JPS587578A - Fm-cw radar - Google Patents

Abstract

PURPOSE:To enable detection of a sharp drop in the signal reception level regardless of relative distance by obtaining a threshold level of a measuring section from the average level of beat signals. CONSTITUTION:Beat signals for transmission or receptio of waves from a transmitter/receiver section 1 are turned to an average level beat signal thereof through the processing by an LPF2. According to the signals, the threshold of a relative distance measuring section 5 and a relative speed measuring section 6 are controlled corresponding to the signal reception level varying with the relative distance. On the other hand, a comparator 4 compares beat signals with the average value thereof and generates a detection signal for sharp drop in the signals when any beat signal drops sharply which invalidates measured data of the measuring sections 5 and 6 unable to be followed by the control of the thereshold and in stead, data immediately therebefore is outputted as correction data. This allows the detection of a sharp drop in the signal reception level regardless of the relative distance thereby preventing such a trouble as the outputting of erroneous distance measured data resulting from a stop of an object to be measured by a sudden braking thereof and others.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an FM-CW system for measuring relative distance and velocity.
It is related to radar.

The FM-CW radar measures relative distance and relative excess using a beat signal generated by a transmitting wave modulated by a wave number with a triangular frequency change and a receiving liquid that receives a reflected liquid. Therefore, it can be applied to a radar system for preventing damage to automobiles.

If the positional relationship between the pigeon coop and the vehicle in front is meandering or curved while driving, the reception level will be large (or fluctuate).If the reception level is extremely low, 8/N will deteriorate and the relative distance and Errors will occur in the relative moderation measurements.

For example, the distance and reception level are shown in Figure 1 (d, (b)).
When the measured distance changes as time t passes, as shown in K, even if the actual distance changes linearly, as the reception level decreases, the measured distance also changes as shown by the solid line. Therefore, a method has been proposed in which the measured distance data obtained when the reception level is below the threshold V hold level is invalidated and the immediately preceding measured distance data is used as correction data. However, since the reception level tends to increase as the distance decreases, as shown in 1g(b), the threshold level 'rli1
≧Threshold level TH, in the case of stopping distance, must be performed, and the configuration for this switching becomes complicated, and it is difficult to set at what distance the switching is to be performed. There are drawbacks that are not easy.

A method has also been proposed in which when the rate of change in measured distance data is large, it is assumed that the reception level has decreased and the adjusted distance is corrected. However, since the inter-vehicle distance changes in a complex manner, deciding whether or not to correct based solely on the magnitude of the rate of change in the measured distance data may result in incorrect distance data being output when a car suddenly brakes, for example. A problem arises. Note that the dotted line in FIG. 1 ((roll)) indicates the adjusted distance corrected using the immediately preceding measured distance data as correction data when the rate of change of the measured distance data is large.

An object of the present invention is to obtain a threshold level from the average level of the beat signal, thereby making it possible to detect a sudden drop in the reception level regardless of the relative side 111. Examples will be described in detail below.

1 is a radar transmission/reception section, 2 is a low-pass filter, 3 is a variable resistor, 4 is a transmission line, 5 is a relative distance measurement section, 6 is a relative speed measurement section, 7μ is an output terminal for distance data, and 8 is a speed data output terminal. It is an output terminal. The beat signal tested is output from the transmitter/receiver 111, and the level 7 corresponds to the received level. This beat signal is applied to a low-pass filter 2, and the output of the low-pass filter 2 indicates the average level of the beat signal. It is desirable to use a low-pass filter 2 with a small phase deviation, such as a Bessel active filter.

The output level of the low-pass filter 2 becomes a voltage-divided level by adjusting the variable resistor 3, and serves as one input of the ratio l11allI4 as a threshold level. Also, since the other input is a beat signal, at Hioenji 4,
Comparing the beat signal level with the threshold level, when the beat signal level suddenly decreases, the threshold level does not follow the rapid change, so the signal indicating that the beat signal level has become low is detected by the relative distance measurement unit 5. and is added to the relative velocity measuring section 6. As a result, the relative distance measurement II 5 and the relative velocity measurement section 6 invalidate the measurement data, retain the immediately previous measurement data, and output it as correction data.

Fig. 3 is an explanatory diagram of the operation, in which the figure (b) shows the relative distance, the figure (b) shows the beat signal level, and the figure (C) shows the invalid signal. The level of the output signal adjusted by the variable resistor 5 and inputted to one side of the comparator circuit 4, that is, the threshold level, is determined at 5 by the dotted line in FIG. The erroneous measured value of the relative distance is invalidated by the invalid signal obtained as a frequency component by the level comparison, and the immediately preceding measured value is output as correction data.

As explained above, the present invention includes the low-pass filter 2 and the comparative logic circuit 4, and the 0-pass filter 2 outputs the average value of the level of the beat signal as a threshold level. Compare the level of the beat signal with a threshold level, and when the beat signal level is low, output an invalid signal to invalidate the measured values in the measuring units such as the relative distance measuring unit 5 and the relative speed measuring unit 6, It is output as correction data that is the measured value just before that, and the threshold level added to the ratio 11 circuit 4 is based on the average value of the beat signal level, so it is possible to adjust the reception level based on the flattening of the relative distance. It changes following the change, and the case where the reception level drops extremely can be detected as positive i1.

In addition, since the beat signal is directly applied to the measuring section, there will be no error in the relative distance or relative speed measuring section, and in the event of an erroneous measurement due to an extreme drop in the reception level, the invalid signal from the comparison path 4 will cause the invalid program to be removed. The present invention is not limited to the above-described embodiments, but can be modified in various ways.

[Brief explanation of drawings]

The first WJ is an explanatory diagram of the conventional reception level and measurement distance, FIG. 2 is a block diagram of the embodiment of the present invention, and FIG. 3 is an explanatory diagram of the operation. 1 is a transmitting/receiving section, 2 is a low-pass filter, 3 is a variable resistor,
4 is a deposition path, 5 is a relative distance measuring section, and 6 is a relative mode measuring section. Patent Applicant Fujitsu Ten Ltd. Representative Patent Attorney Kugobe Tamamushi and 5 others Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] In an FM-CW radar that measures relative distance and relative mode through beat compensation 4# by transmitted waves and received liquid, a low-pass filter is added to the beat signal, and the output threshold V of the low-pass filter is used as an e-hold level. ,
When the level of the beat signal is below the threshold V hold level, an invalid signal output from the K11l recording circuit is used to compare the level of the beat signal. An FM-CW radar comprising: a measurement unit that nullifies relative distance and relative excess, and outputs immediately preceding relative distance and relative velocity as correction data.