A method to improve the ability of navigation radar to suppress sea clutter

Abstract

The present invention proposes a method for improving the sea clutter suppression capability of navigation radar. The method utilizes the fluctuation characteristics of sea clutter, simulates and calculates the decorrelation time of sea clutter, that is, decorrelation can be achieved after 20-30ms, and estimates the accumulation time allowed by the ship motion. Aiming at the time constraints of these two aspects, improved designs are carried out in terms of navigation radar antenna pointing frequency deviation, waveform improvement, decorrelation signal accumulation processing, etc., so as to achieve target accumulation and sea clutter smoothing, thereby improving the signal-to-clutter ratio and improving the sea clutter suppression capability of navigation radar.

Description

Technical Field

[0001] The invention belongs to the technical field of radar detection, and in particular relates to a method for improving the sea clutter suppression capability of a navigation radar. Background Art

[0002] Navigation radar is an essential equipment for safe navigation of ships. The International Maritime Organization, classification societies, etc. all have mandatory requirements for the installation of navigation radar. When used at sea, navigation radar is easily interfered by sea clutter, especially in severe sea conditions. It is difficult to distinguish between obstruction targets that need to be detected and those covered by large areas of sea clutter. Currently, navigation radar uses the wave suppression adjustment switch to reduce the gain of the radar receiver, thereby reducing the interference intensity of sea clutter. This method does not improve the radar signal-to-clutter ratio. While reducing the intensity of sea clutter, it also reduces the intensity of obstruction targets. If the operation is not careful, the radar is very likely to fail to detect the echo of the obstruction, causing a safety accident. Summary of the invention

[0003] The object of the present invention is to provide a method for improving the sea clutter suppression capability of a navigation radar, which can improve the target detection capability of the radar under the sea clutter background.

[0004] The technical solution to achieve the purpose of the present invention is: a method for improving the ability of navigation radar to suppress sea clutter, comprising the following steps:

[0005] 10) Determine the decorrelation time range of sea clutter for X-band navigation radar;

[0006] 20) Determine different operating frequencies based on the rotation speed of the navigation radar antenna, the sea clutter decorrelation time obtained by simulation, and the frequency deviation pointing direction of the antenna to be designed;

[0007] 30) Complete the radar working waveform design according to the requirements of the antenna pointing frequency deviation on the radar working frequency and the radar detection index requirements;

[0008] 40) Sliding information accumulation is performed on echoes with different frequency offsets to smooth clutter signals, accumulate target signals, and extract target signals through constant false alarm processing.

[0009] Preferably, the specific method for determining the decorrelation time range of the X-band navigation radar to the sea clutter is:

[0010] The minimum decorrelation time is the sea clutter interval time, and the calculation formula is:

[0011]

[0012] Where d is the non-correlated ratio, t c is the sea clutter interval time;

[0013] The maximum decorrelation time is the scan accumulation time.

[0014] Preferably, the specific method for determining different operating frequency points is as follows according to the rotation speed of the navigation radar antenna, the sea clutter decorrelation time obtained by simulation, and the frequency deviation pointing direction of the antenna to be designed:

[0015] The decorrelation time is determined according to the frequency deviation direction of the antenna to be designed, and it is determined whether the decorrelation time is within the decorrelation time range. When it is within the decorrelation time range, different frequency points corresponding to the frequency deviation direction of the antenna are calculated.

[0016] Preferably, the decorrelation time is calculated as follows:

[0017] Add the frequency deviation pointing of the antenna to be designed to the beam width and divide the result by 360 degrees. Multiply the result by the rotation speed to obtain the decorrelation time.

[0018] Preferably, the specific method for calculating the different frequency points corresponding to the antenna frequency deviation direction is:

[0019] According to the frequency scanning theory of waveguide slot antenna, the waveguide wavelength λ of the waveguide slot antenna is calculated by the beam pointing θ and the wavelength λ corresponding to the operating frequency f, the slot spacing d, and the waveguide size a. g ;

[0020] According to the waveguide wavelength λ of the waveguide slot antenna g Calculate the beam pointing θ for the set diversity frequency 1 , direct the beam of the set diversity frequency to θ 1 Add the frequency deviation of the antenna to be designed to obtain the final beam pointing θ 2 , the wavelength is re-determined based on the final beam direction, and then θ is determined from the wavelength 2 The corresponding diversity frequency is obtained by rounding the diversity frequency to obtain the corresponding frequency deviation f 0 , use frequency deviation to design three frequency points, the three frequency points are: f, f+f 0 , f+2f 0 .

[0021] Compared with the prior art, the present invention has the following significant advantages: the present invention performs smoothing processing on the sea clutter echo intensity without reducing the existing detection capability of the radar, thereby achieving sea clutter suppression, and theoretically corresponding to a signal-to-clutter ratio improvement of 4.7 dB.

[0022] The technical solution of the present invention makes technical improvements on the existing navigation radar. Through the designs of radar working waveform, radar antenna pointing frequency deviation, radar decorrelation smoothing processing, etc., the radar to noise ratio is improved, and the anti-clutter capability of the navigation radar is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The present invention is a main flow chart of a method for improving the sea clutter suppression capability of a navigation radar.

[0024] Figure 2 This is a graph showing the temporal correlation of sea clutter changing with time.

[0025] Figure 3 is the frequency deviation beam pointing pattern of the designed antenna.

[0026] Figure 4 This is the radar waveform and working timing diagram. DETAILED DESCRIPTION

[0027] like Figure 1 As shown, the present invention provides a method for improving the sea clutter suppression capability of a navigation radar, comprising the following steps:

[0028] 10) Decorrelation time of sea clutter: Simulate and calculate the decorrelation time of sea clutter for X-band navigation radar;

[0029] For shipborne navigation radar operating in the X-band, the relationship between the sea clutter interval time tc and the non-correlation ratio d satisfies

[0030]

[0031] Sea clutter interval time t c It can be considered as the minimum value of sea clutter decorrelation time.

[0032] The scan accumulation time is taken as the maximum value of the sea clutter decorrelation time, specifically: the range unit divided by the target and platform movement speed is taken as the maximum value of the sea clutter decorrelation time.

[0033] Figure 2 The curve of sea clutter time correlation is given. It can be seen from the figure that when the time interval is about 15ms, the non-correlation ratio of different echo signals of sea clutter reaches 0.9. When the time interval is more than 25ms, the non-correlation ratio of different echo signals of sea clutter is infinitely close to 1, which can be considered to be uncorrelated.

[0034] On the shipborne platform, both the target and the platform will move, and during the scan accumulation, it is expected that the target will not move across the distance unit. The current radar sea detection bandwidth is 20M, and the distance unit is 7.5m. Assuming that the target and platform move at 24kn, the relative maximum speed is 48kn, that is, 24m / s. The scan accumulation time is 7.5 / 24=312.5ms. Therefore, when detecting the sea, the scan accumulation needs to be completed within 312.5ms so that the target will not cross the distance unit due to movement.

[0035] Finally, it is concluded that the relevant smoothing processing time needs to be completed between 25ms and 312.5ms.

[0036] 20) Decorrelation antenna pointing frequency deviation design: Determine different operating frequencies based on the navigation radar antenna rotation speed, the sea clutter decorrelation time obtained by simulation, and the antenna frequency deviation pointing to be designed.

[0037] Determine the decorrelation time according to the frequency deviation direction of the antenna to be designed, and determine whether the decorrelation time is within the decorrelation time range. If it is within the decorrelation time range, calculate the different frequency points corresponding to the frequency deviation direction of the antenna

[0038] The decorrelation time is calculated as:

[0039] The frequency deviation pointing of the antenna to be designed plus the beam width, divided by 360 degrees, multiplied by the rotation speed, is the decorrelation time;

[0040] From step 10), it can be seen that the clutter removal correlation time is greater than 25ms to meet the clutter removal correlation requirement. The minimum antenna speed is 20rpm according to the navigation radar standard. Figure 3 , beam width 2°, if the beam pointing deviation θ is designed to be 1.5°, the decorrelation time is It can reach about 30ms, then 1.5° can be selected as the beam pointing deviation.

[0041] According to the frequency scanning theory of waveguide slot antenna, the waveguide wavelength λ of the waveguide slot antenna is calculated by the beam pointing θ and the wavelength λ corresponding to the operating frequency f, the slot spacing d, and the waveguide size a. g ;

[0042] According to the waveguide wavelength λ of the waveguide slot antenna g Calculate the beam pointing θ for the set diversity frequency 1 , direct the beam of the set diversity frequency to θ 1 Add the frequency deviation of the antenna to be designed to obtain the final beam pointing θ 2 , the wavelength is re-determined based on the final beam direction, and then θ is determined from the wavelength 2 The corresponding diversity frequency is obtained by rounding the diversity frequency to obtain the corresponding frequency deviation f 0 , use frequency deviation to design three frequency points, the three frequency points are: f, f+f 0 , f+2f 0 .

[0043] For example, the operating frequency of this radar is 9.2GHz-9.5GHz. To calculate the antenna frequency deviation caused by different frequencies, the steps are as follows:

[0044] According to the frequency scanning theory of waveguide slot antenna, the relationship between beam pointing θ and wavelength λ corresponding to the working frequency, slot spacing d, and waveguide size a is as follows:

[0045]

[0046] Wherein: the waveguide dimension a=22.86 (BJ100), λ is the wavelength corresponding to the 9.2G operating frequency, and the crack spacing d=0.5λ.

[0047] The waveguide wavelength λ of the waveguide slot antenna can be calculated from formula (2): g , substitute into formula 3 to calculate the beam pointing θ at the diversity frequency of 9.2G 1 Since the designed antenna frequency deviation is 1.5°, the designed θ 2 =θ 1 +1.5°, and then use formula (3) and formula (2) to inversely deduce the beam pointing θ 2 The corresponding diversity frequency, after rounding, can be concluded that a beam pointing deviation of 1.5° corresponds to a frequency deviation of approximately 150M.

[0048] Three frequency points are designed for radar waveform improvement.

[0049] Diversity frequency: F1=9.2G, F2=9.35G, F3=9.5G.

[0050] 30) Waveform improvement design: Complete the radar working waveform design based on the antenna pointing frequency deviation requirements for the radar working frequency and the radar detection index requirements.

[0051] Radar waveform and working sequence are as follows Figure 4 The original radar used 10+5+0.1us three-pulse working waveform. Since the clutter is concentrated within 500m, improvement work can be carried out only on short pulses. The improved waveform is as follows Figure 4 As shown, two diversity frequency short pulses are added as retrace pulses.

[0052] 40) Decorrelation signal accumulation processing: Perform sliding information accumulation on echoes with different frequency offsets to smooth clutter signals, accumulate target signals, and extract target signals through constant false alarm processing.

[0053] The present invention further suppresses the echo intensity of sea clutter under the premise of keeping the echo intensity of the obstruction target unchanged, thereby achieving the suppression of sea clutter without reducing the radar detection performance, which is safer and more reliable than the traditional method.

[0054] The technical solution of the present invention carries out technical improvements on the original navigation radar in terms of antenna pointing frequency deviation design, waveform improvement design, decorrelation signal accumulation processing, etc. Theoretically, it can improve the signal-to-noise ratio of the existing navigation radar by 4.7dB, thereby improving the signal-to-noise ratio and enhancing the ability of the navigation radar to suppress sea clutter interference.

Claims

1. A method for improving the sea clutter suppression capability of a navigation radar, characterized in that: The steps include: 10) Determine the decorrelation time range of sea clutter for X-band navigation radar; 20) Determine different operating frequencies based on the rotation speed of the navigation radar antenna, the sea clutter decorrelation time obtained by simulation, and the frequency deviation pointing direction of the antenna to be designed; 30) Complete the radar working waveform design according to the requirements of the antenna pointing frequency deviation on the radar working frequency and the radar detection index requirements; 40) Sliding information accumulation is performed on echoes with different frequency offsets to smooth clutter signals, accumulate target signals, and extract target signals through constant false alarm processing.

2. The method for improving the sea clutter suppression capability of navigation radar according to claim 1, characterized in that: The specific method for determining the decorrelation time range of sea clutter for X-band navigation radar is: The minimum decorrelation time is the sea clutter interval time, and the calculation formula is: Where d is the non-correlated ratio, t c is the sea clutter interval time; The maximum decorrelation time is the scan accumulation time.

3. The method for improving the sea clutter suppression capability of navigation radar according to claim 1, characterized in that: According to the rotation speed of the navigation radar antenna, the sea clutter decorrelation time obtained by simulation, and the frequency deviation pointing direction of the antenna to be designed, the specific method for determining different operating frequencies is as follows: The decorrelation time is determined according to the frequency deviation direction of the antenna to be designed, and it is determined whether the decorrelation time is within the decorrelation time range. When it is within the decorrelation time range, different frequency points corresponding to the frequency deviation direction of the antenna are calculated.

4. The method for improving the sea clutter suppression capability of navigation radar according to claim 3, characterized in that: The decorrelation time is calculated as: Add the frequency deviation pointing of the antenna to be designed to the beam width and divide the result by 360 degrees. Multiply the result by the rotation speed to obtain the decorrelation time.

5. The method for improving the sea clutter suppression capability of navigation radar according to claim 3, characterized in that: The specific method for calculating the different frequency points corresponding to the antenna frequency deviation is: According to the frequency scanning theory of waveguide slot antenna, the waveguide wavelength λ of the waveguide slot antenna is calculated by the beam pointing θ and the wavelength λ corresponding to the operating frequency f, the slot spacing d, and the waveguide size a. g ; According to the waveguide wavelength λ of the waveguide slot antenna g The beam pointing θ1 of the set diversity frequency is calculated, and the beam pointing θ1 of the set diversity frequency is added to the frequency offset pointing of the antenna to be designed to obtain the final beam pointing θ2. The wavelength is re-determined according to the final beam pointing, and the diversity frequency corresponding to θ2 is determined by the wavelength. The corresponding frequency offset f0 is obtained after rounding the diversity frequency. Three frequency points are designed using the frequency offset. The three frequency points are: f, f+f0, and f+2f0.

Images