JP4450802B2 - Radar receiver - Google Patents

Description

The present invention relates to a radar receiver that generates a DC signal corresponding to an output frequency signal with a frequency discriminator, and generates a control frequency signal based on the DC signal with a voltage-controlled oscillator. The present invention relates to a radar receiver suitable for frequency acquisition of an intermediate frequency signal in a receiver .

Conventionally, in a marine radar, a transmission signal (a pulse modulation signal including a carrier wave repeatedly generated within a predetermined time) is transmitted as a radio wave during one rotation of the antenna, and the reflection when the radio wave is reflected by a target. A wave is received by the receiver as a reception signal (a pulse modulation signal including a carrier wave corresponding to the transmission signal) through the antenna. In this case, in the receiver is performed an automatic frequency control for frequency pull-in a short time the reception signal.

For example, in the receiver according to the automatic frequency control circuits disclosed in Non-Patent Document 1, the received signal is converted into a low-frequency intermediate frequency signal (IF signal) in the mixer, the output frequency signal the IF signal Output as. Here, when the frequency of the carrier wave constituting the IF signal (hereinafter also referred to as IF frequency) is detuned from a predetermined tuning frequency, a signal level corresponding to the IF frequency is set by a frequency discriminator. Generating a DC frequency signal, and generating a control frequency signal having a local oscillation frequency corresponding to the DC signal with a voltage controlled oscillator (VCO), and the mixer based on the local oscillation frequency, the received signal It is converted into an IF signal with a tuning frequency and output.

Takayoshi Ohkoshi, University Course Basic Electronic Circuit (2nd revised edition), Ohmsha, published on December 20, 1984

  In the aforementioned ship radar, when the transmission time of the transmission signal during one rotation of the antenna is shortened (for example, when shortened from 1 [μs] to 0.1 [μs]), the distance resolution of the ship radar is As a result, the reception time of the reception signal and the time width of the IF signal converted from the reception signal (hereinafter also referred to as output time) are reduced. Thereby, in the frequency discriminator, when the DC signal rises with time due to the input of the IF signal, the input of the IF signal is completed before the signal level reaches the peak level. There is a problem that a DC signal having a signal level corresponding to the IF frequency cannot be output to the VCO.

  Further, since the VCO generates a control frequency signal based on the DC signal that does not correspond to the IF frequency, when the transmission time, the reception time, or the output time is shortened, the mixer converts the reception signal into There is a problem that it cannot be converted into an IF signal having a tuning frequency.

The present invention has been made to solve the above-described problems, and ensures the response of the frequency discriminator even if the transmission time of the transmission signal, the reception time of the reception signal, and the output time of the output frequency signal are shortened. Another object of the present invention is to provide a radar receiver capable of suppressing the frequency fluctuation of the output frequency signal.

A radar receiver according to the present invention receives a received signal, and generates a first frequency signal in a radar receiver that converts the received signal into an output frequency signal having a frequency lower than that of the received signal . generating a 1 oscillator, a mixer for generating a second frequency signal having a frequency higher than said output frequency signal based on said output frequency signal and said first frequency signal, a DC signal corresponding to the second frequency signal And a second oscillator for generating a control frequency signal for tuning the output frequency signal to a predetermined frequency based on the DC signal.

In this case, the mixer converts the output frequency signal into the high-frequency second frequency signal based on the first frequency signal and outputs the second frequency signal to the frequency discriminator, so that the frequency discriminator It is possible to generate the DC signal according to the above. Therefore, when applying the receiver of the radar receiver marine radar, the transmission time of the transmission signal, even by shortening the output time of the reception time and the output frequency signal of the received signal, said frequency discriminator Responsiveness can be ensured.

  Further, since the responsiveness of the frequency discriminator is ensured, the receiver converts the received signal into an IF signal (output frequency) having a predetermined tuning frequency based on the control frequency signal generated by the second oscillator. Signal). Thereby, in the receiver, the frequency fluctuation of the output frequency signal can be suppressed.

Furthermore, the radar receiver further includes a filter that removes a high-frequency signal component of the output frequency signal included in the DC signal and supplies the signal to the second oscillator, so that the frequency fluctuation of the output frequency signal can be reliably ensured. Can be suppressed.

  According to the present invention, even if the transmission time of the transmission signal, the reception time of the reception signal, and the output time of the output frequency signal are shortened, the response of the frequency discriminator is ensured and the frequency fluctuation of the output frequency signal is suppressed. Can be realized together.

A preferred embodiment in which a radar receiver according to the present invention is applied to a marine radar receiver will be described below with reference to the accompanying drawings. Prior to the description, the assumption of the present embodiment will be described. The configuration of the receiver and its problems will be described with reference to FIGS.

Figure 1 is a block diagram of a marine radar 10 the receiver 1 8 which is a premise of this embodiment is applied.

  The marine radar 10 includes an antenna (hereinafter also referred to as an antenna) 12, a circulator 14, a transmitter 16, a receiver 18, a processing device 20, and a display device 22, and is arranged (mounted) in a marine vessel (not shown). Has been.

  A transmission signal (pulse modulated signal including a carrier wave repeatedly generated within a predetermined time) St output from the transmitter 16 during one rotation of the antenna 12 is radiated from the antenna 12 to the surroundings as a radio wave 34 via the circulator 14. Is done. The radio wave 34 is reflected by a target separated from the marine radar 10 by a predetermined distance, and the reflected wave 30 is received by the receiver 18 via the antenna 12 and the circulator 14 (pulse modulation including a carrier wave corresponding to the transmission signal). Signal) Sr.

  The receiver 18 includes a mixer 32, a distributor (or coupler) 24, a frequency discriminator 26, and a VCO (second oscillator) 28.

  The mixer 32 converts the received signal Sr into a lower frequency IF signal (output frequency signal) So based on the control frequency signal Sc from the VCO 28. The distributor 24 outputs the IF signal So to the processing device 20 and / or the input port 26 a of the frequency discriminator 26. The frequency discriminator 26 generates a DC signal Sd having a signal level corresponding to the IF frequency of the IF signal So, and outputs the DC signal Sd from the output port 26b to the VCO 28. The VCO 28 generates a control frequency signal Sc having a predetermined local oscillation frequency based on the DC signal Sd.

  Here, when the IF frequency is detuned from a predetermined tuning frequency (when the frequency variation of the IF frequency with respect to the tuning frequency occurs), the IF signal by the distributor 24, the frequency discriminator 26, and the VCO 28. Based on the feedback of So, the mixer 32 generates an IF signal So having the tuning frequency from the received signal Sr based on the local oscillation frequency, and outputs the generated IF signal So to the processing device 20 via the distributor 24. To do. When the IF frequency is a tuning frequency, the signal level of the DC signal Sd output from the output port 26b of the frequency discriminator 26 is substantially zero level.

  Based on the input IF signal So, the processing device 20 calculates the azimuth and distance of the target from the ship on which the ship radar 10 is mounted, and outputs it to the display device 22. The display device 22 displays an image of the azimuth and distance of the target from the ship on the display screen.

  Next, problems (first problem to third problem) of the receiver 18 applied to the marine radar 10 will be described.

  In the marine radar 10, when the transmission time of the transmission signal St during one rotation of the antenna 12 is shortened from 1 [μs] to 0.1 [μs], for example, the distance resolution of the marine radar 10 is improved. Correspondingly, however, the reception time of the reception signal Sr and the output time of the IF signal So frequency-converted by the mixer 32 are shortened.

  FIG. 2A shows an IF signal So input to an input port 26a (see FIG. 1) of the frequency discriminator 26 and having an IF frequency (eg, 30 [MHz]) detuned from the tuning frequency (eg, 60 [MHz]). 2B schematically shows the time course of the DC signal Sd output from the output port 26b of the frequency discriminator 26. FIG.

  When the reception time of the reception signal Sr is shortened, the number of carrier waves in the IF signal So is, for example, as shown in FIG. 2A, from the number including the carrier wave indicated by the broken line and the carrier wave indicated by the solid line, The DC signal Sd shown in FIG. 2B rises with the passage of time from time t0 due to the input of the carrier wave, but the input of the carrier wave ends at time t1, A DC signal Sd having a signal level V1 is output from the output port 26b of the discriminator 26 to the VCO 28.

  That is, in the frequency discriminator 26, if there is a carrier input for 6 cycles or more, the signal level of the DC signal Sd reaches the peak level V2 at time t2, and the signal level corresponding to the frequency (IF frequency) of the carrier wave. The DC signal Sd of the frequency discriminator 26 can be generated, but as described above, since the input of the carrier wave is stopped before the peak level V2 is reached, the IF port from the output port 26b of the frequency discriminator 26 is connected to the IF The DC signal Sd having the signal level V1 that does not correspond to the frequency is supplied. Therefore, when the transmission time, the reception time, and the output time are shortened, the VCO 28 generates the control frequency signal Sc based on the DC signal Sd that does not correspond to the IF frequency. This is the first problem.

  In addition, since the VCO 28 generates the control frequency signal Sc based on the DC signal Sd that does not correspond to the IF frequency, the receiver 18 can reduce the transmission time, the reception time, and the output time. Therefore, it is impossible to cope with the frequency variation of the IF signal So (detuning of the IF frequency with respect to the tuning frequency). This is the second problem.

  Further, in the DC signal Sd output from the output port 26b of the frequency discriminator 26, a part of the reception signal Sr and the IF signal So is superimposed on the waveform of the DC signal Sd in FIG. Therefore, the accuracy of the control frequency signal Sc generated by the VCO 28 is lowered, and the frequency fluctuation of the IF signal So cannot be suppressed. This is the third problem.

  The above is the first problem to the third problem of the receiver 18 which is the premise of the present embodiment.

  Next, a marine radar 40 to which the receiver 42 according to this embodiment is applied will be described with reference to FIG.

  In describing the marine radar 40, the same constituent elements as those of the marine radar 10 (see FIG. 1) will be described with the same reference numerals.

  As shown in FIG. 3, the marine radar 40 includes a mixer 46 and an oscillator (first oscillator) 44 between the output side of the distributor 24 and the input port 26 a of the frequency discriminator 26 in the receiver 42. Furthermore, it differs from the marine radar 10 which is the premise of the present embodiment in that a low pass filter (LPF) 48 is provided between the output port 26b of the frequency discriminator 26 and the VCO 28.

  Here, the mixer 46 generates the second frequency signal S2 in which the difference between the first frequency of the first frequency signal S1 from the oscillator 44 and the IF frequency of the IF signal So from the distributor 24 is the second frequency. . In this case, the first frequency is set to a frequency such that the second frequency is higher than the IF frequency (for example, IF frequency: 30 [MHz], first frequency: 210 [MHz], first frequency) 2 frequencies: 180 [MHz]).

  The frequency discriminator 26 generates a DC signal Sd having a signal level corresponding to the second frequency of the second frequency signal S2. The LPF 48 removes the high-frequency signal component caused by the reception signal Sr and the IF signal So included in the DC signal Sd from the output port 26 b of the frequency discriminator 26 and outputs it to the VCO 28. The VCO 28 generates a control frequency signal Sc having a predetermined local oscillation frequency based on the DC signal Sd from which the high frequency signal component has been removed.

  4A schematically illustrates the time course of the second frequency signal S2 input to the input port 26a of the frequency discriminator 26 with respect to the receiver 42 of FIG. 3, and FIG. 4B illustrates the output port 26b of the frequency discriminator 26. 6 schematically shows the time course of the DC signal Sd output from the. 4A shows a case where the IF frequency of the IF signal So (see FIG. 2A) is detuned from the tuning frequency of the receiver 42 (for example, the tuning frequency: 60 [MHz], the IF frequency: 30 [MHz]). ).

  In this case, the high frequency second frequency signal S2 converted from the IF signal So by the mixer 46 is input to the input port 26a (see FIG. 3) of the frequency discriminator 26, and the DC signal Sd is the second frequency signal. The signal level reaches the peak level V2 at time t3 (t3 <t1) before time t1 when the input of the carrier wave ends due to the pulse modulation signal including the carrier wave of S2 and rises with time. To do. Thereby, the DC signal Sd having a signal level corresponding to the second frequency of the carrier wave can be output from the output port 26b of the frequency discriminator 26.

  That is, since the second frequency of the second frequency signal S2 input to the input port 26a of the frequency discriminator 26 is higher than the IF frequency of the IF signal So (see FIG. 2A and FIG. 4A), the time when the carrier wave input ends. Even if the transmission time, the reception time, and the output time are shortened by the signal level of the DC signal Sd reaching the peak level V2 at time t3 before t1, the frequency discriminator 26 in the receiver 42 is The DC signal Sd corresponding to the second frequency can be generated. Therefore, the VCO 28 can generate the control frequency signal Sc based on the DC signal Sd corresponding to the second frequency. Note that the frequency discriminator 26 of FIG. 3 outputs a substantially zero level DC signal Sd from the output port 26b when the second frequency is the difference between the tuning frequency and the first frequency.

  As described above, in the present embodiment, the mixer 46 converts the IF signal So into the high frequency second frequency signal S2 based on the first frequency of the first frequency signal S1, and outputs it to the input port 26a of the frequency discriminator 26. Therefore, the frequency discriminator 26 can generate the DC signal Sd corresponding to the second frequency in response to the input of the second frequency signal S2. Therefore, when the receiver 42 is applied to the marine radar 40, the response of the frequency discriminator 26 can be improved even if the transmission time of the transmission signal St, the reception time of the reception signal Sr, and the output time of the IF signal So are shortened. Can be secured.

  Further, since the response of the frequency discriminator 26 is ensured, the receiver 42 converts the received signal Sr into an IF signal So having a predetermined tuning frequency based on the control frequency signal Sc generated by the VCO 28. Can do. Thereby, the receiver 42 can suppress the frequency fluctuation of the IF signal So.

  Further, since the high-frequency signal component of the reception signal Sr and IF signal So included in the DC signal Sd is removed by the LPF 48 and supplied to the VCO 28, the frequency fluctuation of the IF signal So can be reliably suppressed.

The radar receiver according to the present invention is not limited to the above-described embodiment, and it is needless to say that various configurations can be adopted without departing from the gist of the present invention.

It is a block diagram of a marine radar to which a receiver which is a premise of the present embodiment is applied. 2A is a time chart showing an IF signal input to the input port of the frequency discriminator shown in FIG. 1, and FIG. 2B is a time chart showing a DC signal output from the output port. It is a block diagram of the radar for ships to which the receiver concerning this embodiment is applied. 4A is a time chart showing a second signal input to the input port of the frequency discriminator shown in FIG. 3, and FIG. 4B is a time chart showing a DC signal output from the output port.

Explanation of symbols

24 ... distributor 26 ... frequency discriminator 26a ... input port 26b ... output port 28 ... VCO 32, 46 ... mixer 40 ... marine radar 42 ... receiver 44 ... oscillator 48 ... LPF

Claims (2)

In a radar receiver that receives a received signal and converts the received signal into an output frequency signal having a frequency lower than that of the received signal.
A first oscillator for generating a first frequency signal;
Based on the first frequency signal and the output frequency signal, a mixer for generating a second frequency signal having a frequency higher than said output frequency signal,
A frequency discriminator for generating a DC signal in accordance with the second frequency signal;
A second oscillator that generates a control frequency signal for tuning the output frequency signal to a predetermined frequency based on the DC signal;
A radar receiver characterized by comprising: The radar receiver according to claim 1, wherein
A radar receiver , further comprising a filter that removes a high-frequency signal component of the output frequency signal included in the DC signal and supplies the signal to the second oscillator.

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