A design method for suppressing mutual interference of radar altimeters suitable for dual-satellite formation

Abstract

The present invention belongs to the technical field of radar altimeters for dual-satellite formation flight, and in particular, relates to a design method for mutual interference suppression of radar altimeters suitable for dual-satellite formation flight, including: two radar altimeters of the dual-satellite formation both work with linear frequency modulation signals, which are positive frequency modulation signals and negative frequency modulation signals respectively; two radar altimeter antennas both adopt the same positive feed parabola form, and the electric field directions of linear polarized electromagnetic waves are orthogonally designed. By adopting the design method of the present invention, the mutual interference suppression of the altimeter echo signals on the two satellites reaches more than 60dB, and the influence on the measurement accuracy can be ignored, thereby ensuring that the dual-satellite formation altimeter can work normally.

Description

Technical Field

[0001] The invention belongs to the technical field of radar altimeters for dual-satellite formation flight, and in particular relates to a radar altimeter mutual interference suppression design method suitable for dual-satellite formation flight. Background Art

[0002] Radar altimeter is an active microwave remote sensor that measures the height from the satellite to the sea surface, the effective wave height of the sea surface and the backscatter coefficient by emitting electromagnetic waves to the sea surface and receiving the echoes returned by the sea surface. The sea surface wind speed can be inverted through the backscatter coefficient. At present, the sea surface height measurement accuracy achieved by radar altimeter has reached the centimeter level. Its global high-precision continuous observation data of the sea surface has played an irreplaceable role in global ocean circulation, mesoscale eddies, global and regional sea level changes, ocean shortwave gravity fields, seabed topography, ocean tides, etc. At the same time, it plays an important role in the measurement of effective wave height, sea surface wind speed, ice sheet elevation, sea ice thickness and inland water level.

[0003] Since the 1970s, more than 20 radar altimeter satellites have been launched at home and abroad, including TOPEX, Jason-1 / 2 / 3, Sentinel-3, Sentinel-6, SWOT, etc., and HY-2A / B / C / D, etc., from China.

[0004] The above altimeter satellites all work independently, without using satellite formation. When radar altimeter satellites work in formation, the sub-satellite tracks of the two satellites are parallel, so that the sea surface height gradient in the direction of the satellite along the track can be obtained, and the sea surface height gradient in the direction of the double satellite crossing the track can be obtained, which is of great value for simultaneously obtaining the two-dimensional sea surface height gradient.

[0005] If two radar altimeters with the same hardware status are installed on two satellites flying in formation, the radar pulse signal emitted by one of the altimeters will be received by the altimeters on both satellites after being backscattered by the sea surface, and will interfere with the other altimeter, causing it to malfunction. Summary of the invention

[0006] Aiming at the mutual interference of altimeters in a dual-satellite formation, the present invention aims to overcome the defects of the prior art and proposes a design method for suppressing mutual interference of radar altimeters suitable for a dual-satellite formation.

[0007] In order to achieve the above technical objectives, the present invention proposes a radar altimeter mutual interference suppression design method suitable for a dual-satellite formation, comprising:

[0008] The two radar altimeters of the dual-satellite formation both work with linear frequency modulation signals, namely positive frequency modulation and negative frequency modulation signals;

[0009] Both radar altimeter antennas adopt the same forward-fed parabola form, and the electric field directions of linearly polarized electromagnetic waves are designed to be orthogonal.

[0010] Preferably, the radar altimeter of the A-star in the binary satellite adopts a positive frequency modulation linear frequency modulation signal, and the signal form is as follows:

[0011]

[0012] The radar altimeter of satellite B in the binary satellite adopts negative frequency modulation linear frequency modulation signal, and the signal form is as follows:

[0013]

[0014] Where A represents the signal strength, t represents the time, T represents the length of the linear frequency modulation signal, f0 represents the operating frequency, K represents the modulation rate of the linear frequency modulation signal, and rect(t / T) represents that the pulse envelope of the transmitted signal is rectangular and the time width is T.

[0015] Preferably, each radar altimeter adopts dual-frequency operation, namely Ku band and C band; the linear frequency modulation signal length T is 51.2us or 102.4us; the Ku band operating frequency f0 range is 13.25GHz to 13.75GHz, and the C band operating frequency f0 range is 5.25GHz to 5.57GHz; the linear frequency modulation signal modulation frequency K is 320MHz / 51.2us or 320MHz / 102.4us.

[0016] Preferably, the orthogonal design of the electric field direction of the linearly polarized electromagnetic wave includes:

[0017] The electric field direction of the Ku-band electromagnetic wave of the A-satellite radar altimeter is consistent with the X-axis, and the electric field direction of the C-band electromagnetic wave is consistent with the Y-axis; the electric field direction of the Ku-band electromagnetic wave of the B-satellite radar altimeter is consistent with the Y-axis, and the electric field direction of the C-band electromagnetic wave is consistent with the X-axis.

[0018] Preferably, the Ku-band antenna feed line adopts a BJ140 waveguide, and the C-band antenna feed line adopts a low-loss coaxial cable.

[0019] Preferably, the Ku-band and C-band within a single satellite share a parabolic reflector, and the electric field directions of the linearly polarized electromagnetic waves in the Ku-band and C-band within the single satellite are orthogonal; the electric field directions of the Ku-band electromagnetic waves between two satellites are orthogonal to each other, and the electric field directions of the C-band electromagnetic waves between two satellites are orthogonal to each other.

[0020] Preferably, the Ku-band and C-band dual-frequency feed sources are shared within a single satellite.

[0021] Compared with the prior art, the advantages of the present invention are:

[0022] By adopting the design method of the present invention, the mutual interference suppression of the altimeter echo signals on the two satellites reaches more than 60dB, and the influence on the measurement accuracy can be ignored, thereby ensuring that the dual-satellite formation altimeter can work normally. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the electric field direction of the linear polarization electromagnetic wave of the dual-satellite formation radar altimeter;

[0024] Figure 2 This is a diagram of the radar altimeter antenna structure. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0026] Example

[0027] The embodiment of the present invention provides a radar altimeter mutual interference suppression design method suitable for a dual-satellite formation. The core content includes two parts: the first part is the altimeter linear frequency modulation signal design, and the second part is the orthogonal design of the electric field direction of the linear polarization electromagnetic wave.

[0028] Part 1 Altimeter linear frequency modulation signal design: The radar altimeter uses a linear frequency modulation signal. In the two altimeters in the dual-satellite formation, positive and negative frequency modulation signals are used respectively, thereby providing 40dB of mutual interference suppression for the dual-satellite altimeter echo signals.

[0029] The radar altimeter of satellite A in the binary satellite adopts positive frequency modulation linear frequency modulation signal, and the signal form is as follows:

[0030]

[0031] The radar altimeter of satellite B in the binary satellite adopts negative frequency modulation linear frequency modulation signal, and the signal form is as follows:

[0032]

[0033] In formulas (1) and (2), A represents signal strength; t represents time; T represents the length of the linear frequency modulation signal, and the T value is selected as 51.2us or 102.4us in the design; f0 represents the operating frequency, and the Ku band range is 13.25GHz to 13.75GHz in the design, and 13.58GHz is selected in this implementation; the C band operating frequency f0 range is 5.25GHz to 5.57GHz, and 5.41GHz is selected in this embodiment; K represents the modulation frequency of the linear frequency modulation signal, and 320MHz / 51.2us or 320MHz / 102.4us is selected in the design, and rect(t / T) represents that the pulse envelope of the transmitted signal is rectangular and the time width is T.

[0034] The second part is the orthogonal design of the electric field direction of linear polarization electromagnetic waves: the dual-satellite altimeter antennas use the same forward-feed parabola form. The dual-satellite flight coordinate system for formation flight is as follows: Figure 1 As shown, the X axis is the flight direction of the satellite, the Y axis is the satellite cross-orbit direction, and the Z axis determined by the right-hand rule based on the X and Y axes points to the surface of the earth at the sub-satellite point. Figure 1 As shown in the figure, the electric field direction of the linear polarization electromagnetic wave in the Ku band of star A is consistent with the X-axis, and the electric field direction of the linear polarization electromagnetic wave in the C band is consistent with the Y-axis; the electric field direction of the linear polarization electromagnetic wave in the Ku band of star B is consistent with the Y-axis, and the electric field direction of the linear polarization electromagnetic wave in the C band is consistent with the X-axis. This achieves the orthogonality of the electric field directions of the linear polarization electromagnetic waves in the same frequency band between the two stars, and the orthogonality of the electric field directions of the linear polarization electromagnetic waves in two frequency bands within a single star.

[0035] During formation flight, the X-axis and Y-axis consistency of A and B is maintained at 0.2 0 The mutual interference suppression of dual-satellite echo signals brought by the orthogonality design reaches 20dB.

[0036] The antenna structure diagram to realize the orthogonal electric field direction of this linear polarization electromagnetic wave is as follows Figure 2 As shown in the figure, the Ku-band feed line uses BJ140 waveguide, and the C-band feed line uses low-loss coaxial cable. Its characteristics are that the two bands share a parabolic reflector, and the electric field directions of the linear polarization electromagnetic waves of the Ku / C dual-band are orthogonal, which improves the isolation of the two excitation ports of the dual-band feed source and suppresses the mutual electromagnetic interference between the two bands of the antenna itself. The Ku and C dual-bands share the feed source.

[0037] The above two-part design enables the mutual interference suppression of the sea surface echoes between the dual-satellite altimeters to reach more than 60dB, and the impact on the measurement accuracy can be ignored.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention is described in detail with reference to the embodiments, it should be understood by those skilled in the art that any modification or equivalent replacement of the technical solutions of the present invention does not depart from the spirit and scope of the technical solutions of the present invention and should be included in the scope of the claims of the present invention.

Claims

1. A radar altimeter mutual interference suppression design method suitable for a dual-satellite formation, comprising: The two radar altimeters of the dual-satellite formation both work with linear frequency modulation signals, namely positive frequency modulation and negative frequency modulation signals; The two radar altimeter antennas both adopt the same forward-fed parabola form, and the electric field directions of linearly polarized electromagnetic waves are designed to be orthogonal; The radar altimeter of satellite A in the binary satellite adopts positive frequency modulation linear frequency modulation signal, and the signal form is as follows: The radar altimeter of satellite B in the binary satellite adopts negative frequency modulation linear frequency modulation signal, and the signal form is as follows: Where A represents the signal strength, t represents the time, T represents the length of the linear frequency modulation signal, f0 represents the operating frequency, K represents the modulation frequency of the linear frequency modulation signal, and rect(t / T) represents that the pulse envelope of the transmitting signal is rectangular and the time width is T. Each radar altimeter uses dual-frequency operation, namely Ku band and C band; the linear frequency modulation signal length T is 51.2us or 102.4us; the operating frequency f0 range of Ku band is 13.25GHz~13.75GHz, and the operating frequency f0 range of C band is 5.25GHz~5.57GHz; the linear frequency modulation signal modulation frequency K is 320MHz / 51.2us or 320MHz / 102.4us; The Ku-band and C-band within a single satellite share a parabolic reflector surface, and the electric field directions of the linear polarization electromagnetic waves in the Ku-band and C-band within a single satellite are orthogonal; the electric field directions of the Ku-band electromagnetic waves between binary satellites are orthogonal to each other, and the electric field directions of the C-band electromagnetic waves between binary satellites are orthogonal to each other.

2. The radar altimeter mutual interference suppression design method suitable for a dual-satellite formation according to claim 1, characterized in that: The orthogonal design of the electric field direction of the linearly polarized electromagnetic wave includes: The electric field direction of the Ku-band electromagnetic wave of the A-satellite radar altimeter is consistent with the X-axis, and the electric field direction of the C-band electromagnetic wave is consistent with the Y-axis; the electric field direction of the Ku-band electromagnetic wave of the B-satellite radar altimeter is consistent with the Y-axis, and the electric field direction of the C-band electromagnetic wave is consistent with the X-axis.

3. The radar altimeter mutual interference suppression design method suitable for a dual-satellite formation according to claim 2 is characterized in that: The Ku-band antenna feed line uses BJ140 waveguide, and the C-band antenna feed line uses low-loss coaxial cable.

4. The radar altimeter mutual interference suppression design method suitable for a dual-satellite formation according to claim 2 or 3, characterized in that: Ku-band and C-band dual-frequency shared feed within a single satellite.

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