Radar Receiver

Abstract

To provide a tuning technique that does not lose phase components.SOLUTION: A radar receiver of the present invention includes a frequency conversion unit, a band limiting unit, an A / D conversion unit, a frequency analysis unit, an analog local oscillation unit, a digital local oscillation unit, and an IQ conversion unit. The frequency analysis unit analyzes the frequency of a digital IF signal with respect to a time domain signal in which a leaky transmission signal is output from a transmission / reception discriminator. The analog local oscillation unit outputs a local oscillation signal with frequency adjusted based on a result of the analysis by the frequency analysis unit. The digital local oscillation unit outputs a digital local oscillation signal having the same frequency as the digital IF signal based on the result of the analysis by the frequency analysis unit.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a radar receiver having an automatic tuning function.

Background Art

[0002] In a radar mounted on a ship, a magnetron is often used to generate an RF (Radio Frequency) signal which is a transmission signal. However, the oscillation frequency of the magnetron is unstable. In order to obtain an appropriate received IF (Intermediate Frequency) signal in the receiver, it is necessary to synchronize the received RF frequency determined by the frequency of the local oscillator with the frequency of the transmission signal. For tuning, there are manual tuning in which the user adjusts the received frequency himself / herself by means of volume or the like, and automatic tuning in which the transmission frequency is estimated by signal processing inside the receiver and the received frequency is determined without the intervention of the user. Naturally, automatic tuning is more convenient.

[0003] The basic configuration of a radar system is shown in FIG. 1. In a radar system 900, a transmission signal generated by a magnetron 910 operating as a transmission signal oscillator is radiated from an antenna 930 via a transmit / receive discriminator 920. A reflected wave from a reflector existing in the direction of the antenna 930 is input to the antenna 930 as a received signal and input to a radar receiver 800 via the transmit / receive discriminator 920. The radar system 900 identifies the position of the reflector based on the time from transmission to reception and the direction angle of the antenna 930. Automatic tuning is often performed by analyzing a transmission signal (leakage transmission signal) leaking from the transmit / receive discriminator 920 to the radar receiver 800 during transmission.

[0004] Conventionally, a method of observing the intensity of a leakage transmission signal to determine the received frequency has been used as an automatic tuning method. However, since the frequency is directly determined from the intensity, it is necessary to observe the intensity while changing the received frequency, and there is a problem that tuning takes time. In a situation where the frequency stability of the magnetron 910 is particularly poor, such as immediately after power-on, it is also necessary to increase the variable range of the received frequency, and this tendency becomes more prominent.

[0005] As a solution, there is a technology disclosed in Patent Document 1. In Patent Document 1, frequency analysis processing such as FFT (Fast Fourier Transform) is performed on the leakage transmission signal, and then the received frequency is determined. By analyzing not only the level but also the frequency, the received frequency can be appropriately controlled, and the synchronization speed can be increased.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, in the technology disclosed in Patent Document 1, since the received signal is detected and then used for display, the phase component included in the received signal cannot be utilized for display processing (such as clutter removal). In order to utilize the phase component of the received signal, a method of converting the IF signal into a baseband IQ signal is effective. However, in a state where synchronization has not been performed, since the frequency of the IF signal is unknown, the IQ conversion cannot be appropriately performed. Therefore, an object of the present invention is to provide a synchronization technique that does not lose the phase component.

Means for Solving the Problems

[0008] The radar receiver of the present invention includes a frequency conversion unit, a band limiting unit, an A / D conversion unit, a frequency analysis unit, an analog local oscillator unit, a digital local oscillator unit, and an IQ conversion unit. The frequency conversion unit takes the signal from the transmit / receive discriminator and the local oscillation signal as input signals and outputs a received IF signal. The "signal from the transmit / receive discriminator" includes the received signal input from the antenna and the leakage transmission signal, and the leakage transmission signal exists only when the magnetron is outputting the transmission signal. The band limiting unit limits the band of the received IF signal and outputs a band-limited received IF signal. The A / D conversion unit converts the band-limited received IF signal into a digital signal and outputs a digital IF signal. The frequency analysis unit analyzes the frequency of the digital IF signal for the signal in the time domain when the leakage transmission signal is output from the transmit / receive discriminator. The analog local oscillator unit outputs a local oscillation signal with adjusted frequency based on the result analyzed by the frequency analysis unit. The digital local oscillator unit outputs a digital local oscillation signal with the same frequency as the digital IF signal based on the result analyzed by the frequency analysis unit. The IQ conversion unit takes the digital IF signal and the digital local oscillation signal as inputs and outputs baseband I signal and Q signal.

Effect of the Invention

[0009] According to the radar receiver of the present invention, the frequency analysis unit analyzes the frequency of the digital IF signal for the signal in the time domain when the leakage transmission signal is output from the transmit / receive discriminator. Then, based on the result analyzed by the frequency analysis unit, the frequencies of the analog local oscillator unit and the digital local oscillator unit are respectively controlled. By using two types of local oscillators that share the frequency regions corresponding in this way, high-speed synchronization is possible without losing the phase components of the received signal.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Best Mode for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described in detail. Components having the same function are given the same number, and redundant explanations are omitted.

Examples

[0012] FIG. 2 shows a functional configuration example of the radar receiver of the present invention. FIG. 3 shows an example of a processing flow in the frequency analysis unit of the radar receiver of the present invention. The radar receiver 100 is used in place of the radar receiver 800 in FIG. 1. The radar receiver 100 includes a frequency conversion unit 110, a band limitation unit 120, an A / D conversion unit 130, a frequency analysis unit 140, an analog local oscillation unit 170, a digital local oscillation unit 160, and an IQ conversion unit 150. Further, LPFs 181 and 182 may also be provided. The LPFs 181 and 182 are low-pass filters that pass only baseband signals.

[0013] The frequency conversion unit 110 takes as input signals the signal from the transmission / reception discriminator 920 and the local oscillation signal (the output of the analog local oscillation unit 170 described later), and outputs a received IF signal. The "signal from the transmission / reception discriminator 920" includes the received signal (received RF signal) received by the antenna 930 and the leakage transmission signal, and the leakage transmission signal exists only when the magnetron is outputting the transmission signal.

[0014] The band limitation unit 120 limits the band of the received IF signal and outputs a band-limited received IF signal. In the frequency analysis unit 140 described later, a signal corresponding to the leakage transmission signal included in the received IF signal is searched while considering that the frequency of the magnetron 910 is likely to change. The wider the range of frequencies that can be searched at one time, the easier it is to search for a signal corresponding to the leakage transmission signal. Considering the processing in the frequency analysis unit 140, the band limitation unit 120 may limit the band of the received IF signal to the widest possible band within the maximum band that the A / D conversion unit 130 can convert into a digital signal.

[0015] The A / D conversion unit 130 converts the band-limited received IF signal into a digital signal and outputs the digital IF signal. Since it follows the sampling theorem, when the number of samplings of the A / D conversion unit 130 is 1 G / s, the bandwidth is 500 MHz or less, and when the number of samplings is 500 M / s, the bandwidth is 250 MHz or less. The bandwidth restricted by the above-mentioned band-limiting unit 120 may be determined based on the number of samplings per second of the A / D conversion unit 130.

[0016] The frequency analysis unit 140 analyzes the frequency of the digital IF signal with respect to the signal in the time domain from which the leakage transmission signal is output from the transmission / reception discriminator 920 (S30, S40). Here, the RF signal and the IF signal will be described. For example, when the RF signal is 10 GHz and the IF signal is 0.1 GHz, 9.9 GHz and 10.1 GHz can be considered as the local oscillation signals. In the case of 9.9 GHz, the received IF signal is in phase with the transmission signal. In the case of 10.1 GHz, the received IF signal is out of phase with the transmission signal. Thus, there are two generation methods for the received IF signal. In the frequency conversion unit 110, a signal with a desired phase relationship (in-phase or out-of-phase) is used as the received IF signal, and the other signal (out-of-phase or in-phase) is referred to as the image signal. Next, the processing will be described separately for the case where the phase of the received IF signal is in phase with the transmission signal and the case where it is out of phase.

[0017] First, the case of in-phase will be described. The frequency analysis unit 140 detects the received IF signal while changing the frequency of the analog local oscillator unit 170 from the frequency obtained by subtracting the frequency of the received IF signal from the lowest frequency of the transmission signal to a higher frequency (from S310 to S340). Specifically, the frequency of the analog local oscillator unit 170 is set to the frequency obtained by subtracting the frequency of the received IF signal from the lowest frequency of the transmission signal (S310). For example, if the oscillation frequency range of the assumed magnetron 910 is 9.3 GHz to 9.5 GHz and the received IF signal is 0.1 GHz, it is set to 9.2 GHz. The frequency analysis unit 140 analyzes whether there is a digital IF signal exceeding a predetermined threshold (S320). If there is no digital IF signal (when S330 is NO), the oscillation frequency of the analog local oscillator unit 170 is shifted in the higher direction (S340). By setting a large shift frequency within the band of the band limiting unit 120 at this time, the synchronization speed can be increased. If there is a digital IF signal (when S330 is YES), the process proceeds to step S350. In step S350, the oscillation frequency of the analog local oscillator unit 170 is intentionally changed to be synchronized with the image signal (increase the frequency), and it is confirmed whether a digital IF signal can be obtained even at the upper local oscillation frequency (S350). If a digital IF signal can be confirmed even at the upper local oscillation frequency (when step S350 is YES), the process proceeds to step S40. If a digital IF signal cannot be confirmed at the upper local oscillation frequency (when step S350 is NO), assuming that the image signal was detected in the previous determination (S330), the local oscillation frequency is set to a frequency that is twice lower than the received IF frequency from the frequency detected in S330 (S360). Then, it is confirmed that the received IF signal and the image signal exist in the assumed frequency relationship, and the process proceeds to step S40.

[0018] Next, the case of reverse phase will be described. The frequency analysis unit 140 detects the received IF signal while changing the frequency of the analog local oscillator unit 170 from the frequency obtained by adding the frequency of the received IF signal to the highest frequency of the transmission signal to a lower frequency (from S310 to S340). Specifically, the frequency of the analog local oscillator unit 170 is set to the frequency obtained by adding the frequency of the received IF signal to the highest frequency of the transmission signal (S310). For example, if the oscillation frequency range of the assumed magnetron 910 is 9.3 GHz to 9.5 GHz and the received IF signal is 0.1 GHz, it is set to 9.6 GHz. The frequency analysis unit 140 analyzes whether there is a digital IF signal exceeding a predetermined threshold (S320). If there is no digital IF signal (when S330 is NO), the oscillation frequency of the analog local oscillator unit 170 is shifted in the lower direction (S340). By taking a large frequency shift within the band of the band limiting unit 120 at this time, the synchronization speed can be increased. If there is a digital IF signal (when S330 is YES), the process proceeds to step S350. In step S350, the oscillation frequency of the analog local oscillator unit 170 is intentionally changed to be synchronized with the image signal (lower the frequency), and it is confirmed whether a digital IF signal can be obtained even at the lower local oscillation frequency (S350). If a digital IF signal can be confirmed even at the lower local oscillation frequency (when step S350 is YES), the process proceeds to step S40. If a digital IF signal cannot be confirmed at the lower local oscillation frequency (when step S350 is NO), assuming that the image signal was detected in the previous determination (S330), the local oscillation frequency is set to a frequency twice as high as the received IF frequency from the frequency detected in S330 (S360). Then, it is confirmed that the received IF signal and the image signal exist in the assumed frequency relationship, and the process proceeds to step S40.

[0019] Based on the result analyzed by the frequency analysis unit 140, the digital local oscillator unit 160 outputs a digital local oscillation signal with the same frequency as the digital IF signal (S40). The frequency analysis unit 140 analyzes the frequency of the digital IF signal for the signal in the time domain where the leakage transmission signal is output from the transmission / reception discriminator 920 (S410). The digital local oscillator unit 160 outputs a digital local oscillation signal with the same frequency as the digital IF signal based on the result analyzed by the frequency analysis unit (S420).

[0020] Since the oscillation frequency of the magnetron 910 always fluctuates depending on temperature and the like, frequency analysis and confirmation of the presence of the received IF signal will be repeated hereafter. The frequency analysis unit 140 analyzes the frequency of the digital IF signal for the signal in the time domain where the leakage transmission signal is repeatedly output from the transmission / reception discriminator 920 (S430), and confirms the presence of the digital IF signal (S440). If the digital IF signal exists (when step S440 is YES), it returns to step S410. If the digital IF signal does not exist (when step S440 is NO), the oscillation frequency of the analog local oscillator unit 170 is changed (S450). More specifically, since the frequency of the digital IF signal is measured until the digital IF signal no longer exists, the oscillation frequency of the analog local oscillator unit 170 may be changed based on the trend of the digital IF signal immediately before it no longer exists.

[0021] Based on the result analyzed by the frequency analysis unit 140, the analog local oscillator unit 170 outputs a locally oscillated signal with the frequency adjusted. The analog local oscillator unit 170 oscillates at a frequency different only for the received IF signal with respect to the received RF signal and generates a local oscillation signal. By oscillating at such a frequency, the frequency conversion unit 110 can input the signal from the transmission / reception discriminator 920 and the local oscillation signal as input signals and output the received IF signal.

[0022] The IQ conversion unit 150 takes a digital IF signal and a digital local oscillation signal as inputs and outputs a signal including a baseband I signal and a signal including a Q signal. Also, LPFs 181 and 182 are low-pass filters that allow only baseband signals to pass through. A received I signal is output from LPF 181, and a received Q signal is output from LPF 182.

[0023] Generally, since the digital local oscillator unit 160 can change frequencies faster than the analog local oscillator unit 170, by widening the pass frequency bandwidth of the band-limiting unit 120, it becomes possible to speed up frequency synchronization. Finally, the limitation to the narrow band required by the radar receiver can be achieved by LPFs 181 and 182. However, if the followability is too high, it may react overly sensitively to even slight frequency fluctuations, causing a sense of discomfort in the radar display. Therefore, when a sense of discomfort occurs in the radar display, it may be made to follow gently to the extent that no discomfort is felt.

[0024] According to the radar receiver 100 of the present invention, the frequency analysis unit 140 analyzes the frequency of the digital IF signal with respect to the signal in the time domain in which the leakage transmission signal is output from the transmission / reception discriminator 920. Then, based on the result analyzed by the frequency analysis unit 140, the frequencies of the analog local oscillator unit 170 and the digital local oscillator unit 160 are controlled respectively. By using two types of local oscillators that share the frequency range to be corresponded in this way, high-speed synchronization is possible without losing the phase component of the received signal. Therefore, it becomes possible to contribute to the advancement of signal processing received by the radar. For example, it also becomes easier to detect the Doppler effect caused by the movement of an object. Also, it becomes easier to analyze the characteristics of reflection on the sea surface. Furthermore, by widening the pass band of the band-limiting unit 120 within an acceptable range by the A / D conversion unit 130 and widening the corresponding frequency range of the digital local oscillator unit 160, it becomes possible to follow a higher oscillation frequency.

Explanation of Reference Numerals

[0025] 100 Radar Receiver 110 Frequency Conversion Unit 120 Band-limiting section 130 A / D conversion section 140 Frequency analysis section 150 IQ conversion section 160 Digital local oscillator 170 Analog local oscillator 800 Radar receiver 900 Radar system 910 Magnetron 920 Transmit / receive discriminator 930 Antenna

Claims

1. A frequency conversion unit that takes the signal from the transceiver discriminator and the local oscillation signal as input signals and outputs a received IF signal, A band limiting unit that limits the band of the received IF signal and outputs a band-limited received IF signal, An A / D conversion unit that converts the band-limited received IF signal into a digital signal and outputs a digital IF signal, A frequency analysis unit that analyzes the frequency of the digital IF signal with respect to the signal in the time domain where the leakage transmission signal is output from the transceiver discriminator, An analog local oscillator unit that outputs a locally oscillated signal with its frequency adjusted based on the result analyzed by the frequency analysis unit, A digital local oscillator unit that outputs a digital locally oscillated signal with the same frequency as the digital IF signal based on the result analyzed by the frequency analysis unit, An IQ conversion unit that takes the digital IF signal and the digital locally oscillated signal as inputs and outputs baseband I signal and Q signal A radar receiver comprising the above components.

2. The radar receiver according to Claim 1, wherein the band limiting unit limits the band of the received IF signal to be equal to or less than the maximum band that the A / D conversion unit can convert into a digital signal A radar receiver characterized by the above.

3. The radar receiver according to Claim 1 or 2, wherein the frequency analysis unit detects the received IF signal while changing the frequency of the analog local oscillator unit from the frequency obtained by subtracting the frequency of the received IF signal from the lowest frequency of the transmission signal to a higher frequency, when the received IF signal is detected, checks whether a digital IF signal can be obtained even at the upper local oscillation frequency at which an image signal corresponding to the received IF signal can be received, if a digital IF signal cannot be confirmed at the upper local oscillation frequency, determines the previously detected received IF signal as an image signal and detects the received IF signal existing at a lower frequency A radar receiver characterized by the above.

4. The radar receiver according to Claim 1 or 2, wherein the frequency analysis unit detects the received IF signal while changing the frequency of the analog local oscillator unit from the frequency obtained by adding the frequency of the received IF signal to the highest frequency of the transmission signal to a lower frequency, when the received IF signal is detected, checks whether a digital IF signal can be obtained even at the lower local oscillation frequency at which an image signal corresponding to the received IF signal can be received, When a digital IF signal cannot be confirmed at the lower local oscillation frequency, the previously detected received IF signal is determined to be an image signal, and a received IF signal existing at a higher frequency is detected. A radar receiver characterized by the above.

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