Method for judging forward direction and backward direction in direction finding of double-antenna interferometer

Abstract

The invention relates to the field of search and rescue positioning, in particular to a method for judging forward and backward directions in direction finding of a double-antenna interferometer, which comprises the following steps: a search and rescue device sends a wireless telecommunication inquiry signal at a frequency f1, a device to be rescued receives the inquiry signal sent by the search and rescue device, outputs a frequency word m to a phase-locked loop, and tracks the frequency f1; the to-be-rescued equipment returns a radio response signal to the search and rescue equipment at the frequency f2, the response signal comprises a frequency word m, and the search and rescue equipment receives the response signal sent by the to-be-rescued equipment, outputs a frequency word n to the phase-locked loop and tracks the frequency f2; the search and rescue equipment analyzes the response signal to obtain a frequency word m; and judging whether the to-be-rescued equipment is in front of or behind the search and rescue equipment based on the frequency word m and the frequency word n. According to the method, hardware cost is not increased, forward and backward judgment can be completed through one-time inquiry response, and the accuracy and efficiency of search and positioning are improved.

Description

Technical Field

[0001] The present invention relates to the field of search and rescue positioning, and particularly to a method for determining the front and rear directions in dual-antenna interferometer direction finding. Background Art

[0002] In the field of search and rescue, in order to locate the rescue target, it is necessary to position the rescue target. Since satellite signals are transmitted through electromagnetic waves, it is very likely that the satellite signals are blocked by buildings, making the GPS or Beidou of the device to be rescued unavailable. In the absence of positioning satellite signals, the search and rescue device must use other methods to measure the distance and direction of the device to be rescued to obtain the location of the rescue target. Existing search and rescue devices send wireless inquiry signals at a certain frequency. After the device to be rescued receives the inquiry signal at the same frequency, it returns a response signal. The search and rescue device receives the response signal through two antennas and uses the interferometer direction finding method to obtain the direction of the device to be rescued. And the search and rescue device is generally installed on a rescue aircraft. Many small helicopters or drones are too small in size to install too many antennas, so the multi-dimensional multi-baseline direction finding method cannot be applied on the rescue aircraft. Currently, the most commonly used is the one-dimensional single-baseline phase interferometer direction finding method.

[0003] The principle of one-dimensional single-baseline phase interferometer direction finding is as Figure 1 shown. In the figure, a plane electromagnetic wave with a signal wavelength of λ arrives at the direction finding antennas A and B from a direction with an angle θ to the antenna visual axis. The received signals are respectively:

[0004] S A (t) = a × sin(2πft)

[0005] S B (t) = a × sin(2πft + φ)

[0006] where f is the signal frequency, a is the signal amplitude, and the phase difference between the signals received by the two antennas is:

[0007]

[0008] where L is the distance between the two antennas. If the phase responses of the two channels of the receiver are exactly the same, the phase difference of the signals output by the receiver is still φ. Then the direction of arrival θ of the signal can be obtained:

[0009]

[0010] However, when using a dual-antenna interferometer for direction finding, a mirror image problem will occur, as Figure 2 shown. This is because the measured phase difference is ambiguous, resulting in two angle solutions symmetric about the antenna connection line in direction finding, so it is impossible to determine whether the signal coming direction is the real signal or the mirror image signal. Generally, it can be solved by the following methods:

[0011] (a) Adding an antenna

[0012] Adding an auxiliary antenna to form a triple - antenna array. By comparing information such as the phase difference between different antenna pairs, it is possible to effectively eliminate the ambiguous mirror - angle solutions and thus obtain the true direction of the incoming wave.

[0013] (b) Utilizing prior information

[0014] If there is certain prior knowledge about the area where the signal source is located, for example, it is known that the signal source is roughly in a certain range, such as in the front rather than the back, the mirror direction can be excluded.

[0015] For the first method of adding an antenna, due to the size limitation of the aircraft fuselage, it may not be possible to install an auxiliary antenna, and adding an antenna will increase costs. For the second method of utilizing prior information, since prior information cannot be obtained in most cases, it is not applicable either.

[0016] The existing search - and - rescue equipment uses a dual - antenna interferometer system. On the search - and - rescue aircraft, the baseline is generally perpendicular to the fuselage direction. One method is to determine the signal direction based on the distance difference obtained from two interrogation - response operations. However, affected by the ranging accuracy, in actual use, this method is unreliable, and at least two interrogation - response operations are required, resulting in low efficiency. Another method is to utilize the sensitivity of the carrier frequency to the relative speed between the search - and - rescue equipment and the equipment to be rescued. By calculating the Doppler frequency shift, the front - back direction can be determined with one interrogation - response operation. However, due to the frequency error in the frequency synthesizers of the search - and - rescue equipment and the equipment to be rescued, and since the flight speed of the aircraft is generally not very high, about 250 Km / h, the obtained Doppler frequency shift is in the order of dozens of Hertz, and a small frequency error can render this method ineffective., Summary of the Invention

[0017] In view of the deficiencies of the prior art, the present invention proposes a method for determining the front - back direction in dual - antenna interferometer direction finding, which does not increase the hardware cost and can complete the front - back direction determination through one interrogation - response operation, improving the accuracy and efficiency of search and positioning.

[0018] To achieve the above - mentioned purpose, the present invention adopts the following technical solutions:

[0019] The present invention proposes a method for determining the front - back direction in dual - antenna interferometer direction finding, including the following steps:

[0020] S1. The search - and - rescue equipment sends a radio interrogation signal at frequency f1. The equipment to be rescued receives the interrogation signal sent by the search - and - rescue equipment, outputs the frequency word m to the phase - locked loop, and tracks to frequency f1;

[0021] S2. The device to be rescued returns a radio response signal to the rescue device at frequency f2. The response signal contains a frequency word m. The rescue device receives the response signal sent by the device to be rescued, outputs the frequency word n to the phase-locked loop, and tracks to frequency f2;

[0022] S3. The rescue device analyzes the response signal to obtain the frequency word m;

[0023] S4. Determine whether the device to be rescued is in front of or behind the rescue device based on the frequency word m and the frequency word n.

[0024] Specifically, in S1, the rescue device outputs the frequency word m to the phase-locked loop through a carrier tracking loop; in S2, the device to be rescued outputs the frequency word n to the phase-locked loop through a carrier tracking loop.

[0025] Specifically, S1 includes the following sub-steps:

[0026] S101. The inquiry electrical signal received by the device to be rescued passes through the channel and is converted by AD to become an intermediate frequency signal;

[0027] S102. The intermediate frequency signal is mixed with a digital local oscillator signal (NCO), and after low-pass filtering, it becomes two-channel baseband signals of I and Q;

[0028] S103. The two-channel baseband signals of I and Q enter the carrier loop discriminator, and the frequency difference and phase difference are output;

[0029] S104. The frequency difference and phase difference enter the carrier loop filter, and the frequency word m is output. After the frequency word m enters the numerically controlled oscillator, it controls the numerically controlled oscillator to output a digital local oscillator signal.

[0030] Specifically, the carrier loop discriminator includes a frequency difference discriminator and a phase difference discriminator.

[0031] Specifically, the frequency difference discriminator adopts a cross product dot product algorithm:

[0032]

[0033] Specifically, the phase difference discriminator adopts a Q / I phase discriminator.

[0034] Specifically, the carrier loop filter adopts a 3rd-order phase-locked loop filter assisted by a 2nd-order frequency-locked loop.

[0035] Specifically, in S4, the specific method for determining the direction of the device to be rescued based on the frequency word m and the frequency word n is: calculate the gain u of the carrier tracking loop through the frequency word m and the frequency word n. If u < 0, it is determined that the device to be rescued is in front of the rescue device; otherwise, it is determined that the device to be rescued is behind the rescue device, where u is calculated by the following formula:

[0036] u = m + n.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] The search and rescue device of the present invention sends a polling signal at frequency f1. After the device to be rescued receives the polling signal, it outputs a frequency word m to the phase-locked loop through the carrier tracking loop, tracks frequency f1, and returns a response signal at frequency f2. The search and rescue device receives the response signal, outputs a frequency word n to the phase-locked loop through the carrier tracking loop, tracks frequency f2 and resolves m; calculates the gain u of the carrier tracking loop through m and n; judges whether the device to be rescued is in front of or behind the search and rescue device through u. There is no need to add hardware facilities, and the judgment can be completed through one response, while ensuring the accuracy and efficiency of search and rescue positioning. Description of the Drawings

[0039] Figure 1 It is the schematic diagram of the direction finding principle of the one-dimensional single-baseline phase interferometer;

[0040] Figure 2 It is the schematic diagram of the appearance of the mirror image signal in the one-dimensional single-baseline phase interferometer;

[0041] Figure 3 It is the schematic diagram of the structure of the carrier tracking loop;

[0042] Figure 4 It is the schematic diagram of the structure of the carrier loop filter. Detailed Embodiment

[0043] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0044] Embodiment 1

[0045] The existing search and rescue device uses a dual-antenna interferometer system. The baseline is generally perpendicular to the fuselage direction of the search and rescue aircraft. The following method is used to judge the direction of the device to be rescued:

[0046] (1) The distance difference obtained from two polling responses:

[0047] The airborne search and rescue device sends a polling signal. After the device to be rescued receives the polling signal, it returns a response signal. The airborne life-saving radio station can obtain the distance between the search and rescue device and the device to be rescued by calculating the time difference between sending the polling signal and receiving the response signal.

[0048] Assume that the search and rescue aircraft is flying directly towards the device to be rescued, that is, the device to be rescued is in front of the search and rescue equipment. The first interrogation response gives a distance L1, and the second interrogation response gives a distance L2. Then, L2 < L1 will be obtained. On the contrary, if the search and rescue aircraft is flying away from the device to be rescued, that is, the device to be rescued is behind the search and rescue equipment, the first interrogation response gives a distance L1, and the second interrogation response gives a distance L2. Then, L2 > L1 will be obtained.

[0049] Affected by the ranging accuracy, in actual use, this method is not reliable, and at least two interrogation responses are required, resulting in very low efficiency.

[0050] (2) Calculate the Doppler frequency shift:

[0051] Assume that the frequencies of the search and rescue equipment and the device to be rescued are f0. Ideally, according to the Doppler effect formula, the theoretical frequency is calculated. Assume that the component of the relative motion speed of the signal source with respect to the interferometer along the line connecting the search and rescue equipment and the device to be rescued is Vr, and the speed of light is c. Then, the relationship between the received frequency fr and the transmitted frequency is as follows: when the two are approaching, fr = (c + Vr)f0 / c; when the two are moving away, fr = (c - Vr)f0 / c.

[0052] Therefore, if fr > f0, it is determined that the device to be rescued is in front of the search and rescue equipment; otherwise, it is determined that the device to be rescued is behind the search and rescue equipment.

[0053] This method can fail even with a small frequency error.

[0054] This embodiment proposes a method for determining the front and back directions in a dual-antenna interferometer direction finding, including the following steps:

[0055] S1. The search and rescue equipment sends a radio interrogation signal at frequency f1. The device to be rescued receives the interrogation signal sent by the search and rescue equipment, and outputs a frequency word m to the phase-locked loop through a carrier tracking loop (reference Figure 3 ) to track the frequency f1. The specific process after the device to be rescued receives the interrogation signal is as follows:

[0056] S101. The received interrogation electrical signal of the device to be rescued is converted by AD after passing through the channel to become an intermediate frequency signal;

[0057] S102. The intermediate frequency signal is mixed with a digital local oscillator signal (NCO), and after passing through a low-pass filter, it becomes two baseband signals of I (in-phase) and Q (quadrature);

[0058] S103. The two baseband signals of IQ enter a carrier loop discriminator (reference Figure 4 ) to output a frequency difference and a phase difference; Figure 4 where ω 0f is the natural circular frequency of the FLL, ω 0pis the natural circular frequency of the PLL; they are calculated from the value of the noise bandwidth of the loop filter selected by the designer.

[0059] S104. The frequency difference and phase difference enter the carrier loop filter, and the output frequency word m enters the numerically controlled oscillator, which controls the numerically controlled oscillator to output a digital local oscillator signal.

[0060] S2. The device to be rescued returns a radio response signal to the rescue device at frequency f2. The response signal contains the frequency word m. The rescue device receives the response signal sent by the device to be rescued, and outputs the frequency word n to the phase-locked loop through the carrier tracking loop to track the frequency f2. The specific process after the rescue device receives the response signal is the same as S1.

[0061] S3. The rescue device analyzes the response signal to obtain the frequency word m.

[0062] S4. Calculate the gain u of the carrier tracking loop. If u < 0, it is determined that the device to be rescued is in front of the rescue device; otherwise, it is determined that the device to be rescued is behind the rescue device. u is calculated by the following formula:

[0063] u = m + n

[0064] Among them, the theoretical calculations of m and n are as follows:

[0065] When the rescue device is approaching the device to be rescued (the device to be rescued is in front of the rescue device):

[0066] m = [(f0 + x2) - (f0 + x1) - |Fd|] × u

[0067] n = [(f0 + x1) - (f0 + x2) - |Fd|] × u

[0068] m + n = -2 × |Fd| × u;

[0069] If the rescue device is moving away from the device to be rescued (the device to be rescued is behind the rescue device):

[0070] m = [(f0 + x2) - (f0 + x1) + |Fd|] × u

[0071] n = [(f0 + x1) - (f0 + x2)) + |Fd|] × u

[0072] m + n = 2 × |Fd| × u;

[0073] The actual frequency of the search and rescue device is f1, where f1 = f0 + x1, and the actual frequency of the device to be rescued is f2, where f2 = f0 + x2. x1 and x2 are the frequency errors generated by the frequency synthesizers of the search and rescue device and the device to be rescued respectively, and can be positive or negative. The Doppler frequency shift is Fd, which can be positive or negative. When the search and rescue device is approaching the device to be rescued, Fd > 0; when the search and rescue device is moving away from the device to be rescued, Fd < 0.

[0074] In this embodiment, the carrier loop discriminator includes a frequency difference discriminator and a phase difference discriminator. The phase difference discriminator uses an atan(Q / I) phase discriminator, and the frequency difference discriminator uses a cross product dot product algorithm, specifically:

[0075]

[0076] The loop filter uses a third-order phase-locked loop (PLL) filter assisted by a second-order frequency-locked loop (FLL).

[0077] The method proposed in this embodiment does not increase the hardware cost. By one inquiry and response, it can be determined whether the device to be rescued is in front of or behind the search and rescue device. Compared with the traditional method, it improves the accuracy and efficiency of the determination.

[0078] The specific implementation manners of the present invention enable those skilled in the art to understand or implement the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention.

[0079] It should be understood that the present invention is not limited to the content described above, and various modifications and changes can be made without departing from its scope. The scope of the present invention is only limited by the appended claims.

Claims

1. A method for determining forward and backward directions in dual-antenna interferometer direction finding, characterized in that: The following steps are involved: S1, the search and rescue equipment sends a wireless telecommunication inquiry signal at frequency f1, the rescue equipment receives the inquiry signal sent by the search and rescue equipment, outputs the frequency word m to the phase-locked loop, and tracks the frequency f1; S2, the device to be rescued returns a radio response signal at frequency f2 to the search and rescue device, the response signal includes frequency word m, the search and rescue device receives the response signal sent by the device to be rescued, outputs frequency word n ​​to the phase-locked loop, and tracks the frequency f2; S3, the search and rescue equipment analyzes the response signal and obtains the frequency word m; S4. Determine whether the device to be rescued is in front of or behind the search and rescue device based on the frequency word m and the frequency word n.

2. The method for determining forward and backward directions in dual-antenna interferometer direction finding according to claim 1, characterized in that: In S1, the search and rescue equipment outputs the frequency word m to the phase-locked loop through the carrier tracking loop; in S2, the equipment to be rescued outputs the frequency word n ​​to the phase-locked loop through the carrier tracking loop.

3. The method for determining forward and backward directions in dual-antenna interferometer direction finding according to claim 2, characterized in that: S1 includes the following sub-steps: S101, the inquiry electrical signal received by the rescue device is converted into an intermediate frequency signal through AD conversion after passing through the channel; S102, the intermediate frequency signal is mixed with a digital local oscillator signal (NCO), and after low-pass filtering, it is converted into an IQ two-way baseband signal; S103, the IQ two-path baseband signal enters the carrier loop discriminator, and outputs the frequency difference and phase difference; S104, the frequency difference and phase difference enter the carrier loop filter, and output the frequency word m. After the frequency word m enters the digital controlled oscillator, the digital controlled oscillator is controlled to output a digital local oscillation signal.

4. The method for determining forward and backward directions in dual-antenna interferometer direction finding according to claim 3, characterized in that: The carrier loop identifier includes a frequency difference identifier and a phase difference identifier.

5. The method for determining forward and backward directions in dual-antenna interferometer direction finding according to claim 4, characterized in that: The frequency difference discriminator uses the cross product dot product algorithm:

6. The method for determining forward and backward directions in dual-antenna interferometer direction finding according to claim 4, characterized in that: The phase difference discriminator adopts Q / I phase detector.

7. The method for determining forward and backward directions in dual-antenna interferometer direction finding according to claim 3, characterized in that: The carrier loop filter adopts a third-order phase-locked loop filter assisted by a second-order frequency-locked loop.

8. The method for determining forward and backward directions in dual-antenna interferometer direction finding according to claim 2, characterized in that: In S4, the specific method for determining the direction of the device to be rescued based on the frequency word m and the frequency word n ​​is: the gain u of the carrier tracking loop is calculated by the frequency word m and the frequency word n. If u<0, it is determined that the device to be rescued is in front of the search and rescue equipment; otherwise, it is determined that the device to be rescued is behind the search and rescue equipment, where u is calculated by the following formula: u=m+n.

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