antenna remain large, which makes it impossible to use it on an unmanned aerial vehicle.

The closest to the proposed device, adopted as a prototype, is an antenna [3], consisting of a carrier dielectric unit, having on one side a surface of revolution covered with a layer of electrically conductive material, which acts as the main mirror, and on the opposite side, a surface of revolution, also covered with a layer of electrically conductive material, acting as an auxiliary feed, and a feed unit located inside the carrier dielectric block. In such an antenna, not only the axial parameters are reduced approximately by half due to the use of a counter-reflector, but also all generating equipment, including waveguide paths, complicated by a factor of four with the monopulse radar principle, can be removed behind the reflector, which also contributes to a decrease in the overall parameters of the antenna.

At the same time, under severe restrictions in terms of weight and size parameters, when the diameter of the reflector is no more than 7-8 times the wavelength, the presence of a hole in the center of the reflector with a diameter commensurate with the wavelength, and the presence of a shading counterreflector with a diameter of about 2 times the wavelength, significantly reduces the antenna gain and makes it ineffective to use it on an unmanned aerial vehicle, especially if it is necessary to scan the space of the possible position of objects, for example, by rotating the reflector, which requires an increase in the diameter of the hole in its center.

The technical result of the proposed invention is to provide the maximum possible antenna gain with a limited diameter of the reflector, turning in two mutually perpendicular directions relative to the longitudinal axis of the antenna, as well as expanding the operating frequency band of the antenna to increase the noise immunity of the radar.

The essence of the invention lies in the fact that in the antenna device of a monopulse radar system containing a sum-difference converter connected to the feed, a movable reflector with an antenna drive and a fixed counter-reflector, the movable reflector is made in the form of a paraboloid with a cut upper segment, the fixed counter-reflector is made in the form of a plate , the projection of which on the vertical plane of symmetry of the antenna device is located obliquely, at an angle of 22.5 ° to the projection on the same plane of the movable reflector in its neutral position, the four-channel feed connected to the sum-difference converter is installed in the segment of the movable reflector released after the cut, is made curved towards the fixed counter-reflector with the location of the center of its front end at the focal point of the movable parabolic reflector in its neutral position and consists of rear and front end four-channel sections and a straight line will connect separate two-channel section, which is docked with the above-mentioned lower and upper final four-channel sections by means of two four-channel sections rotatable at an angle of 22.5 ° in the form of toroidal waveguide sectors, and to compensate for the difference in the length of the outer and inner channel pairs of the rotary sections of the feed between the inner pairs of channels of the first and the second rotary four-channel sections, symmetrically relative to the plane of symmetry of the irradiator, two compensation sections are inserted, while the counter-reflector plate is made of radio-transparent material, on which a linear polarization selector is applied, reflecting electromagnetic waves with vertical polarization and transmitting electromagnetic waves with horizontal polarization, the movable reflector is made with an element for transforming the polarization of the reflected signal to the perpendicular direction of polarization, which is made in the form of a linear polarization selector rotated at an angle of 45 ° to the direction as horizontal and vertical polarization, and located at a distance of one quarter of the wavelength of the radio signal from the short-circuit reflective layer.

In addition, the antenna drive has a two-way port for receiving control signals of the antenna device from the receiving device, signal processing and control and transmitting angular information from the antenna to it, the sum-difference converter is connected to the rear end of the four-channel feed, has a two-way waveguide port for transmission to the antenna a probing signal of a given power and transmission from the antenna of the echo signal of the summed channel, and also has two waveguide outputs for transmitting difference echo signals mutually perpendicular in the direction of the beam.

The essence of the invention is illustrated by further description and drawings, which show:

in fig. 1 - general structure of the antenna device as part of the radar;

in fig. 2 and FIG. 3 - details of the design and explanations for the operation of the reflector;

in fig. 4 - general structure of the antenna device with a refined design of the feed;

in fig. 5 - the design of the feed.

FIG. 1 are marked:

1 - reflector;

2 - counterreflector;

3 - irradiator;

4 - antenna drive;

5 - sum-difference converter.

The antenna device operates as part of a monopulse radar, which additionally contains:

6 - signal synthesizer;

7 - power amplifier;

8 - circulator connecting the antenna device with the power amplifier and with the receiver;

9 - amplifier of the total receiver channel;

10 - amplifier of the differential azimuth channel of the receiver;

11 - amplifier of the differential elevation channel of the receiver;

12 - a device for receiving, processing signals and control.

Along the outer contours, the antenna device repeats the shape of the radome and UAV radome, into which it is installed with the necessary clearances.

Shown in FIG. 1 elements of the antenna device are connected as follows.

The illuminator 3 is docked to the total-difference transducer 5 with its rear end and is directed towards the counter-reflector 2 with its upper front end, the transverse plane of which is rotated relative to the transverse plane of the rear end by an angle of π / 4 rad (45 °).

The reflector 1 is installed on the antenna drive 4, ensuring its rotation at a given angle in the horizontal plane (X-Z) and in the vertical plane (X-Y).

The sum-difference converter 5 is connected by its transceiver input to the circulator 8, which is connected by its power input through the power amplifier 7 to the synthesizer 6, and the output is connected to the amplifier 9 of the total receiver channel.

Two difference channels of the sum-difference converter 5 are connected, respectively, to the amplifier 10 of the differential azimuth channel of the receiver and to the amplifier 11 of the differential elevation channel of the receiver. The outputs of the amplifiers 9, 10, and 11 are connected to a device 12 for receiving, processing signals and control connected by a two-way communication channel with the synthesizer 6 and connected by its control output to the antenna drive 4, which controls the angular position of the reflector 1.

Along the outer contours, the antenna device repeats the shape of the radar and UAV fairing, into which it is installed with the necessary clearances.

Counterreflector 2 is made in the form of a fixed plate located perpendicular to the vertical plane X-Y. The projection of the plate is located at an angle of π / 8 rad (22.5 °) to the vertical Y-axis and to the projection on the vertical plane of the movable reflector 1 in the neutral state. The counter-reflector plate is made of a radio-transparent material on which metal strips are printed parallel to the horizontal Z axis with a step Δ that is significantly less than the wavelength λ:

which ensures its polarization-selective properties: reflection from the counter-reflector of radio signals with vertical polarization of an electromagnetic wave and transmission of radio signals with horizontal polarization of an electromagnetic wave through the radio-transparent material.

The reflector 1 is made of a radio-transparent material in the form of a paraboloid, which is a two-layer mirror (Fig. 2), two layers of which are located at a distance L equal to one fourth of the wavelength λ:

In this case, metal strips are applied to the layer closest to the counterreflector with a step according to expression (1) at an angle of π / 4 rad (45 °) to the Y and Z axes, forming its polarization-selective properties. A continuous metallic short-circuit coating is applied to the far layer to reflect the incident wave. This design of the reflector allows you to transform the signal polarization by π / 2 rad (90 °) as follows (Fig. 3).

An electromagnetic wave with vertical polarization on the near layer of the reflector (vector 1 in Fig. 3a) is divided into two orthogonal waves (vectors 2 and 3). In this case, the wave corresponding to vector 2 is reflected from the near layer (Fig. 3b), and the wave corresponding to vector 3 (Fig. 3c) passes through it and is reflected from the far short-circuit coating. At the same time, it passes an additional path equal to the doubled distance 2L between the near and far layers. In accordance with (2), the quantity 2L is equal to half the wavelength

which is equivalent to changing the phase of the wave by 180 °. Thus, vector 3, after the wave passes the additional path, turns into vector 4, directed in the opposite direction. This wave is added to the wave corresponding to vector 2 (Fig. 3d) and forms a common wave reflected from the reflector, corresponding to vector 5 with horizontal polarization.

In the reflector 1, the upper segment of the paraboloid is cut off by the amount necessary to install the feed 3 in the space formed between the reflector and the outer fairing. The specified cut does not affect the aperture and, accordingly, the antenna radiation pattern in the horizontal plane and slightly expands the main beam of the radiation pattern in the vertical plane, which does not reduce the efficiency of the device.

FIG. 4, the designations are the same as in FIG. one.

The irradiator 3 is made structurally in accordance with FIG. 5, which has the following designations.

13 - rear end four-channel section,

14 - front end four-channel section,

15, 16 - the first and second rotary (at an angle of 22.5 °) four-channel sections,

17 - straight connecting two-channel section,

18, 19 - the first and second compensating connecting sections.

At the same time, in the direction from the rear end of the irradiator to its front end, the following are connected in series: the rear end four-channel section 13, the first rotary four-channel section 15, the straight two-channel connecting section 17, the second rotary four-channel section 16 and the front end four-channel section 14, and between the rotary sections 15 and 16, symmetrically relative to the plane of symmetry of the feed, single-channel compensation sections 18 and 19 are inserted.

Sections 13 and 14 are each four-channel straight-through waveguide with standard 3cm channels with vertical polarization for section 13 and polarization rotated π / 4 rad (45 °) in the vertical plane for section 14. In these sections, the short sides of the channel are parallel to the vertical XY plane, and the long ones are perpendicular to this plane. In this case, the projection of the end cut of the section 13 is parallel to the Y axis, and the projection of the end cut of the section 14 is inclined to the Y axis at an angle of π / 4 rad (45 °).

Rotary sections 15 and 16 are sector segments of a 4-channel toroidal waveguide with standard channel sizes for the 3-cm wavelength range and with a minimum (technologically feasible) inner radius of the torus. The sectorial angle of the sections is about π / 8 rad (22.5 °), providing a total rotation of the waveguide channels of the feed through an angle of about π / 4 rad (45 °).

Section 17 is a two-channel straight waveguide with standard channels for the 3-cm wavelength range, while the projection of section 17 on the X-Y plane is inclined relative to the X axis by an angle of about π / 8 rad (22.5 °).

Sections 18 and 19 are symmetric waveguides with standard channels bent in a plane perpendicular to the X-Y plane, the projection of which on the X-Y plane is inclined with respect to the X-axis at an angle of about π / 8 rad (22.5 °). The bend of the waveguides is made from the axis of symmetry located between the channels to the outside. The amount of bending is chosen such that the increase in the length of the waveguide in comparison with the length of the straight section 17 exactly compensates for the difference in the lengths of the outer and inner pair of waveguide channels in the sector four-channel sections 15 and 16 of the toroidal waveguide.

The antenna device operates as follows. The antenna device operates as part of a monopulse radar.

The location of the compensation sections 18 and 19 with bends in a plane perpendicular to the XY plane at an angle of π / 8 rad (22.5 °) to the X axis provides the possibility of free rotation of the reflector 1 with the cut off upper segment both in the vertical and horizontal planes with using the drive 4 to the required angle for viewing space and tracking the detected objects.

The synthesizer 6 generates sounding radio pulses, which are amplified in the amplifier 7, and then, through the circulator 8, the sum-difference converter 5 and the feed 3 are emitted towards the counter-reflector 2 in the form of a spherical wave with vertical polarization. The specified wave is reflected from the counter-reflector towards the parabolic reflector 1, remaining spherical. In reflector 1, the wave is converted from spherical to flat, changes its polarization from vertical to horizontal by π / 2 rad (90 °), is reflected towards the counter-reflector and passes through it in the direction of the field of view and object detection.

The echo signal, like the sounding signal, has horizontal polarization. It passes through the counterreflector 2 towards the reflector 1, changes its polarization from horizontal to vertical in it and is reflected from the reflector 1 towards the counterreflector 2 in the form of a converging (focusing) beam. Further, the echo signal with vertical polarization is reflected from the counterreflector 2 to the focal point of the reflector 1, where the feed 3 is located, passes to the sum-difference converter 5 and is divided there into three signals: the total signal passes through the circulator 8 to the amplifier 9 of the sum channel, the difference azimuth signal passes to the amplifier 10, and the differential elevation signal passes to the amplifier 11. The signals of the three amplifiers are fed to the device 12 for receiving, signal processing and control connected to the synthesizer 6 and controlling the antenna drive 4 in a known manner.

To combat active interference, synthesizer 6 generates a sounding signal at a new carrier frequency for each sounding interval. The frequency range in which the carrier frequency changes determines the noise immunity of the system, to increase which all blocks have the maximum possible bandwidth of the operating frequencies.

In the claimed antenna device, the bandwidth of the operating frequencies is provided by the design of the feed 3 as follows.

The probing signal from the output of the sum-difference converter 5 is fed in phase to all four waveguide channels of section 13 of the feed 3. Then the in-phase signal comes from section 13 to the rotary section 15, in which, simultaneously with a rotation through an angle of π / 8 rad (22.5 °) there is a phase lag of the signal of the two outer channels relative to the two inner channels due to the difference in the length of their axial lines. (The names "outer" and "inner" channels correspond to their location relative to the center of the toroidal waveguide). Further, the signal of the outer two channels enters section 17, and the signals of the two internal channels, respectively, in sections 18 and 19, in which not only the delay compensation occurs, but also the phase advance of the signals of section 17 relative to the signals of sections 18 and 19, which have a greater the length of the curved center lines in comparison with the straight center lines of the channels in section 17. After that, the signals enter the rotary section 16, in which, due to the difference in the length of the center lines, the phase lag of the inner channels relative to the outer channels is compensated simultaneously with an additional rotation of the center line channels at an angle of π / 8 rad (22.5 °). As a result, the in-phase channel, rotated by π / 4 rad (45 °), from all four channels enters section 14 and is then emitted in the direction of counter-reflector 2.

Due to the equality of the length of the axial lines of all four waveguide channels of the irradiator 3, the emitted signal remains in phase regardless of the value of the carrier frequency of the signal. A similar path through the sections of the feed 3, only in reverse order, passes the radar echo reflected from radio-contrast objects. The difference between the echo signal and the probing signal is that a signal with a different phase can arrive at each of the four channels of the feed. In this case, the phase difference in the channels of the feed is maintained from the beginning of the front end section 14 to the end of the rear end section 13, regardless of the value of the signal carrier frequency.

Thus, the working band of the antenna device carrier frequencies is expanded to the full frequency range, which is actually limited only by the dimensions of the used waveguide channels, which significantly increases the noise immunity of the monopulse radar.

Based on the above description and drawings, the proposed antenna device can be manufactured using known components and technological equipment known in the electronic industry and used in monopulse radars for unmanned aerial vehicles.

Literature

1. M. Skolnik "Handbook of Radar". M., "Sov. Radio", 1977 T2, p. 101, fig. one.

2. M. Skolnik "Handbook of Radar". M., "Sov. Radio", 1977 T2, p. 112, fig. fifteen.

3. RF patent No. 2 124 253, IPC H01Q 19/18, publ. 12/27/1998 (prototype).

Claims (2)

1. Antenna device of a monopulse radar system containing a sum-difference converter connected to a feed, a movable reflector with an antenna drive and a fixed counter-reflector, characterized in that the movable reflector is made in the form of a paraboloid with a cut off upper segment, the fixed counter-reflector is made in the form of a plate, the projection which on the vertical plane of symmetry of the antenna device is located obliquely, at an angle of 22.5 ° to the projection on the same plane of the movable reflector in its neutral position, the four-channel feed connected to the sum-difference converter is installed in the segment of the movable reflector released after the cut, made curved towards the fixed counter-reflector with the location of the center of its front end at the focal point of the movable parabolic reflector in its neutral position and consists of rear and front end four-channel sections and a straight connecting two-channel section, which is docked with the aforementioned lower and upper end four-channel sections by means of two four-channel sections rotatable at an angle of 22.5 ° in the form of toroidal waveguide sectors, and to compensate for the difference in the length of the outer and inner pair of channels of the rotary sections of the feed of rotary four-channel sections, symmetrically relative to the plane of symmetry of the irradiator, two compensation sections are inserted, while the counter-reflector plate is made of radio-transparent material, on which a linear polarization selector is applied, reflecting electromagnetic waves with vertical polarization and transmitting electromagnetic waves with horizontal polarization, the movable reflector is made with an element transformation of the polarization of the reflected signal to the perpendicular direction of polarization, which is made in the form of a linear polarization selector rotated at an angle of 45 ° to the direction of both horizontal and and vertically polarized and located at a distance of one quarter of the wavelength of the radio signal from the short-circuit reflective layer. 2. Antenna device according to claim 1, characterized in that the antenna drive has a two-way port for receiving control signals of the antenna device from the receiving device, signal processing and control and transmitting angular information from the antenna to it, the sum-difference converter is connected to the rear end of the four-channel feed, has a double-sided waveguide port for transmitting a probing signal of a given power to the antenna and transmitting the total channel echo signal from the antenna, and also has two waveguide outputs for transmitting difference echo signals mutually perpendicular in the direction of the beam.

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