JPS5811881A - Fm-cw radar - Google Patents

Abstract

PURPOSE:To detect a relative speed and polarity with simple constitution by repeating a CW and an FM mode, and performing frequency modulation by an up sweep and a down sweep DN repeatedly and then transmission in FM mode. CONSTITUTION:A modulating circuit 6 performs switching between a CW and an FM mode. In FM mode, triangular-wave modulation is performed to output an FM signal generated by repeating sweeps UP and DN at a constant period from a transmitter 4 through a driving circuit 5, and in CW mode, an unmodulated signal is outputted. Those signals are transmitted from an antenna 1 through a directional coupler 2. The received signals are applied partially to a mixer circuit 3, which output a Doppler beat signal to an amplifier 9 through a high-pass filter 8. The beat signal is counted in the CW mode to obtain a speed signal VS, and also counted in the FM mode to obtain a polarity signal PMS.

Description

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

CW radar uses Doppler frequency to measure relative speed. For example, when applied to a vehicle's (1) collision prevention radar system, it can measure the relative speed with the vehicle in front or the vehicle behind. However, it is not possible to distinguish whether the difference in absolute speed is positive or negative, that is, whether the vehicle is approaching or separating.

Therefore, the phase is set to π/2 for the received signal or local oscillation signal.
A method was used in which two systems of mixer circuits were provided in a staggered manner, and the polarity of the relative speed was detected based on the output phase relationship of each mixer circuit. However, the provision of two systems of mixer circuits, etc. has the disadvantage of complicating the configuration and increasing the cost.

An object of the present invention is to enable relative velocity and its polarity to be detected with a relatively simple configuration. Examples will be described in detail below.

FIG. 1 is a block diagram of an embodiment of the present invention, where 1 is an antenna for transmitting and receiving, 2 is a directional coupler, 3 is a mixer circuit, 4 is an oscillator using a Gunn diode, etc., and 5 is an oscillator. A drive circuit, 6 a modulation circuit for modulating the oscillation frequency of the oscillator, and 7 a timing signal & * b *
(A timing circuit that outputs !, 8 is a bypass filter, 9 is an amplifier, 10 is a waveform shaping circuit, 11 and 13 are counters, 12 is a latch circuit, 14 is a positive/negative determination circuit, TG
is the target such as the vehicle in front, vS is the speed output signal, PMS
is the polar output signal.

The output of the oscillator 4 is unradiated via the directional coupler 2. The received signal of the antenna 1 and a part of the transmitted signal via the directional coupler 2 are added to the mixer circuit 3, and the mixer circuit 3 outputs a Doppler beat signal.
It is added to a bias current A whose cutoff frequency is Fm (Fm = modulation frequency).

) The modulation circuit 6 switches between the CW portion and the 2M mode. In the 2M mode, the bias current applied from the drive circuit 5 to, for example, the Gunn diode of the oscillator 4 is used as a triangular wave modulation signal to perform frequency modulation. It is something that can be done. Through such triangular wave modulation, the oscillator 4 outputs an FM signal in which an up sweep where the frequency gradually increases and a down sweep (3) where the frequency gradually decreases are repeated at a constant cycle. A frequency-unmodulated signal is output from the oscillator 4.

Fig. 2 is an explanatory diagram of the operation, and Fig. 2 (a) shows the modulation waveform. In FM mode A, upsweep UP and downsweep DN are repeated at a constant cycle, and in CW mode B, becomes unmodulated.

The beat signal from the mixer circuit 3 is applied to an amplifier 9 via a no-pass filter 8, and the amplified output is shaped into a rectangular wave pulse by a waveform shaping circuit 10 and sent to a counter 11.
, 13. The counter 11 performs a counting operation in the CW mode according to the timing signal a, and the content of the count is latched by the timing signal to the shutter circuit 12 and becomes the speed output signal vS. Count, count down at down sweep DN, FM
The polarity determination circuit 14 determines the polarity according to the count contents at the end of the mode and outputs the polarity output signal PMS.

The relationship between relative distance R and beat frequency when approaching the target at relative speed V is shown in FIG. 3. That is, if the range frequency is Fr1 and the Doppler frequency is Fd, then the beat frequency during upsweep Fup = F
r-Fd and beat frequency Fdn during downsweep =
Fr +Fd decreases as the relative distance decreases, and frequency Ful) becomes O at the relative distance of RA, and then gradually increases as the relative distance decreases further. When the relative distance becomes 0, Fup = Fdn becomes. Note that during separation, the relationship Fup>Fdn is established, contrary to FIG. 3.

The range frequency Fr and Doppler frequency Fd are the modulation frequency Fm (Hz), the frequency deviation ΔF (Hz), the wavelength of the transmission frequency λ (m), and the relative velocity Vr (m/s).
ee ), the speed of light is c (a x 1o8m/sec)
, and the relative distance is R(m).

FIG. 4 is an explanatory diagram of the 2M mode, in which the transmitted signal SS and received signal R8 are modulated with a frequency deviation of ΔF and a period of 1/F'r11, as shown in FIG. During the approach, the relationship Fup < Fdn is established as shown in FIG. 2(b). Also, FIG. 2(c) shows an outline of the beat signal.

The pulses whose waveforms have been shaped by the waveform shaping circuit 10 are converted into beat signals shown in FIG. 4(C) during upsweep UP and downsweep DN, as shown in FIG. 2(b), for example. As can be seen, the number of pulses is different. Further, as shown in FIG. 2(c), the timing signal a from the timing circuit 7 is "θ" in FM mode A,
CW, CW mode becomes 8 o'clock'', and the counter 11 counts pulses at CW momo''.

Further, the timing signal S is applied to the latch circuit 12 at the timing shown in FIG. 2(d) to latch the count contents of the counter 110.

FIG. 2(e) shows the timing signal C for up counting, and FIG. 2(f) shows the timing signal C for down counting.
Pulses during upsweep UP in mode A are counted up, and pulses during downsweep are counted down. FIG. 2(B) shows the timing of polarity determination, and the polarity of the relative velocity is determined by the positive/negative determination circuit 14 based on the count content of the counter 13 at the end of FM mode A.

In other words, the difference between the count number Nup in upsweep UP and the count number Ndn in downsweep DN is Nup - Ndn > O- (3) The polarity of the relative velocity indicating whether the vehicle is approaching or separating is determined. .

When the relative distance becomes smaller than the RA point in FIG. 3, the frequencies Fup and Fdn become close to each other, making it impossible to determine polarity due to a counting error caused by the period of the modulation frequency dance. Note that the relative distance RA is expressed by the following equation.

If the minimum distance at which polarity can be determined is Rmin, the count number Nup' during upsweep UP (7) and the number Ndn during downsweep DN when they are closer than the relative distance RA are as follows. . In order to be able to determine the magnitude of the frequencies Fup and Fdn, the condition (Nup' - Ndn) must be within the range of 1 to 2, that is, Ndn l < 2. For example, ΔF' = 1
When it is 5MHz, 5(m) (Rmin (10(m) ---
--・-=-(9) (8) This means that the polarity of relative velocity can be determined up to at least 10 m.

As explained above, the present invention repeats CW mode B and FM mode A, and in FM mode A, repeats frequency modulation by changing the frequency of upsweep UP and downsweep DN. An oscillator that outputs a beat signal based on the signal 4. Drive circuit 5. Modulation circuit 6.
Antenna 1. Directional coupler 2. A transmitter/receiver section composed of a mixer circuit 3, etc., and a counter 11 that counts beat signals and outputs a speed output signal vS at the time of CW-F--D B.
．． A relative speed measuring section composed of a latch circuit 12 and the like;
A counter 13 that outputs a polarity output signal PMS based on the difference between the count contents in up sweep UP and the count contents in down sweep DN in FM mode A. A conventional CW radar equipped with a polarity determination section constituted by a positive/negative determination circuit 14, etc., can determine the polarity of relative velocity by simply adding a few configurations to the conventional CW radar.

Note that the present invention is not limited to the above-described embodiments; for example, the counter 13 may be configured with an upsweep UP counter and a downsweep DN counter whose counting period is controlled by the timing signal C. Alternatively, the speed measuring section and the polarity determining section may be configured by a microprocessor or the like.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is an explanatory diagram of the operation, FIG. 3 is an explanatory diagram of the relationship between relative distance and beat frequency, and FIG. 4 is an explanatory diagram of the operation in FM mode. 1 is an antenna, 2 is a directional coupler, 3 is a mixer circuit, 4
is an oscillator, 5 is a drive circuit, 6 is a modulation circuit, 7 is a timing circuit, 8 is a bypass filter, 9 is an amplifier, 10 is a waveform shaping circuit, 11 and 13 are counters, 12 is a latch circuit, and 14 is a positive/negative determination circuit. be. Patent applicant Fujitsu Ten Ltd.

Claims (1)

[Claims] A transmitting/receiving unit that repeats CW mode and FM mode, repeatedly transmits frequency modulation by frequency changes of up sweep and down sweep in FM-[need], and outputs a beat signal based on the transmitted signal and the received signal; a relative speed measurement unit that counts the beat signal in the CW mode and outputs a speed output signal;
FM-CW characterized by comprising a polarity determination section that performs p polarity determination based on the difference between the count content in up sweep and the count content in down sweep mode and outputs a polarity output signal. Radar.