JP7716756B2 - radar receiver - Google Patents

Description

The present invention relates to a radar receiver with an automatic tuning function.

Radars installed on ships often use magnetrons to generate the RF (Radio Frequency) signal that is transmitted, but magnetrons have an unstable oscillation frequency. To obtain an appropriate received IF (Intermediate Frequency) signal at the receiver, the received RF frequency, which is determined by the frequency of the local oscillator, must be tuned to the frequency of the transmitted signal. Tuning can be done manually, where the user adjusts the receiving frequency using a volume control or other device, or automatically, where the receiver estimates the transmitting frequency using signal processing internal to the receiver and determines the receiving frequency without user intervention. Naturally, automatic tuning is more convenient.

The basic configuration of a radar system is shown in Figure 1. In radar system 900, a transmission signal generated by magnetron 910, which operates as a transmission signal oscillator, is radiated from antenna 930 via transmission/reception discriminator 920. A reflected wave from a reflecting object in the direction of antenna 930's pointing is input to antenna 930 as a received signal, and then input to radar receiver 800 via transmission/reception discriminator 920. Radar system 900 identifies the position of the reflecting object based on the time from transmission to reception and the pointing angle of antenna 930. Automatic tuning is often performed by analyzing the transmission signal (leakage transmission signal) that leaks from transmission/reception discriminator 920 to radar receiver 800 during transmission.

Traditionally, automatic tuning methods have involved observing the strength of the leaked transmission signal to determine the receiving frequency. However, because the frequency is determined directly from the strength, it is necessary to observe the strength while changing the receiving frequency, which presents an issue of time-consuming tuning. In situations where the frequency stability of the magnetron 910 is particularly poor, such as immediately after power-on, the variable range of the receiving frequency must also be widened, and this tendency becomes even more pronounced.

One solution to this problem is the technology disclosed in Patent Document 1. In Patent Document 1, the receiving frequency is determined after frequency analysis processing such as FFT (Fast Fourier Transform) is performed on the leaked transmission signal. By analyzing not only the level but also the frequency, it is possible to appropriately control the receiving frequency and speed up tuning.

JP 2007-333481 A

However, with the technology disclosed in Patent Document 1, the received signal is detected before being displayed, so the phase component contained in the received signal cannot be utilized for display processing (such as clutter removal). Converting the IF signal into a baseband IQ signal is an effective way to utilize the phase component of the received signal, but without tuning, the frequency of the IF signal is unknown, making it impossible to perform IQ conversion appropriately. Therefore, the present invention aims to provide tuning technology that does not lose the phase component.

The radar receiver of the present invention comprises 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 conversion unit receives as input a signal from the transmission/reception discriminator and a local oscillation signal, and outputs a received IF signal. The "signal from the transmission/reception discriminator" includes the received signal input from the antenna and the leaked transmission signal, and the leaked 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 time domain signal in which the leaked transmission signal is output from the transmission/reception discriminator. The analog local oscillation unit outputs a local oscillation signal with its frequency adjusted based on the results of the analysis by the frequency analysis unit. The digital local oscillator outputs a digital local oscillator signal with the same frequency as the digital IF signal based on the results of the frequency analysis. The IQ converter receives the digital IF signal and digital local oscillator signal as inputs and outputs baseband I and Q signals.

In the radar receiver of the present invention, the frequency analysis unit analyzes the frequency of the digital IF signal for the time domain signal in which the leakage transmission signal is output from the transmission/reception discriminator. Then, based on the results of the analysis by the frequency analysis unit, the frequencies of the analog local oscillator unit and the digital local oscillator unit are controlled, respectively. By using two types of local oscillators that share the corresponding frequency domains in this way, high-speed tuning is possible without losing the phase components of the received signal.

A diagram showing the basic configuration of a radar system. FIG. 1 is a diagram showing an example of the functional configuration of a radar receiver according to the present invention. FIG. 3 is a diagram showing an example of a processing flow in a frequency analysis unit of the radar receiver of the present invention.

Embodiments of the present invention will be described in detail below. Components with the same functions will be assigned the same numbers, and duplicate explanations will be omitted.

Figure 2 shows an example of the functional configuration of a radar receiver of the present invention. Figure 3 shows an example of the processing flow in the frequency analysis unit of the radar receiver of the present invention. Radar receiver 100 is used in place of radar receiver 800 in Figure 1. Radar receiver 100 includes a frequency conversion unit 110, a band limiting 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. It may also include LPFs 181 and 182. LPFs 181 and 182 are low pass filters that pass only baseband signals.

The frequency conversion unit 110 receives as input the signal from the transmission/reception discriminator 920 and a local oscillation signal (the output of the analog local oscillation unit 170, described below), 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 a leaked transmission signal, with the leaked transmission signal only present when the magnetron is outputting the transmission signal.

The band limiting unit 120 limits the band of the received IF signal and outputs a band-limited received IF signal. The frequency analysis unit 140, which will be described later, searches for a signal corresponding to the leaked transmission signal contained in the received IF signal, taking into account that the frequency of the magnetron 910 is prone 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 leaked transmission signal. Considering the processing in the frequency analysis unit 140, the band limiting unit 120 should limit the band of the received IF signal to as wide a band as possible within the maximum band that the A/D conversion unit 130 can convert to a digital signal.

The A/D conversion unit 130 converts the band-limited received IF signal into a digital signal and outputs the digital IF signal. According to the sampling theorem, when the sampling rate of the A/D conversion unit 130 is 1 G/sec, the bandwidth is 500 MHz or less, and when the sampling rate is 500 M/sec, the bandwidth is 250 MHz or less. The bandwidth limited by the above-mentioned band limiting unit 120 can be determined based on the number of samples per second taken by the A/D conversion unit 130.

The frequency analysis unit 140 analyzes the frequency of the digital IF signal for the time-domain signal output from the transmission/reception discriminator 920 as the leaked transmission signal (S30, S40). Here, we will explain the RF signal and the IF signal. For example, if the RF signal is 10 GHz and the IF signal is 0.1 GHz, local oscillation signals of 9.9 GHz and 10.1 GHz are possible. 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. As such, there are two methods for generating the received IF signal. In the frequency conversion unit 110, the signal with the desired phase relationship (in-phase or out-of-phase) is called the received IF signal, and the other signal (out-of-phase or in-phase) is called the image signal. Next, we will explain the processing for cases where the phase of the received IF signal is in phase with the transmission signal and when it is out-of-phase.

First, we will explain the case where the signals are in phase. The frequency analysis unit 140 detects the received IF signal by changing the frequency of the analog local oscillator 170 from the frequency obtained by subtracting the frequency of the received IF signal from the lowest frequency of the transmitted signal to a higher frequency (S310 to S340). Specifically, the frequency of the analog local oscillator 170 is set to the frequency obtained by subtracting the frequency of the received IF signal from the lowest frequency of the transmitted signal (S310). For example, if the possible oscillation frequency range of the magnetron 910 is 9.3 GHz to 9.5 GHz and the received IF signal is 0.1 GHz, the frequency is set to 9.2 GHz. The frequency analysis unit 140 analyzes whether there is a digital IF signal that exceeds a predetermined threshold (S320). If there is no digital IF signal (NO in S330), the oscillation frequency of the analog local oscillator 170 is shifted upward (S340). In this case, the frequency shift can be set to a large value within the bandwidth of the band-limiting unit 120, enabling faster tuning. If a digital IF signal is present (YES in S330), proceed to step S350. In step S350, the oscillation frequency of the analog local oscillator 170 is deliberately changed to tune to the image signal (increased), and a check is made to see if a digital IF signal can be obtained at the upper local oscillation frequency (S350). If a digital IF signal can be detected at the upper local oscillation frequency (YES in step S350), proceed to step S40. If a digital IF signal cannot be detected at the upper local oscillation frequency (NO in step S350), the previous determination (S330) is made to detect an image signal, and the local oscillation frequency is set to a frequency twice the received IF frequency lower than the frequency detected in S330 (S360). After confirming that the received IF signal and image signal are present in the expected frequency relationship, proceed to step S40.

Next, we will explain the case of reverse phase. The frequency analysis unit 140 detects the received IF signal while changing the frequency of the analog local oscillator 170 from the frequency obtained by adding the frequency of the received IF signal to the highest frequency of the transmitted signal to a lower frequency (S310 to S340). Specifically, the frequency of the analog local oscillator 170 is set to the frequency obtained by adding the frequency of the received IF signal to the highest frequency of the transmitted signal (S310). For example, if the possible oscillation frequency range of the magnetron 910 is 9.3 GHz to 9.5 GHz and the received IF signal is 0.1 GHz, the frequency 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 (NO in S330), the oscillation frequency of the analog local oscillator 170 is shifted downward (S340). By shifting the frequency significantly within the bandwidth of the band-limiting unit 120, faster tuning is possible. If a digital IF signal is present (YES in S330), proceed to step S350. In step S350, the oscillation frequency of the analog local oscillator 170 is deliberately changed to tune it to the image signal (lowering the frequency), and a check is made to see if a digital IF signal can be obtained at the lower local oscillation frequency (S350). If a digital IF signal is detected at the lower local oscillation frequency (YES in step S350), proceed to step S40. If a digital IF signal is not detected at the lower local oscillation frequency (NO in step S350), the previous determination (S330) is made that an image signal was detected, and the local oscillation frequency is set to a frequency twice the received IF frequency higher than the frequency detected in S330 (S360). Then, after confirming that the received IF signal and image signal exist in the expected frequency relationship, proceed to step S40.

The digital local oscillator 160 outputs a digital local oscillator signal with the same frequency as the digital IF signal based on the results of the analysis by the frequency analysis unit 140 (S40). The frequency analysis unit 140 analyzes the frequency of the digital IF signal for the time domain signal in which the leaky transmission signal is output from the transmission/reception discriminator 920 (S410). The digital local oscillator 160 outputs a digital local oscillator signal with the same frequency as the digital IF signal based on the results of the analysis by the frequency analysis unit (S420).

Because the oscillation frequency of the magnetron 910 constantly fluctuates depending on factors such as temperature, frequency analysis and confirmation of the presence of a received IF signal are repeated. The frequency analysis unit 140 repeatedly analyzes the frequency of the digital IF signal for the time domain signal in which the leaked transmission signal is output from the transmission/reception discriminator 920 (S430) and confirms the presence of a digital IF signal (S440). If a digital IF signal is present (YES in step S440), the process returns to step S410. If a digital IF signal is not present (NO in step S440), the oscillation frequency of the analog local oscillator 170 is changed (S450). More specifically, since the frequency of the digital IF signal is measured until the digital IF signal disappears, the oscillation frequency of the analog local oscillator 170 can be changed based on the trend of the digital IF signal immediately before it disappears.

The analog local oscillator 170 outputs a local oscillator signal with an adjusted frequency based on the results of the analysis by the frequency analysis unit 140. The analog local oscillator 170 oscillates at a frequency that is different from the received RF signal by the received IF signal, thereby generating a local oscillator signal. By oscillating at such a frequency, the frequency conversion unit 110 can use the signal from the transmission/reception discriminator 920 and the local oscillator signal as input signals and output a received IF signal.

The IQ conversion unit 150 receives a digital IF signal and a digital local oscillation signal as input, and outputs a signal containing a baseband I signal and a signal containing a baseband Q signal. Furthermore, LPFs 181 and 182 are low pass filters that pass only baseband signals. The received I signal is output from LPF 181, and the received Q signal is output from LPF 182.

Since the digital local oscillator 160 generally changes frequency faster than the analog local oscillator 170, widening the passband width of the band limiter 120 enables faster frequency tuning. Ultimately, limiting the frequency to the narrow band required by the radar receiver can be performed by LPFs 181 and 182. However, if the tracking ability is too high, the system may react too sensitively to even slight frequency fluctuations, causing the radar display to appear strange. Therefore, if the radar display appears strange, it is best to track it gently enough so that the strangeness does not occur.

In the radar receiver 100 of the present invention, the frequency analysis unit 140 analyzes the frequency of the digital IF signal for the time-domain signal output from the transmission/reception discriminator 920, which is the leaked transmission signal. Then, based on the results of the analysis by the frequency analysis unit 140, the frequencies of the analog local oscillator 170 and the digital local oscillator 160 are controlled, respectively. Using two types of local oscillators that share corresponding frequency domains in this way enables high-speed tuning without losing the phase components of the received signal. This contributes to the sophistication of signal processing received by the radar. For example, it becomes easier to detect the Doppler effect caused by object movement. It also makes it easier to analyze the characteristics of reflections from the sea surface. Furthermore, by widening the passband of the band-limiting unit 120 within the range allowable by the A/D conversion unit 130 and widening the frequency range supported by the digital local oscillator 160, it becomes possible to track faster oscillation frequencies.

100 Radar receiver 110 Frequency conversion section 120 Bandwidth limiting section 130 A/D conversion section 140 Frequency analysis section 150 IQ conversion section 160 Digital local oscillation section 170 Analog local oscillation section 800 Radar receiver 900 Radar system 910 Magnetron 920 Transmission/reception discriminator 930 Antenna

Claims (4)

a frequency conversion unit that receives a signal from the transmission/reception discriminator and a local oscillation signal as input signals and outputs a reception 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 converter that converts the band-limited received IF signal into a digital signal and outputs the digital IF signal;
a frequency analysis unit that analyzes the frequency of the digital IF signal for a time domain signal in which the leakage transmission signal is output from the transmission/reception discriminator;
an analog local oscillation unit that outputs a local oscillation signal whose frequency has been adjusted based on the result of analysis by the frequency analysis unit;
a digital local oscillation unit that 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;
a radar receiver comprising an IQ conversion unit that receives the digital IF signal and the digital local oscillation signal as inputs and outputs baseband I and Q signals. 2. The radar receiver of claim 1,
The radar receiver, wherein the band limiting unit limits the band of the received IF signal to a maximum band that can be converted into a digital signal by the A/D conversion unit. 3. A radar receiver according to claim 1 or 2,
The frequency analysis unit
Detecting the received IF signal while changing the frequency of the analog local oscillator from a frequency obtained by subtracting the frequency of the received IF signal from the lowest frequency of the transmission signal to a higher frequency;
When a received IF signal is detected, it is confirmed whether a digital IF signal can be obtained even at an upper local oscillation frequency at which an image signal corresponding to the received IF signal can be received;
A radar receiver characterized in that, if a digital IF signal cannot be confirmed at the upper local oscillation frequency, the previously detected received IF signal is determined to be an image signal, and a received IF signal present at a lower frequency is detected. 3. A radar receiver according to claim 1 or 2,
The frequency analysis unit
The frequency of the analog local oscillator is changed from a frequency obtained by adding the frequency of the received IF signal to the highest frequency of the transmission signal to a lower frequency, and the received IF signal is detected.
When a received IF signal is detected, it is confirmed whether a digital IF signal can be obtained even at a lower local oscillation frequency at which an image signal corresponding to the received IF signal can be received;
A radar receiver characterized in that, if a digital IF signal cannot be confirmed at a lower local oscillation frequency, the previously detected received IF signal is determined to be an image signal, and a received IF signal present at a higher frequency is detected.