Space object image detection antenna device using large improved Cassegrain beam waveguide antenna

Abstract

The present invention relates to an improved large reflector-type beamway guide Cassegrain antenna. When the improved large reflector-type beamway guide Cassegrain antenna is applied to an imaging radar, a difference in the radiation pattern of the reflection mirror within the beamway guide occurs when operating a single Cassegrain beamway guide antenna with two frequency bands, one of which is approximately 10 times the wavelength of the low frequency of the L band or S band and the other of the high frequency of the Ku band or Ka band. Therefore, when operating in the low L / S band, the low frequency band mirror of the L / S band and the high frequency band mirror of the Ku / Ka band are duplicated within the beamway guide to make the L / S band and Ku / Ka band efficiencies nearly identical. Here, if the loss in the Ku / Ka band is acceptable, the Ku / Ka frequency band mirror may be omitted. Furthermore, to compensate for gain attenuation caused by deformation of the main reflector due to its own weight as the reflector is large, a main reflector deformation compensation device including an actuator is attached behind the sub-reflector. In the absence of a radome, four panels of the main reflector are automatically adjusted by an ACU for each of the four panel modules. Attach the actuator.

Description

Technology Field

[0001] The present invention is an automatic tracking detection antenna device used in an inverse SAR imaging radar for detecting or locating low-orbit / geostationary satellites and space launch debris in space via imaging or for tracking detection from the ground, which transmits L / S bands and Ku / Ka bands through the same antenna to receive reflected signals from space objects as images. Background Technology

[0002] Currently, there are over 10,000 low-orbit satellites launched worldwide, including SPACE X, Amazon, STARNET, and GLOBASTAR, and thousands of satellites for intelligence gathering have also been launched by various countries. Each low-orbit satellite has a lifespan of approximately three years, and if satellite operations are discontinued or their lifespan ends, they are decommissioned and relaunched. Conventional satellites are designed to burn up in the atmosphere through orbital adjustments following disposal procedures when their lifespan ends; however, if recovery is impossible, they are discarded in space and become space debris. If such space debris collides with newly launched satellites, it can cause significant damage. Therefore, there is an urgent need for an antenna capable of tracking and detecting space debris via imaging. Furthermore, the antenna device of the present invention can be used for communication, astronomical and space surveillance simply by replacing the transmitter and receiver.

[0003] Antennas used in ground radars for imaging detection must detect in both vertical and horizontal directions simultaneously, and most are active phased array antennas designed for short ranges. However, using active phased array antennas for space detection, which requires a range of 1,000 to 36,000 km, is impossible due to their excessive cost and large size; consequently, even for communication purposes, reflectors with a diameter of 30 m or more are used in imaging radars. Prior art literature

[0004] Registered Patent Publication No. 10-1893207 (August 23, 2018) The problem to be solved

[0005] According to an embodiment of the present invention, the present invention provides an antenna device that can be used in an inverse SAR radar, in which two frequencies—a low frequency band such as an L band or an S band and a high frequency band such as a Ku band or a Ka band—are simultaneously operated in a 35m diameter reflector-type antenna, so that the L band is mainly operated for detecting direction and vertical elevation angle and the Ku band is used for detecting moving targets as images. means of solving the problem

[0006] When a 35m diameter antenna is applied to an inverse SAR radar, when narrowband high-power transmission signals of L-band frequencies and wideband high-power transmission signals of Ku-band frequencies are simultaneously transmitted to the beam waveguide mirror, the L-band curved mirror and the Ku-band frequency selective mirror are installed in dual configuration, and the L-band and high-efficiency Ku-band signals are uplinked and radiated to the antenna, and the radio waves reflected from the target are received again at the antenna by the same beam waveguide.

[0007] For example, using a large reflector 35m antenna, L-band is used to detect the horizontal and vertical target directions, and Ku-band frequencies are used to detect the target image. Two frequency bands are transmitted simultaneously, and the horizontal rotation speed is, for example, 24° / sec, so that it rotates once every 15 seconds and 4 times every minute. When L-band gain is about 52dBi and radiated beam width is about 0.4°, the elevation angle is 0.4° per horizontal rotation. When Ku-band gain is about 70dBi or higher and radiated beam width is about 0.04°, L-band detects an elevation angle of 40° after 100 rotations (25 minutes) and an elevation angle of 80° after 200 rotations (50 minutes).

[0008] If an elevation target is detected while rotating horizontally at 4 revolutions per minute in the L-band, the elevation rotation motor is temporarily paused, and only horizontal rotation continues. However, although detection continues via the L-band, there are locations within the 0.4° range that cannot be detected because the Ku-band beamwidth is approximately 0.04°. In this case, at the L-band elevation detection range location (L-band beamwidth of 0.4° divided into approximately 10 equal parts), the Ku-band 0.04° If a horizontal rotation is continuously performed for every change in elevation angle at intervals, and a target within the 0.4° range is detected in the Ku band, this point is a state where both L and Ku band detection antennas have detected the target. The vertical and horizontal motor rotations are temporarily paused, and the ACU (Automatic Antenna Control Unit) operates the drive motor to automatically track horizontal and vertical elevation angles within the 0.04° range using a monopulse in the Ku band. In this case, the radar detects the target in the Ku band and receives the Ku band reflected signal reflected from the moving target at the antenna. The received signal is decomposed into a distance direction signal and a Doppler signal to form a 2D FFT spectrum, and the Doppler frequency multi-decomposition spectrum is converted into an image through an image signal processing process to detect the target. The present invention relates to an inverse SAR imaging radar antenna used in a Ku band radar system in this manner. Effects of the invention

[0009] It is impossible to detect objects at long distances of 1,000 km to 36,000 km or more with an active phased array antenna, and according to an embodiment of the present invention, it is possible to detect satellites in use in space and small space debris and instruct installers to remove them, or to provide collision avoidance information in advance by informing launchers of the location of space debris to launching new satellites. Brief explanation of the drawing

[0010] FIG. 1 is a perspective view of an antenna device according to the present invention. A large beam waveguide antenna is installed inside a radar dome, and a power supply, transmitting and receiving device, and radiating horn are installed at the bottom. FIG. 2a is a front view of an antenna device according to the present invention. An embodiment is illustrated in which the base and the high-power transmitting device are separated from the receiving device operating room at a long distance because they have a high electric field. FIG. 2b illustrates a bull gear of an antenna device according to the present invention. Fig. 2c shows the support wheel of the bull gear. Figure 2d is a rear hub support diagram of the main reflector. FIG. 3 is a side view of an antenna device according to the present invention. Figure 4 illustrates a main reflector deformation compensation device attached to the rear of the sub-reflector and the main reflector. Figure 5 illustrates a double-band curved reflector of the L band and Ku band within a beam waveguide. Figure 6a is a frequency-selective sub-reflector system attached to a Ku-band main reflector hub and an optical transmission configuration diagram. Figure 6b is a detailed optical transmission system diagram. Figure 7 is a schematic diagram of the automatic tracking image receiver of the L / Ku band inverse SAR imaging radar antenna horn system. Figure 8 roughly illustrates the vertical beam width when the narrow beam width of the Ku band is simultaneously vertically radiated within the wide beam width range of the L band. Specific details for implementing the invention

[0011] The following description of the present invention with reference to the drawings is not limited to specific embodiments and may be subject to various modifications and have various embodiments. Furthermore, it should be understood that the content described below includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the present invention.

[0012] In the following description, terms such as "first," "second," etc., are used to describe various components and are not limited in their meaning; they are used solely for the purpose of distinguishing one component from another.

[0013] Identical reference numbers used throughout this specification indicate identical components.

[0014] The singular expressions used in the present invention include the plural expressions unless the context clearly indicates otherwise. Furthermore, terms such as “comprising,” “equipping,” or “having,” as used below, should be understood as not precluding the existence or addition of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification.

[0015] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by those skilled in the art to which the present invention pertains. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in this application.

[0016] Furthermore, in the description referring to the attached drawings, identical components are assigned the same reference numeral regardless of drawing symbols, and redundant descriptions thereof are omitted. In describing the present invention, if it is determined that a detailed description of related prior art could unnecessarily obscure the essence of the present invention, such detailed description is omitted.

[0017] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings.

[0018] A detailed description of the antenna of the present invention used in an inverse SAR imaging radar is provided in detail with reference to the provided drawings. Because the antenna according to the present invention is large in size, it cannot detect elevation angles in the horizontal and vertical directions simultaneously. Since it must rotate once horizontally for every change in elevation angle of about 0.4° in the vertical beam width direction while rotating at high speed in the horizontal direction, the antenna must be designed to be lightweight. Additionally, it must rotate inside a radome so as not to be affected by external wind pressure.

[0019] Accordingly, as shown in Fig. 1, a radome is installed on the antenna foundation building (1-1) to prevent the influence of external wind pressure, an antenna (1-2) and a radome (1-3) are installed on the antenna foundation building, and power facilities, a transmitting device, and a receiving device are installed inside the foundation building, and an L-band horn (2-6) and a Ku-band horn (2-5) are installed.

[0020] FIG. 2a is a front view of the antenna of the present invention, wherein a main reflector deformation compensation device (2-3) is installed behind the main reflector (2-1) and the sub-refor (2-2) so that when the reflector is completely deformed and the radiated power decreases, the sub-refor is automatically adjusted. The L-band signal received from the sub-refor is fed to the beam waveguide (2-4), reflected by the reflector mirrors M1, M2, M3, M4, and M5, and received by the L-band horn. The signal reflected from the frequency-selective reflector (2-5) is received by the Ku-band horn (2-6), and the signal passing through the frequency-selective reflector (2-5) is received by the L-band horn (2-7). Conversely, the L-transmission signal from the L-band radiating horn (2-7) passes through the frequency-selective reflector (2-5), is reflected by M5, M4, M3, M2, and M1, is reflected by the sub-refor (2-2), and is radiated from the main reflector (2-1). Additionally, the radiation signal from the Ku band radiation horn (2-6) is reflected by the frequency-selective reflector (2-5), passes through the same path M5 to M1, and is radiated into space from the sub-reflector and the main reflector.

[0021] A vertical beam waveguide rotation device is attached between mirrors M1 and M2 within the beam waveguide to enable transmission via both fixed and rotating beam waveguides. The signal received by the feedhorn is shielded to avoid high-power interference from the high-power transmitter, and the receiver control unit is operated in the control room, which is separated by an underground duct.

[0022] The bull gear of FIG. 2b is attached to the vertical direction of the hub of the main reflector, and the hub of the main reflector is supported at four points by vertical rotation bearings (2-13). Guide wheels (2-2-8, 2-2-9) are attached to both sides of the bull gear to support the support wheels (2-2-10), thereby preventing deformation of the main reflector hub. Additionally, two sets of pinion gears (2-2-12) are connected to the gearbox motor (2-2-11) to rotate the bull gear (2-8) so that it rotates vertically at an angle of elevation.

[0023] FIG. 2c illustrates an embodiment in which four support wheels, two on each side of the guide wheel, are installed.

[0024] FIG. 2d shows the vertical drive bearing support attachment position (AA) on the rear hub of the main reflector. ' ) and bull gear attachment position (B, B ' )to An embodiment is illustrated in which vertical drive bearings and bull gears are attached and balancedly supported at four points to prevent deformation of the main reflector.

[0025] FIG. 3 is a side view of an antenna with a bearing (2-13), a rotating body counterweight, and a bull gear (2-8) attached to rotate a main reflector rotating body base (3-1) connected to a main reflector support (3-2) that supports the main reflector hub.

[0026] Additionally, two sets of horizontal rotation reduction motors (3-4) are attached to the slewing bearing gear (3-3) to provide backlash for distributed reverse rotation (80%+20%) and forward rotation (0°), and the slewing bearing gear (3-3) is rotated through the pinion gear (3-6). Furthermore, the slewing bearing gear (3-3) is rotated at high speed to spray lubricating oil through the oil circulation pump (3-5). Additionally, power is supplied to the rotating part through the sling terminals to the Ku band transceiver and curved deformation compensation device, and other control signals are transmitted.

[0027] A stop limit switch, a full limit switch, and a buffer are attached to the horizontal and vertical rotation parts, and vertical and horizontal angle detection sensors are attached.

[0028] FIG. 4 illustrates an embodiment in which actuators are attached to the main reflector deformation compensation device (4-1) on the rear of the sub-reflector. Six actuators of the compensation device (4-1) are attached to the rear of the primary sub-reflector. Since the total diameter of the main reflector is very large, approximately 30 to 40 m, severe deformation of the main reflector may occur due to wind pressure when there is no radome. Therefore, four actuators (4-2) are attached per four panels of the main reflector to allow automatic control by the ACU (automatic control unit).

[0029] FIG. 5 is a side view of a beam weight guide shared between L-band and Ku-band, where M1 is a flat mirror, M2-L and M3-L are Gaussian beam curved mirrors for the L-band, and M2-K and M3-K are Ku-band frequency-selective curved mirrors. The L-band of the received signal, reflected from the target and reflected from the main reflector (2-1) and the sub-refor (2-2), passes through M1, M2-L, M3-L, M4, M5, and M6 and is received by the L-band horn (2-6), and the Ku-band is reflected from M1, M2-K, M3-K, M4, M5, and M6 (frequency-selective reflectors) and is received by the Ku-band horn (2-5). In the case of transmission, it is reflected in reverse and reflected to the sub-refor and the main reflector to be radiated into space.

[0030] In FIG. 6, when one of the high frequency bands among the X / Ku / Ka bands is transmitted via beam waveguide, if the received signal is weak due to significant mirror reflection loss of the received signal, a frequency-selective reflector (6-1) is installed between the frequency downlink signal M1 and the sub-reflector (2-2) to reflect Ku or Ka and transmit it to the Ku or Ka horn (6-2). After passing through the mono-plus coupler (6-2-2) and the high-speed cutoff switch (6-3-1), the signal is synthesized in the signal synthesizer (6-3), converted into light by the laser diode (6-4), and then input into the optical diplexer (6-5) to be transmitted via the optical cable (6-6). The vertical rotation value is transmitted via the flexible optical cable, and the horizontal rotation value is transmitted to the optical transmission device in the center of M4 and M5 and input into the optical diplexer (6-7) inside the antenna base building. The optical diplexer reception output is converted into an input electrical signal of a photodiode (6-8), then distributed by a digital distributor (6-9) and transmitted to an image receiving device, and also transmitted to an automatic antenna control unit (ACU) to automatically track a monitored object.

[0031] The uplink transmission signal is formed by synthesizing the transmission signal and control signals in a digital signal synthesizer (6-10), converting them into optical signals in a laser diode (6-11), transmitting them through an optical cable via an optical diplexer (6-7), transmitting them uplink through an optical cable (6-6) via optical rotary joints OPT2 and OPT1, inputting them into an optical diplexer (6-5), passing through a photodiode (6-12), distributing them using a digital splitter (6-13), amplifying them in a transmission signal high-power amplifier (HPA) (6-13-1), passing through an OMT (Orthomode Transducer) (6-14), passing through a polarizer (6-6-14) to convert them into circular polarization, radiating them to a radiation horn (6-2), reflecting them from a frequency selection reflector (6-1), reflecting them from a sub-reflector (2-2), and radiating them into space through a main reflector (2-1).

[0032] Figure 7 is a schematic diagram of a horn system, which is a system schematic diagram used in two frequency bands, one of a low frequency L or S and one of a high frequency X or Ku or Ka, on a single antenna. Since the L / S and X / Ku / Ka bands are configured in almost the same way, the L band and the Ku band will be described in detail below.

[0033] The L band is input to the OMT (7-2-1) after the signal received from the transmitting device (7-1) is upconverted to a high frequency and then amplified to a 1MW high output using a klystron in the high-output amplifier (7-2). Since the receiving LNA may be damaged if a signal of +30 dBm to +60 dBm or higher is generated at the output terminal of the OMT, a high-speed transmission signal blocking switch (7-②) is additionally attached to protect the LNA, and a limiter (7-20) is attached to the front of the LNA to protect the LNA.

[0034] In addition, a high-speed transmission signal cutoff switch is attached to the monopulse coupler to minimize transmission interference, and in the case of transmission, the high-output OMT (7-2-1) and polarizer cooling device (7-3) include a cooling water or air circulation pump to cool the polarizer. The LNA and receiving system are also shielded in a separate space. Furthermore, since damage to the receiving device and control device may occur due to high-power electric field strength in the foundation building, a receiving control room facility is operated by being separated by an underground duct at a distance of several hundred meters or more. Optical transmission is possible.

[0035] The signal input to the OMT passes through the polarizer (7-3), is converted into circular polarization, and is radiated from the horn (7-6). In the case of reception, a monopulse coupler (7-4) is attached around the horn (7-6) feed line to produce a monopulse E-order A Z The signal is converted into a difference signal and input to a monopulse comparator (7-7), and compared with the output of the ∑ received signal splitter to output a tracking error signal, which is then input to a tracking receiver (7-8) after frequency conversion to operate the ACU (7-9), and the I / Q signal is separated from the PDU (7-10) to rotate the horizontal deceleration motor (7-11) and the vertical deceleration motor (7-12) so that the antenna tracks the object.

[0036] The transmission failure signal blocking switch (7-②) is formed by inserting a dielectric / ferrite, etc., into a two-way distribution waveguide (7-18) in a magic T-type input signal splitter (7-17), winding a magnetizing coil on the outside, and using a driving pulse generator (7-22) and an electronic high-speed switch (7-21). When a high-speed signal below the control high speed (macrosecond) is transmitted from the ACU, it is converted to 180° and converted to 0° upon reception, and the B waveguide is always converted to 0°. When a signal is output after combining the A and B waveguides into a magic T-type, the output of the A and B cancellation synthesizer (7-23) becomes 0 and is blocked when B is transmitted at 180°, and upon reception, the A and B in-phase input signals are output without loss and input to the LNA. In this way, damage to the LNA is prevented by using the electronic high-speed switch (7-21) during high-power transmission.

[0037] For example, if the L band gain is 52 dBi and the half-angle is approximately 0.4°, and the Ku band gain is approximately 70 dBi or higher, the half-angle is 0.04°. When the L band detects a target within 0.4° of an arbitrary elevation angle, the L band no longer tracks the elevation angle and only performs horizontal rotation. However, if an elevation angle position that cannot be detected occurs, the Ku band rotates horizontally in increments of 0.04° for every vertical elevation rotation within the 0.4° range. Finally, when the Ku band detects a target within the 0.4° range of the L band, both L and Ku bands detect the target, stop tracking the azimuth and elevation angles, and operate the ACU to perform automatic tracking using the Ku band monopulse. The inverse SAR radar image receiver processes the Ku band received signal using 2D FFT (Distance, Direction, Angle + Dopeer Spectrum Frequency Decomposition) to detect the image.

[0038] FIG. 8 illustrates an embodiment in which a target is detected and tracked using the Ku band. The antenna's ACU detects the target using the primary L band, but when the target is detected with a gain of approximately 52 dBi and an elevation angle of approximately 0.4° (8-1) (magnified beam width of 0.4°), it issues a command to stop the elevation angle drive. When the Ku band has a higher gain of approximately 70 dbi or more, a beam width of approximately 0.04° (8-2) (magnified beam width of 0.04°) is expected. Since there are positions that cannot be detected within the 0.4° range, the 0.4° range is continuously subdivided. After approximately 1 to 10 stages of rotational detection, when the target (8-3) is detected, both the L band and the Ku band are in a detection state. The Ku band is automatically tracked to enable image detection of the moving target. The distance direction and Doppler signals are each processed by multi-frequency division into 2D and FFT to output an image radar signal.

[0039] The above description is merely an example for understanding purposes and may be applied in various ways by referring to the content above. It may be applied as compensation for explanation within the scope of the patent claims and does not limit the scope of the patent.

[0040] For example, a 35m diameter Ku band 16.5GH Z RCS cross-sectional area of ​​0.1m² at peak power with a transmit power of 20kW to 30kW over 1000km 2 target's When calculating the detection estimate, antenna gain = and, here, A t is the RCS reflection area, λ is the wavelength, and P is the efficiency (0.5 to 0.7).

[0041] The round-trip spatial path loss for a distance of 1,000 km to the target is And, where R is the distance and λ is the wavelength.

[0042] Target RCS cross-sectional area, for example, 30cm x 30cm = (0.09m 2 ≒0.1m 2 The target's reflection gain is am.

[0043] If the loss (LF) of the receiving antenna feed system is approximately 2 dB, the signal reflected from the target results in a received signal level of approximately -105 dBm or higher at the ground antenna receiver, enabling stable image reception at the image tracking receiver. If possible, coherent integration allows even smaller objects (RCS: 0.01 m 2 Video reception is possible. In addition, when adding another frequency band during operation, the antenna device of the present invention can be used for multi-frequency band communication by installing an additional frequency selection reflector between the frequency selection reflector and the L / S band horn within the antenna base building that supports the antenna device and is installed at the bottom of the antenna device, and by installing another frequency band horn.

[0044] Although embodiments of the present invention have been described above with reference to the attached drawings, those skilled in the art will understand that the present invention can be implemented in other specific forms without changing the technical concept or essential features of the invention. Therefore, it is understood that the embodiments described above are merely illustrative for explaining the present invention and are not limiting. Explanation of the symbols

[0045] 1-1 Building the Antenna Foundation 1-2 Antenna 1-3 Radome 2-1 Main Reflector 2-2 Part Reflector 2-3 Deformation Compensator 2-4 Beam Waveguide M2 L , M3 L , M4, M5: Beam waveguide L-band mirror M2 K , M3 K : Ku Band Mirror 2-5 Frequency Selective Reflector 2-6 Ku Band Horn 2-7 L band horn 2-8 ball gear 2-13 Vertical Rotating Bearing 2-2-8, 2-2-9 guide wheels 2-2-10 support wheels 2-2-11 reduction motor 2-2-12 pinion gear 3-1 Main Reflector Rotating Body Base 3-2 Main reflector support 4-1 Part Reflector Deformation Guarantee Device 4-2 Part Reflector Actuator 6-1 Frequency Selective Reflector 6-2 Ku Hon 6-3 Signal Synthesizer 6-4 Laser Diode 6-5 Optical Diplexer 6-6 optical cable OPT1, OPT2: Optical Rotary Joint 6-7 Optical Diplexer Inside Antenna Foundation Building 6-8 Photodiode 6-9 Digital Splitter 6-10 Digital Signal Synthesizer 6-11 Laser Diode 6-12 Photodiode 6-13 digital splitter 7-1 L-band transmitter 7-2-1 OMT 7-② High-speed transmission signal blocking switch 7-20 limiter 7-3 Polarizer Cooling Device 7-4 Monopulse Coupler (L Band / Ku Band) Each separately 7-6 Horn (L , Ku) 7-7 Monopulse Comparator L / Ku IQ (E L , A Z ) Synthesis 7-8 Tracking Receiver 7-9 ACU (Automatic Antenna Control Unit) 7-10 PDU 7-11 Horizontal reduction motor (including angle sensor) 7-12 Vertical reduction motor (including angle sensor) 8-1 L band beam width 0.4° magnified view 8-2 Ku Band Beamwidth 0.04° Magnified View 8-3 Target Satellite

Claims

Claim 1 As an improved large reflector-type beam waveguide Cassegrain antenna, when the improved large reflector-type beam waveguide Cassegrain antenna is applied to an imaging radar, a difference in the radiation patterns of the reflection mirrors within the beam waveguide occurs when operating a single beam waveguide Cassegrain antenna with two frequency bands—one of the low frequencies in the L band or S band and one of the high frequency bands in the X band, Ku band, or Ka band. Therefore, when operating the low band, the low frequency band mirror and the high frequency band mirror are duplicated within the beam waveguide to equalize the efficiency of the two frequency bands. Here, if the loss in the high frequency band is acceptable, the high frequency band mirror may be omitted. It is an antenna device for an inverse SAR imaging radar in which the low frequency detects the target position and the high frequency band performs image detection after segmented tracking of moving targets. To compensate for gain attenuation caused by deformation of the main reflector due to its own weight as the reflector is large, a main reflector deformation compensation device including an actuator is attached behind the sub-reflector to enable automatic tracking by the ACU, and in the absence of a radome, the four of the main reflector An improved large reflector-type beam wave guide Cassegrain inverse SAR imaging radar antenna device equipped with four actuators automatically controlled by the ACU for each panel module. Claim 2 An improved large reflector-type beam waveguide Cassegrain inverse SAR imaging radar antenna device according to claim 1, wherein when the low frequency band of L / S and the high frequency band of the X / Ku / Ka band act as target detection antennas and the respective transmission or reception frequencies are the same, the device includes a high-speed transmission signal cutoff switch during transmission to prevent the transmitted signal from being input to the receiving terminal and being damaged during high-power transmission in the low frequency band L / S band. Claim 3 An improved large reflector-type beam waveguide Cassegrain inverse SAR imaging radar antenna device according to claim 1, which uses a horn system including an air-cooled or water-cooled cooling device to cool heat generated in the waveguide, OMT, and polarizer when operating at maximum transmit power because the RCS of a small target in space is small. Claim 4 An improved large reflector-type beam waveguide Cassegrain inverse SAR imaging radar antenna device according to claim 1, wherein, in cases where high frequency band transmission power cannot be increased, beam waveguide pass loss is large, or the distance to the target is far and the signal received reflected from the target is weak, a frequency selection reflector is attached below the sub-reflector and the main reflector, so that the signal in the low frequency band of L / S is transmitted through the beam waveguide to the antenna foundation building installed at the bottom of the antenna device and supporting the antenna device, and the signal in the high frequency band of X / Ku / Ka is transmitted through the frequency selection reflector below the hub of the main reflector, the transmission signal high-power amplifier and the transmission / reception LNA signal are converted into optical signals and transmitted via an optical cable, transmitted through an optical rotary joint to an optical space transmission device, and input into an optical diplexer inside the antenna foundation building. Claim 5 An improved large reflector-type beam waveguide Cassegrain inverse SAR imaging radar antenna device according to claim 1, wherein when a target is detected while rotating horizontally by one rotation for every wide elevation angle (0.4°) in the low frequency band and rotating vertically 100 times (elevation angle 40°) to 200 times (elevation angle 80°), the antenna rotation is temporarily stopped by controlling the horizontal rotation motor and the vertical rotation motor to receive the continuously moving target by controlling the horizontal left / right and vertical up / down rotation motors by the antenna automatic tracking device (ACU) to automatically track the target moving in the high frequency band using monopulse or program, and then performing 2D FFT (multi-decomposition spectrum of changes in directional distance and moving Doppler frequencies) signal processing to enable inverse SAR imaging radar. Claim 6 An improved large reflector-type beam waveguide Cassegrain inverse SAR imaging radar antenna device according to claim 1, which protects the receiving device LNA by attaching an ON / OFF switch that blocks the transmission signal between the circulator / OMT receiving terminal and the LNA only during pulse transmission to prevent damage to the receiving LNA when high power is supplied to the circulator / OMT receiving terminal when a high-power transmitter is connected to the antenna radiating horn, and passes the signal only when it is a receiving time and not a transmission time, and turns ON to pass the signal when the phase of the high-speed non-contact RF output signal (automatically controlled by a high-speed switching pulse for automatic switching between phases 0° and 180°) is 0°, and turns OFF to automatically block the signal when the output phase is 180°. Claim 7 An improved large reflector-type beam waveguide Cassegrain inverse SAR imaging radar antenna device according to claim 1, which can also be used for multi-frequency band communication by installing an additional frequency selection reflector between the frequency selection reflector and the L / S band horn within the antenna foundation building installed at the bottom of the antenna device and supporting the antenna device when adding another frequency band during operation.

Images