JP5019316B2 - FM-CW polarization radar equipment - Google Patents

Description

  The present invention relates to an FM-CW (Frequency Modulation-Cotinuous Wave) polarization radar apparatus using polarized waves used for target identification by radio waves.

  The target has characteristic scattering depending on its material and shape. For example, a pole standing vertically reflects a vertical polarization (V polarization) well, but hardly reflects a horizontal polarization (H polarization). In addition, the metal surface reflects the right-handed polarization as a left-handed polarization. The clockwise polarization and the counterclockwise polarization are states in which the phases of the V polarization and the H polarization are shifted by 90 degrees. In addition, there are obliquely polarized waves and elliptically polarized waves, all of which are determined by the amplitude and phase relationship between the V polarization and the H polarization. That is, an HH polarization or VH polarization in which a signal transmitted by H polarization is received by H polarization or V polarization, and an HV polarization in which a signal transmitted by V polarization is received by H polarization or V polarization. By observing and analyzing the four components of waves and VV polarized waves, it is possible to observe the material and shape of the target depending on how the target scatters and its scattering state.

As an FM-CW polarization radar apparatus for observing the four components of the HH polarization, VH polarization, HV polarization, and VV polarization, for example, there is a polarimetric synthetic aperture radar apparatus disclosed in Patent Document 1.
This polarimetric synthetic aperture radar device is mounted on a flying object such as an artificial satellite or an aircraft, and transmits a linear frequency modulated transmission signal alternately from a horizontal polarization antenna and a vertical polarization antenna, In an apparatus for acquiring a SAR image relating to an arbitrary polarization from data acquired by a combination of horizontal / vertical polarization signals from an object received by both antennas, a transmission signal is transmitted to two antenna systems for each of two transmission triggers. And a means for switching and outputting the reception signals of the two antennas for each transmission trigger, and a reception means for performing reception processing on the two systems of reception signals switched and extracted.

  The conventional FM-CW polarization radar apparatus observes four types of polarization signals of HH polarization signal, VH polarization signal, HV polarization signal, and VV polarization signal in time series, and performs polarization basis conversion and the like. I went to identify the surface condition and target shape. The reason for observing in time series is that the conventional FM-CW polarization radar apparatus cannot observe target data in principle if radio waves are simultaneously emitted. This is because if the H-polarized radio wave and the V-polarized radio wave are transmitted simultaneously, the scattered waves will interfere with each other.

  For example, a VH polarization in which a signal transmitted by H polarization is received by V polarization and a VV polarization in which a signal transmitted by V polarization is received by V polarization are both V polarization at the time of reception. Because they are one another, they cannot be separated. In addition, the HH polarization in which a signal transmitted with H polarization is received in H polarization and the HV polarization in which a signal transmitted in V polarization is received with H polarization are both H polarization at the time of reception. Because they are one another, they cannot be separated. Therefore, in order to avoid interference, at least HH polarization and VH polarization, and HV polarization and VV polarization are alternately observed.

  In general, the FM-CW polarization radar apparatus is mounted and operated on a moving object such as an artificial satellite, an aircraft, or a vehicle, and therefore its position changes from moment to moment. Also, the position changes with the movement of the target. For this reason, since the positional relationship between the target and the FM-CW polarization radar device always changes, the target when the HH polarization base and the VH polarization base and the HV polarization base and the VV polarization base are observed is actually It will be different from the position. If the positions are different, the amplitude and phase of the received signal change, and therefore, the HH polarization base and the VH polarization base, and the HV polarization base and the VV polarization base have observed different target states.

JP-A-5-87919 (paragraph 0011)

Since the conventional FM-CW polarization radar apparatus is configured as described above, the observed target is different from the actual position, and the state of a different target is observed, and target information cannot be obtained accurately. There has been a problem that target identification performance deteriorates.
In recent years, high-resolution signal processing has been developed, and this error becomes a major issue when more advanced signal processing is performed.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an FM-CW polarization radar apparatus that can accurately obtain target information and improve target identification performance. And

The FM-CW polarization radar apparatus according to the present invention generates a code H whose cross-correlation with the code V is equal to or less than a predetermined value, and code-modulates the chirp signal whose frequency changes according to the input voltage with the code H. H-polarization code modulation means for transmitting the H-polarization transmission signal H, which is horizontal polarization, to the target, and a code V whose cross-correlation with the code H is a predetermined value or less is generated, and the chirp signal is represented by the code V-polarization code modulation means for code-modulating with V and transmitting a V-polarized transmission signal V, which is vertically polarized, to the target, and an H-polarized wave reflected by the transmission signal H reflected by the target And a reception signal H obtained by synthesizing a reflected wave of H polarization by the transmission signal V reflected by the target and multiplying the reception signal H by a delay code H which is a delay code of the code H. HH polarization that generates signal HH A receiving signal V obtained by synthesizing a V-polarized wave reflected by the transmission signal H reflected from the target and the V-polarized wave reflected by the transmission signal V reflected by the target; VH polarization extracting means for multiplying the signal V and the delay code H to generate a received chirp signal VH; receiving the received signal H; and receiving a delay code V which is a delay code of the received signal H and the code V HV polarization extraction means for generating a reception chirp signal HV by multiplication, and VV polarization extraction means for receiving the reception signal V and multiplying the reception signal V and the delay code V to generate a reception chirp signal VV The delay amounts of the delay code H and the delay code V correspond to the reflection delay time from the target at the maximum measurement distance .

  According to the present invention, it is possible to obtain target information precisely and to improve the target identification performance.

Embodiment 1 FIG.
1 is a block diagram showing the configuration of an FM-CW polarization radar apparatus according to Embodiment 1 of the present invention. This FM-CW polarization radar apparatus includes a sawtooth wave generator 101, a voltage control signal generator (VCO) 102, code generators 103 and 104, modulators 105 and 106, H polarization antennas 107 and 109, V polarization. Antennas 108, 110, multipliers 111, 112, 113, 114, delay circuits 115, 116, multipliers 117, 118, 119, 120, receiving units 121, 122, 123, 124, a signal processing unit 125, and a memory 126 are provided. The radio wave is transmitted to the target 1 and the reflected wave from the target 1 is received to identify the target 1 and measure the distance to the target 1.

  In FIG. 1, the code generator 103, the modulator 105, and the H polarization antenna 107 constitute an H polarization code modulation means, and the code generator 104, the modulator 106, and the V polarization antenna 108 constitute a V polarization code modulation means. Is configured.

  Further, in FIG. 1, the code generator 103, the delay circuit 115, the multiplier 111, the multiplier 117, and the receiving unit 121 constitute an HH polarization extraction means, and the code generator 103, the delay circuit 115, the multiplier 112, and the multiplication The generator 118 and the receiver 122 constitute VH polarization extraction means, and the code generator 104, the delay circuit 116, the multiplier 113, the multiplier 119, and the receiver 123 constitute HV polarization extraction means, and the code generator 104 The delay circuit 116, the multiplier 114, the multiplier 120, and the receiving unit 124 constitute a VV polarization extraction means.

Next, the operation will be described.
The sawtooth wave generator 101 generates a sawtooth wave signal whose voltage temporally changes in accordance with a command from the signal processing unit 125 and outputs the sawtooth wave signal to the voltage control signal generator 102. The voltage control signal generator 102 outputs a sine wave signal having a frequency specified by an input voltage, and outputs a chirp signal whose frequency changes according to the voltage of the sawtooth wave signal from the sawtooth wave generator 101. The chirp signal output from the voltage control signal generator 102 is input to the modulators 105 and 106 and the multipliers 117, 118, 119 and 120.

  The codes generated by the code generator 103 and the code generator 104 are different from each other, and generate a code H and a code V of a code sequence whose cross-correlation value is a predetermined value or less. A value close to zero is set as the predetermined value. That is, if the cross-correlation value between the code H and the code V is less than or equal to a predetermined value, the cross-correlation value between the code H and the code V is very small or theoretically zero. Such codes include, for example, orthogonal codes such as GOLD sequence pseudo-random codes and Hadamard sequences. Here, it is a feature of the present invention that the code rate is sufficiently larger than the reciprocal of the round-trip propagation time of the maximum measurement distance of the target 1. In the spread spectrum radar that measures the target distance from the delay time of the code, a high code rate is used. Here, a low code rate that delays only about 1/4 chip at the maximum measurement distance is selected. . The code lengths of the codes H and V are preferably as short as possible. One cycle of the code and the sweep time may be the same time, but it is better to include as many cycles as possible.

  The code H generated by the code generator 103 is input to the modulator 105, and the modulator 105 phase-modulates the chirp signal based on the code H and outputs a transmission signal H. The code V generated by the code generator 104 is input to the modulator 106, and the modulator 106 phase-modulates the chirp signal based on the code V and outputs a transmission signal V.

  The transmission signal H is transmitted as an H-polarized radio wave that is a horizontal polarization by the H-polarization antenna 107, and the transmission signal V is transmitted as a V-polarization radio wave that is a vertical polarization by the V-polarization antenna 108.

  As described above, the H-polarization code modulation means including the code generator 103, the modulator 105, and the H-polarization antenna 107 has a code whose cross-correlation with the code V is equal to or less than a predetermined value (very low or zero). H is generated, a chirp signal whose frequency changes according to the input voltage is code-modulated with the code H, and a H-polarized transmission signal H that is a horizontal polarization is transmitted to the target 1, and the code generator 104 modulates V-polarization code modulation means constituted by the device 106 and the V-polarization antenna 108 generates a code V whose cross-correlation with the code H is not more than a predetermined value (very low or zero), and converts the chirp signal into the code V The V-polarized transmission signal V, which is vertically polarized, is transmitted to the target 1 by code modulation.

  The transmitted radio wave of the H-polarized transmission signal H is reflected by the target 1 as an H-polarized reflected wave and a V-polarized reflected wave, and the H-polarized reflected wave is received by the H-polarized antenna 109 as HH. The V-polarized reflected wave is received as a VH received signal by the V-polarized antenna 110.

  On the other hand, the transmitted radio wave of the V-polarized transmission signal V is reflected by the target 1 as an H-polarized reflected wave and a V-polarized reflected wave, and the H-polarized reflected wave is reflected by the H-polarized antenna 109. The signal is received as an HV reception signal, and the reflected wave of V polarization is received by the V polarization antenna 110 as a VV reception signal.

  The H polarization antenna 109 receives a reception signal H obtained by combining the HH reception signal and the HV reception signal, and the V polarization antenna 110 receives a reception signal V obtained by combining the VH reception signal and the VV reception signal. Received signal H is input to multiplier 111 and multiplier 113, and received signal V is input to multiplier 112 and multiplier 114.

  The code H output from the code generator 103 is also input to the delay circuit 115, and the delay circuit 115 delays the code H and outputs the delay code H. The code V output from the code generator 104 is also input to the delay circuit 116, which delays the code V and outputs the delay code V.

  The delay amounts of the delay circuit 115 and the delay circuit 116 are the number of chips that are delayed by the maximum measurement distance. Here, since a low-speed code rate is selected so as to delay only about 1/4 chip at the maximum measurement distance, the delay amount is set to 1/4 chip. The 1/4 chip delay can be realized by, for example, a flip-flop driven by a quadruple clock.

  In this way, by making the delay amounts of the delay code H and the delay code V correspond to the reflection delay time from the target at the maximum measurement distance, the target scattering level in the vicinity can be suppressed and the target scattering level in the distance can be increased. The dynamic range of the system can be suppressed, and remote targets can be measured more precisely.

  The delay code H from the delay circuit 115 is output to the multipliers 111 and 112, and the delay code V from the delay circuit 116 is output to the multipliers 113 and 114.

  Multiplier 111 multiplies reception signal H and delay code H and outputs reception chirp signal HH to multiplier 117, and multiplier 112 multiplies reception signal V and delay code H to multiply reception chirp signal VH by multiplier 118. The multiplier 113 multiplies the received signal H and the delay code V to output the received chirp signal HV to the multiplier 119, and the multiplier 114 multiplies the received signal V and the delay code V to receive the received chirp signal VV. Is output to the multiplier 120.

Multiplier 117 multiplies reception chirp signal HH by the chirp signal output from voltage control signal generator 102 and outputs beat signal HH to receiving section 121. Multiplier 118 generates reception chirp signal VH and a voltage control signal. The beat signal VH is multiplied by the chirp signal output from the multiplier 102 and output to the receiver 122. The multiplier 119 multiplies the received chirp signal HV and the chirp signal output from the voltage control signal generator 102. The beat signal HV is output to the reception unit 123, and the multiplier 120 multiplies the reception chirp signal VV and the chirp signal output from the voltage control signal generator 102 and outputs the beat signal VV to the reception unit 124.
The process of obtaining a beat signal by multiplying the received chirp signal and the chirp signal output from the voltage control signal generator 102 is the same as the principle of a general FM-CW polarization radar apparatus.

The receiving unit 121 removes the high frequency component of the beat signal HH, extracts the low frequency beat signal HH, converts it into a digital signal HH, and outputs it to the signal processing unit 125. The receiving unit 122 outputs the high frequency component of the beat signal VH. The low-frequency beat signal VH is taken out, converted into a digital signal VH and output to the signal processing unit 125, and the reception unit 123 removes the high-frequency component of the beat signal HV and outputs the low-frequency beat signal HV. Extracted, converted into a digital signal HV and output to the signal processing unit 125, the receiving unit 124 removes the high frequency component of the beat signal VV to extract the low frequency beat signal VV, converted into the digital signal VV, and converted into a digital signal VV It outputs to 125.
Here, the conversion start timing at which the receiving units 121, 122, 123, and 124 convert into digital signals is based on the command of the signal processing unit 125, and is synchronized with the sawtooth wave generation timing of the sawtooth wave generator 101. .

  As described above, the HH polarization extraction unit configured by the code generator 103, the delay circuit 115, the multiplier 111, the multiplier 117, and the reception unit 121 reflects the H polarization by the transmission signal H reflected by the target 1. The received signal H obtained by synthesizing the reflected wave of the H polarization with the transmission signal V reflected by the target 1 is received, and the received signal H is multiplied by the delay code H to generate the received chirp signal HH. The beat signal HH is generated by multiplying the chirp signal HH and the chirp signal, and the high frequency component of the generated beat signal HH is removed to output the digital signal HH.

  Further, the VH polarization extraction means constituted by the code generator 103, the delay circuit 115, the multiplier 112, the multiplier 118, and the reception unit 122 is a reflected wave of V polarization by the transmission signal H reflected by the target 1. A reception signal V obtained by synthesizing a reflected wave of V polarization by the transmission signal V reflected by the target 1 is received, the reception signal V and the delay code H are multiplied to generate a reception chirp signal VH, and the generated reception chirp signal The beat signal VH is generated by multiplying VH and the chirp signal, and the high frequency component of the generated beat signal VH is removed to output the digital signal VH.

  Further, the HV polarization extraction means configured by the code generator 104, the delay circuit 116, the multiplier 113, the multiplier 119, and the reception unit 123 receives the reception signal H and multiplies the reception signal H by the delay code V. Then, the reception chirp signal HV is generated, the generated reception chirp signal HV and the chirp signal are multiplied to generate the beat signal HV, the high frequency component of the generated beat signal HV is removed, and the digital signal HV is output.

  Further, the VV polarization extraction means configured by the code generator 104, the delay circuit 116, the multiplier 114, the multiplier 120, and the reception unit 124 receives the reception signal V and multiplies the reception signal V and the delay code V. The reception chirp signal VV is generated, the generated reception chirp signal VV and the chirp signal are multiplied to generate the beat signal VV, the high frequency component of the generated beat signal VV is removed, and the digital signal VV is output.

  The signal processing unit 125 accumulates the digital signal HH, the digital signal VH, the digital signal HV, and the digital signal VV in the memory 126 until the rising of the sawtooth wave is completed. Since the rising time of the sawtooth wave is defined in advance as a sweep time, the end of the rising can be found by measuring the time from the start of the command.

  After the rising of the sawtooth wave, that is, after the measurement is completed, the signal processing unit 125 reads out the digital signal HH, the digital signal VH, the digital signal HV, and the digital signal VV stored in the memory 126, and respectively performs Fourier transform. The frequency spectrum after Fourier transform corresponds to the target response in the distance direction, and when there is one target 1 as shown in FIG. 1, a peak appears at the frequency corresponding to the distance of the target 1. This is the same principle as a general FM-CW polarization radar apparatus. Further, as general radar processing, resolution can be improved by pulse compression in the range direction and synthetic aperture processing in the operation direction. The amplitude and phase of this peak position are complex target scattering signals.

  A target distance and a complex target scattering signal are obtained from the digital signal HH, the digital signal VH, the digital signal HV, and the digital signal VV, respectively, by Fourier transform by the signal processing unit 125. Although the target distance can be set to four, it becomes one value by correcting the physical position difference between the H polarization antenna 107, the V polarization antenna 108, the H polarization antenna 109, and the V polarization antenna 110. The target scattering signal is an HH polarization signal, a VH polarization signal, an HV polarization signal, a VV polarization signal, and a polarization four component, respectively.

  The signal processing unit 125 extracts the feature quantity of the target 1 by signal processing relating to polarization such as basis conversion of the four polarization components, and outputs analysis information as a measurement result of the apparatus.

  FIG. 2 is a diagram for explaining the processing of the H polarization code modulation means and the V polarization code modulation means. The sawtooth wave 201 output from the sawtooth wave generator 101 changes its voltage level with time in a sawtooth manner. The voltage control signal generator 102 generates a chirp signal 202 at a frequency corresponding to the voltage level of the sawtooth wave 201. The chirp signal 204 is an enlargement of a part of the chirp signal 202 for explanation. The H-polarization code modulation means and the V-polarization code modulation means respectively generate a code 205 corresponding to a code H and a code V whose cross-correlation is equal to or smaller than a predetermined value (very low or theoretically zero) and generate a chirp signal. Phase modulation is performed, and a transmission signal 206 corresponding to the transmission signal H and the transmission signal V is generated and transmitted to the target 1.

  FIG. 3 is a diagram for explaining the processing of the HH polarization extraction means. A multiplication signal HH303 (reception chirp signal) that is a multiplication result of the HH reception signal 301 returned from the target 1 at the maximum measurement distance and the delay code H302 is obtained. Show. In this way, the HH polarization extraction unit can remove the code component from the HH received signal 301.

  FIG. 4 is a diagram for explaining the processing of the VH polarization extracting means. A multiplication signal VH303 (reception chirp signal) that is a multiplication result of the HH reception signal 301 returned from the target 1 at the maximum measurement distance and the delay code V401 is obtained. Show. As described above, the VH polarization extraction unit does not remove the code component of the HH reception signal 301.

  The multiplication signal from which the code component has been removed is multiplied by the chirp signal output from the voltage control signal generator 102 in the same manner as a reception signal of a general FM-CW polarization radar apparatus, and the beat signal obtained as a result of multiplication is multiplied. Target information can be obtained by analysis by Fourier transform, but the low frequency component of the beat signal of the signal in which the code component remains is suppressed by the code and becomes the frequency of the code rate. This is removed by the operation of removing the high-frequency components of the receiving units 121 to 124, and as a result, a component not correlated with the delay code is removed.

  Therefore, the HH polarization extraction means extracts the component of the HH reception signal, the VH polarization extraction means extracts the component of the VH reception signal, the HV polarization extraction means extracts the component of the HV reception signal, and the VV polarization The extraction means can extract a component of the VV reception signal.

  Now, in the short-distance target 1, the code included in the received signal does not match the delay code, but the code difference is ¼ chip at the shortest distance. The correlation calculation of the 1/4 chip difference is known to have a power of 1/4 and can be corrected later from the target distance. In addition, since the radar apparatus normally receives a far target 1 more greatly, for example, in a pulse radar apparatus, this is realized by using a reception amplifier whose degree of amplification increases with time. However, in the first embodiment, the same operation can be realized by this delay code. Thereby, the dynamic range of the system can be suppressed, and the far target 1 can be measured more precisely.

  FIG. 5 is a diagram for explaining the processing after extracting the beat signal. The beat signal 502 obtained by multiplying the received chirp signal 501 by the chirp signal 202 output from the voltage control signal generator 102 and the beat signal 502 are obtained by Fourier transform. A frequency spectrum 503 is shown. In FIG. 5, a frequency spectrum 503 is a reflected signal of the target 1, and the frequency axis corresponds to the distance axis.

Here, the reason why the code lengths of the codes H and V should be as short as possible is described.
In general, since the level of the reflected wave from the target 1 varies depending on the frequency, the received chirp signal is not constant. In particular, there is frequency selective fading in which a specific frequency component is reduced due to multipath interference. This can adversely affect the correlation properties of the code. In a short cycle code, the reception power is almost constant within the code cycle interval, so that the influence of the level difference in the correlation can be minimized.

Thus, since the radio waves generated by the H polarization code modulation means and the V polarization code modulation means have no correlation, the transmission signal H transmitted by the H polarization code modulation means is reflected as H polarization. Since the polarization signal and the HV polarization signal reflected by the transmission signal V transmitted by the V polarization code modulation means are converted to the H polarization, the HH polarization extraction means converts the HH polarization. The HV polarization can be separated by the HV polarization extraction means. Similarly, the transmission signal H transmitted from the H polarization code modulation means is reflected as V polarization, and the transmission signal V transmitted from the V polarization code modulation means is reflected as V polarization. Since the VV polarization is modulated with a different code, the VH polarization extraction unit can separate the VH polarization, and the VV polarization extraction unit can separate the VV polarization.
Therefore, HH polarization, VH polarization, HV polarization, and VV polarization can be separated even if H polarization and V polarization are transmitted simultaneously. This is measured at the same time, so that the target information can be obtained accurately and the target identification performance can be improved.

  As described above, according to the first embodiment, the H-polarized transmission signal H and the V-polarized transmission signal V are codes having a cross-correlation of a predetermined value or less (very low or theoretically zero). Since it is code-modulated, it can be transmitted to the target 1 at the same time, and since the received HH polarization signal, VH polarization signal, HV polarization signal, and VV polarization signal are measured at the same time, The physical positional relationship between the FM-CW polarization radar apparatus and the target 1 is the same, so that the target information can be obtained accurately and the identification performance of the target 1 can be improved.

  Further, according to the first embodiment, multiplication of the delay codes by the multipliers 111, 112, 113, and 114 suppresses the target scattering level in the vicinity and raises the target scattering level in the distance, so that the dynamic range of the system is increased. The effect of being able to measure the target 1 far away and more accurately can be obtained.

It is a block diagram which shows the structure of the FM-CW polarized wave radar apparatus by Embodiment 1 of this invention. It is a figure explaining the process of the H polarization code modulation means and the V polarization code modulation means of the FM-CW polarization radar apparatus by Embodiment 1 of this invention. It is a figure explaining the process of the HH polarized wave extraction means of the FM-CW polarized wave radar apparatus by Embodiment 1 of this invention. It is a figure explaining the process of the VH polarized wave extraction means of the FM-CW polarized wave radar apparatus by Embodiment 1 of this invention. It is a figure explaining the process after the beat signal extraction of the FM-CW polarized wave radar apparatus by Embodiment 1 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 101 Sawtooth wave generator, 102 Voltage control signal generator (VCO), 103,104 code generator, 105,106 modulator, 107,109 H polarization antenna, 108,110 V polarization antenna, 111,112,113 , 114, 117, 118, 119, 120 multiplier, 115, 116 delay circuit, 121, 122, 123, 124 receiver, 125 signal processor, 126 memory.

Claims (1)

A code H whose cross-correlation with the code V is equal to or less than a predetermined value is generated, and a chirp signal whose frequency changes in accordance with the input voltage is code-modulated with the code H, so that an H-polarized transmission signal H that is a horizontally polarized wave H-polarization code modulation means for transmitting to the target;
A code V whose cross-correlation with the code H is a predetermined value or less is generated, the chirp signal is code-modulated with the code V, and a V-polarized transmission signal V which is a vertical polarization is transmitted to the target V Polarization code modulation means;
Receiving a reception signal H obtained by combining a reflected wave of H polarization by the transmission signal H reflected by the target and a reflection wave of H polarization by the transmission signal V reflected by the target; HH polarization extraction means for multiplying a delay code H which is a delay code of the code H to generate a reception chirp signal HH;
A received signal V obtained by synthesizing a reflected wave of V polarization by the transmission signal H reflected by the target and a reflected wave of V polarization by the transmission signal V reflected by the target is received. VH polarization extraction means for multiplying the delay code H to generate a reception chirp signal VH;
HV polarization extraction means for receiving the received signal H and multiplying the received signal H by a delay code V that is a delay code of the code V to generate a received chirp signal HV;
VV polarization extraction means for receiving the received signal V and generating the received chirp signal VV by multiplying the received signal V and the delay code V ;
The FM-CW polarization radar apparatus , wherein delay amounts of the delay code H and the delay code V correspond to a reflection delay time from a target at a maximum measurement distance .

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