A design method of high resolution wide swath SAR based on reflector mechanism

Abstract

The application relates to a high-resolution wide-width SAR design method based on a reflector system. Through distance multi-feed wide-beam coverage, simultaneous multi-beam transmission and reception high-gain imaging technology and high-isolation feed distribution technology, the SAR can realize sub-meter resolution, 50-kilometer wide-width high-resolution wide-width imaging, and meets the future reflector system high-resolution wide-width SAR requirement.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of space microwave remote sensing, in particular to a high-resolution wide swath SAR design method based on reflector system. BACKGROUND

[0002] Synthetic Aperture Radar (SAR) is a kind of microwave remote sensing radar that uses range pulse compression and azimuth Doppler effect for imaging, which can obtain images by transmitting pulse signals and processing the received echoes. Unlike passive remote sensing devices such as optics and hyperspectrum, SAR is not affected by bad weather such as clouds, rain and fog, and can realize all-weather and all-day imaging. At the same time, since the electromagnetic frequency band worked by SAR has certain penetration ability, it can find targets hidden under vegetation or ground, and has been widely used in topographic mapping, geological exploration, marine application, forest monitoring, disaster assessment, military reconnaissance and scientific research. High-resolution wide-swath SAR, which can realize high resolution and wide swath at the same time, is an important direction of future SAR system development. However, due to the limitation of the minimum antenna area, the SAR designed in the prior art has a contradiction in realizing high resolution and wide swath at the same time. SUMMARY

[0003] In order to overcome at least one deficiency in the prior art, the present application provides a high-resolution wide-swath SAR design method based on reflector system.

[0004] In a first aspect, a high-resolution wide-swath SAR design method based on reflector system is provided, comprising:

[0005] The total beam width is calculated according to the observation swath, and the beam width of each beam is calculated according to the range antenna aperture; the number of range beams is determined according to the total beam width and the beam width of each beam.

[0006] A plurality of feed sources are designed, the plurality of feed sources generate a plurality of beams, and the plurality of beams are independently transmitted and received; the arrangement principle of the plurality of feed sources is that the overlap loss of the plurality of beams in the range direction is less than 3dB, and the overlap loss of the plurality of beams in the azimuth direction is greater than 13dB.

[0007] In one embodiment, the total beam width is calculated according to the observation swath, and the following formula is used:

[0008]

[0009] wherein, is the total beam width, θ Inc is the beam incidence angle, R f is the far-end slant range, W r is the observation swath.

[0010] In one embodiment, the beam width of each beam is calculated according to the distance-to-antenna aperture, using the following formula:

[0011]

[0012] wherein, is the beam width of each beam, and λ is the wavelength, and D is the distance-to-antenna aperture.

[0013] In one embodiment, the number of distance-to-beams is determined according to the total beam width and the beam width of each beam, using the following formula:

[0014]

[0015] wherein, N is the number of distance-to-beams, is the total beam width, is the beam width of each beam, represents the upward rounding.

[0016] In one embodiment, the multiple beams are independently transmitted and received, and the required pulse repetition frequency satisfies the following formula:

[0017]

[0018] wherein, PRF is the pulse repetition frequency, i is a positive integer greater than 1, R n,j is the near-end slant range of the jth beam, R f,j is the far-end slant range of the jth beam, c is the speed of light, τ nadir is the sub-satellite point echo width, Δτ is the transmission and reception protection time, H is the satellite height, τ p is the transmission pulse width.

[0019] Compared with the prior art, the high-resolution wide-width SAR design method based on the reflector system has the following beneficial effects: through the distance-to-multiple-feed wide-beam coverage, the simultaneous multi-beam transmission and reception high-gain imaging technology, and the high-isolation feed distribution technology, the SAR can realize sub-meter resolution, 50-kilometer wide-width high-resolution wide-width imaging, and meet the future reflector system high-resolution wide-width SAR requirements. BRIEF DESCRIPTION OF DRAWINGS

[0020] The present application can be better understood by reference to the following description taken in conjunction with the accompanying drawings, which together with the detailed description, illustrate the principles of the application. In the drawings:

[0021] Figure 1 A flow chart of the high-resolution wide-width SAR design method based on the reflector system is shown;

[0022] Figure 2 A diagram showing the geometric relationship of the simultaneous operation of the multi-beam of the reflecting surface is shown;

[0023] Figure 3 A diagram showing the timing design result is shown;

[0024] Figure 4 A diagram showing the beam coverage after the arrangement design of the multi-beam feed source is shown;

[0025] Figure 5 A diagram showing the arrangement of the high spatial isolation feed source of the beam is shown;

[0026] Figure 6 A diagram showing the system range ambiguity (RASR) curve under different PRF is shown. DETAILED DESCRIPTION

[0027] In the following, exemplary embodiments of the present application will be described with reference to the accompanying drawings. In the description, not all the features of the actual embodiments are described in order to make the description clear and concise. It should be appreciated, however, that many embodiment-specific decisions can be made in the process of developing any such actual embodiment in order to achieve the specific objectives of the developer, and these decisions can vary from embodiment to embodiment.

[0028] It should also be noted that, in order not to obscure the present application with unnecessary details, only the structures of the devices closely related to the scheme according to the present application are shown in the accompanying drawings, and other details not closely related to the present application are omitted.

[0029] It should be understood that the present application is not limited to the described embodiments by virtue of the following description with reference to the accompanying drawings. In this context, the embodiments can be combined with each other, features can be replaced or borrowed between different embodiments, and one or more features can be omitted in one embodiment.

[0030] The embodiments of the present application provide a high-resolution wide-range SAR design method of a reflecting surface system, Figure 1 A flow chart of the high-resolution wide-range SAR design method of the reflecting surface system is shown, referring to Figure 1 , the method comprises:

[0031] In step S1, the total beam width is calculated according to the observation width, the beam width of each beam is calculated according to the antenna aperture in the range direction, and the number of beams in the range direction is determined according to the total beam width and the beam width of each beam.

[0032] Figure 2 A diagram showing the geometric relationship of the simultaneous operation of the multi-beam of the reflecting surface is shown. The total beam width is calculated according to the observation width, and the following formula is used:

[0033]

[0034] wherein, is the total beam width, θ Inc is the beam incidence angle, R f is the far-end slant range, W r is the observation swath width.

[0035] The beam width of each beam is calculated according to the antenna aperture in the range direction, and the following formula is used:

[0036]

[0037] wherein, is the beam width of each beam, λ is the wavelength, and D is the antenna aperture in the range direction.

[0038] The number of beams in the range direction is determined according to the total beam width and the beam width of each beam, and the following formula is used:

[0039]

[0040] wherein, N is the number of beams in the range direction, is the total beam width, is the beam width of each beam, indicates the upward rounding.

[0041] Table 1 shows the parameters of a reflector spaceborne SAR system.

[0042] Table 1

[0043]

[0044]

[0045] According to the system parameters in Table 1, through calculation, 5 beams in the range direction are needed to achieve coverage of a 50km swath.

[0046] Step S2, a plurality of feed sources are designed, the plurality of feed sources generate a plurality of beams, and the plurality of beams independently transmit and receive; the arrangement principle of the plurality of feed sources is that the overlapping loss of the plurality of beams in the range direction is less than 3dB, and the overlapping loss of the plurality of beams in the azimuth direction is greater than 13dB.

[0047] In order to realize sub-meter high resolution, the system needs high antenna gain to meet the image signal-to-noise ratio requirement. In order to realize high antenna gain, multiple beams in range direction adopt simultaneous independent transmitting and receiving technology, N independent beams are transmitted simultaneously to irradiate the whole wide width, and each beam is connected with independent transmitter. Because each sub-beam is a narrow beam, the whole aperture gain of the antenna can be maximized, and the transmitting and receiving gain of the system is improved by N2 times, which effectively meets the high resolution wide width imaging requirement. When multiple beams are used for transmitting and receiving, the echo of different beams needs to be received in sequence through reasonable timing design, Figure 3 The timing design result is shown. N independent beams are designed to be transmitted simultaneously, and the transmission pulse width is τ p Multiple beams are independently transmitted and received, and the pulse repetition frequency needs to meet the following formula:

[0048]

[0049] Wherein, PRF is the pulse repetition frequency, i is a positive integer greater than 1, R n,j is the near range of the jth beam, 1≤j≤N, R f,j is the far range of the jth beam, c is the speed of light, τ nadir is the echo width of the subsatellite point, Δτ is the transmission and reception protection time, H is the satellite height, τ p is the transmission pulse width.

[0050] The calculation formula of SAR system sensitivity (NESZ) is as follows:

[0051]

[0052] Wherein, v s is the platform flight speed, k is the Boltzmann constant, T is the system temperature, F n is the noise factor, P is the average transmission power, G is the antenna gain, and ρ is the resolution. According to the system parameter calculation in table 1, the system sensitivity is-21.24dB, which meets the system design requirement, and proves the correctness of the system design.

[0053] Because multiple beams transmit and receive signals simultaneously, although different regions can be irradiated to distinguish different beam signals in echo space and time, due to the existence of sidelobes of the antenna, other beam signals will enter a certain beam signal through the sidelobes to form aliasing signals, causing image distance blur. Therefore, the transmitting and receiving isolation of multiple beams needs to be improved, and the transmitting and receiving isolation is realized to be ≤-26dB through spatial isolation of the feed arrangement, so as to ensure that the image blur is better than-20dB. The arrangement principle of multiple feeds is that the overlapping loss of multiple beams in range direction is less than 3dB, which can ensure that the beams can form a large width; the overlapping loss of multiple beams in azimuth direction is greater than 13dB. That is, the transmitting and receiving isolation of the beams is better than-26dB.Figure 4 The beam coverage diagram after the multi-beam feed arrangement design is shown.

[0054] Figure 5 The beam high spatial isolation feed arrangement diagram is shown, X f The axis represents the azimuth direction, Y f The distance direction is represented, and the beam footprint formed thereby is continuous in the distance direction and is staggered in space in the azimuth direction, so that the beams are not overlapped, the transmit-receive isolation is better than-26dB, and the system range ambiguity (RASR) can be effectively improved. The system range ambiguity calculation formula is as follows:

[0055]

[0056] Where, θ Inc,i represents the beam incidence angle of the i-th ambiguity zone, G(θ Inc,i ) represents the antenna receiving gain of the i-th ambiguity zone beam incidence angle θ Inc,i , which is approximately equal to the antenna gain minus the transmit-receive isolation. R f (θ Inc,i ) represents the far-off slant range of the i-th ambiguity zone beam incidence angle θ Inc,i , G is the antenna gain, R f is the far-off slant range, and θ Inc is the beam incidence angle.

[0057] According to the system parameters in Table 1, the range ambiguity in the imaging range can be calculated to be better than-22dB, Figure 6 The system range ambiguity (RASR) curves under different PRFs are shown, which meet the requirement of ≤-20dB range ambiguity, proving the correctness of the system design.

[0058] In summary, the present application has the following technical effects:

[0059] The high-resolution wide-width SAR design method based on the reflector system of the present application realizes sub-meter resolution, 50-kilometer wide-width high-resolution wide-width imaging of the SAR through distance direction multi-feed wide-beam coverage, simultaneous multi-beam transmit-receive high-gain imaging technology, and high-isolation feed distribution technology, and meets the future demand of high-resolution wide-width SAR of the reflector system.

[0060] The above is only various embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical scope disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A design method of high resolution wide swath SAR based on reflector system, characterized in that, Comprise: According to the total beam width calculated by the observation width, the beam width of each beam is calculated according to the distance to the antenna aperture; According to the total beam width and the beam width of each beam, the number of distance beams is determined; Design a plurality of feed sources, the plurality of feed sources produce a plurality of beams, the plurality of beams are independently transmitted and received; The arrangement principle of the plurality of feed sources is that the overlapping loss of the plurality of beams in the distance direction is less than 3dB, and the overlapping loss of the plurality of beams in the azimuth direction is greater than 13dB; The plurality of beams independently transmits and receives, and the required pulse repetition frequency satisfies the following formula: where PRF is the pulse repetition frequency, i is a positive integer greater than 1, R n,j is the near range of the jth beam, R f,j is the far range of the jth beam, c is the speed of light, τ nadir is the sub-satellite point echo width, Δτ is the transmit-receive protection time, H is the satellite altitude, τ p is the transmit pulse width.

2. The method of claim 1, wherein, Wherein, According to the total beam width calculated by the observation width, the following formula is used: wherein, is the total beam width, θ Inc is the beam incidence angle, R f is the far end slant range, W r is the observed swath width.

3. The method of claim 1, wherein, Wherein, According to the distance to the antenna aperture, the beam width of each beam is calculated, and the following formula is used: wherein, is the beam width for each beam, λ is the wavelength, and D is the distance to the antenna aperture.

4. The method of claim 1, wherein, Wherein, According to the total beam width and the beam width of each beam, the number of distance beams is determined, and the following formula is used: wherein N is the number of distance direction beams, is the total beam width, is the beam width of each beam, denotes the ceiling function.

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