A high-orbit LS dual-frequency full-polarization SAR system based on a ring reflector antenna

Abstract

The application discloses a high-orbit LS dual-frequency full-polarization SAR system based on a ring-shaped reflector antenna, which comprises a dual-frequency radar central control processor, an LS dual-frequency common-aperture full-polarization feed array, a ring-shaped antenna reflector, an L-band full-polarization receiver and an S-band full-polarization receiver. The application has L and S dual-frequency bands and full-polarization ground imaging capability, and dual-frequency band data can be used for ionosphere measurement and ground surface deformation monitoring, thereby improving the application efficiency and competitiveness of the high-orbit SAR system.

Description

Technical Field

[0001] This invention belongs to the field of spaceborne dual-frequency synthetic aperture radar (SAR) design technology, and particularly relates to a high-orbit LS dual-frequency fully polarized SAR system based on a ring reflector antenna. Background Technology

[0002] SAR systems enable two-dimensional high-resolution Earth observation. Spaceborne SAR systems offer a wide imaging range, unrestricted by national borders. High-orbit SAR satellites operate in geosynchronous orbit at an altitude of 36,000 km or in geostationary orbit with an inclination of 0°, achieving an imaging range of hundreds of kilometers and a revisit period of one day. This effectively meets the basic needs of various industries for high revisit rates, fast response times, and wide-swath imaging.

[0003] Electromagnetic waves of different frequencies have different penetrability. Low-frequency electromagnetic waves such as L and S have strong penetrability, with the equivalent scattering center close to the ground surface. They can even observe targets below the shallow ground surface. They are less affected by rainfall attenuation and are suitable for areas with dense forest cover and frequent cloud and rain. They are often used for monitoring surface changes, disaster prevention and mitigation, land cover classification, crop monitoring, and forest and vegetation observation.

[0004] Searching for terms like "Geosynchronous SAR," "GEOSAR," "SAR system based on Reflector Antenna," and "Dual-Frequency SAR System" in foreign language databases such as IEEE, Elsevier, and Springer, and for keywords like "high-orbit SAR system," "reflector antenna SAR system," and "dual-frequency SAR system" in Chinese databases such as Wanfang and CNKI, and reviewing relevant literature on the websites of institutions such as the German DLR, the European Space Agency, and the US JPL Laboratory, reveals that most current domestic and international spaceborne SAR systems operate on a single frequency band. The only dual-frequency SAR systems previously launched are the SIR-C / L-SAR and SRTM-C / L-SAR systems jointly developed by the US and Germany. Dual-frequency SAR systems under development include the NISAR system jointly developed by the US and India, and the Canadian UrtheCastSAR-XL. Domestic and international L-band reflector antenna SAR satellites include Germany's TanDEM-L and the US-India NISAR; S-band reflector antenna SAR satellites include China's HJ-1C, Russia's Kondor-E, and the US-India NISAR. Domestic and international research on high-orbit SAR primarily focuses on system feasibility studies, imaging mode design, azimuth resolution and ambiguity analysis, and currently, there is no publicly available information on the development of high-orbit SAR satellites. Although NISAR operates in the L+S bands and uses a ring reflector antenna system, it is a low-orbit SAR satellite with an orbital altitude of 747 km and an antenna aperture of only 12 m, which cannot meet the imaging requirements of high-orbit SAR. In addition, NISAR uses a one-dimensional antenna feed array in the elevation direction, with the L-band and S-band antenna feed arrays installed independently, lacking two-dimensional antenna beam scanning capability. Summary of the Invention

[0005] The technical problem solved by this invention is to overcome the shortcomings of the prior art and provide a high-orbit LS dual-frequency fully polarized SAR system based on a ring reflector antenna, which has the capability of L and S dual-band and fully polarized ground imaging. The dual-band data can be used for ionospheric measurement and surface deformation monitoring, thereby improving the application efficiency and competitiveness of the high-orbit SAR system.

[0006] The objective of this invention is achieved through the following technical solution: a high-orbit LS dual-frequency fully polarized SAR system based on a ring reflector antenna, comprising: a dual-frequency radar central control processor, an LS dual-frequency common-aperture fully polarized feed array, a ring antenna reflector, an L-band fully polarized receiver, and an S-band fully polarized receiver; wherein, the dual-frequency radar central control processor: outputs L-band radio frequency pulse signals and S-band radio frequency pulse signals to the LS dual-frequency common-aperture fully polarized feed array; and receives L-band fully polarized echoes and S-band fully polarized echoes; the LS dual-frequency common-aperture fully polarized feed array: receives L-band radio frequency pulse signals and S-band radio frequency pulse signals, amplifies the L-band radio frequency pulse signals to generate amplified L-band radio frequency pulse signals, amplifies the S-band radio frequency pulse signals to generate amplified S-band radio frequency pulse signals, and transmits the amplified L-band radio frequency pulse signals and amplified S-band radio frequency pulse signals to the ring antenna reflector; The system receives L-band and S-band ground-scattered echoes, transmits the L-band ground-scattered echo to the L-band fully polarized receiver, and transmits the S-band ground-scattered echo to the S-band fully polarized receiver; the loop antenna reflector reflects the amplified L-band and S-band radio frequency pulse signals; receives L-band and S-band ground-scattered echoes, and transmits the L-band and S-band ground-scattered echoes to the receiver. The system comprises an LS dual-frequency common-aperture fully polarized feed array; an L-band fully polarized receiver that receives L-band ground-scattered echoes, processes the L-band ground-scattered echoes to obtain L-band fully polarized echoes, and transmits the L-band fully polarized echoes to the dual-frequency radar central control processor; and an S-band fully polarized receiver that receives S-band ground-scattered echoes, processes the S-band ground-scattered echoes to obtain S-band fully polarized echoes, and transmits the S-band fully polarized echoes to the dual-frequency radar central control processor.

[0007] In the aforementioned high-orbit LS dual-frequency fully polarized SAR system based on a ring reflector antenna, the LS dual-frequency common-aperture fully polarized feed array includes multiple LS dual-frequency common-aperture fully polarized feed elements; wherein, each LS dual-frequency common-aperture fully polarized feed element includes 4 S-band radiating elements and 1 L-band radiating element; wherein, the 4 S-band radiating elements are disposed on the vibrator of the L-band radiating element.

[0008] In the aforementioned high-orbit LS dual-frequency fully polarized SAR system based on a ring reflector antenna, the center frequency of the L-band radio frequency pulse signal is 1.25 GHz, and the center frequency of the S-band radio frequency pulse signal is 3.2 GHz.

[0009] In the aforementioned high-orbit LS dual-frequency fully polarized SAR system based on a ring reflector antenna, the electrical aperture of the ring antenna reflector is 30m to 40m, the focal length is 21m to 27m, and the feed array is offset by 24.5m.

[0010] In the aforementioned high-orbit LS dual-frequency fully polarized SAR system based on a ring reflector antenna, the area of ​​the LS dual-frequency common-aperture fully polarized feed array is 7.29m². 2 ~12.96m 2 .

[0011] In the aforementioned high-orbit LS dual-frequency fully polarized SAR system based on a ring reflector antenna, the ring antenna reflector includes a mesh deployable reflector and a circular ring truss; wherein, the mesh deployable reflector is disposed on the circular ring truss; the mesh deployable reflector reflects amplified L-band radio frequency pulse signals and amplified S-band radio frequency pulse signals; receives L-band ground scattered echoes and S-band ground scattered echoes, and transmits the L-band ground scattered echoes and S-band ground scattered echoes to the LS dual-frequency common-aperture fully polarized feed array.

[0012] In the aforementioned high-orbit LS dual-frequency fully polarized SAR system based on a ring reflector antenna, the L-band radio frequency pulse signal is a linear frequency modulated signal, and the S-band radio frequency pulse signal is a linear frequency modulated signal.

[0013] In the aforementioned high-orbit LS dual-frequency fully polarized SAR system based on a ring reflector antenna, the widths of the L-band radio frequency pulse signal and the S-band radio frequency pulse signal are both 400μs to 750μs.

[0014] In the aforementioned high-orbit LS dual-frequency fully polarized SAR system based on a ring reflector antenna, the bandwidths of the L-band radio frequency pulse signal and the S-band radio frequency pulse signal are both 20MHz to 120MHz.

[0015] In the aforementioned high-orbit LS dual-frequency fully polarized SAR system based on a ring reflector antenna, the PRF of both the L-band radio frequency pulse signal and the S-band radio frequency pulse signal is 100Hz to 400Hz.

[0016] In the aforementioned high-orbit LS dual-frequency fully polarized SAR system based on a ring reflector antenna, the electrical aperture of the ring antenna reflector is obtained by the following formula:

[0017]

[0018] Where D is the electrical aperture of the loop antenna reflector, and θ b K is the beamwidth requirement, K is the gain reduction at the beam edge relative to the center, λ is the operating wavelength, and k1 is the scaling factor.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] (1) Compared with phased array antennas, when the present invention uses a ring reflector antenna to realize dual-frequency multi-polarization SAR imaging, the dual-frequency radar can share the antenna reflector and support arm. Only the antenna feed sources of different frequency bands need to be added to radiate dual-frequency radar beams. It is easy to achieve lightweight design and the dual-frequency implementation cost is low.

[0021] (2) Compared with solid-surface dual-reflector antennas, the ring reflector antenna of the present invention has a higher storage ratio and can easily achieve the folding and folding of ultra-large aperture antennas. It is suitable for scenarios with long operating distance and large antenna aperture requirements. Currently, the maximum aperture of this type of antenna can exceed 30 meters and the antenna area can exceed 700 square meters.

[0022] (3) This invention realizes high-orbit L+S dual-band imaging, estimates ionospheric propagation error through dual-frequency joint observation, obtains ground object information with different penetration and scattering characteristics, improves the accuracy of deformation measurement, biomass measurement and ground object classification, and expands the application scope of satellites;

[0023] (4) This invention realizes high-orbit fully polarimetric SAR imaging and extracts target scattering information of the observation scene by utilizing the differences in polarization characteristics of SAR images between multiple polarization channels. Fully polarimetric SAR data contains more complete target physical characteristics and structural information, such as surface roughness, distribution symmetry, dielectric properties, humidity, etc. The scattering mechanism of the target can be obtained through polarization decomposition and other means, and the target can be accurately classified and identified. Attached Figure Description

[0024] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0025] Figure 1 This is a structural block diagram of a high-orbit LS dual-frequency fully polarized SAR system based on a ring reflector antenna provided in an embodiment of the present invention;

[0026] Figure 2 This is a schematic diagram of the LS dual-frequency common-aperture fully polarized radiation unit provided in an embodiment of the present invention;

[0027] Figure 3 This is a schematic diagram of the transmission and reception of pulse signals by a high-orbit LS dual-frequency fully polarized SAR system based on a ring reflector antenna provided in an embodiment of the present invention;

[0028] Figure 4This is a schematic diagram of the system sensitivity of the L-band SAR system for 5m / 300km dual-polarization imaging provided in an embodiment of the present invention;

[0029] Figure 5 This is a schematic diagram of the range ambiguity of 5m / 300km dual-polarization imaging of the L-band SAR system provided in an embodiment of the present invention;

[0030] Figure 6 This is a schematic diagram of the azimuth ambiguity of 5m / 300km dual-polarization imaging of the L-band SAR system provided in an embodiment of the present invention;

[0031] Figure 7 This is a schematic diagram of the system sensitivity of the L-band SAR system for 20m / 200km fully polarized imaging provided in an embodiment of the present invention;

[0032] Figure 8 This is a schematic diagram of the system sensitivity of the S-band SAR system for 5m / 120km dual-polarization imaging provided in an embodiment of the present invention;

[0033] Figure 9 This is a schematic diagram of the range ambiguity of 5m / 120km dual-polarization imaging of the S-band SAR system provided in an embodiment of the present invention;

[0034] Figure 10 This is a schematic diagram of the azimuth ambiguity of 5m / 120km dual-polarization imaging of the S-band SAR system provided in an embodiment of the present invention;

[0035] Figure 11 This is a schematic diagram of the system sensitivity of the S-band SAR system for 20m / 120km fully polarized imaging provided in an embodiment of the present invention. Detailed Implementation

[0036] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0037] High-orbit SAR satellites refer to satellites with an orbital altitude higher than 30,000 kilometers, equipped with L-band and S-band synthetic aperture radar systems. This embodiment mainly considers the selection of radar frequency bands and antenna systems for high-orbit dual-frequency fully polarimetric SAR, determines the system composition and signal transmission / reception workflow, designs the parameters of the dual-reflector antenna and the transmitted signal parameters, and designs the imaging mode and imaging performance of the high-orbit dual-frequency fully polarimetric SAR system.

[0038] Figure 1 Block diagram of a high-orbit LS dual-frequency fully polarized SAR system based on a ring reflector antenna. (See diagram for reference.) Figure 1 As shown, the system includes a dual-band radar central control processor, an LS dual-band common-aperture fully polarized feed array, a ring antenna reflector, an L-band fully polarized receiver, and an S-band fully polarized receiver; among which,

[0039] Dual-band radar central control processor: outputs L-band and S-band radio frequency pulse signals to the LS dual-band common-aperture fully polarized feed array; receives L-band and S-band fully polarized echoes;

[0040] The LS dual-band common-aperture fully polarized feed array receives L-band and S-band radio frequency pulse signals, amplifies the L-band radio frequency pulse signal to generate an amplified L-band radio frequency pulse signal, amplifies the S-band radio frequency pulse signal to generate an amplified S-band radio frequency pulse signal, and transmits the amplified L-band and S-band radio frequency pulse signals to the loop antenna reflector; it also receives L-band and S-band ground scattered echoes, transmits the L-band ground scattered echo to the L-band fully polarized receiver, and transmits the S-band ground scattered echo to the S-band fully polarized receiver.

[0041] The loop antenna reflector reflects the amplified L-band RF pulse signal and the amplified S-band RF pulse signal; it receives the L-band ground scattered echo and the S-band ground scattered echo, and transmits the L-band ground scattered echo and the S-band ground scattered echo to the LS dual-frequency common aperture fully polarized feed array.

[0042] L-band fully polarized receiver: Receives L-band ground scattered echoes, processes the L-band ground scattered echoes to obtain L-band fully polarized echoes, and transmits the L-band fully polarized echoes to the dual-frequency radar central control processor.

[0043] S-band fully polarized receiver: Receives S-band ground scattered echoes, processes the S-band ground scattered echoes to obtain S-band fully polarized echoes, and transmits the S-band fully polarized echoes to the dual-frequency radar central control processor.

[0044] The transmitted signal of the LS dual-frequency common-aperture fully polarized feed array is:

[0045]

[0046] Among them, s feed This indicates the transmitted signal from the LS dual-frequency common-aperture fully polarized feed array. L,p (τ L ,PRF L ,w L () represents the amplified L-band RF pulse signal, () represents the amplified S-band RF pulse signal, and case 1 indicates that only S-band RF pulse signal is transmitted. L,p (τ L ,PRF L ,w L Case 2 indicates that only s is emitted. S,p (τ S ,PRF S ,w S Case 3 indicates simultaneous launch of s L,p (τ L ,PRF L ,w L ) and s S,p (τ S ,PRF S ,w S ). τ L PRF L w L These represent the pulse width, pulse repetition frequency, and time window position of the amplified L-band radio frequency pulse signal, respectively. τ S PRF S w S These represent the pulse width, pulse repetition frequency, and time window position of the amplified S-band radio frequency pulse signal, respectively. The subscript L indicates the L-band, the subscript S indicates the S-band, and p indicates the transmit polarization mode of the LS dual-band common-aperture fully polarized feed array.

[0047] The advantages of the LS dual-band common-aperture fully polarized feed array transmission formula are: the polarization mode of the transmitted signal is selectable and can be varied between adjacent pulses, thus enabling the system to transmit fully polarized signals. When simultaneously transmitting amplified L-band RF pulse signals and amplified S-band RF pulse signals, the pulse width, pulse repetition frequency, and time window position of the two signals are the same, avoiding mutual interference between the two frequency bands.

[0048] The dual-frequency radar central control processor receives the fully polarized echo signal as follows:

[0049] s cu =Q[s L,qp ]+Q[s S,qp ];

[0050] Among them, scu This indicates that the dual-frequency radar central control processor receives the fully polarized echo signal, s L,qp This represents the L-band fully polarized echo signal, s S,qp The signal represents the S-band fully polarized echo signal. The subscript L indicates the L-band, the subscript S indicates the S-band, p indicates the transmit polarization of the LS dual-frequency common-aperture fully polarized feed array, q indicates the receive polarization of the LS dual-frequency common-aperture fully polarized feed array, and Q[·] indicates quantization acquisition and compression processing.

[0051] The advantages of the formula for receiving fully polarized echo signals by the central control processor of dual-frequency radar: The high-orbit LS dual-frequency fully polarized SAR system shares the radar central control and processor, which reduces the complexity of the dual-frequency radar system, facilitates the small and lightweight integrated design of the central electronic equipment, improves the synchronization accuracy of dual-frequency signal reception, and facilitates the realization of dual-frequency collaborative imaging mode.

[0052] The relationship between the number of oscillators in the L-band radiating element and the number of oscillators in the S-band radiating element of an LS dual-band common-aperture fully polarized feed array: N L =4N S ;

[0053] Where, N L N represents the number of oscillators in the L-band radiating element. S This indicates the number of oscillators in the S-band radiating element.

[0054] The advantage of the relationship formula is that the relationship between the number of radiating elements in the L-band and the number of radiating elements in the S-band takes into account the spacing requirements of the radiating elements in both the L-band and S-band, realizes the common aperture design of the L-band fully polarized feed array and the S-band fully polarized feed array, and avoids the antenna gain loss caused by the defocusing of the fully polarized feed array.

[0055] The electrical aperture of a loop antenna reflector is determined by the beamwidth and operating frequency:

[0056]

[0057] Where D is the electrical aperture of the loop antenna reflector, and θ b K is the beamwidth requirement, K is the gain reduction at the beam edge relative to the center, λ is the operating wavelength, and k1 is the scaling factor.

[0058] The advantage of the electrical aperture formula for a loop antenna reflector is that the design of the loop antenna reflector aperture takes into account factors such as antenna beamwidth, center frequency of the dual-frequency fully polarized SAR system, and beam gain roll-off rate. The selected loop antenna reflector aperture can meet the swath width and signal-to-noise ratio requirements of high-orbit LS dual-frequency fully polarized SAR imaging.

[0059] The parameters of a loop reflector antenna should be selected to avoid reflected waves entering the feed. The parameters of the loop reflector antenna should satisfy the following constraints:

[0060]

[0061] Where H is the offset distance, and D array Here, F is the feed array size, P is the feed array push-forward distance, and θ is the feed array size. feed Let θ be the angle between the feed array coordinate system and the antenna coordinate system. scan denoted as , k2 as , sin(·) as sine function, cos(·) as cosine function, and tan(·) as tangent function.

[0062] The advantages of the constraint relationship formula are: the various parameters of the ring reflector antenna are mutually constrained. Based on the requirements of the input radar beamwidth and scanning angle, and considering the envelope constraints of the satellite platform, the focal length, offset distance, feed array size, and feed array push-forward distance of the ring reflector antenna are optimized through analysis to achieve the optimal gain of the ring reflector antenna. The gain loss and sidelobe rise after antenna beam scanning meet the imaging performance requirements. The antenna deployment arm and antenna deployment design engineering can be realized. The size of the antenna after folding meets the envelope constraints of the satellite platform.

[0063] The dual-frequency radar central control processor simultaneously outputs L-band and S-band radio frequency pulse signals, and simultaneously receives L-band and S-band fully polarized echoes, performing down-conversion and quantization acquisition processing; the LS dual-frequency common-aperture fully polarized feed array and the ring antenna reflector constitute an offset-fed parabolic ring reflector antenna; the dual-frequency radar central control processor, the LS dual-frequency common-aperture fully polarized feed array, the ring antenna reflector, and the L-band fully polarized receiver constitute an L-band SAR; the dual-frequency radar central control processor, the LS dual-frequency common-aperture fully polarized feed array, the ring antenna reflector, and the S-band fully polarized receiver constitute an S-band SAR.

[0064] The LS dual-frequency common-aperture fully polarized feed array includes multiple LS dual-frequency common-aperture fully polarized feed elements; wherein each LS dual-frequency common-aperture fully polarized feed element includes 4 S-band radiating elements and 1 L-band radiating element; wherein the 4 S-band radiating elements are arranged on the oscillator of the L-band radiating element.

[0065] L-band SAR and S-band SAR can operate simultaneously or independently in a time-division manner. When L-band SAR and S-band SAR operate simultaneously, the L-band radio frequency pulse signal and the S-band radio frequency pulse signal have the same pulse width, signal bandwidth and transmit pulse repetition frequency (PRF).

[0066] During signal transmission, the LS dual-band common-aperture fully polarized feed array amplifies the input L-band and S-band RF pulse signals, generating amplified L-band and S-band RF pulse signals, forming the L-band and S-band feed array transmit beams, respectively. During signal reception, the LS dual-band common-aperture fully polarized feed array forms a fully polarized receive beam, receiving the L-band and S-band ground-scattered echoes reflected by the loop antenna reflector, and inputting these echoes to the L-band and S-band fully polarized receivers, respectively.

[0067] The LS dual-band co-aperture fully polarized feed array consists of LS dual-band co-aperture fully polarized radiating elements. The LS dual-band co-aperture fully polarized feed array adopts a stacked configuration of L-band and S-band radiating elements with a common aperture. Four S-band radiating elements are placed on the oscillator of one L-band radiating element, such as... Figure 2 As shown.

[0068] The center frequency of the L-band radio frequency pulse signal is 1.25 GHz, and the center frequency of the S-band radio frequency pulse signal is 3.2 GHz. The polarization of the transmitting beam of the LS dual-band common aperture fully polarized feed array is H or V, and the polarization of the receiving beam is H or / and V.

[0069] The loop antenna reflector includes a mesh-like deployable reflective surface and a circular annular truss. The mesh-like deployable reflective surface is disposed on the circular annular truss. When transmitting signals, the mesh-like deployable reflective surface reflects amplified L-band and S-band radio frequency pulse signals, and when receiving signals, it reflects L-band and S-band ground scattered echoes. The circular annular truss supports the mesh-like deployable reflective surface after unfolding, ensuring that the root mean square error of the mesh-like deployable reflective surface is better than 5 mm.

[0070] Both L-band and S-band radio frequency pulse signals are linear frequency modulated signals; the width of both L-band and S-band radio frequency pulse signals is 400μs to 750μs, and the bandwidth of both L-band and S-band radio frequency pulse signals is 20MHz to 120MHz.

[0071] L-band SAR and S-band SAR can operate simultaneously or independently in a time-division manner. When L-band SAR and S-band SAR operate simultaneously, the L-band RF pulse signal and the S-band RF pulse signal have the same pulse width, signal bandwidth, and transmit PRF. The PRF of both L-band RF pulse signals is 100Hz to 400Hz.

[0072] L-band SAR and S-band SAR can operate in dual-polarization imaging mode or full-polarization imaging mode. In dual-polarization imaging mode, the radar transmits H-polarized or linear frequency modulated (LFM) pulse signals and simultaneously receives H and V-polarized ground-scattered echo signals. In full-polarization imaging mode, the radar transmits H or V-polarized LFM pulse signals in alternating pulses and simultaneously receives H and V-polarized ground-scattered echo signals, such as... Figure 3 As shown.

[0073] Example

[0074] This embodiment designs a high-orbit LS dual-frequency fully polarized SAR system based on a ring reflector antenna. The orbital altitude of the system is determined to be 35,786 kilometers, the orbital inclination angle is 18°, and the orbital eccentricity is 0.

[0075] Calculate the system sensitivity (NESZ), image ground distance resolution, image azimuth ambiguity (AASR), and image range ambiguity (RASR) of the SAR system based on the radar equations and radar system parameters.

[0076] The embodiment of the high-orbit dual-frequency SAR system based on a ring reflector antenna consists of L-band SAR and S-band SAR. The antenna is a ring reflector antenna based on a dual-frequency fully polarized phased array feed array. The antenna has an electrical aperture of 36m, a mechanical aperture of 42m, a focal length of 21m, and a feed array offset of 24.5m. The L-band dual-frequency common-aperture fully polarized feed array has an area of ​​2.56m × 3.84m and consists of 384 L-band radiating elements and 1536 S-band radiating elements. The L-band radiating elements are arranged in a 24×16 array, and the S-band radiating elements are arranged in a 48×32 array.

[0077] The antenna forms two beams: one L-band beam and one S-band beam. The L-band radar beam has an azimuth width of 0.47° and an elevation width of 0.6°, pointing towards the antenna normal in both the azimuth and elevation directions. The S-band radar beam has an azimuth width of 0.19° and an elevation width of 0.24°, also pointing towards the antenna normal in both the azimuth and elevation directions.

[0078] The L-band radar operates in either dual-polarization or full-polarization imaging mode. Its peak transmit power is 48,000 W. The radar transmits H- or V-polarized linear frequency modulated (RF) pulse signals and simultaneously receives H- and V-polarized ground-scattered echo signals. The transmit pulse width is 500 μs, the RF selection range is 100 Hz to 400 Hz, and the transmit RF signal bandwidth is 20 MHz to 120 MHz. In dual-polarization imaging mode, the L-band radar has an imaging resolution of 5 m and an imaging swath width of 300 km, with an operating incident angle range of 15° to 60°. In full-polarization imaging mode, the imaging resolution and imaging swath width are 20 m and 200 km, respectively, with an operating incident angle range of 15° to 45°.

[0079] The S-band radar operates in either dual-polarization or full-polarization imaging mode. Its peak transmit power is 46080W. The radar transmits H- or V-polarized linear frequency modulated (RF) pulse signals and simultaneously receives H- and V-polarized ground-scattered echo signals. The transmit pulse width is 500 μs, the RF selection range is 100 Hz to 400 Hz, and the transmit RF signal bandwidth is 20 MHz to 120 MHz. In dual-polarization imaging mode, the S-band radar has an imaging resolution of 5 m and an imaging swath width of 120 km, with an operating incident angle range of 15° to 60°. In full-polarization imaging mode, the imaging resolution and imaging swath width are 20 m and 120 km, respectively, with an operating incident angle range of 15° to 60°.

[0080] Analysis and calculation results show that the imaging system sensitivity of the high-orbit LS dual-frequency fully polarized SAR system based on a ring reflector antenna designed in this invention is better than -22dB ( Figure 4 , Figure 7 , Figure 8 , Figure 11 As shown), the image orientation blur is better than -20dB. Figure 6 and Figure 10 As shown), the distance ambiguity is better than -21dB. Figure 5 and Figure 9 (As shown).

[0081] Compared to phased array antennas, using a ring reflector antenna for dual-frequency multi-polarization SAR imaging allows the dual-frequency radar to share the antenna reflector and support arm. Only the antenna feeds for different frequency bands need to be added to radiate dual-frequency radar beams, facilitating lightweight design and reducing the cost of dual-frequency implementation. Compared to solid-surface dual reflector antennas, ring reflector antennas have a higher compactness, making it easier to fold and retract ultra-large aperture antennas. They are suitable for scenarios with long operating distances and large antenna aperture requirements; currently, the largest aperture of this type of antenna exceeds 30 meters, and the antenna area exceeds 700 square meters. This invention achieves high-orbit L+S dual-band imaging, using joint dual-frequency observation to estimate ionospheric propagation errors, acquiring ground feature information with different penetration and scattering characteristics, improving the accuracy of deformation measurement, biomass measurement, and ground feature classification, and expanding the application range of satellites. This invention also achieves high-orbit L-band and S-band fully polarimetric SAR imaging, utilizing the differences in polarization characteristics between multiple polarization channels of SAR images to extract target scattering information of the observed scene. Fully polarimetric SAR data contains more complete information on the target's physical characteristics and structure, such as surface roughness, distribution symmetry, dielectric properties, and humidity. By means of polarization decomposition, the scattering mechanism of the target can be obtained, enabling accurate classification and identification of the target.

[0082] This invention realizes a high-orbit LS dual-frequency fully polarized SAR imaging system based on a ring reflector antenna system. The system employs a ring reflector antenna based on an LS dual-frequency common-aperture fully polarized feed array, with an electrical aperture of 30m–40m for the ring antenna reflector. In the LS dual-frequency common-aperture fully polarized feed array, the L-band and S-band radiating elements are stacked in a common-aperture configuration, and the feed array area is 7.29m². 2 ~12.96m 2 The high-orbit LS dual-frequency fully polarimetric SAR system transmits linear frequency modulated pulse signals with a pulse width of 400µs–750µs, a transmission signal bandwidth of 20MHz–120MHz, and a transmission pulse repetition frequency of 100Hz–400Hz. When the L-band and S-band SAR systems operate simultaneously, the dual-band radars have the same transmission pulse width, signal bandwidth, and pulse repetition frequency. The high-orbit LS dual-frequency fully polarimetric SAR system simultaneously achieves high-orbit L and S dual-frequency fully polarimetric Earth observation imaging, with an imaging observation range of several hundred kilometers, a maximum resolution of 5m, and a revisit period of less than 4 hours, significantly improving the Earth observation capabilities of spaceborne SAR systems.

[0083] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

Claims

1. A high-orbit LS dual-frequency fully polarized SAR system based on a ring reflector antenna, characterized in that... include: The system includes a dual-frequency radar central control processor, an LS dual-frequency common-aperture fully polarized feed array, a ring antenna reflector, an L-band fully polarized receiver, and an S-band fully polarized receiver; among these components... The dual-frequency radar central control processor outputs L-band and S-band radio frequency pulse signals to the LS dual-frequency common-aperture fully polarized feed array; and receives L-band and S-band fully polarized echoes. The LS dual-band common-aperture fully polarized feed array: receives L-band and S-band radio frequency pulse signals, amplifies the L-band radio frequency pulse signal to generate an amplified L-band radio frequency pulse signal, amplifies the S-band radio frequency pulse signal to generate an amplified S-band radio frequency pulse signal, and transmits the amplified L-band and S-band radio frequency pulse signals to the loop antenna reflector; it also receives L-band and S-band ground scattered echoes, transmits the L-band ground scattered echo to the L-band fully polarized receiver, and transmits the S-band ground scattered echo to the S-band fully polarized receiver; The loop antenna reflector reflects the amplified L-band radio frequency pulse signal and the amplified S-band radio frequency pulse signal; receives the L-band ground scattered echo and the S-band ground scattered echo, and transmits the L-band ground scattered echo and the S-band ground scattered echo to the LS dual-frequency common aperture fully polarized feed array. The L-band fully polarized receiver receives L-band ground scattered echoes, processes the L-band ground scattered echoes to obtain L-band fully polarized echoes, and transmits the L-band fully polarized echoes to the dual-frequency radar central control processor. The S-band fully polarized receiver receives S-band ground scattered echoes, processes the S-band ground scattered echoes to obtain S-band fully polarized echoes, and transmits the S-band fully polarized echoes to the dual-frequency radar central control processor. The LS dual-frequency common-aperture fully polarized feed array includes multiple LS dual-frequency common-aperture fully polarized feed elements; wherein each LS dual-frequency common-aperture fully polarized feed element includes 4 S-band radiating elements and 1 L-band radiating element; wherein the 4 S-band radiating elements are disposed on the oscillator of the L-band radiating element.

2. The high-orbit LS dual-frequency fully polarized SAR system based on a ring reflector antenna according to claim 1, characterized in that: The center frequency of the L-band radio frequency pulse signal is 1.25 GHz, and the center frequency of the S-band radio frequency pulse signal is 3.2 GHz.

3. The high-orbit LS dual-frequency fully polarized SAR system based on a ring reflector antenna according to claim 1, characterized in that: The electrical aperture of the ring antenna reflector is 30m~40m, the focal length is 21m~27m, and the feed array is offset at 24.5m.

4. The high-orbit LS dual-frequency fully polarized SAR system based on a ring reflector antenna according to claim 1, characterized in that: The area of ​​the LS dual-frequency common-aperture fully polarized feed array is 7.29m². 2 ~12.96m 2 .

5. The high-orbit LS dual-frequency fully polarized SAR system based on a ring reflector antenna according to claim 1, characterized in that: The ring antenna reflector includes a mesh-like deployable reflective surface and a perfectly circular ring truss; wherein... The unfoldable mesh reflective surface is disposed on the circular annular truss; The mesh-like deployable reflective surface reflects amplified L-band radio frequency pulse signals and amplified S-band radio frequency pulse signals; receives L-band ground scattered echoes and S-band ground scattered echoes, and transmits the L-band ground scattered echoes and S-band ground scattered echoes to the LS dual-frequency common-aperture fully polarized feed array.

6. The high-orbit LS dual-frequency fully polarized SAR system based on a ring reflector antenna according to claim 1, characterized in that: The L-band radio frequency pulse signal is a linear frequency modulated signal, and the S-band radio frequency pulse signal is a linear frequency modulated signal.

7. The high-orbit LS dual-frequency fully polarized SAR system based on a ring reflector antenna according to claim 1, characterized in that: The widths of the L-band radio frequency pulse signal and the S-band radio frequency pulse signal are both ~ .

8. The high-orbit LS dual-frequency fully polarized SAR system based on a ring reflector antenna according to claim 1, characterized in that: The bandwidth of both the L-band radio frequency pulse signal and the S-band radio frequency pulse signal is 20MHz~120MHz; The PRF of both the L-band radio frequency pulse signal and the S-band radio frequency pulse signal is 100Hz~400Hz.

9. The high-orbit LS dual-frequency fully polarized SAR system based on a ring reflector antenna according to claim 1, characterized in that: The electrical aperture of the loop antenna reflector is obtained by the following formula: ； in, The electrical aperture of the loop antenna reflector. It's a beamwidth requirement. It is the gain reduction value at the beam edge relative to the center. It is the operating wavelength. It is the proportionality coefficient.

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