CN112327300B - GEO SAR satellite imaging method based on single reflection surface antenna - Google Patents
GEO SAR satellite imaging method based on single reflection surface antenna Download PDFInfo
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/88—Radar or analogous systems specially adapted for specific applications
- G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
- G01S13/90—Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques
- G01S13/9004—SAR image acquisition techniques
- G01S13/9005—SAR image acquisition techniques with optical processing of the SAR signals
Abstract
The invention discloses a GEO SAR satellite imaging method based on a single reflecting surface antenna, which belongs to the field of overall design of high-orbit microwave imaging satellites, and can be used for carrying out beam design on GEO SAR of a phased array feed source single transmitting surface antenna without gesture adjustment, and only covering all incident angle ranges by distance to electric scanning. In order to achieve the above purpose, the technical scheme of the invention comprises the following steps: s1, selecting an antenna caliber according to the minimum non-fuzzy area and the resolution requirement of the antenna, and selecting an antenna focal length according to the antenna caliber. S2, calculating a lower visual angle range according to the requirement of an incident angle to obtain a scanning range required to be reached by the antenna; the corresponding relation between SAR lower viewing angle and incident angle is thatWherein θ is the incident angle, α is the downward viewing angle, H is the track height, R e The earth radius. S3, setting an antenna feed source to form a scanning range required to be achieved by the antenna, and performing satellite imaging.
Description
Technical Field
The invention provides a geosynchronous orbit synthetic aperture radar (Geosynchronous Synthetic Aperture Radar, GEO SAR) satellite imaging method based on a single reflecting surface antenna, belongs to the field of overall design of high-orbit microwave imaging satellites, and particularly relates to a GEO SAR satellite beam design method based on a single reflecting surface antenna with range-wise scanning capability.
Background
In 1978, K.Tomiyasu cooperates with the national aviation and space agency (National Aeronautics and Space Administration, NASA for short) (item number NAS-2-9580) to first put forward the concept of GEO SAR and to perform initial parametric analysis on GEO SAR.
Compared with low-orbit synthetic aperture radar (Low Earth OrbitSynthetic Aperture Radar, LEO SAR for short), the GEO SAR has the advantages of large imaging range and short revisit time: for example, the revisit time for GEO SAR is maximally one day, while the revisit time for LEO SAR is typically 3-10 days or even longer. However, the synthetic aperture time, required transmission power, antenna size, etc. of GEO SAR are much larger than those of LEO SAR, which is difficult to achieve under the current technical conditions. Thus, during a subsequent period of time, research work on GEO SAR presents a stagnant state.
After the twenty-first century, with the rapid development of technology, research work on GEO SAR was again entered into the active phase. Under the support of NASA, the jet propulsion laboratory (Jet Propulsion Laboratory, JPL for short) in the United states has conducted a great deal of research on GEO SAR, and has achieved important research results in the key technology and application of the geosynchronous orbit system.
In 2001, JPL in the United states proposed a set of GEO SAR satellite solutions. GEO SAR, due to its high antenna area, will make the active phased array antenna very heavy with existing technology, which is a huge load for the transmitting platform, thus the antenna weight must be reduced. With the antenna area remaining unchanged, this can only be achieved by reducing the antenna mass density. The solution proposed by JPL in the united states is to use a thin film material as the antenna material and in 2003 a conceptual design of a 30m×30m L band thin film phased array large antenna was given.
The satellite design adopts a flat-plate phased array antenna with the caliber of 30m, and the phased array substrate is made of flexible foldable materials and can be folded during carrying and transmitting. The satellite adopts an expandable truss structure, 12 expandable rods are expanded into a plane after entering the orbit, and a stay bar is arranged in the middle and connected with the 12 cross bars by stay ropes. The whole structure is like a central rod penetrating a plane disc. In order to meet the extremely huge emission power of the load under any illumination condition, the satellite adopts a solar cell arrangement scheme with conical surfaces and conical bottom surfaces so as to ensure that the satellite can meet the power requirement of the load under any orbit inclination angle and any illumination condition.
At present, the GEO SAR of the phased array feed source single transmitting surface antenna needs to be subjected to beam design, so that a scheme for carrying out feed source design without attitude adjustment so as to cover all incident angle ranges is needed.
Disclosure of Invention
In view of the above, the invention provides a GEO SAR satellite imaging method based on a single reflection plane antenna, which can perform beam design for GEO SAR of a phased array feed source single transmission plane antenna without performing attitude adjustment, and cover all incident angle ranges only by distance to electric scanning.
In order to achieve the above purpose, the technical scheme of the invention comprises the following steps:
s1, selecting an antenna caliber according to the minimum non-fuzzy area and the resolution requirement of the antenna, and selecting an antenna focal length according to the antenna caliber.
S2, calculating a lower visual angle range according to the requirement of an incident angle to obtain a scanning range required to be reached by the antenna;
the corresponding relation between SAR lower viewing angle and incident angle is thatWherein θ is the incident angle, α isLower viewing angle, H is track height, R e The earth radius.
S3, setting an antenna feed source to form a scanning range required to be achieved by the antenna, and performing satellite imaging.
Further, in S1, according to the minimum non-ambiguous area and resolution requirements of the antenna, the antenna aperture is specifically selected as follows: the minimum non-ambiguous area of the antenna is A min ；
Wherein the constraint of the antenna pitching dimension is that
The requirements of the azimuth dimension of the antenna are that
I.e.
Wherein l r Is the elevation dimension of the antenna, lambda is the wavelength of SAR emitted electromagnetic wave, R f F for SAR distance to the long-distance end of the observation band r For the repetition frequency of SAR transmit pulse, θ f For observing the beam incidence angle of the far-end of the band, c is the speed of light, l a For the antenna azimuth dimension, v s Is the operating speed of the satellite.
Resolution ρ a ，ρ a And/l a The relation of (2) is that
Wherein v is B For the operating speed, v, of the antenna beam ground coverage area s For the running speed of the satellite, l is the aperture size of the antenna along the azimuth direction, k a For waveform stretching coefficients, k, associated with weighting functions in azimuthal compression imaging processing n M is the equivalent apparent number of SAR azimuth processing in order to process the waveform widening coefficient caused by circuit non-ideal.
Further, the orbit height of the GEO SAR satellite is 36000km, the earth radius is 6731km, the incident angle theta is in the range of [15 degrees, 55 degrees ] and the corresponding lower view angle range is [2.3 degrees, 7.4 degrees ]; the lower view angle range is the scanning range required to be achieved by the antenna.
Further, in S3, the antenna feed source is specifically set as follows: according to the lower view angle range of [2.3 degrees, 7.4 degrees ], the scanning range required to be achieved by the antenna is 5.1 degrees; the single beam has a width of 0.5 DEG, 1.5 DEG, and a 10% overlapping area between the two beams forms 4-12 beams, wherein four feed source units form one beam, and 12-28 feed source units are arranged.
The beneficial effects are that:
according to the minimum non-fuzzy area and resolution requirements of the antenna, the aperture of the antenna is selected, and the focal length of the antenna is selected according to the aperture of the antenna; calculating a lower visual angle range according to the requirement of the incident angle to obtain a scanning range required to be reached by the antenna; and designing an antenna feed source form according to the scanning range requirement. The invention provides a GEO SAR wave beam working method based on a single-reflecting-surface antenna, which is characterized in that the GEO SAR wave beam working method based on a phased array feed source single-transmitting-surface antenna does not need to carry out attitude adjustment and covers all incident angle ranges only by distance to electric scanning because the GEO SAR satellite has high orbit height and can meet the working requirements from an electric scanning angle of about 5 degrees.
Drawings
Fig. 1 is a flowchart of a GEO SAR satellite imaging method based on a single reflection antenna according to an embodiment of the present invention;
FIG. 2 is a schematic view of an antenna ranging to a transmit beam section;
fig. 3 is a schematic diagram of an antenna feed array arrangement;
fig. 4 is a schematic diagram of a GEO SAR satellite based on a single reflector antenna.
Detailed Description
The invention will now be described in detail by way of example with reference to the accompanying drawings.
The invention provides a GEO SAR satellite imaging method based on a single reflection surface antenna, which has a flow shown in a figure 1 and specifically comprises the following steps:
s1, selecting an antenna caliber according to the minimum non-fuzzy area and the resolution requirement of the antenna, and selecting an antenna focal length according to the antenna caliber.
The antenna area selection is mainly limited by factors such as the minimum non-fuzzy area of the antenna, resolution and the like.
First is the requirement of minimum non-ambiguous area of the antenna. The constraint of the antenna pitching dimension is thatThe requirement of the antenna azimuth dimension is +.>The minimum area of the antenna can be obtained by the restriction conditions of the antenna azimuth and the distance aperture length>Wherein l r Is the elevation dimension of the antenna, lambda is the wavelength of SAR emitted electromagnetic wave, R f For SAR distance to the long-range end of the observation band (skew), F r For the repetition frequency of SAR transmit pulse, θ f For observing the beam incidence angle of the far-end of the band, c is the speed of light, l a ，v s For the running speed of the satellite, A min Is the minimum area of the antenna.
Secondly, the resolution requirement is that the relation between the antenna caliber and SAR resolution is thatWherein v is B For the operating speed, v, of the antenna beam ground coverage area s For the running speed of the satellite, l is the aperture size of the antenna along the azimuth direction, k a For waveform stretching coefficients, k, associated with weighting functions in azimuthal compression imaging processing n In order to process the waveform widening coefficient caused by circuit non-ideal (amplitude and phase characteristic mismatch, nonlinearity and the like), M is the equivalent apparent number of SAR azimuth processing. ρ a Is the resolution.
The constraint of the above factors should be considered in the practical engineering implementation, and a certain margin is reserved at the same time, so that the area and the size of the SAR antenna are obtained.
S2, calculating a lower visual angle range according to the requirement of the incident angle to obtain a scanning range required to be reached by the antenna
The corresponding relation between SAR lower viewing angle and incident angle is thatWherein θ is the incident angle, α is the downward viewing angle, H is the track height, R e The earth radius. The orbit height of GEO SAR is 36000km, the earth radius is 6731km, the incidence angle of SAR is generally in the range of 15-55 DEG, and the corresponding lower viewing angle is 2.3-7.4 deg. The lower view angle range is the scanning range required to be achieved by the antenna.
S3, setting an antenna feed source to form a scanning range required to be achieved by the antenna, and performing satellite imaging.
According to the lower view angle range of 2.3-7.4 degrees, the electric scanning range required by the antenna feed source is 5.1 degrees. If the single beam has a width of 0.5 deg. -1.5 deg., 4-12 beams would need to be formed, considering a 10% overlap area between the two beams (as in fig. 2). If four feed elements form a beam, as shown in fig. 3, 12-28 feed elements are required to form the desired beam sweep range. A schematic diagram of a GEO SAR satellite based on a single reflector antenna is shown in fig. 4.
According to the GEO SAR wave beam design method based on the phased array feed source single-transmitting-face antenna, gesture adjustment is not needed, and all incident angle ranges can be covered only through distance scanning.
In summary, the above embodiments are only preferred embodiments of the present invention, and are not intended to limit the scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (3)
1. The GEO SAR satellite imaging method based on the single reflection surface antenna is characterized by comprising the following steps of:
s1, selecting an antenna caliber according to the minimum non-fuzzy area and the resolution requirement of an antenna, and selecting an antenna focal length according to the antenna caliber;
s2, calculating a lower visual angle range according to the requirement of an incident angle to obtain a scanning range required to be reached by the antenna;
the corresponding relation between SAR lower viewing angle and incident angle is thatWherein θ is the incident angle, α is the downward viewing angle, H is the track height, R e An earth radius;
s3, setting an antenna feed source to form a scanning range required to be achieved by the antenna, and performing satellite imaging;
in the step S1, according to the minimum non-fuzzy area and resolution requirements of the antenna, the antenna aperture is selected as follows: the minimum non-fuzzy area of the antenna is A min ；
Wherein the constraint of the antenna pitching dimension is that
The requirements of the azimuth dimension of the antenna are that
I.e.
Wherein l r Is the elevation dimension of the antenna, lambda is the wavelength of SAR emitted electromagnetic wave, R f F for SAR distance to the long-distance end of the observation band r For the repetition frequency of SAR transmit pulse, θ f For observing the beam incidence angle of the far-end of the band, c is the speed of light, l a For the antenna azimuth dimension, v s Is the operating speed of the satellite;
the resolution is ρ a ，ρ a And/l a The relation of (2) is that
Wherein v is B For the operating speed, v, of the antenna beam ground coverage area s For the running speed of the satellite, l is the aperture size of the antenna along the azimuth direction, k a For waveform stretching coefficients, k, associated with weighting functions in azimuthal compression imaging processing n M is the equivalent apparent number of SAR azimuth processing in order to process the waveform widening coefficient caused by circuit non-ideal.
2. The method of claim 1, wherein the GEO SAR satellite has an orbital altitude of 36000km, an earth radius of 6731km, an incident angle θ in the range of [15 °,55 ° ] and a corresponding downward viewing angle range of [2.3 °,7.4 ° ]; the lower view angle range is the scanning range required to be achieved by the antenna.
3. The method of claim 2, wherein in S3, the antenna feed is set specifically as follows: according to the lower view angle range of [2.3 degrees, 7.4 degrees ], the scanning range required to be achieved by the antenna is 5.1 degrees; the single beam has a width of 0.5 DEG, 1.5 DEG, and a 10% overlapping area between the two beams forms 4-12 beams, wherein four feed source units form one beam, and 12-28 feed source units are arranged.
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