JPS6118142B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention has a configuration in which an ultra-short wave pulse signal is generated by changing the bias of an oscillation element that generates an ultra-high wave signal without using an ultra-high wave switch, and This invention relates to a range-cut Doppler radar that detects a highly stable video signal by demodulating a received wave at its rear end.

FIG. 1 shows a block diagram of the configuration of a conventionally used range-cut Doppler radar. Further, FIG. 2 is a diagram showing a target object detection area.

Range cutting is to limit the area DR in which the radar R detects the presence of a target object to within a predetermined distance R ₀ from the antenna A, as shown in FIG.

In Fig. 1, an extremely high frequency signal from an extremely high frequency generator G is applied to an extremely high frequency switch SW together with a pulse signal f _a having a pulse width T _w from a transmitting pulse generator SG, and a transmitting pulse f _b is directionally coupled. It is given as an input to device 3.

This transmission pulse f _b is sampled and held by the pulses from the circulator 4, mixer 6, video amplifier 7, and gate pulse generator 9, passing through the sample and hold circuit 8, the low-pass wave generator 10, and the low-frequency amplifier, and becomes a Doppler signal. Sent out.

However, the extremely high frequency switch used in this conventionally used range-cut Doppler radar is a high-speed switch that turns microwaves on and off, and requires advanced technology to manufacture, and is also expensive. It has the disadvantage of being

In order to solve the above-mentioned difficulties with conventional devices, the range cut-off radar according to the present invention includes an oscillation circuit that emits an extremely high frequency signal with a frequency of 10 gigahertz or more and an oscillation active element that drives the oscillation circuit. a drive circuit that drives the oscillation active element in a pulsed manner to generate an ultra-high frequency pulse signal from the ultra-high frequency generator; and a received signal reflected from a target by the ultra-high frequency pulse signal. The present invention is characterized by having a configuration including an area discriminating device that discriminates whether or not the target object is in a stable detection area from a video signal that detects a signal excluding a certain period of time from the rise of the signal. This makes it possible to detect stable Doppler signals without using an ultra-high frequency switch.

FIG. 5 is a diagram showing the principle of construction of the range-cut Doppler radar according to the present invention, and FIGS. 6 and 7 are signal waveform diagrams at each component of the device.

First, an overview of the operation of the range-cut Doppler radar according to the present invention will be explained with reference to these drawings.

In FIG. 5, a bias pulse signal f 1 having a period T _p and a pulse width T _W is applied from a bias pulse drive circuit ₂ to a bias terminal of a pulse modulated ultrahigh frequency generator 1 .

As a result, the pulse-modulated ultrahigh frequency generator 1
The bias of the oscillating active elements such as diodes, transistors, and FETs changes in a pulsed manner, and an extremely short wave pulse signal f ₂ having a frequency f _T and a pulse width T _W is emitted.

The pulse signal f ₂ is given to the directional coupler 3, where it is divided into the transmission signal _ST and the local signal S _L , and the transmission signal S
_T passes through the circulator 4 and is radiated from the antenna 5 as a radio wave.

In Fig. 5, the range cut distance R _W = T _W · c/2 where the speed of light is c, and the reflected wave from the target object D _A existing at a distance of R ₁ from the antenna 5 with the relationship R ₁ ≦ R _W. Let the received signal captured by antenna 5 be f _3-1 .

Similarly, the received signal of the reflected wave from the target D _B existing at a distance of R ₂ >R _W from the antenna 5 is assumed to be f _3-2 .

With these received signals as _f3 , the above targets D _A and D _B
The received signals f _3-1 and f _{3-2 from}
As shown in the figure, the propagation delay time τ ₁ of the received signal f _3-1 to the target object is in the relationship τ ₁ ≦T _W , so the received signal f 3-1 is synchronized with the local oscillation signal S _L and the detected output video signal
f ₄ is obtained.

However, since the propagation delay time τ ₂ to the target object of the received signal _3-2 is in a relationship such that τ ₂ >T _W , it is not possible to synchronize with the local oscillation signal _SL , and the video signal of the detection output cannot be obtained. I can't.

The video signal f ₄ whose pulse height envelope is a pulse signal is amplified by a video amplifier 7 and given as an input to a sampling and holding circuit 8 .

In the sampling hold circuit 8, the video signal
f ₄ is obtained by the gate pulse generator 9, and the pulse width T whose rear end almost coincides with the rear end of the pulse signal f _1
G is sampled with a gate pulse signal _f5 to generate a pulsating flow signal _f6 .

This pulsating flow signal f ₆ is passed through a low-pass filter 10 to remove the high frequency component of sampling frequency f _P =1/T _P and amplified by a low frequency amplifier 11 with automatic gain control _. and the relative speed of the target,
Frequency f _d = 2v _r /cf where f _T is the frequency of the transmitted radio wave
A Doppler signal f ₇ of _T is obtained.

This demodulation process is shown in FIG.

In FIG. 7, the time axis is sufficiently longer than in FIG. 6, and FIG. 6 corresponds to an enlarged view of time _{A B} in FIG.

As shown in FIG. 7, the video signal f ₄ output from the mixer 6 is a pulse train signal with a period T _p that is generated with a delay of τ ₁ from the bias pulse signal f ₁ .

This envelope is a Doppler signal, so if you sample the video signal _f4 with the gate pulse signal _f5 and hold it until the next cycle, you will get a pulsating current signal _f6 , which is passed through the low-pass waveform. If it is allowed to pass, a pulse signal f ₇ of frequency f _d will be demodulated.

Based on the above overview of the range-cut Doppler radar according to the present invention, details of the device and operation of specific embodiments will be described below.

First, the ultra high frequency generator, which is the main component of the range-cut Doppler radar according to the present invention, will be described using examples.

As a first embodiment, a Gunn diode, an impact diode, etc. can be used as the oscillating active element of the ultra-high frequency generator.

FIG. 8 is a circuit configuration diagram in this case, FIG. 9 is a signal waveform diagram thereof, and FIG. 10 is a diagram showing the relationship between active voltages.

In Figure 8, D is, for example, a Gunn diode or an impact diode, CH ₁ is a chain coil, and C
_D is a DC blocking capacitor, C _B is a bypass capacitor, z ₀ , θ ₀ is characteristic impedance z ₀ , electrical length θ ₀
shows the distributed constant line.

As shown in FIG. 9, the bias signal V _B is normally held at the voltage V ₁ and is kept at the voltage V ₂ during the oscillation time T _W.
, an output signal e ₀ of frequency f _T is obtained.

For example, in the case of a Gunn diode, these operating voltages V ₁ and V ₂ are set so that the DC operating point p ₁ during non-oscillation and the DC operating point p ₂ during oscillation are as close as possible to each other as shown in FIG. It is necessary to reduce the temperature difference between the diodes during oscillation and during oscillation, and to reduce frequency fluctuations at the rise of oscillation.

As a second embodiment, an FET may be used as an oscillating active element of an extremely high frequency generator.

FIG. 11 shows a circuit diagram in this case, FIG. 12 shows its signal waveform diagram, and FIG. 13 shows the relationship between operating voltages.

As shown in FIG. 11, in this case, a series feedback type oscillation circuit is constructed. In the figure, C _B , C _B ′
are bypass capacitors, z ₁ , θ ₁ , z ₂ , θ ₂ ,
z ₃ and θ ₃ are the characteristic impedance Z _j and
A distributed constant circuit with electrical length θ _j (j=1, 2, 3) is shown.

In this case as well, the bias signal V _B is always the voltage V ₃
If the value is set to V ₄ only during the oscillation time T _W , an output signal e ₀ with a frequency f _T is obtained during this period. At this time, the steady voltage V ₃ is set below the pinch-off voltage VP of the static characteristic curve of the gate-source voltage _{V GS} and drain current _ID of the FET, and the DC operating point is set to P ₃ to normally shut off the FET. state.

During the oscillation time T _W , the bias signal V _B is set to _{V 4} which is greater than the pinch-off voltage VP, and the DC operating point of the FET is moved from P ₃ to P ₄ to be activated and oscillate.

Thirdly, there is an example in which a transistor is used as an oscillating active element of an ultrahigh frequency generator.

FIG. 14 shows a circuit diagram in this case, FIG. 15 shows a signal waveform diagram, and FIG. 16 shows a pulse drive waveform diagram.

In Fig. 14, R _B is the limiting resistance of the base current I _B ;
z ₄ , θ ₄ , z ₅ , θ ₅ , and z ₆ , θ ₆ are characteristic impedance z _i and electrical length θ _i (i=4,5,
6) shows the distributed constant line.

In this case, the bias signal V _B is normally set to V ₅ =0 and the transistor is in a cut-off state, but at the oscillation time T _W the voltage becomes V ₅ and the transistor oscillates.

Let us now consider the pulse drive conditions of the ultrahigh frequency generators of the three embodiments described above.

First, the bypass capacitor C _B needs to have sufficiently low impedance with respect to the oscillation frequency f _T , and the following equation holds from 1/2πf _T C _B 1.

C _B 1/2πf _T ...(1) Also, from FIG. 16, the rise and fall times t _r and t _f of the bias signal V _B are the bias pulse signal
It must be sufficiently shorter than the pulse width T _w of f ₁ =e _B , and formula (2) can be obtained from t _r , t _f =2.2·z ₀ ·C _B <<T _W .

C _B <<T _W /2.2·z ₀ ...(2) Equation (3) is obtained from Equations (1) and (2).

T _W /2.2・z ₀ >>C _B 1/2πf _T ...(3) For example, f _T =10GHz, T _W =200ns, _z0 =10Ω
If so, 9090≧C _B 16 (PF) can be obtained from equation (3).

Next, the bias pulse drive circuit 2 shown in FIG. 5 will be explained.

The bias pulse drive circuit requires high-speed operation and low output impedance, and as shown in Figure 17, it consists of an emitter-coupled high-speed logic circuit consisting of Q ₁ and Q ₂ , and an emitter follower circuit Q with high-speed response to drive the load. Consists of ₃ .

In the figure, the pulse wave high voltage V _H (V ₂ , V ₄ , V ₆ ) of the bias pulse signal f ₁ =e _B is expressed as the following equation using the power supply voltage V _X of the emitter-coupled high-speed logic circuit. It can be done.

V _H ≒ V _X −0.8 ...(4) On the other hand, the steady voltage V _L of the bias pulse signal e _B
(V ₁ , V ₃ , V ₅ ) is expressed by the following equation using constant current power supply I.

V _L ≒V _H -I・R _C ...(5) Also, the output impedance z ₀ of the drive circuit is I _C ≒
The current amplification factor of Q ₃ at V _L /R _E is expressed _by the following equation.

z ₀ ≈R _C /h _fe (6) In this way, the operating point and output impedance z ₀ of the bias pulse drive circuit are set.

Now, let us consider the case where the bias of the pulse-modulated ultra-high frequency generator is pulse-driven to generate an ultra-high frequency signal in the form of a pulse as described above.

FIG. 3 shows the transient characteristics of the oscillation frequency f _T in this case. As is clear from the figure, the oscillation frequency is unstable between the oscillation start time T _S and the time T _X due to a thermal time constant accompanying a change in the bias operating point of the oscillation active element.

If the maximum fluctuation width of time T _X is Δf, for example, in a Gunn diode, _T
It becomes 10-50MHz.

Therefore, if the reflected wave from the target object is detected synchronously with a part of the transmitted wave in the unstable region T _X of the oscillation frequency f _T , a stable Doppler signal for the target object will not be obtained.

The simple range cut-off Doppler radar according to the present invention also takes measures regarding this point.

Here, based on the above description, the range-cut Doppler radar according to the present invention will be described in more detail by taking up specific examples.

FIG. 18 is a block diagram showing the configuration of an embodiment of the range-cut Doppler radar according to the present invention.

In the figure, the target object detection region DR is composed of an unstable region UR and a stable region SR, and the targets existing in each region are D ₄ and D ₃ .

The configuration of the device is common to the configuration principle diagram already shown in FIG.
9, a target object existence area determination device A is specifically shown, which is comprised of a low-pass wave generator 31, a waveform shaper 32, a retriggerable monostable multivibrator 36, and an analog switch 34.

19 and 4 are signal waveform diagrams of each component of the embodiment of the range-cut Doppler radar according to the present invention shown in FIG. 18.

As already mentioned, a pulsed ultra-high frequency wave with a pulse width T _W is generated from _the pulse-modulated ultra-high frequency wave generator 21 which is pulse-driven with the bias pulse signal f ₁₁ having a pulse width T _{w period T P} from the bias pulse drive circuit 20. The oscillation frequency f _T of the signal f ₁₂ fluctuates for a certain time T _X from the oscillation start time.

In FIGS. 19 and 4, unstable portions of each signal caused by this frequency fluctuation are distinguished by diagonal lines.

In addition, in Fig. 18, the distance that can be reached from the antenna with a propagation delay time equal to the pulse width T _W of the transmitted signal S _T is R _W =1/2C・T _W , and the oscillation frequency f _T varies from the pulse width T _W. The distance that can be reached within the propagation delay time equal to _the time T _Y minus the time T _X is R _Y = 1/2C ₍ T _W - _T Let the reachable distance be R _x = 1/2 _CT
We will call them the stable region and the unstable region.

The ultra-high frequency signal f ₁₂ from the pulse-variable ultra-high frequency generator 21 is given to the directional coupler 22 and divided into a transmission signal S _T and _a local oscillation signal S _L. antenna 24
radiated as radio waves.

In this state, the target existing in the stable region SR is
It is assumed that D ₃ and the target existing in the unstable region UR are D ₄ , and that the target D ₃ and the target D ₄ do not exist at the same time.

First, let us consider the operation for the target _D3 existing in the stable region SR.

The received signal f _13-1 =S _R obtained by capturing the reflected wave from the target D ₃ by the antenna 24 is received with a delay of propagation delay time τ ₃ =2R ₃ /c from the transmitted signal _ST .

When the received signal f _13-1 is inputted to the mixer 25 via the circulator 23 and synchronously detected with the local oscillation signal S _L , a detected output video signal f _14-1 is obtained.

As already mentioned, since the frequency of the first portion T _X of the received signal f _13-1 fluctuates, the peak value of the first portion T _X of the video signal f _14-1 is unstable.

This video signal f _14-1 is amplified to a predetermined level by a video amplifier 26 and is provided as an input to sampling and holding circuits 29 and 30.

Meanwhile, bias pulse signal f ₁₁ is applied to gate pulse generators 27 and 28 to obtain gate pulses f ₁₅ and f ₁₆ .

The gate pulse f ₁₅ is generated before the trailing edge of the bias pulse signal f ₁₁ by T _X +T _G and has a pulse width of T
It is _G. Further, the gate pulse f ₁₆ is generated such that the trailing edge of the pulse coincides with the trailing edge of the bias pulse signal f ₁₁ , and its pulse width is T _G .

Therefore, the time difference between gate pulses _f15 and _f16 is set to be _Tx .

When the video signal f _14-1 is sampled by the sampling and holding circuit 29 using the gate pulse signal f ₁₅ , the pulsating current signal f _17-1 is obtained since the condition τ ₃ <T _{W −T} 3
0, and by sampling with the gate pulse signal f ₁₆ , a pulsating flow signal f _18-1 can be obtained.

The low frequency signal f ₂₀ obtained by passing the pulsating flow signal f _17-1 through the low-pass transducer 31 and removing the high frequency component of the sampling frequency f _p =1/T _P is as shown in FIG. This was obtained by sampling an unstable part of the video signal _f14-1 .

The frequency f _d ' of this low frequency signal f ₂₀ is given as follows.

f _d '=2Vr/cf _T + {(f _T (t _o ) ~ f _T (T _X )
) ~( _fT '( _t0 )~ _fT '( _Tx ))}...(7) However, _t0 < _Tx . Here, f _T (t ₀ ) is the frequency t ₀ seconds after the pulse-modulated ultrashort wave generator 21 starts oscillating under pulse drive, and f _T ′
(t ₀ ) is the frequency at the previous pulse modulation. However, since t ₀ <T _X , this is an unstable part. Equation (7) is expressed by the first term in which the frequency f _d ' is determined by the relative speed to the target, the oscillation frequency f _T (t ₀ ) when time t ₀ < T _X , and the stable oscillation frequency
_{T ( T}
(T _X ) is a stable oscillation frequency, so f _T (T
_X ) to f _T ′(T _X )=0. Therefore, equation (7) is f _d ′=2Vr/cf _T +{f _T (t ₀ ) ~ f _T ′ (t ₀ )}
...(8) That means. In equation (8), the Doppler frequency fluctuation in the unstable region is represented by the second term. Generally, frequency fluctuations in this region are random, and f _T (t ₀ ) to f _T ' in the second term above
(t ₀ ) will be distributed between zero and Δf shown in FIG.

Therefore, the measurement frequency f _d ' in the unstable region is f _d '≧f _d .

Therefore, the low frequency signal _f20 has more noise components than the Doppler signal component for the target _D3 .

This low-frequency signal f _{20 is pulse-shaped by a waveform shaper 32 and converted into a retriggerable monostable multivibrator 36 having a metastable time slightly larger than the period T dnio =} 1/f _dnio of the lower detection limit frequency f dnio of the Doppler signal. In addition, while the target D ₃ is moving in the stable region R ₃ < _RY , a gate signal f ₂₁ whose logical value is “1” can be obtained.

Since the Doppler frequency f _d ' in the unstable region is higher than the Doppler frequency in the stable region, if the retriggerable monostable multivibrator 36 is set as described above, it is possible to investigate the presence of a target in the unstable region. becomes possible.

Here, f _T = 10 GHz, and the minimum detected relative speed is 0.1
If Km/h, f _d =2Vr/cf _T =2×3.6×0.1×10×1
0 ⁹ /3×10 ⁸ = 24 [Hz] T _dnio = 1/24 = 0.0417 sec Therefore, it is desirable to set it to 50 milliseconds or more. When the carrier frequency is below 10 GHz, the T _d becomes even longer. If this T _d is too long, it will take a long time to recover in the event of a malfunction.

Therefore, in the present invention, for the above reasons,
An extremely high frequency signal with a frequency of 10 GHz or more is used as the oscillation frequency f _T .

On the other hand, the low frequency signal f ₁₉ obtained by giving the pulsating flow signal f _18-1 as an input to the low-pass wave generator 33 and removing the high frequency component of the sampling frequency f _P is expressed as τ ₃ <
Since there is a condition T _W −T _X , the video signal f _14-1
It is a sample of the stable part T _S of the target object
It is a stable Doppler signal for D ₃ .

Since the logic value of the gate signal f ₂₁ is "1" as described above, this low frequency signal f ₁₉ passes through the analog switch 34, is amplified by the low frequency amplifier 35, and a stable Doppler signal f ₂₂ is detected. It turns out.

Next, consider the operation for the target _D4 existing in the unstable region UR.

The received signal f _13-2 obtained by capturing the reflected wave from the target D ₄ by the antenna 24 is detected with a delay of propagation delay time τ ₄ =2R ₄ /c from the transmitted signal S _T .

This received signal _f13-2 is sent to the mixer 25 as a local oscillator signal.
By performing synchronous detection with f ₁₂ , a video signal f _14-2 can be obtained as a detection output.

In the first T _X portion of the received signal f _13-2 , the frequency fluctuates, so the wave height of the video signal f _14-2 becomes unstable.

The output of the video signal f _14-2 amplified by the video amplifier 26 is applied to a sampling and holding circuit 29 and a sampling and holding circuit 30, and sampled with respective gate pulses f ₁₅ and f ₁₆ .

In the sampling hold circuit 29, τ ₄ ≧T
Since _there is _a condition _{W −T}
The logic value of _17-2 is “0”, so the gate signal
The logical value of _f21 remains "0" while the target _D4 is moving in the unstable region _R4 ≧ _RY .

On the other hand, in the sampling and hold circuit 30, the unstable video signal f _14-2 is sampled by the gate pulse f ₁₆ , so that a pulsating current signal f _18-2 whose amplitude value is unstable is obtained.

The Doppler signal f ₁₉ obtained by passing this pulsating flow signal f _18-2 through the low-pass transducer 33 and removing the high frequency component of the sampling frequency f _P also becomes unstable with many noise components. However, as mentioned above, since the logic value of the gate signal f ₂₁ is "0", this unstable Doppler signal f ₁₉ does not appear at the output terminal, and the target object D _{4 is}
An unstable Doppler signal will not be detected when moving through an unstable region where ≧ _RY .

As described above, in the range-cut Doppler radar according to the present invention, the detection from a target existing in the unstable region of the condition R _W ≧R≧R _{W −R X based} on the frequency initial fluctuation time T It is possible to block unstable Doppler signals due to reflected waves and stably demodulate and detect only stable Doppler signals due to reflected waves from targets existing in the stable region of R<R _W -R _X .

In addition, in an extremely high frequency switch, as shown in Fig. 1 and 2, when the passing power when the switch is "ON" is P _A and the leakage power when the switch is "OFF" is P _B , the iso power is expressed as P _A /P _B. The ratio is about 30dB.

On the other hand, for a target with the same reflection intensity, the ratio of the Doppler signal level when it exists within the detection area and the signal level when it exists outside the detection area is approximately equal to the switch isolation. .

Therefore, the range cut function is not good when using an extremely high frequency switch for a target with a large reflection intensity.

Regarding this point as well, in the range-cut Doppler radar according to the present invention, since the ultrahigh-frequency wave generator is operated in a pulse-like manner to generate ultra-high-frequency waves in a pulse-like manner, the isolation is theoretically infinite and the reflection intensity is The range cut function for large targets is also excellent.

As explained in detail above, the range-cut Doppler radar according to the present invention has a simple configuration, does not require large manufacturing costs, and provides stable Doppler radar that responds to targets existing in the stable region except for the unstable period at the initial stage of oscillation. It can only detect signals and has an extremely excellent range cut function.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the configuration of a conventionally used range-cut Doppler radar, Fig. 1 is a waveform diagram of the output signal of the transmitting pulse generator and the output signal of the ultra-high frequency switch, and Fig. 2 is the target target. A diagram showing the detection area, FIG. 3 is a transient characteristic diagram of the ultrahigh frequency generator output, FIG. 5 is a diagram of the configuration principle of a range-cut Doppler radar, and FIGS. 6 and 7 are signal waveform diagrams of each part of the device configuration. Figure 8 is a circuit diagram of an embodiment of an extremely high frequency generator using a diode as an oscillation active element;
The figure is a signal waveform diagram, Figure 10 is a diagram showing the relationship between operating voltages, Figure 11 is a circuit diagram of an embodiment of an extremely high frequency generator using FET as an oscillation active element, and Figure 12 is a diagram showing the relationship between operating voltages.
Figure 13 is a diagram showing the signal waveform, Figure 13 is a diagram showing the relationship between operating voltages, Figure 14 is a circuit diagram of an embodiment of an extremely high frequency generator using a transistor as an oscillation active element,
FIG. 15 is a signal waveform diagram, FIG. 16 is a pulse drive waveform diagram, FIG. 17 is a diagram showing an embodiment of the bias pulse drive circuit, and FIG. 18 is a diagram showing an embodiment of the range cut Doppler radar according to the present invention. FIGS. 4 and 19 are block diagrams showing the configuration, and are signal waveform diagrams of each component of the range-cut Doppler radar according to an embodiment of the present invention. Explanation of symbols: 1... Pulse-modulated ultrahigh frequency generator, 2... Bias pulse drive circuit, 3... Directional coupling section, 4... Circulator, 5... Antenna, 6...
Mixer, 7... Video amplifier, 8... Sampling hold circuit, 9... Gate pulse generator, 10... Low pass wave generator, 11... Low frequency amplifier, 20... Bias pulse drive circuit, 21... Pulse modulated ultra high frequency generator , 22... Directional coupler, 23... Circulator, 24... Antenna, 25... Mixer, 26
...Video amplifier, 27...Gate pulse generator, 2
8... Gate pulse generator, 29... Sampling hold circuit, 30... Sampling hold circuit,
31...Low pass wave generator, 32...Waveform shaper, 33
...Low pass waver, 34...Analog switch, 3
5...Low frequency amplifier, 36...Retriggerable monostable multivibrator.

Claims (1)

[Claims] 1. An ultra-high frequency generator having an oscillation circuit that emits an ultra-high frequency signal having a frequency of 10 gigahertz or more and an oscillation active element that drives the oscillation circuit, and an ultra-high frequency generator that drives the oscillation active element in a pulsed manner. a drive circuit that generates an ultra-high frequency pulse signal; and an area determination circuit that receives a reflected reception signal of the ultra-high frequency pulse signal from the target object and determines whether the target object is in a stable detection area or an unstable detection area. and,
and a Doppler demodulator for obtaining a stable Doppler signal from a video signal that detects a signal excluding a certain period of time from the rise of the received signal when the area discriminating circuit determines that the area is in a stable detection area. Features a range-cut doppler radar.