Frequency conversion device, radar device, frequency conversion method, and frequency conversion program

Abstract

To detect a speed and a movement direction of a detection target with a simple configuration in a radar device.SOLUTION: A frequency conversion device includes: a first conversion unit which generates an analog signal by performing analog conversion on data representing a pulsed waveform; an up-conversion unit which generates a RF signal by multiplying the analog signal by a first local signal; a transmission unit which transmits the RF signal; a reception unit which receives a reflected signal that is obtained by reflecting the RF signal; a down-conversion unit which generates an IF signal by multiplying the reflected signal by a second local signal that has a different frequency from the first local signal; a second conversion unit which generates a digital signal by digital conversion on the IF signal; and a cancellation unit which generates a baseband signal in which a component of phase rotation based on a frequency difference between the first local signal and the second local signal is canceled on the basis of the digital signal.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a frequency conversion device, a radar device, a frequency conversion method, and a frequency conversion program. [Background technology]

[0002] 2. Description of the Related Art Conventionally, in communication devices, radar devices, and the like, a technique is used in which a radio frequency (RF) signal received via an antenna is down-converted by using a local signal to generate a baseband signal.

[0003] For example, Patent Document 1 (JP Patent Publication 2009-272830A) describes the following communication device. That is, the communication device includes an RF transmission / reception processing means for performing RF processing of transmission / reception signals, a baseband processing means for performing baseband processing, a signal detection means for detecting a transmission signal from another communication system, and an interference avoidance means for suppressing an interfering signal to the other communication system in the RF transmission processing of the RF transmission / reception processing means when a signal is detected by the interference signal detection means. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2009-272830 A [Patent Document 2] Special Publication No. 2019-512195 Summary of the Invention [Problem to be solved by the invention]

[0005] There is a demand for a technology that goes beyond the technologies described in Patent Documents 1 and 2 and that is capable of detecting the speed and moving direction of a detection target with a simple configuration in a radar device.

[0006] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a frequency conversion device, a radar device, a frequency conversion method, and a frequency conversion program that are capable of detecting the speed and moving direction of an object to be detected in a radar device with a simple configuration. [Means for solving the problem]

[0007] (1) In order to solve the above problem, a frequency conversion device according to an aspect of the present invention includes a digital-to-analog conversion unit that generates an analog signal by converting data representing a pulsed waveform into analog, an up-conversion unit that generates an RF signal by multiplying the analog signal by a first local signal, a transmission unit that transmits the RF signal, a reception unit that receives a reflected signal obtained by reflecting the RF signal, a down-conversion unit that generates an intermediate frequency (IF) signal by multiplying the reflected signal by a second local signal having a frequency different from that of the first local signal, an analog-to-digital conversion unit that generates a digital signal by digitally converting the IF signal, and a cancellation unit that generates a baseband signal in which a component of phase rotation based on a frequency difference between the first local signal and the second local signal is cancelled, based on the digital signal.

[0008] In this way, in a frequency conversion device in which the frequency of the first local signal used to up-convert a transmission signal and the frequency of the second local signal used to down-convert a received reflected signal are different from each other, a configuration that generates a baseband signal in which the phase rotation component based on the frequency difference between the first local signal and the second local signal is cancelled makes it possible to detect the speed and moving direction of an object at the reflection point of the RF signal based on the phase rotation component included in the generated baseband signal that corresponds to the propagation delay time of the RF signal while reducing the circuit scale compared to the double superheterodyne method. Therefore, the radar device can detect the speed and moving direction of an object to be detected with a simple configuration.

[0009] (2) In the above (1), the cancellation unit may generate the baseband signal by multiplying the digital signal by a third local signal having a frequency based on the frequency difference, and the third local signal may be a free-running signal.

[0010] With this configuration, it is possible to generate a baseband signal from which the component of phase rotation based on the frequency difference between the first local signal and the second local signal has been removed, without requiring any arithmetic processing or the like.

[0011] (3) In the above (1), the cancellation unit may generate the baseband signal by subtracting the phase rotation component calculated based on the frequency difference and a transmission period of the RF signal from a signal obtained by multiplying the digital signal by a third local signal having a frequency based on the frequency difference.

[0012] With this configuration, for example, it is possible to generate a baseband signal from which the phase rotation component based on the frequency difference between the first local signal and the second local signal has been removed, while suppressing the generation of unnecessary components resulting from up-conversion of the transmission signal and down-conversion of the reception signal, by using the third local signal whose initial phase at the transmission timing of the RF signal is zero.

[0013] (4) To achieve the above object, a radar device according to an aspect of the present invention includes the frequency conversion device according to any one of (1) to (3) above.

[0014] With this configuration, for example, a radar device can notify a user of the speed and moving direction of a detected object.

[0015] (5) In order to solve the above-mentioned problems, a frequency conversion method according to an aspect of the present invention is a frequency conversion method in a frequency conversion device, comprising the steps of: generating an analog signal by converting data representing a pulsed waveform into analog; generating an RF signal by multiplying the analog signal by a first local signal; transmitting the RF signal; receiving a reflected signal from the RF signal; generating an IF signal by multiplying the reflected signal by a second local signal having a frequency different from that of the first local signal; digitally converting the IF signal to generate a digital signal; and generating a baseband signal in which a phase rotation component based on a frequency difference between the first local signal and the second local signal is cancelled based on the digital signal.

[0016] In this way, in a frequency conversion device in which the frequency of the first local signal used to up-convert a transmission signal and the frequency of the second local signal used to down-convert a received reflected signal are different from each other, the method of generating a baseband signal in which the phase rotation component based on the frequency difference between the first local signal and the second local signal is cancelled makes it possible to detect the speed and moving direction of an object at the reflection point of the RF signal based on the phase rotation component included in the baseband signal that corresponds to the propagation delay time of the RF signal while reducing the circuit scale compared to the double superheterodyne method. Therefore, the radar device can detect the speed and moving direction of the detection target with a simple configuration.

[0017] (6) In order to solve the above-mentioned problems, a frequency conversion program according to an aspect of the present invention is a frequency conversion program used in a frequency conversion device that generates an analog signal by converting data representing a pulsed waveform into analog, generates an RF signal by multiplying the analog signal by a first local signal, transmits the RF signal, receives a reflected signal from the RF signal, generates an IF signal by multiplying the reflected signal by a second local signal having a frequency different from that of the first local signal, and generates a digital signal by digitally converting the IF signal, the frequency conversion program causing a computer to execute a process of generating a baseband signal in which a component of phase rotation based on a frequency difference between the first local signal and the second local signal is cancelled, based on the digital signal.

[0018] In this way, in a frequency conversion device in which the frequency of the first local signal used to up-convert a transmission signal and the frequency of the second local signal used to down-convert a received reflected signal are different from each other, a configuration that generates a baseband signal in which the phase rotation component based on the frequency difference between the first local signal and the second local signal is cancelled makes it possible to detect the speed and moving direction of an object at the reflection point of the RF signal based on the phase rotation component included in the baseband signal that corresponds to the propagation delay time of the RF signal while reducing the circuit scale compared to the double superheterodyne method. Therefore, the radar device can detect the speed and moving direction of an object to be detected with a simple configuration. Effect of the Invention

[0019] According to the present invention, in a radar device, the speed and moving direction of a detection target can be detected with a simple configuration. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is a diagram showing a configuration of a radar device according to a first embodiment of the present invention. [Diagram 2]FIG. 2 is a diagram showing the configuration of a radar device according to a conventional double superheterodyne system. [Diagram 3] FIG. 3 is a timing chart of a local signal used in a radar device according to a conventional double superheterodyne system. [Figure 4] FIG. 4 is a diagram showing a timing chart of a local signal used in the frequency conversion device according to the first embodiment of the present invention. [Diagram 5] FIG. 5 is a flowchart showing an example of an operation performed by the radar device according to the first embodiment of the present invention when performing a detection process. [Figure 6] FIG. 6 is a diagram showing a configuration of a radar device according to the second embodiment of the present invention. [Figure 7] FIG. 7 is a timing chart of a local signal used in a frequency conversion device according to the second embodiment of the present invention. [Figure 8] FIG. 8 is a flowchart showing an example of an operation performed by the radar device according to the second embodiment of the present invention when performing a detection process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference characters and their description will not be repeated. In addition, at least some of the embodiments described below may be arbitrarily combined.

[0022] <First embodiment> [Configuration and basic operation] Fig. 1 is a diagram showing a configuration of a radar device according to a first embodiment of the present invention. With reference to Fig. 1, the radar device 201 includes a frequency conversion device 101. The frequency conversion device 101 includes a signal output unit 10, a digital to analog converter (DAC) 20, an up-converter unit 30, a transceiver unit 40, a down-converter unit 50, an analog to digital converter (ADC) 60, and a digital processing unit 70. The radar device 201 is a radar that conforms to a direct conversion method and is a solid-state radar that uses solid-state elements. The radar device 201 is mounted on a ship, for example.

[0023] The radar device 201 performs a detection process to detect the presence or absence of a target in a detection target area, which is an area to be monitored, and the distance between the radar device 201 and the target. The target is an example of a detection target. More specifically, in the detection process, the radar device 201 transmits an RF signal Srf1, which is a transmission wave, to the detection target area at a transmission timing Tt according to a predetermined transmission period Tprf. The transmission period Tprf is, for example, 1 millisecond. The radar device 201 receives an RF signal Srf2, which is a reflected signal of the RF signal Srf1 reflected in the detection target area. The radar device 201 performs a process to display an echo image indicating the presence or absence of a target in the detection target area and the distance between the radar device 201 and the target on a display device (not shown) based on the received RF signal Srf2. In the following, it is assumed that the propagation delay time of the signal inside the radar device 201 is small compared to the propagation delay time of the RF signal in the detection target area and can be ignored.

[0024] The up-conversion unit 30 includes a low pass filter (LPF) 31, a mixer 32, a local oscillator 33, and a band pass filter (BPF) 34. The local oscillator 33 outputs a local signal La having a frequency fa in the RF band to the mixer 32. The local signal La is an example of a first local signal.

[0025] The transceiver unit 40 includes a transmitter unit 41, a circulator 42, an antenna 43, and a receiver unit 44.

[0026] The down-conversion unit 50 includes a mixer 51, a local oscillator 52, and a BPF 53. The local oscillator 52 outputs a local signal Lb of a frequency fb in the RF band to the mixer 51. The local signal Lb has a different frequency from the local signal La. For example, the frequency fb of the local signal Lb is several tens of megahertz lower than the frequency fa of the local signal La. The local signal Lb is an example of a second local signal.

[0027] The frequency fb of the local signal Lb may be several tens of megahertz higher than the frequency fa of the local signal La. However, by setting the frequency fb to a frequency lower than the frequency fa, it is possible to use an ADC 60 with a lower sampling frequency than when the frequency fb is set to a frequency higher than the frequency fa.

[0028] The digital processing unit 70 includes mixers 71A and 71B, which are the mixer 71, a local oscillator 72, and a signal processing unit 73. The digital processing unit 70 is an example of a cancellation unit. The local oscillator 72 outputs a local signal Lc of frequency fc to the mixer 71. The local signal Lc is a signal of a frequency based on the frequency difference between the local signals La and Lb. As an example, the frequency fc of the local signal Lc is a frequency equivalent to the difference between the frequencies fa and fb. The local signal Lc is an example of a third local signal.

[0029] In the following, for simplicity of explanation, it is assumed that the initial phases of the local signals La, Lb, and Lc at the start of the radar device 201 are zero. The local signal La at time t is expressed by the following equation (1), where ωa is the angular frequency of the local signal La.

number

[0030] Moreover, the local signal Lb at time t is expressed by the following equation (2): Here, ωb is the angular frequency of the local signal Lb.

number

[0031] Moreover, the local signal Lc at time t is expressed by the following equation (3): Here, ωc is the angular frequency of the local signal Lc.

number

[0032] The signal output unit 10 outputs data Da representing a pulse waveform to the DAC 20. For example, the signal output unit 10 outputs data Da representing a pulse signal that transitions from a low level to a high level at a transmission timing Tt and transitions from a high level to a low level after a predetermined time T1 has elapsed from the transmission timing Tt to the DAC 20. The predetermined time T1 is a time shorter than the transmission period Tprf, and is, for example, 150 microseconds.

[0033] The DAC 20 generates an analog signal Sa by analog-converting data Da representing a pulse waveform. More specifically, the DAC 20 generates an analog pulse signal by analog-converting data Da received from the signal output unit 10, and outputs the generated analog signal Sa to the up-conversion unit 30.

[0034] The up-conversion unit 30 generates an RF signal Srf1 by multiplying the analog signal Sa by the local signal La. More specifically, the LPF 31 in the up-conversion unit 30 attenuates components outside a predetermined passband among the frequency components of the analog signal received from the DAC 20. The mixer 32 generates an RF signal Srf1 by multiplying the analog signal Sa that has passed through the LPF 31 by the local signal La received from the local oscillator 33, and outputs the RF signal Srf1 to the BPF 34. The BPF 34 attenuates components outside a predetermined passband among the frequency components of the RF signal Srf1 received from the mixer 32.

[0035] The transmitter 41 in the transceiver unit 40 transmits the RF signal Srf1. More specifically, the transmitter 41 transmits the RF signal Srf1 that has passed through the BPF 34 via the circulator 42 and the antenna 43 to the detection target area.

[0036] The receiver 44 in the transmitter / receiver 40 receives the RF signal Srf2, which is a reflected signal of the RF signal Srf1. More specifically, the receiver 44 receives the RF signal Srf2, which is a signal of the RF signal Srf1 reflected by a target or the like in the detection target area, via the antenna 43 and the circulator 42, and outputs the received RF signal Srf2 to the down-converter 50.

[0037] Hereinafter, each of the RF signals Srf1 and Srf2 will also be referred to as an RF signal Srf. The RF signal Srf transmitted and received at the transmitting / receiving unit 40 at time t is expressed by the following equation (4) taking into account the phase of the local signal La at the transmission timing Tt.

number

[0038] Moreover, the reception timing Tr of the RF signal Srf2 in the receiver 44 is expressed by the following equation (5).

number

[0039] Here, R is the distance between the reflection point of the RF signal Srf and the antenna 43, c is the speed of light (m / s), and 2×R / c is the propagation delay time of the RF signal Srf in the detection target area.

[0040] The down-conversion unit 50 generates an IF signal Sif by multiplying the RF signal Srf2 and the local signal Lb. More specifically, the mixer 51 in the down-conversion unit 50 generates an IF signal Sif by multiplying the RF signal Srf2 received from the receiving unit 44 by the local signal Lb received from the local oscillator 52, and outputs the IF signal Sif to the BPF 53. The BPF 53 attenuates frequency components of the IF signal Sif received from the mixer 51 that are outside a predetermined passband. As an example, the BPF 53 attenuates frequency components of the IF signal Sif received from the mixer 51 other than the frequency component of the difference between the frequency of the RF signal Srf2 and the frequency fb of the local signal Lb. The IF signal Sif that has passed through the BPF 53 is expressed by the following formula (6), taking into account the phase of the local signal Lb at the reception timing Tr.

number

[0041] The ADC 60 generates a digital signal Sd by digitally converting the IF signal Sif. More specifically, the ADC 60 generates a digital signal Sd by digitally converting the IF signal Sif received from the down-conversion unit 50, and outputs the generated digital signal Sd to the digital processing unit 70.

[0042] The digital processing unit 70 multiplies the digital signal Sd by the local signal Lc. More specifically, the mixer 71A in the digital processing unit 70 multiplies the digital signal Sd received from the ADC 60 by the local signal Lc received from the local oscillator 72 to generate a baseband digital signal SdI and outputs the baseband digital signal SdI to the signal processing unit 73. The mixer 71B in the digital processing unit 70 multiplies the digital signal Sd received from the ADC 60 by the local signal Lc_90, which is the local signal Lc output from the local oscillator 72 and to which a phase difference of 90° has been added by a phase shifter (not shown), to generate a baseband digital signal SdQ and outputs the baseband digital signal SdQ to the signal processing unit 73.

[0043] The signal processing unit 73 receives the digital signal SdI from the mixer 71A, and extracts, from the frequency components of the received digital signal SdI, a frequency component that is a difference between the frequency of the IF signal Sif and the frequency fc of the local signal Lc, as a demodulated signal SI. The signal processing unit 73 also receives the digital signal SdQ from the mixer 71B, and extracts, from the frequency components of the received digital signal SdQ, a frequency component that is a difference between the frequency of the IF signal Sif and the frequency fc, as a demodulated signal SQ. The signal processing unit 73 calculates the presence or absence of a target in the detection target area and the distance between the radar device 201 and the target, based on the baseband signal SBB represented by the extracted demodulated signals SI and SQ. Then, the signal processing unit 73 performs a process of displaying an echo image indicating the presence or absence of a target in the detection target area and the distance between the radar device 201 and the target on a display device (not shown).

[0044] (assignment) Fig. 2 is a diagram showing the configuration of a radar device according to a conventional double superheterodyne method. Referring to Fig. 2, the radar device 301 includes a signal output unit 111, a DAC 112, a BPF 113, a mixer 114, a BPF 115, a mixer 116, a BPF 117, a transmitter 118, a circulator 119, an antenna 120, a receiver 121, a mixer 122, a BPF 123, a mixer 124, a BPF 125, an ADC 126, mixers 127A and 127B, a signal processor 128, and local oscillators 131A, 131B, and 131C. The local oscillators 131A, 131B, and 131C output local signals L1, L2, and L3 having frequencies f1, f2, and f3, respectively.

[0045] For example, at a transmission timing Tt, the signal output unit 111 outputs data representing a sine wave waveform with an initial phase of zero to the DAC 112. The DAC 112 generates an IF signal Stx by analog conversion of the data received from the signal output unit 111 and outputs the IF signal Stx to the BPF 113.

[0046] The mixer 114 generates an up-converted IF signal by multiplying the IF signal Stx that has passed through the BPF 113 by the local signal L1 received from the local oscillator 131A, and outputs the up-converted IF signal to the BPF 115. Here, the IF signal generated by the mixer 114 is given a phase rotation P1 based on the phase of the local signal L1 at the transmission timing Tt.

[0047] Mixer 116 generates an RF signal by multiplying the IF signal that has passed through BPF 115 by local signal L2 received from local oscillator 131B, and outputs the RF signal to BPF 117. Here, a phase rotation P2 based on the phase of local signal L2 at transmission timing Tt is applied to the RF signal generated by mixer 116.

[0048] The transmitter 118 transmits the RF signal that has passed through the BPF 117 to the detection target area via the circulator 119 and the antenna 120. The receiver 121 receives an RF signal that is a reflection of the RF signal transmitted by the transmitter 118 via the antenna 120 and the circulator 119, and outputs the received RF signal to the mixer 122.

[0049] The mixer 122 generates an IF signal by multiplying the RF signal received from the receiver 121 by the local signal L2 received from the local oscillator 131B, and outputs the IF signal to the BPF 123. That is, in the radar device 301, a local signal used for up-converting the IF signal and a local signal used for down-converting the RF signal are shared. Here, the IF signal generated by the mixer 122 is given a phase rotation Px1 of the local signal L2 that corresponds to the propagation delay time of the RF signal in the detection target area, while the phase rotation P2 is removed from the IF signal.

[0050] The mixer 124 generates a down-converted IF signal by multiplying the IF signal that has passed through the BPF 123 by the local signal L1 received from the local oscillator 131A, and outputs the down-converted IF signal to the BPF 125. That is, in the radar device 301, a local signal used for up-converting the IF signal and a local signal used for down-converting the IF signal are shared. Here, the IF signal generated by the mixer 124 is given a phase rotation Px2 of the local signal L1 that corresponds to the propagation delay time of the RF signal in the detection target area, while the phase rotation P1 is removed from the IF signal.

[0051] The ADC 126 generates a digital signal by digitally converting the IF signal that has passed through the BPF 125, and outputs the digital signal to the mixers 127A and 127B. The mixer 127A multiplies the digital signal received from the ADC 126 by a local signal L3 received from the local oscillator 131C, and generates a baseband digital signal, and outputs the baseband digital signal to the signal processing unit 128. The mixer 127B multiplies the digital signal received from the ADC 126 by a local signal L3_90, which is the local signal L3 that is output from the local oscillator 131C and to which a phase difference of 90° has been added by a phase shifter (not shown), and generates a baseband digital signal, and outputs the baseband digital signal to the signal processing unit 128.

[0052] 3 is a timing chart of a local signal used in a radar device according to a conventional double superheterodyne system, in which the horizontal axis represents time.

[0053] 3, the local signals L1 and L2 output by the local oscillators 131A and 131B are free-running signals. On the other hand, the local signal L3 output by the local oscillator 131C is reset at the transmission timing Tt. More specifically, the local signal L3 is controlled so that the initial phase at the transmission timing Tt becomes zero. This makes it possible to prevent the demodulated signals generated by the mixers 127A and 127B from including unnecessary components caused by the multiplication of signals in the mixers 114, 116, 122, and 124.

[0054] While the double superheterodyne system is a robust system, the radar device 301 that uses the double superheterodyne system has a large circuit scale and a large number of parts. For this reason, in recent years, it has been proposed to adopt a direct conversion system, which can be realized with a simple configuration, instead of the double superheterodyne system for marine radar devices.

[0055] However, referring back to FIG. 1, in the digital processing unit 70 of the radar device 201 that follows the direct conversion method, when the demodulated signals SI, SQ are generated using the local signal Lc that is reset at the transmission timing Tt, similar to the local signal L3 in the radar device 301, it may not be possible to detect the speed and moving direction of the target in the detection area based on the demodulated signals SI, SQ.

[0056] More specifically, the signal processor 73 in the digital processor 70 receives the digital signal SdI generated using the local signal Lc reset at the transmission timing Tt from the mixer 71A, and extracts, from the frequency components of the received digital signal SdI, a frequency component that is the difference between the frequency of the IF signal Sif and the frequency fc, as the demodulated signal SI. The demodulated signal SI extracted by the signal processor 73 is expressed by the following equation (7).

number

[0057] Here, the angular frequency ωc is equal to the difference between the angular frequencies ωa and ωb, so the term for time t is zero. The term 2×R / c is a term indicating the component of the phase rotation Pd corresponding to the propagation delay time of the RF signal Srf in the detection target area, and is a term necessary for the detection process. On the other hand, the term for the transmission timing Tt is a term indicating the component of the phase rotation Pt based on the frequency difference between the transmission timing Tt and the local signals La and Lb, and is a term unnecessary for the detection process. The demodulated signal SQ includes the term for the transmission timing Tt, just like the demodulated signal SI. In this case, the signal processing unit 73 cannot detect the speed or moving direction of the target based on the demodulated signals SI and SQ.

[0058] Therefore, the radar device 201 according to the embodiment of the present invention solves the above problems by adopting the following configuration.

[0059] (Processing in digital processing unit) The digital processing unit 70 generates, based on the digital signal Sd generated by the ADC 60, a baseband signal SBB_ca1, which is a baseband signal SBB in which the component of the phase rotation Pt based on the frequency difference between the local signals La and Lb has been cancelled.

[0060] 4 is a timing chart of a local signal used in the frequency conversion device according to the first embodiment of the present invention, in which the horizontal axis represents time.

[0061] 4, a local oscillator 72 in a digital processing unit 70 outputs a local signal Lc_fr, which is the local signal Lc, to a mixer 71. The local signal Lc_fr is a free-running signal. That is, the local signal Lc_fr is the local signal Lc that is not reset at the transmission timing Tt.

[0062] Mixer 71A multiplies the digital signal Sd received from ADC 60 by the local signal Lc_fr received from local oscillator 72 to generate digital signal SdI_fr, which is the digital signal SdI, and outputs the digital signal SdI_fr to signal processing unit 73. Mixer 71B also multiplies the digital signal Sd received from ADC 60 by local signal Lc_fr90, which is the local signal Lc_fr that is output from local oscillator 72 and has a phase difference of 90° added by a phase shifter (not shown), to generate digital signal SdQ_fr, which is the digital signal SdQ, and outputs the digital signal SdQ_fr to signal processing unit 73.

[0063] The signal processing unit 73 receives the digital signal SdI_fr from the mixer 71A, and extracts, from the frequency components of the received digital signal SdI_fr, a frequency component that is the difference between the frequency of the IF signal Sif and the frequency fc, as a demodulated signal SI_fr. The signal processing unit 73 also receives the digital signal SdQ_fr from the mixer 71B, and extracts, from the frequency components of the received digital signal SdQ_fr, a frequency component that is the difference between the frequency of the IF signal Sif and the frequency fc, as a demodulated signal SQ_fr. The demodulated signal SI_fr extracted by the signal processing unit 73 is expressed by the following equation (8).

number

[0064] Here, since the angular frequency ωc is equal to the difference between the angular frequencies ωa and ωb, the terms of the time t and the transmission timing Tt are zero. Therefore, the demodulated signal SI_fr extracted by the signal processing unit 73 is expressed by the following equation (9).

number

[0065] That is, the demodulated signal SI_fr is a demodulated signal SI that does not include a term of the transmission timing Tt and in which the component of the phase rotation Pt has been cancelled. On the other hand, the demodulated signal SI_fr includes a term of 2×R / c that is necessary in the detection process.

[0066] Moreover, the demodulated signal SQ_fr extracted by the signal processing unit 73 is expressed by the following equation (10).

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[0067] That is, like the demodulated signal SI_fr, the demodulated signal SQ_ft is a demodulated signal SQ in which the component of the phase rotation Pt is cancelled and which includes the term 2×R / c.

[0068] The signal processing unit 73 detects the speed and moving direction of the target based on a baseband signal SBB_ca1 in which the component of the phase rotation Pt is cancelled, as expressed by the following equation (11).

number

[0069] [Operation flow] The radar device according to the embodiment of the present invention includes a computer including a memory, and a processor such as a CPU in the computer reads out from the memory a program including some or all of the steps of the following flowcharts and executes it. The program of this device can be installed from the outside. The program of this device is distributed in a state stored on a recording medium or via a communication line.

[0070] 5 is a flowchart showing an example of an operation performed by the radar device according to the first embodiment of the present invention when the radar device 201 performs a detection process. The radar device 201 performs the process shown in FIG. 5 at each transmission timing Tt according to the transmission period Tprf.

[0071] 5, first, the radar device 201 generates an analog signal Sa by analog-converting data Da representing a pulse waveform (step S11).

[0072] Next, the radar device 201 generates an RF signal Srf1 by multiplying the analog signal Sa that has passed through the LPF 31 by the local signal La that is output by the local oscillator 33 (step S12).

[0073] Next, the radar device 201 transmits the RF signal Srf1 that has passed through the BPF 34 to the detection target area via the circulator 42 and the antenna 43 (step S13).

[0074] Next, the radar device 201 receives the RF signal Srf2, which is a signal resulting from the RF signal Srf1 being reflected by a target or the like in the detection area, via the antenna 43 and the circulator 42 (step S14).

[0075] Next, the radar device 201 generates the IF signal Sif by multiplying the RF signal Srf2 by the local signal Lb output by the local oscillator 52 (step S15).

[0076] Next, the radar device 201 generates a digital signal Sd by digitally converting the IF signal Sif that has passed through the BPF 53 (step S16).

[0077] Next, the radar device 201 multiplies the digital signal Sd by the local signal Lb_fr, which is a free-running signal output by the local oscillator 52, to generate demodulated signals SI_fr, SQ_fr in which the component of the phase rotation Pt based on the frequency difference between the local signals La, Lb is canceled (step S17).

[0078] Next, the radar device 201 detects the speed and moving direction of the target in the detection area based on the baseband signal SBB_ca1 represented by the demodulated signals SI_ft and SQ_fr (step S18).

[0079] Next, another embodiment of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference characters and their description will not be repeated.

[0080] <Second embodiment> [Configuration and basic operation] This embodiment relates to a radar device 202 that performs a process of subtracting a component of the phase rotation Pt, as compared with the radar device 201 according to the first embodiment. Contents other than those described below are the same as those of the radar device 201 according to the first embodiment.

[0081] Fig. 6 is a diagram showing a configuration of a radar device according to a second embodiment of the present invention. With reference to Fig. 2, compared to the radar device 202, the radar device 201 includes a frequency conversion device 102 instead of the frequency conversion device 101. The frequency conversion device 102 includes a digital processing device 80 instead of the digital processing device 70. Compared to the digital processing device 70, the digital processing device 80 includes mixers 81A and 81B which are mixer 81 instead of mixer 71, includes a local oscillator 82 instead of the local oscillator 72, and includes a signal processing device 83 instead of the signal processing device 73. The digital processing device 80 is an example of a cancellation unit.

[0082] 7 is a timing chart of a local signal used in a frequency conversion device according to a second embodiment of the present invention, in which the horizontal axis represents time.

[0083] 7, a local oscillator 82 in a digital processing unit 80 outputs a local signal Lc_rs, which is a local signal Lc, to a mixer 81. The local signal Lc_rs is a local signal Lc that is reset at a transmission timing Tt. More specifically, the local signal Lc_rs is controlled so that the initial phase at the transmission timing Tt becomes zero. This makes it possible to suppress the generation of unnecessary components in the baseband signal SBB caused by the up-conversion in the up-conversion unit 30 and the down-conversion in the down-conversion unit 50.

[0084] The digital processing unit 80 subtracts the component of phase rotation Pt calculated based on the frequency difference between the local signals La, Lb and the transmission period Tprf of the RF signal Srf1 from the baseband signal SBB obtained by multiplying the digital signal Sd and the local signal Lc_rs, thereby generating a baseband signal SBB_ca2, which is the baseband signal SBB from which the component of phase rotation Pt has been cancelled.

[0085] More specifically, mixer 81A multiplies digital signal Sd received from ADC 60 by local signal Lc_rs received from local oscillator 82 to generate digital signal SdI_rs, which is digital signal SdI, and outputs the digital signal SdI_rs to signal processing unit 83. Mixer 81B multiplies digital signal Sd received from ADC 60 by local signal Lc_rs90, which is local signal Lc_rs that is output from local oscillator 82 and has a phase difference of 90° added by a phase shifter (not shown), to generate digital signal SdQ_rs, which is digital signal SdQ, and outputs the digital signal SdQ_rs to signal processing unit 83.

[0086] The signal processing unit 83 receives the digital signal SdI_rs from the mixer 81A and extracts, from the frequency components of the received digital signal SdI_rs, a frequency component that is a difference between the frequency of the IF signal Sif and the frequency fc as a demodulated signal SI_rs. Also, the signal processing unit 83 receives the digital signal SdQ_rs from the mixer 81B and extracts, from the frequency components of the received digital signal SdQ_rs, a frequency component that is a difference between the frequency of the IF signal Sif and the frequency fc as a demodulated signal SQ_rs.

[0087] Moreover, the signal processing unit 83 counts the number of times n that the radar device 302 transmits the RF signal Srf1 by monitoring the data Da output by the signal output unit 10. More specifically, the signal processing unit 83 counts the number of times that the pulse signal represented by the data Da transitions from a low level to a high level as the number of times n that the radar device 302 transmits. Hereinafter, the n-th transmission timing Tt is also referred to as the "transmission timing Ttn". In addition, the demodulated signal SI_rs corresponding to the RF signal Srf2 resulting from the reflection of the RF signal Srf1 transmitted at the transmission timing Ttn is also referred to as the "demodulated signal SI_rsn". In addition, the demodulated signal SQ_rs corresponding to the RF signal Srf2 resulting from the reflection of the RF signal Srf1 transmitted at the transmission timing Ttn is also referred to as the "demodulated signal SQ_rsn". The demodulated signal SI_rsn is expressed by the following equation (12).

number

[0088] The signal processor 83 performs a calculation process to subtract a value corresponding to the transmission period Tprf from the demodulated signal SI_rsn based on the known angular frequencies ωa, ωb and transmission period Tprf, and the counted number of transmissions n. The demodulated signal SI_rsn after the calculation process is expressed by the following equation (13).

number

[0089] Similarly, the signal processing unit 83 performs a calculation process to subtract a value corresponding to the term of the transmission period Tprf from the demodulated signal SQ_rsn. The demodulated signal SQ_rsn after the calculation process is expressed by the following equation (14).

number

[0090] Here, the demodulated signals SI_rsn, SQ_rsn after the calculation process include a term of the transmission timing Tt1. The term of the transmission timing Tt1 is a component of the phase rotation Pt, but since it is a fixed value C, it can be ignored in the process of detecting the speed and moving direction of the target. Note that even if the transmission period Tprf is not a constant value but a variable value, the signal processing unit 83 can subtract a value corresponding to the transmission period Tprf from the demodulated signals SI_rsn, SQ_rsn based on the monitoring result of the data Da output by the signal output unit 10.

[0091] The signal processing unit 83 detects the speed and moving direction of the target based on a baseband signal SBB_ca2 in which the components of the phase rotation Pt excluding the fixed value C are cancelled, as expressed by the following equation (15).

number

[0092] [Operation flow] 8 is a flowchart showing an example of an operation performed by the radar device according to the second embodiment of the present invention when the radar device 202 performs a detection process. The radar device 202 performs the process shown in FIG. 8 at each transmission timing Tt according to the transmission period Tprf.

[0093] 8, the radar device 202 performs the same processes as steps S11 to S16 in FIG. 5 as the processes of steps S21 to S26.

[0094] Next, the radar device 202 multiplies the digital signal Sd by the local signal Lc_rs output by the local oscillator 52 to generate demodulated signals SI_rsn and SQ_rsn (step S27).

[0095] Next, the radar device 202 performs a calculation process to subtract a value corresponding to the term of the transmission period Tprf from the demodulated signals SI_rsn and SQ_rsn (step S28).

[0096] Next, the radar device 202 detects the speed and moving direction of the target in the detection area based on the baseband signal SBB_ca2 represented by the demodulated signals SI_rsn and SQ_rsn after the arithmetic processing (step S29).

[0097] The above-described embodiments should be considered as illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0098] 10 Signal output section 20 DAC 30 Upconversion section 31 LPF 32 Mixer 33 Local Oscillator 34 BPF 40 Transmitter / receiver 41 Transmitter 42 Circulator 43 Antenna 44 Receiving section 50 Down conversion section 51 Mixer 52 Local Oscillator 53 BPF 60 ADC 70,80 Digital processing section 71, 71A, 71B, 81, 81A, 81B Mixers 72,82 Local Oscillator 73,83 Signal Processing Unit 101,102 Frequency conversion device 111 Signal output section 112DAC 113 BPF 114 Mixer 115 BPF 116 Mixer 117 BPF 118 Transmitter 119 Circulator 120 Antenna 121 Receiving unit 122 Mixer 123 BPF 124 Mixer 125 BPF 126 ADC 127A, 127B Mixer 128 Signal Processing Section 131A, 131B, 131C Local Oscillator 201,202 Radar equipment

Claims

1. a digital / analog conversion unit that converts data representing a pulse waveform into an analog signal; an up-conversion unit that generates an RF (Radio Frequency) signal by multiplying the analog signal by a first local signal; A transmitter for transmitting the RF signal; a receiving unit for receiving a reflected signal of the RF signal; a down-conversion unit that generates an intermediate frequency (IF) signal by multiplying the reflected signal by a second local signal having a frequency different from that of the first local signal; an analog / digital conversion unit that generates a digital signal by digitally converting the IF signal; a cancellation unit that generates, based on the digital signal, a baseband signal in which a phase rotation component based on a frequency difference between the first local signal and the second local signal is cancelled.

2. the cancellation unit generates the baseband signal by multiplying the digital signal by a third local signal having a frequency based on the frequency difference; The frequency conversion device according to claim 1 , wherein the third local signal is a free-running signal.

3. 2. The frequency conversion device according to claim 1, wherein the cancellation unit generates the baseband signal by subtracting a component of the phase rotation calculated based on the frequency difference and a transmission period of the RF signal from a signal obtained by multiplying the digital signal by a third local signal having a frequency based on the frequency difference.

4. A radar device comprising the frequency conversion device according to any one of claims 1 to 3.

5. A frequency conversion method in a frequency conversion device, comprising: An analog signal is generated by converting the data representing the pulse waveform into an analog signal; generating an RF signal by multiplying the analog signal by a first local signal; Transmitting the RF signal; receiving a reflected signal of the RF signal; generating an IF signal by multiplying the reflected signal by a second local signal having a different frequency from the first local signal; generating a digital signal by digitally converting the IF signal; a frequency conversion method for generating, based on the digital signal, a baseband signal in which a phase rotation component based on a frequency difference between the first local signal and the second local signal is cancelled.

6. 1. A frequency conversion program used in a frequency conversion device that generates an analog signal by analog converting data representing a pulse waveform, generates an RF signal by multiplying the analog signal by a first local signal, transmits the RF signal, receives a reflected signal of the RF signal, generates an IF signal by multiplying the reflected signal by a second local signal having a frequency different from that of the first local signal, and generates a digital signal by digitally converting the IF signal, a frequency conversion program for causing a computer to execute a process of generating, based on the digital signal, a baseband signal in which a phase rotation component based on a frequency difference between the first local signal and the second local signal is cancelled.

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