JPS5872078A - Fm-cw radar - Google Patents

Abstract

PURPOSE:To reduce measuring errors by changing the phase or time length of the count periods of the beat signal in every period and determining the average value of the count contents. CONSTITUTION:A synchronizing signal generating circuit 4 generates a synchronizing signal of a modulating frequency Fm and applies the synchronizing signal to a modulating circuit 3 and a timing control circuit 5. The circuit 3 changes the transmission frequency in synchronization with the synchronizing signal and the circuit 5 outputs the timing signal shifted of the phase with respect to the synchronizing signal successively at every application of the synchronizing signal thereto. More specifically, this radar is so constituted as to count the synchronizing signals and to control the delay time according to the count contents thereof. The timing signal can be outputted by the repetition of the same operation at every counting of N. A gate signal generating circuit 6 generates a gate signal of a specified time length and applies the same to a gate circuit 11 at every application of the timing signal thereto. The gate signal is opened by said signal and applies the pulses from a pulse forming circuit 10 to an arithmetic circuit 12 which calculates a relative distance and applies the same to a display circuit 13, whereby the relative distance is displayed analogically or digitally.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an FM-
This relates to CW radar.

FM-CW radar is capable of changing the transmission frequency, for example, in the shape of a triangular wave, forming a beat signal from the transmission signal and the reception signal of the reflected wave, and measuring relative distance and relative velocity based on the beat frequency. It is. FIG. 1 is an explanatory diagram of the transmission signal SS, reception signal RE, and beat frequency Fb. DWN and the total period is 1/F1, and it is sent repeatedly, and the received INIt number RE is obtained after a time T corresponding to the distance R (m) to the target object such as the vehicle in front, and the speed of light is fC(3x1
0"'/age ), the time T becomes . Then, by mixing a part of the transmitted signal SS and the received signal RE, a beat signal of the sibeat frequency F6 is obtained.

The beat frequency ph is expressed as, where the frequency deviation is ΔF<Hz) and the modulation frequency is pm (Hz), and the distance R is Fb-C R knee□-・・・・・・・・・・・・・・・・・・・・・・・・
(3) 4・F information・ΔF Therefore, the entire distance can be measured depending on the beat frequency.

Also, the beat frequency Fbu during the upsweep period UP
and the beat frequency Fb during the downsweep period DWN
The relative velocity can be determined by the difference between d and d. In addition, the respective beat frequencies Fbx and F for each period UP and DWN
Measurement of the relative distance when bd is different can be done by setting (Fb body + Fbd )/2 = Fb in equation (3).

The beat frequency Fb can be determined by counting the heat signal for a certain period within one period 1/F□.

In this case, since the count is an integer, it includes an error equivalent to one cycle of sea pulses. Fb here/
Setting Fm = 1 and substituting this relationship into equation (3), we get
The distance error due to one pulse is ΔR. That is, ΔR-(m) ・・・・・・・・・・・・・・・
・・・・・・・・・・・・(4) 4・ΔF If ΔF−15MH3, then ΔR=5 m.

In other words, due to the difference in count m of one pulse, the measurement distance is 51n.
This will result in an error of

When the distance to the target object is constant, the beat signal has the same waveform every period 1/F□. Therefore, the beat signal is counted for a certain period based on the synchronization signal with the period '/pm. In this case, the count will always be constant. That is, even if the average value is simply determined, the measurement accuracy cannot be improved.

The present invention aims to reduce measurement errors by changing the phase or time length of the count period of the beat signal for each cycle and finding the average value of the count contents of the beat signal for each cycle. It is something to do. Examples will be described in detail below.

FIG. 2 is a block diagram of an embodiment of the present invention, in which 1 is a transmitting antenna, 2 is a transmitting circuit, 6 is a modulation circuit, 4 is a synchronization signal generation circuit, 5 is a timing control circuit, and 6 is a one-shot multi Gate signal generation circuit consisting of a vibrator etc.
7 is a receiving antenna that receives all reflected waves; 8 is a mixer that mixes a part of the transmitted signal and the received signal to output a beat signal; 9 is a bandpass filter; 10 is a pulse forming circuit that pulses the hubby 141; 11 is a gate circuit, 12
1 is an arithmetic circuit including a kakunta and the like, and 13 is a display circuit.

Although this embodiment has separate antennas for transmitting and receiving, it is also possible to use a shared antenna for transmitting and receiving.

The synchronization signal generation circuit 4 generates the synchronization signal of the above-mentioned modulation frequency Fm and applies the synchronization signal to the modulation circuit 6 and the timing control circuit 5, and the modulation circuit 3 changes the transmission frequency in synchronization with the synchronization signal. The timing system (a11 circuit 5 outputs all the timing signals with the phase shifted from the synchronizing signal sequentially every time the synchronizing signal is added. For example, all the synchronizing signals are counted and the delay time is set according to the count contents. The timing signal can be output by repeating the same operation every N counts.

The gate signal generation circuit 6 generates a gate signal of a certain length every time a timing signal is applied and applies it to the gate circuit 11, opens the gate circuit 11, applies the pulse from the pulse forming circuit 10 to the arithmetic circuit 12, and generates a gate signal of a fixed time length. The distance is calculated and added to the display circuit 13, and the relative distance is displayed in analog or digital form.

FIG. 3 is an explanatory diagram of the operation, and shows a case where the transmission frequency is changed in a sawtooth waveform, and (,) to ω indicate signals α to ttf of each part in FIG. The output signal of the modulation circuit 6 is changed from frequency 'fF to F+ΔF every 1 h period, as shown in FIG. ). A part of the transmission signal branched at the transmission diagram wt2 and the reception signal whose reflected wave was received at the reception antenna 7 are mixed at the mixer 8, and unnecessary harmonic components are removed at the bandpass filter 9, resulting in the beat signal 0, for example. Figure 6 (1
), the pulse forming circuit 10 performs waveform shaping of the beat signal C, zero cross point detection, etc.
A pulse signal dt'' shown in d) is outputted and applied to the gate circuit 11.

Also, the timing control circuit 5 operates based on the synchronization signal as shown in FIG.
1) Output the timing signal ε as shown in
The initial phase occurs at a period of n. That is, when the initial phase for the synchronization signal is set to zero, the timing signal - shown in FIG. 5 (#) is (=+1 to (
#-1), Ti-(1/Fm)・(1/2#)-(...
As expressed in (1), the phase of the timing signal - is sequentially shifted.

The gate signal generating circuit 6 is triggered by a timing signal (-) and outputs a gate signal / of a constant time width of TG as shown in FIG.

The time TG of this gate signal f is ra< (1/F-)-
(1h) (1/2N) (#-1)...(2
) will be selected based on the relationship.

Therefore, the pulse signal g applied to the arithmetic circuit 12 is as shown in FIG.
That's it! ' , the average value within the period of N/p□ is calculated.

Figure 4 is for explaining the reduction in measurement error by sequentially shifting the phase of the gate signal f as described above. Assuming that the gate signal shown in FIG. 1 (1) is generated from the gate signal generation circuit 6, 94 pulse signals are applied to the arithmetic circuit 12 by the gate signal at time TG. By sequentially shifting the phase of the timing signal from the timing control circuit 5, when the phase of the gate signal is sequentially shifted as shown in FIGS. 4(d) to (h), each gate signal causes When four pulse signals are applied to the arithmetic circuit 12 and the pulse signals for each gate signal are counted and the average value is determined, the number of pulse signals becomes "4".

In addition, when the beat signal shown in FIG. 4 (j) is obtained, the pulse signal shown in FIG. 4 (0) is formed, and the pulse signals shown in FIG.
), the arithmetic circuit 12 receives 4,
When the number of pulse signals 3.3.5.3.5 is added and the average value of the count contents is calculated using 6 gate signals, it becomes "317". In this case, the frequency of the beat signal shown in FIG. 4 (1) is 0.8 times the beat signal frequency shown in FIG. 4 (0), so the average value of the count contents is J3
．． 2j would be fine, but if only the gate signal with the phase shown in FIG. 4(1) is used, the average value of the count contents will be 1-4, which will increase the error. However, as mentioned above, by completely shifting the phase of the beat signal, the average value of the count contents approaches 112j,
The error in distance measurements is reduced.

In addition, when the beat signal shown in Fig. 4 (&) is obtained, the pulse signal shown in Fig. 4 (phantom) is formed, and the pulse signal shown in Fig. 4 (cL)
Since the frequency is 1.25 times the frequency of the beat signal shown in Figure 4 (1) to G), the average value of the count contents should be exactly i'5.3j. The number of pulse signals for the gate signal shown is 6.5.6.5.6.5
Therefore, the average value of the count contents is 1-s,s. However, when only the gate signal with the phase shown in FIG. 4(1) is used, the average value of the count contents is 16'', and the error becomes large.

For example, the phase of the gate signal is set to 0 for the modulation period 1/F1.
~2π, and the phase of the gate signal is changed from 0 to 2π (1-
δ) (However, when L, o<δ<1), count mountain and valley force M,
If the count content becomes M+1 when 2π(1-δ) to 2π, then the average value M of the count content is Since an average value intermediate between and M+1 can also be obtained, the error can be brought to zero or close to zero.

Note that the initial phase of the gate signal is not particularly limited, and the same result can be obtained by finding the average value of the count contents of one period of phase shift. Furthermore, although the case where the phase is sequentially shifted while the gate time fTG is constant has been described, even if the phase is changed randomly and the fc multi-gate time is changed, the same result as when the entire phase is shifted can be obtained. However, in this case, the calculation to obtain the average value becomes somewhat complicated. In order to change the time of the gate signal, for example, output a gate signal of OR logic between the signal shown in FIG. This can also be realized by controlling the time constant of the mono-multivibrator with the timing signal shown in FIG. 3(1).

As explained above, the present invention converts a beat signal into a pulse signal and provides a gate signal f for controlling the gate circuit 11.
Gate signal generation circuit 6 that sequentially changes the phase or time of
It is equipped with means such as a calculation circuit 12 which calculates a pulse signal sound via a gate circuit 11, calculates an average value, and calculates a distance measurement value. Depending on the average value of the signal count contents, the error in the distance measurement value can be reduced to a small value of one pulse or less. It is of course possible to modulate the transmission signal with a triangular wave as shown in FIG. 1 other than the sawtooth wave shown in FIG. 6 (α), and in this case, the up-sweep period and down-sweep period may It would be a good idea to control the gate. Furthermore, the present invention is not limited to the above-described embodiments, but can be modified in various ways.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the transmitted signal, received signal and beat signal,
FIG. 2 is a block diagram of an embodiment of the present invention, FIG. 6 is an explanatory diagram of the operation, and FIG. 4 is an explanatory diagram of the operation based on the phase shift of the gate signal. 1 is a transmission antenna, 2 is a transmission circuit, 6 is a modulation circuit, 4 is a synchronization signal generation circuit, 5 is a timing control circuit, 6 is a gate signal generation circuit, 7 is a reception antenna, 8 is a mixer, 9 is a bandpass filter, 10 is a pulse forming circuit, 11 is a gate circuit, 12 is an arithmetic circuit, and 16 is a display circuit. Patent applicant: Fujitsu Ten Co., Ltd. Representative Patent Attorney Tamamushi Gobu and five others

Claims (1)

[Claims] In an FM-CW radar that measures distance by mixing a part of a transmitted signal and a received signal to form a beat signal, and then pulses and counts the beat signal, the beat signal is pulsed. A gate circuit that applies a pulse signal that is applied, a gate signal generating means that changes the phase or time of a gate signal that opens the gate circuit, an average value of the count contents of the pulse signal that has passed through the gate circuit, and based on the average value. 9. An FM-CW radar comprising: calculation means for calculating a distance measurement value.