JP2015081851A - Dual-frequency cw radar device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To calculate a distance with high accuracy without changing the transmission frequency of a transmission radio wave for each sampling cycle of A/D conversion.SOLUTION: Provided is a dual-frequency CW radar device, wherein the dual-frequency CW radar device performs transmission in a transmission unit that alternately transmits a first transmission wave and a second transmission wave differing in frequency every transmission period, and includes, in a receiving unit that receives a reflection wave of the first transmission wave and a reflection wave of the second transmission wave: an A/D conversion unit for A/D converting a received signal pertaining to the first transmission wave and generating first sampling data, and A/D converting a received signal pertaining to the second transmission wave and generating second sampling data; a Fourier transformation unit for Fourier-transforming the first sampling data while its time-series alignment sequence is reversed and its phase is inverted, and Fourier-transforming the second sampling data while its time-series alignment sequence is not reversed and its phase is not inverted; and a distance calculation unit for calculating a distance to a reflection object on the basis of the result of Fourier transformation by the Fourier transformation unit.

Description

  The present disclosure relates to a dual frequency CW (Continuous Wave) radar apparatus.

  Conventionally, in a distance measuring device that detects a measurement object by radiating a radio wave, receiving a reflected wave from the measurement object, A / D converting the received signal and performing signal processing, A / D conversion is performed. A distance measuring device that switches the transmission frequency of a transmission radio wave for each sample period is known (see, for example, Patent Document 1).

JP 2009-042061 A

  However, the configuration described in Patent Document 1 requires an oscillator that can switch the frequency at a high speed, which increases the hardware cost of the transmitter.

  In this regard, when A / D conversion is performed a plurality of times for each of the first frequency and the second frequency, switching between the first frequency and the second frequency is performed at high speed (for each sample period of A / D conversion). There is no need. However, in such a case, on the other hand, since the transmission periods of the transmission wave related to the first frequency and the transmission wave related to the second frequency become longer, the reception of the reception wave (reflection wave) related to the first frequency is started. There is a significant shift between the timing and the reception start timing of the received wave (reflected wave) related to the second frequency. For this reason, in order to compensate for such a shift (in order to virtually match the reception start timing related to the first frequency with the reception start timing related to the second frequency), a phase shift process is required. Such a phase shift process requires the use of a Doppler frequency detection result, and there is a problem that the accuracy of distance calculation deteriorates due to the influence of an error caused by a Doppler frequency detection error.

  Therefore, an object of the present disclosure is to provide a dual-frequency CW radar apparatus that can calculate the distance with high accuracy without switching the transmission frequency of the transmission radio wave for each A / D conversion sampling period.

According to one aspect of the present disclosure, a transmission unit that alternately transmits a first transmission wave having a first frequency and a second transmission wave having a second frequency different from the first frequency for each predetermined transmission period. When,
A receiving unit configured to receive a reflected wave of the first transmission wave transmitted in one transmission period and a reflected wave of the second transmission wave transmitted in one transmission period subsequent to the one transmission period; ,
The received signal related to the reflected wave of the first transmission wave is A / D converted at a plurality of sampling timings to generate first sampling data, and the received signal related to the reflected wave of the second transmission wave is converted to a plurality of sampling timings. An A / D converter that performs A / D conversion to generate second sampling data;
The first sampling data is Fourier-transformed with the time-series order reversed and the phase reversed, and the second sampling data is phase-reversed without reversing the time-series order. A Fourier transform unit that performs a Fourier transform without inverting
A dual-frequency CW radar apparatus is provided that includes a distance calculation unit that calculates a distance to a reflector based on a Fourier transform result in the Fourier transform unit.

  According to the present disclosure, it is possible to obtain a two-frequency CW radar apparatus that can accurately calculate the distance without switching the transmission frequency of the transmission radio wave for each A / D conversion sampling period.

It is a figure which shows roughly the structure of the dual frequency CW radar apparatus 1 by one Example (1st Example). It is a figure which shows the phase relationship of 1st sampling data and 2nd sampling data. It is explanatory drawing of the generation | occurrence | production factor of the distance calculation error resulting from a phase shift process. It is an illustration of a cause of detection error of the Doppler frequency f _d. 3 is an explanatory diagram conceptually showing processing in a data conversion / phase inversion unit 30. FIG. It is a figure which shows an example of the more concrete structure of the receiving system of the dual frequency CW radar apparatus. It is a figure which shows the time series of the 1st sampling data and 2nd sampling data obtained in the period of a certain one period transmission operation. It is a figure which shows schematically the structure of 1 A of 2 frequency CW radar apparatuses by other one Example (2nd Example). It is a figure which shows an example of the 1st window function (alpha) and the 2nd window function (beta). It is a figure which compares a symmetric window function process and an asymmetric window function process.

  Hereinafter, embodiments will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a diagram schematically showing a configuration of a dual-frequency CW radar apparatus 1 according to one embodiment (first embodiment). The dual-frequency CW radar device 1 may be provided in an arbitrary manner, but is assumed to be mounted on a vehicle below. In this case, the dual-frequency CW radar device 1 may be provided to detect an object in front of the vehicle, or may be provided to detect an object on the side of the vehicle or behind the vehicle.

  In the example shown in FIG. 1, the two-frequency CW radar apparatus 1 includes a transmission unit 10, a reception unit 12, a two-frequency modulation unit 14, a low-pass filter (LPF) 16, an A / D conversion unit 18, and a data memory. 20, a data conversion / phase inversion unit 30, a Fourier transform unit (FFT) 40, a peak detection / phase inversion unit 50, a peak detection unit 58, and a phase difference detection / distance / velocity calculation unit 60.

  Various functions of the data conversion / phase inversion unit 30, Fourier transform unit 40, peak detection / phase inversion unit 50, peak detection unit 58, and phase difference detection / distance / velocity calculation unit 60 (including the functions described below). May be realized by any hardware, software, firmware, or a combination thereof. Various functions such as the data conversion / phase inverting unit 30 may be realized by a plurality of processing devices.

  The transmission unit 10 includes a transmission antenna 10a. The transmission unit 10 alternately transmits the first transmission wave having the first frequency f1 and the second transmission wave having the second frequency f2 via the transmission antenna 10a every predetermined transmission period T. That is, the transmission unit 10 transmits the first transmission wave and the second transmission wave by switching in time division for each predetermined transmission period T. The first frequency f1 and the second frequency f2 are different frequencies, but the difference may be slight (for example, several MHz). Hereinafter, for the sake of convenience, the operation of transmitting the first transmission wave in the transmission period T and then transmitting the second transmission wave in the transmission period T will be referred to as “one-cycle transmission operation”. Therefore, the period of one cycle of the transmission operation is 2T. During the operation of the dual frequency CW radar apparatus 1, the transmission unit 10 repeatedly executes this one-cycle transmission operation. The transmission period T is arbitrary, but may be determined according to a necessary distance measurement distance (maximum detectable distance) or the like.

  The two-frequency modulation unit 14 modulates a carrier wave generated by a local oscillator (for example, a VCO (Voltage Controlled Oscillator)), and converts the local signals of the first frequency f1 and the second frequency f2 for each predetermined transmission period T. Generate alternately. The frequency of the carrier wave may be arbitrary. Each signal generated by the two-frequency modulation unit 14 is amplified by the amplifier 10b and transmitted via the transmission antenna 10a.

  The receiving unit 12 includes a receiving antenna 20a. The receiving unit 12 receives the reflected wave of the first transmission wave and the reflected wave of the second transmission wave via the reception antenna 20a. These reflected waves are generated when the first transmission wave and the second transmission wave are reflected by an object (reflector) around the vehicle. That is, the receiving unit 12 receives the reflected wave reflected from the object around the vehicle by the receiving antenna 20a. A signal received by the receiving antenna 20a is amplified by an amplifier (for example, a low noise amplifier) 12b. The amplified received signal is multiplied (mixed) by the local signal having the first frequency f1 or the second frequency f2 input to the mixer 13 to generate a beat signal. Note that the frequency of the local signal (first frequency f1 or second frequency f2) input to the mixer 13 is switched to the frequency of the transmission wave transmitted from the transmission unit 10 (first frequency f1 or second frequency f2). It may be switched synchronously.

  The beat signal after mixing is expressed by the following equations.

ここで、Ｂ_ｆ１は、第１送信波の反射波に係るビート信号であり、Ｂ_ｆ２は、第２送信波の反射波に係るビート信号である。また、ｃは光速であり、ｆ_ｄはドップラ周波数であり、Ｒは物体までの距離である。ドップラ周波数ｆ_ｄは、以下で表される。
ｆ_ｄ＝２ｖ／λ
ここで、ｖは物体との相対速度であり、λは波長である。第１周波数ｆ１及び第２周波数ｆ２の差は、上述の如く僅かであることから、両ビート信号Ｂ_ｆ１及びＢ_ｆ２におけるドップラ周波数ｆ_ｄは等しいとして問題はない。

Here, B _f1 is a beat signal related to the reflected wave of the first transmission wave, and B _f2 is a beat signal related to the reflected wave of the second transmission wave. Also, c is the speed of light, f _d is the Doppler frequency, and R is the distance to the object. The Doppler frequency f _d is expressed as follows.
f _d = 2v / λ
Here, v is a relative velocity with respect to the object, and λ is a wavelength. The difference between the first frequency f1 and the second frequency f2, since it is just as described above, the Doppler frequency f _d at both beat signals B _f1 and B _f2 and to issue not equal.

  The low pass filter 16 extracts only the bands around the beat frequency. The beat signal (received signal) passed through the low-pass filter 16 is input to the A / D converter 18.

  The A / D converter 18 A / D converts the beat signal (received signal) passed through the low-pass filter 16 at a predetermined sampling period to obtain sampling data (received data). Hereinafter, sampling data related to the reception signal related to the first transmission wave among the sampling data obtained by the A / D conversion unit 18 is referred to as “first sampling data”, and sampling related to the reception signal related to the second transmission wave. The data is referred to as “second sampling data”. The number of samplings for obtaining the first sampling data corresponding to one transmission period T is two or more, and may be the same as the number of samplings for obtaining the second sampling data corresponding to one transmission period T. In the following, the processing for the first sampling data and the second sampling data obtained corresponding to a transmission operation in one cycle will be mainly described. However, the same processing corresponds to the transmission operation in another cycle. The first sampling data and the second sampling data obtained in this way are also executed.

  The data memory 20 stores the first sampling data and the second sampling data generated by the A / D conversion unit 18. For example, when the first sampling data related to the transmission operation in one cycle is accumulated in the data memory 20, the accumulated first sampling data may be input to the data conversion / phase inverting unit 30. Similarly, when the second sampling data related to the transmission operation in one cycle is accumulated in the data memory 20, for example, the accumulated second sampling data may be input to the Fourier transform unit 40.

  The data conversion / phase inverting unit 30 processes the first sampling data (received data related to the first frequency). The data conversion / phase inversion unit 30 inverts the time-series arrangement order of the first sampling data and inverts the phase of the first sampling data. The significance of this process will be described later.

  The Fourier transform unit 40 performs Fourier transform (fast Fourier transform) on the first sampling data whose arrangement order and phase are reversed by the data conversion / phase reversal unit 30 and the first sampling data generated by the A / D conversion unit 18. Two-sampled data is Fourier transformed. That is, the Fourier transform unit 40 performs Fourier transform on the first sampling data in a state where the order of the time series is inverted and the phase is inverted, and on the second sampling data, the order of the time series Is Fourier-transformed without inversion and phase inversion.

  The peak detection / phase inversion unit 50 detects a peak frequency (hereinafter, referred to as “first peak frequency f1 ′”) based on the FFT conversion result of the first sampling data, and a phase corresponding to the first peak frequency ( (Hereinafter referred to as “first phase”) is calculated (extracted). That is, the peak detection / phase inversion unit 50 obtains the first peak frequency and the first phase corresponding to the first peak frequency by the peak detection process from the frequency spectrum converted by the Fourier transform unit 40. Further, the peak detection / phase inversion unit 50 inverts the obtained first phase.

  The peak detection unit 58 detects a peak frequency (hereinafter referred to as “second peak frequency f2 ′”) based on the FFT conversion result of the second sampling data, and a phase corresponding to the second peak frequency (hereinafter, “ Second phase ”). That is, the peak detection unit 58 obtains the second peak frequency and the second phase corresponding to the second peak frequency from the frequency spectrum converted by the Fourier transform unit 40 by peak detection processing.

  The phase difference detection / distance / velocity calculation unit 60 calculates the distance and speed to the object based on the detection / calculation results of the peak detection / phase inversion unit 50 and the peak detection unit 58. Specifically, the phase difference detection / distance / velocity calculation unit 60 calculates the distance R to the object based on the difference Δθ between the inverted first phase and the second phase. For example, the distance R may be calculated by the following formula.

また、位相差検出／距離・速度算出部６０は、検出したドップラ周波数ｆ_ｄ（例えば第１ピーク周波数ｆ１'又は第２ピーク周波数ｆ２'）に基づいて、物体との間の相対速度ｖを算出する。例えば、相対速度ｖは、以下の式で算出されてよい。

Further, the phase difference detection / distance / velocity calculation unit 60 calculates the relative velocity v between the object and the object based on the detected Doppler frequency f _d (for example, the first peak frequency f1 ′ or the second peak frequency f2 ′). To do. For example, the relative speed v may be calculated by the following formula.

図２は、第１サンプリングデータ及び第２サンプリングデータの位相関係を示す図であり、（Ａ）は、送信部１０における１周期の送信動作の時系列を模式的に示し、（Ｂ）は、１周期の送信動作に対応して得られる第１サンプリングデータ及び第２サンプリングデータの時系列を示す図である。

FIG. 2 is a diagram illustrating a phase relationship between the first sampling data and the second sampling data, (A) schematically illustrates a time series of transmission operations in one cycle in the transmission unit 10, and (B) is It is a figure which shows the time series of the 1st sampling data and 2nd sampling data obtained corresponding to the transmission operation of 1 period.

  In FIG. 2B, ◯ represents a sampling point, the first sampling data (however, the first sampling data before the arrangement order and the phase are inverted) is indicated in S1, and the second sampling data is Instructed in S2. The first sampling data is acquired in synchronization with the transmission period T of the first transmission wave having the first frequency f1. That is, the first sampling data is synchronized with the transmission start timing (switching timing from the first transmission wave to the second transmission wave) of the second transmission wave from the time t1 synchronized with the transmission start timing of the first transmission wave. Acquired in the period between. Similarly, the second sampling data is acquired in synchronization with the transmission period T of the second transmission wave having the second frequency f2. That is, the second sampling data is acquired in a period from time t2 synchronized with the transmission start timing of the second transmission wave to time (not shown) synchronized with the transmission start timing of the next first transmission wave. . In this example, the first sampling data is acquired by performing sampling (A / D conversion) at seven sampling points schematically. However, as long as the number of samplings is 2 or more, it is arbitrary. is there.

  3 and 4 are explanatory diagrams of the cause of the error caused by the phase shift process. FIG. 3 shows the waveform D1 of the received wave (reflected wave) related to the first transmission wave obtained corresponding to the transmission operation of one cycle and the second transmission wave obtained corresponding to the transmission operation of the same cycle. A waveform D2 of the received wave (reflected wave) is schematically shown. FIG. 4 shows an example of the FFT conversion result. In FIG. 4, ● represents the FFT conversion result (discrete value).

  In the two-frequency CW system, as described above, the first transmission wave and the second transmission wave are alternately transmitted every predetermined transmission period T, and therefore the reception start times of the reflected waves are not the same. That is, as shown in FIG. 2B, the sampling start timing of the first sampling data and the second sampling data is shifted by the time corresponding to the transmission period T. Therefore, the phase difference Δθ cannot be obtained as it is. On the other hand, as shown in FIG. 3, the phase of the second sampling data is such that the reception start time of the reception wave related to the first transmission wave and the reception wave related to the second transmission wave are virtually the same time. A configuration (hereinafter referred to as “comparison configuration”) that performs a process (phase shift process) for shifting the signal by a time corresponding to the transmission period T is conceivable. In such a comparison configuration, the distance R is calculated by the following equation.

数４の式において、２πｆ_ｄＴの項は、位相シフト処理に対応する。即ち、比較構成では、抽出した位相差Δθを２πｆ_ｄＴだけシフトする位相シフト処理を行うことで、距離Ｒを算出する。しかしながら、ＦＦＴ変換結果は離散値であるので、検出したドップラ周波数ｆ_ｄは、図４に模式的に示すように、真のドップラ周波数ｆ_ｄに対して誤差を含みうる。この点、比較構成では、数４の式において２πｆ_ｄＴの項を含むので、ドップラ周波数ｆ_ｄの誤差に起因して、距離Ｒの精度が悪化するという問題がある。

In the equation (4), the term of 2πf _d T corresponds to the phase shift process. That is, in the comparison configuration, the distance R is calculated by performing a phase shift process that shifts the extracted phase difference Δθ by 2πf _d T. However, since the FFT conversion result is a discrete value, the detected Doppler frequency f _d may include an error with respect to the true Doppler frequency f _d as schematically shown in FIG. In this regard, the comparative configuration includes a term of 2πf _d T in the equation (4), and thus there is a problem that the accuracy of the distance R deteriorates due to an error of the Doppler frequency f _d .

On the other hand, according to the present embodiment, since the term of 2πf _d T is not included in the formula (2), the deterioration of the accuracy of the distance R due to the error of the Doppler frequency f _d can be reduced. That is, according to the present embodiment, the error caused by the phase shift process can be reduced by performing the process in the data conversion / phase inversion unit 30 or the like instead of the phase shift process. Thereby, in the present embodiment, even when the transmission period T is lengthened, the calculation accuracy of the distance R can be maintained high. That is, it is possible to increase the calculation accuracy of the distance R without having to increase the switching period between the first frequency and the second frequency. Accordingly, it is possible to maintain the calculation accuracy of the distance R high while extending the transmission period T to increase the distance measurement distance.

  Next, processing in the data conversion / phase inversion unit 30 and the like will be described in detail.

  FIG. 5 is an explanatory diagram conceptually showing processing in the data conversion / phase inverting unit 30. FIG. 5 is a diagram corresponding to FIG. 2B, and is a diagram illustrating a time series of the first sampling data and the second sampling data obtained corresponding to the transmission operation of one cycle. In FIG. 5, ◯ represents a sampling point, the first sampling data before the arrangement order and phase are inverted is indicated by S1, and the first sampling data before the arrangement order and phase is inverted is S1. Instructed by '.

  As schematically indicated by arrows in FIG. 5, the first sampling data S1 is converted into the first sampling data S1 ′ by inverting the order and the phase in the time series. The As shown in FIG. 5, the first sampling data S1 ′ is data synchronized with the sampling data S2 of the second sampling data. That is, the first sampling data S1 ′ can be handled as data based on the time t2, similarly to the second sampling data. Therefore, Formula 2 can be obtained by setting T = 0 in Formula 4. Thus, by inverting the arrangement order and the phase, the phase shift process becomes unnecessary, and errors caused by the phase shift process can be reduced.

  As shown in FIG. 5, in this embodiment, since the phase of the first sampling data S1 ′ is inverted with respect to the original first sampling data S1, the FFT conversion for the first sampling data S1 ′ is performed. The first phase obtained from the result cannot be used as it is. Therefore, in the present embodiment, as described above, the peak detection / phase inversion unit 50 inverts the first phase obtained from the FFT conversion result for the first sampling data S1 ′.

  Next, an example of more specific processing in the data conversion / phase inversion unit 30 will be described.

  FIG. 6 is a diagram illustrating an example of a more specific configuration of the reception system of the dual frequency CW radar apparatus 1. FIG. 7 is a diagram showing a time series of the first sampling data and the second sampling data obtained in a certain period of transmission operation (from time t1 to time t3) in the configuration shown in FIG. In FIG. 6, the same reference numerals are assigned to the components corresponding to the components shown in FIG. In FIG. 6, the data memory 20 shown in FIG. 1 is not shown. In FIG. 6, the data conversion / phase inversion unit 30 is separated into a data conversion unit 31 and a phase inversion unit 32 for convenience.

First, between time t1 and t2, the transmission part 10 (refer FIG. 1) transmits the 1st transmission wave of the 1st frequency f1. During this time, the receiving unit 12 receives the reflected wave related to the first transmission wave reflected from the object by the receiving antenna 12a and amplifies it by the amplifier 12b. The amplified received signal is mixed with the local signal of the first frequency f1 input to the mixer 13, and a beat signal is output. In the example shown in FIG. 6, since the quadrature detection method is used, the received signal is divided into two systems, and the received signals of the respective systems are mixed with orthogonal local signals cos (2πf1t) and sin (2πf1t). . The beat signal of the first system is A / D converted by the A / D converter 18a, and the sampling data a ₁ (k) of the first system is generated. The second system beat signal is A / D converted by the A / D converter 18b to generate second system sampling data b ₁ (k). As a result, as shown in FIG. 7, the A / D converter 18a obtains n (n> 1) of {a ₁ (1), a ₁ (2), ... a ₁ (n)}. In the A / D converter 18b, n pieces of {b ₁ (1), b ₁ (2),... B ₁ (n)} are obtained. In addition, 1, 2,... N represents a time-series order.

In the data conversion unit 31, the arrangement order of the sampling data a ₁ (k) of the first system and the sampling data b ₁ (k) of the second system is reversed. Specifically, it is inverted as follows.
{A ₁ (1), a ₁ (2), ... a ₁ (n)} = {a ₁ (n), a ₁ (n-1), ... a ₁ (1)}
{B ₁ (1), b ₁ (2),... B ₁ (n)} = {b ₁ (n), b ₁ (n−1),... B ₁ (1)}
The phase inversion unit 32 combines the two systems of data from the data conversion unit 31 into a complex signal as follows.
r ₁ (k) = a ₁ (k) −jb ₁ (k) (k = 1, 2,... n)
Here, the inversion of the phase (inversion of the rotation direction of the phase) is realized by making the sign of the complex component negative.

In the Fourier transform unit 40, the complex signal r ₁ (k) is transformed into a frequency spectrum by fast Fourier transform as follows.

ピーク検出／位相反転部５０では、上述の如く、周波数スペクトルＲ_１（ｆ）上からピーク検出処理により第１ピーク周波数ｆ１'が検出されると共に、第１ピーク周波数ｆ１'に対応する第１位相φ１が抽出される。但し、上述の如くフーリエ変換部４０で処理されたサンプリングデータは並び順及び位相回転方向が逆転されているため、抽出された第１位相φ１は反転される。即ち、θ１＝−φ１とされる。

In the peak detection / phase inversion unit 50, as described above, the first peak frequency f1 ′ is detected from the frequency spectrum R ₁ (f) by the peak detection process, and the first phase corresponding to the first peak frequency f1 ′ is detected. φ1 is extracted. However, since the sampling order processed by the Fourier transform unit 40 as described above is reversed in order and phase rotation direction, the extracted first phase φ1 is inverted. That is, θ1 = −φ1.

Next, between time t2 and t3, the transmission part 10 (refer FIG. 1) transmits the 2nd transmission wave of the 2nd frequency f2. As a result, as schematically shown in FIG. 7, the A / D conversion unit 18a obtains n pieces of {a ₂ (1), a ₂ (2),... A ₂ (n)}, In the A / D converter 18b, n pieces of {b ₂ (1), b ₂ (2),... B ₂ (n)} are obtained.

From time t2 to t3, the data conversion unit 31 and the phase inversion unit 32 do not function (that is, the inversion order and the phase rotation direction are not executed), and the two systems of data are converted into complex signals as follows: Combined.
r ₂ (k) = a ₂ (k) + jb ₂ (k) (k = 1, 2,... n)
Here, since the phase inversion is not executed, the sign of the complex component is positive.

Similarly, in the Fourier transform unit 40, the complex signal r ₂ (k) is transformed into a frequency spectrum by fast Fourier transform. Then, as described above, the peak detector 58 detects the second peak frequency f2 ′ from the frequency spectrum R ₂ (f) by the peak detection process, and the second phase φ2 corresponding to the second peak frequency f2 ′. Is extracted. The extracted second phase φ2 is used as it is without being inverted. That is, θ2 = φ2.

  The phase difference detection / distance / velocity calculation unit 60 calculates the phase difference Δθ (= θ1-θ2) based on θ1 and θ2 calculated as described above, and based on the calculated phase difference Δθ up to the object The distance R is calculated (see the formula 2).

  FIG. 8 is a diagram schematically showing a configuration of a dual-frequency CW radar apparatus 1A according to another embodiment (second embodiment).

  The dual-frequency CW radar apparatus 1A according to the present embodiment includes the first asymmetric window function processing unit 22 and the second asymmetric window function processing unit 24, and the dual-frequency CW radar apparatus 1 according to the first embodiment described above. Mainly different. In the dual-frequency CW radar apparatus 1 according to the first embodiment described above, the window function processing is applied as preprocessing of the conversion processing in the Fourier transform unit 40 (preprocessing for maintaining the continuity of both ends of the data). However, the window function used is symmetrical, for example. For example, in the dual-frequency CW radar apparatus 1 according to the first embodiment described above, window function processing using a general left-right symmetric Hanning function may be executed. On the other hand, in the dual frequency CW radar apparatus 1A of the present embodiment, the first window function α and the second window function β used in the first asymmetric window function processing unit 22 and the second asymmetric window function processing unit 24 are , Each has left-right asymmetry. In the following, the configuration peculiar to the second embodiment will be described mainly, and other configurations may be the same as those of the first embodiment described above.

  The first asymmetric window function processing unit 22 implements window function processing by multiplying the first sampling data by the first window function α. The first window function α has a left-right asymmetric characteristic such that the first sampling data related to the transmission operation in one cycle is multiplied by a left-right asymmetric gain. An example of the first window function α and the significance of the left-right asymmetric characteristic will be described later.

  The second asymmetric window function processing unit 24 implements window function processing by multiplying the second sampling data by the second window function β. The second window function β has a left-right asymmetric characteristic such that the second sampling data related to the transmission operation in one cycle is multiplied by a left-right asymmetric gain. An example of the second window function β and the significance of the left-right asymmetric characteristic will be described later.

  FIG. 9 is a diagram illustrating an example of the first window function α and the second window function β. In FIG. 9, the first window function α and the second window function β schematically show the relationship between the first sampling data S1 and the second sampling data S2 to be applied.

  As described above, the first window function α is multiplied by the first sampling data S1 (first sampling data before the arrangement order and phase are inverted). As for the first window function α, the time-sequential data (data closer to the time t2 with respect to the center of the data) of the first sampling data related to the transmission operation of one cycle is the previous data (data It has a left-right asymmetric characteristic that is multiplied by a larger gain than the central portion (data closer to time t1). However, the gain of the first window function α is substantially zero at the left and right ends in order to maintain the continuity of both ends of the data.

  As described above, the second window function β is multiplied by the second sampling data S2. As for the second window function β, the time-series previous data (data closer to the time t2 with respect to the center of the data) of the second sampling data related to the transmission operation in one cycle is the later data (data It has a left-right asymmetric characteristic that is multiplied by a larger gain than the central portion (data closer to time t3). However, since the second window function β maintains continuity at both ends of the data, the gain at the both left and right ends is substantially zero. For example, the second window function β may be expressed by the following equation.

ここで、ｍは係数であり、例えば２であってよい。また、ｔは、時刻ｔ２を０（原点）とした時間である。
この場合、第１窓関数αは、数６の式を左右反転させた式であってよい。

Here, m is a coefficient, and may be 2, for example. Further, t is a time when the time t2 is 0 (origin).
In this case, the first window function α may be an equation obtained by horizontally inverting the equation of Equation 6.

  FIG. 10 is a diagram comparing symmetric window function processing and asymmetric window function processing. FIG. 10A shows a case of symmetric window function processing (processing by a Hanning function in this example), and FIG. The case of window function processing is shown. In each of (A) and (B), in order from the top, a diagram showing each sampling timing of the first sampling data S1 and the second sampling data S2 related to the transmission operation of one cycle, corresponding to the transmission operation of the same cycle. The figure which shows the waveform D1 (waveform of 1st sampling data S1) concerning the 1st transmission wave obtained in this way, and the waveform D2 (waveform of 2nd sampling data S2) of the reception wave which concerns on a 2nd transmission wave, window function And a diagram showing a waveform D1 ′ and a waveform D2 ′ after the window function processing.

By the way, according to the first embodiment described above, the phase shift processing is not necessary as described above, but the Doppler frequency f _d (first peak frequency f1 ′ and second peak frequency f2 ′) as shown in FIG. Detection errors still exist. In the left-right symmetric window function (Hanning function in this example) as shown in FIG. 10A, the weight (gain) decreases toward both ends, and is greatly affected by the data center (time t4, t5). That is, the detected Doppler frequency error (and the first and second phase errors extracted based on the error, and hence the calculation error of the distance R) is proportional to the time differences | t4-t2 | and | t5-t2 |. Become bigger.

  In this regard, according to the second embodiment, by performing the left-right asymmetric window function processing as described above, a portion (data near time t4 ′ and data near time t5 ′) that is most influenced by the phase is timed. It can be close to t2. As a result, the time differences | t4′−t2 | and | t5′−t2 | are reduced, so that the error of the detected Doppler frequency (and the errors of the first phase and the second phase extracted based on the error), and thus the distance R (Calculation error) can be reduced.

  In the example shown in FIGS. 8 to 10, the first window function α is multiplied by the first sampling data before the arrangement order and the phase are inverted, but the multiplication position is more than that of the Fourier transform unit 40. It is optional as long as it is the previous stage. For example, the first window function α may be multiplied by a reception signal (analog signal) before A / D conversion by the A / D conversion unit 18. Alternatively, the first window function α may be multiplied by the first sampling data after the arrangement order and the phase are inverted. That is, the first asymmetric window function processing unit 22 may be provided after the data conversion / phase inversion unit 30. In this case, the first window function α may be the same as the second window function β.

  Although each embodiment has been described in detail above, it is not limited to a specific embodiment, and various modifications and changes can be made within the scope described in the claims. It is also possible to combine all or a plurality of the components of the above-described embodiments.

  For example, in the above-described embodiment, the order of the time series of the first sampling data is inverted as the data conversion process, but the same rearrangement may be realized in another equivalent manner. For example, the similar rearrangement may be realized by inverting the reading order and the writing order with respect to the data memory 20.

  In the above-described embodiment, the A / D converter 18 performs sampling at a predetermined sampling period regardless of switching between the first frequency and the second frequency. The sampling timing may be determined using the switching timing between frequencies as a trigger. However, in this case, the number of times of sampling for obtaining each of the first sampling data and the second sampling data per transmission operation in one cycle is at least 2 or more. That is, at least two times of sampling is performed in order to obtain the first sampling data per one transmission operation of one cycle, and at least two times of sampling is performed to obtain the second sampling data. In addition, the A / D converter 18 may synchronize the sampling timing so that the switching timing between the first frequency and the second frequency (see, for example, t2 in FIG. 2) is an intermediate point in one sampling period. Good.

  In the above-described embodiment, as a one-cycle transmission operation, the first transmission wave of the first frequency is transmitted in the transmission period T, and then the second transmission wave of the second frequency higher than the first frequency is transmitted. Although transmission is performed at T, the reverse may be possible. That is, the one-cycle transmission operation may transmit the second transmission wave of the second frequency in the transmission period T and then transmit the first transmission wave of the first frequency in the transmission period T. In this case, the arrangement order and phase of the second sampling data may be reversed.

  In the above-described embodiment, the distance and the like are calculated for each transmission operation in one cycle based on the first sampling data and the second sampling data. However, the distance and the like are calculated for each transmission operation in a half cycle. May be. For example, in the example shown in FIG. 7, from time t3 to time t4 (not shown) after the transmission period T, the transmission unit 10 transmits the first transmission wave of the first frequency f1 again. At this time, the distance or the like may be calculated based on the second sampling data from time t2 to time t3 and the first sampling data from time t3 to time t4. In this case, the arrangement order and phase of the second sampling data may be reversed. Such a configuration is advantageous when the transmission period T is relatively long because the processing load is high but the distance calculation cycle is high.

  Moreover, in Example 2 mentioned above, although both the 1st window function (alpha) and the 2nd window function (beta) are applied as a preferable Example, only one may be applied. That is, one of the first window function α and the second window function β may be replaced with, for example, a Hanning function.

DESCRIPTION OF SYMBOLS 1 Two frequency CW radar apparatus 10 Transmitting part 10a Transmitting antenna 12 Receiving part 12a Receiving antenna 16 Low pass filter 18 A / D conversion part 20 Data memory 22 1st asymmetric window function processing part 24 2nd asymmetric window function processing part 30 Data conversion / Phase inversion unit 31 Data conversion unit 32 Phase inversion unit 40 Fourier transform unit 50 Peak detection / phase inversion unit 58 Peak detection unit 60 Phase difference detection / distance / speed calculation unit

Claims (5)

A transmission unit that alternately transmits a first transmission wave having a first frequency and a second transmission wave having a second frequency different from the first frequency for each predetermined transmission period;
A receiving unit configured to receive a reflected wave of the first transmission wave transmitted in one transmission period and a reflected wave of the second transmission wave transmitted in one transmission period subsequent to the one transmission period; ,
The received signal related to the reflected wave of the first transmission wave is A / D converted at a plurality of sampling timings to generate first sampling data, and the received signal related to the reflected wave of the second transmission wave is converted to a plurality of sampling timings. An A / D converter that performs A / D conversion to generate second sampling data;
The first sampling data is Fourier-transformed with the time-series order reversed and the phase reversed, and the second sampling data is phase-reversed without reversing the time-series order. A Fourier transform unit that performs a Fourier transform without inverting
A dual-frequency CW radar apparatus, comprising: a distance calculation unit that calculates a distance to a reflector based on a Fourier transform result in the Fourier transform unit. A data converter that reverses the time-series order of the first sampling data;
The dual frequency CW radar apparatus according to claim 1, further comprising a phase inverting unit that inverts the phase of the first sampling data. A peak phase inversion unit that inverts a first phase corresponding to a first peak frequency obtained from a Fourier transform result for the first sampling data;
The distance calculation unit calculates the distance based on a difference between the inverted first phase and a second phase corresponding to a second peak frequency obtained from a Fourier transform result for the second sampling data. Item 3. The dual-frequency CW radar device according to item 1 or 2. A first window function processing unit that multiplies the first sampling data by a predetermined first window function as pre-processing for Fourier transform in the Fourier transform unit;
The first window function has an asymmetric characteristic in which the later data is multiplied by a larger gain than the previous data with respect to the center of the time series of the first sampling data. The dual-frequency CW radar device according to any one of the above. A second window function processing unit that multiplies the second sampling data by a predetermined second window function as preprocessing for Fourier transform in the Fourier transform unit;
5. The second window function according to claim 4, wherein the second window function has an asymmetric characteristic in which the previous data is multiplied by a larger gain than the subsequent data with respect to the center of the time series of the second sampling data. Dual-frequency CW radar device.

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