JPS6340885A - Doppler speedometer - Google Patents

Abstract

PURPOSE:To measure a relative velocity with a high accuracy while suppressing the effect of noises even when the relative velocity is low by forming an apparent Doppler frequency by mixing a third fundamental frequency that is formed by mixing a fundamental transmission frequency with a second fundamental frequency with received signals. CONSTITUTION:A fundamental transmission frequency f0 from an oscillator 11 is Doppler-shifted to a received frequency f0+ or -fd in accordance with a relative velocity with respect to a target object 0. The received frequency is mixed with the fundamental frequency f0 from a branching filter 2 and a third fundamental frequency f0-fv derived from a second fundamental frequency fv from an oscillator 12 via a mixer 10, a filter 13 and the like in a mixer 6' and an apparent Doppler frequency f'd that satisfies the accompanying expression is taken out of a filter 7'. The frequency f'd due to a synergistic effect is far higher than a Doppler frequency fd and the effect of noises is suppressed. Even though the frequency fd is reduced, the frequency f'd that changes in accordance with the relative velocity is fairly taken out and also the low relative velocity is measured with a high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a Doppler velocimeter that measures relative speed to a target object using the Doppler phenomenon.

Generally speaking, in this type of Doppler speedometer, as shown in FIG. is given, thereby transmitting the fundamental frequency f from the transmitter/receiver 4 via the antenna 5. Radio waves with ○ are emitted towards target ○. A reflected wave that has undergone a Doppler frequency shift due to the relative velocity V of the target object is received by the transceiver 4 via the antenna 5, and the frequency (f) that has undergone the Doppler shift is received by the transceiver 4 via the antenna 5.

±fd) and the signal from the oscillator 1 with the fundamental frequency f0 are mixed in the mixer 6. As a result, a signal with a Doppler frequency fd, which is a beat component due to the frequency difference between each signal, is generated, and the Doppler frequency f
d is measured by a frequency meter 8 through a low-pass filter 7, and the measured signal is given to a processing circuit 9, which calculates the relative velocity V with the target object ○, which is proportional to the Doppler frequency fd according to the relationship in equation (1). The speed signal Sv can be obtained by

fd=f, s2 l V l /c (c: speed of light)
-(1) However, in such a conventional Doppler velocimeter,
When the relative velocity V with respect to the target object O becomes extremely small, the Doppler frequency fd also becomes proportionally small, making it difficult to accurately measure it.

Further, in the low speed range, noise is likely to be mixed into the Doppler frequency fd that passes through the low-pass filter 7.

Further, in the conventional Doppler speedometer, the relative velocity V with respect to the target object 0 may be incorrectly detected due to noise contamination.

From the measured Doppler frequency fd, only the magnitude of the relative velocity V to the target object ○ can be determined, and it is not possible to determine the direction of the relative velocity V, such as whether the target object O is approaching or going away. It has become a big deal.

1. The present invention has been made in consideration of the above points, and it is possible to measure the Doppler frequency with high accuracy even when the relative speed to the target object becomes small, and while effectively suppressing the influence of noise. In addition, the present invention provides a Doppler velocimeter that can also determine directionality.

Sentence 11 In order to achieve the object, the present invention includes means for emitting a signal wave having a first fundamental frequency toward a target, means for receiving a reflected wave from the target, and a signal wave having a first fundamental frequency. Means for mixing a separately oscillated second fundamental frequency to produce a third fundamental frequency, and means for mixing the third fundamental frequency and the frequency of the received signal to produce an apparent Doppler frequency. Then, the apparent Doppler frequency is measured to determine the relative velocity with respect to the target object.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the accompanying drawings.

In the Doppler velocimeter according to the present invention, as shown in FIG. 1, the first fundamental frequency f emitted from the first oscillator 11,
The signal with the fundamental frequency
A radio wave (or ultrasonic wave, etc.) with 0 is emitted toward the target Q, and the reflected wave, which has undergone a Doppler frequency shift due to the relative velocity V from the target 0, is transmitted by the transmitter/receiver 4 via the antenna 5. Received.

Further, the first fundamental frequency f0 demultiplexed by the duplexer 2 and the second fundamental frequency fv emitted from the oscillator 12 are mixed in the mixer 10, and a signal A having the mixed frequency is sent to the filter 13. given to. The spectrum of the signal A is -(fl, -fv) as shown in Figure 2.
, fo, (fo + fv), the filter 13 suppresses the component (fo + fv) on one side, extracts only the component of fo, (f, -fv), and uses it as the third fundamental frequency. Let signal B have . FIG. 3 shows the spectrum of signal B. Note that at this time, the (f, -fv) component may be suppressed by the filter 13.

The received signal with the frequency (f, ±fd) subjected to the Doppler frequency shift by the target O and the third fundamental frequency (
f, -fv) are mixed in mixer 6'. As a result, a signal having an apparent Doppler frequency fd' is generated due to the frequency difference between each signal, and the apparent Doppler frequency fd' is measured by a frequency meter 8 through a low-pass filter 7, and the measured signal is sent to a processing circuit 9'.
The relative speed V is calculated by giving a speed signal Sv.

Here, the apparent Doppler frequency fd' is given by the following equation.

fd'= l (f, ±fd) (fo-fv)I=
l fv+fdl - (2) If the relative velocity V is such that the target object 0 approaches with the vector shown, the frequency of the received signal is (f, +fd)
, and if there is a relationship that moves away, it becomes (f, -f
d), and in the mixer 6', 1, for example, the frequency (f, +fd) of the received signal and the third fundamental frequency (f, -f
v) is mixed, the spectrum of the signal C with the mixed frequency becomes as shown in Fig. 4,
By appropriately selecting the characteristics of filter 7', fv+
It becomes possible to extract only the component of fd (=fd').

Therefore, in the processing circuit 9', the true Doppler frequency fd is obtained by subtracting the second fundamental frequency fv, which can be known in advance, from the apparent Doppler frequency fd' measured by the frequency meter 8, and the relationship of equation (1) is obtained. From this, the target relative velocity V is calculated.

However, with something like this, things@! Even if the relative velocity V with respect to 40 becomes very small and V → 0, that is, the true Doppler frequency fd becomes fd-GO, the apparent Doppler frequency fd' (=fv) is obtained from the mixer 6, so it is 1 frequency. With a total of 8, the Doppler frequency fd' can be measured easily and accurately. In this regard, in the conventional device shown in Fig. 5, when V→0, the output of the mixer 6 becomes fd→0, and the range of the frequency meter 8 decreases, making it impossible to accurately measure the minute Doppler frequency fd. It ends up.

Further, in the Doppler velocimeter according to the present invention, the apparent Doppler frequency fd' measured by the frequency meter 8 has a relatively large second fundamental frequency fv added to the true Doppler frequency fd. This makes it possible to eliminate the effects of noise and other contamination. At that time, by providing a bandpass filter near fd' after the lowpass filter.

It is possible to cut extra frequency components.

Furthermore, in the Doppler velocimeter according to the present invention, by checking the magnitude of the apparent Doppler frequency fd' measured by the frequency meter 8 in the processing circuit 9', it is possible to determine whether the target object O is approaching or receding. Directionality can be determined.

In other words, from the relationship in equation (2), when target 0 is approaching, fd'=fv+fd, and fd'>fv
-, and if target 0 is far away, fd
'=fv-fd, and fd'<fv. Therefore, the directionality can be determined by comparing the measured apparent Doppler frequency fd' with a constant frequency fv.

In the Doppler velocimeter according to the present invention, the beat frequency is generated by mixing the fundamental frequency signal with the received signal of the reflected wave that has undergone a Doppler frequency shift depending on the relative speed with the target object. At this time, the third fundamental frequency obtained by mixing the first fundamental frequency during transmission and the second fundamental frequency is multiplied to produce an apparent Doppler frequency, which is then measured. Therefore, it has the excellent advantage of being able to determine the relative velocity with high accuracy even when the relative velocity with the target object becomes small, and the relative velocity can be determined with directionality while effectively suppressing the influence of noise.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the Doppler velocimeter according to the present invention, FIG. 2 is a spectral distribution diagram of signal A in the same embodiment, FIG. 3 is a spectral distribution diagram of signal B, and FIG. The figure is also a spectral distribution diagram of signal C, No. 5
The figure is a block configuration diagram showing a conventional Doppler speed meter6 1.11.12... Oscillator 2, 3... Duplexer 4
...Transmitter/receiver 5...Antenna 6.6', 10
...Mixer 7, 7', 13...Filter 8.
...Frequency meter 9.9'...Processing circuit

Claims (1)

[Claims] means for emitting a signal wave having a first fundamental frequency toward a target; means for receiving a reflected wave from the target; and a second fundamental frequency oscillated separately from the first fundamental frequency. means for mixing the third fundamental frequency to produce a third fundamental frequency; means for producing an apparent Doppler frequency by mixing the third fundamental frequency and the frequency of the received signal; and measuring the apparent Doppler frequency. and a means for determining the relative velocity with respect to the target object.