DE2702416A1 - DOPPLER RADAR ARRANGEMENT - Google Patents

Description

The invention relates to a Doppler radar arrangement, in particular a miniature Doppler radar arrangement, and also to a suitable microwave receiver.

A Doppler radar arrangement is used to detect moving Objects by using a pulse-modulated or keyed or Impulse radio signal or a continuous wave radio signal from a transmission source Sent via a transmission antenna and sent to a moving one Object or moving target is directed. This signal is reflected at the moving target and, subject to a Doppler frequency shift, in the receiver of the radar arrangement fed in. This radar arrangement has a receiving antenna that can be constructed like the transmitting antenna and that receives the reflected signal and feeds it into a mixer, where it is mixed with a reference signal whose Frequency (in simple arrangements) corresponds to the frequency of the transmitted signal. The reference signal can either be taken from the

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Transmission source or from a separate local or superimposed oscillator come. The mixer generates a mixer output signal from the reflected signal and the reference signal, whose frequency is the difference or doubling frequency, and that to indicate the presence of the Moving target can be used.

With the recent development of solid-state components like transfer electron arrangements (also called Gunn elements), the signals in the microwave range it is now possible to produce miniature Doppler radar assemblies to develop. Such a radar arrangement is described in GB-PS 1 214 833, for example. Miniature radar arrays are currently used in low-speed short-range applications, z. B. used for burglary A lariaanlagen and road traffic detectors.

Miniature radar arrangements that have already been developed work in continuous wave operation. The disadvantage here, however, is that the noise level occurring with continuous wave detection of slowly moving objects is very high. In order to detect a reflected signal above the noise level, the power of the transmitted or reference signal must be at least 15 mW or 5 n **. Since commercially available plague sources capable of producing this power have an efficiency in converting direct current energy to microwave energy of 2 % or less, the total direct current input power must be about 1 watt. The power consumption is therefore extremely high and normally has to be covered by a mains-fed direct current source, so that a battery can only be used in emergency operation.

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It is therefore the object of the invention to overcome the disadvantages associated with the miniaturization of a Doppler radar arrangement, in particular to avoid the large dimensions of the power supply source.

This task is accomplished by one for a miniature doubler radar arrangement suitable microwave receiver solved, comprising: a receiving antenna for receiving one at a remote target object reflected pulse-modulated received microwave signal; a signal generator for generating a pulse-modulated microwave reference signal that is associated with the pulse-modulated Received microwave signal coincides in time; a mixer for mixing the received microwave signal with the microwave reference signal and for generating a pulse modulated mixer output signal; an electric one Pulse integrator; a gate that, when open, feeds the mixer output into the pulse integrator feeds; and a gate control unit for switching the gate through in coincidence with the mis-output signal pulses.

An advantageous embodiment of the invention is given by a miniature Doppler radar arrangement which comprises: a solid state microwave source; a pulse generator for periodic pulse modulation or keying of the Solid state microwave source; a transmission antenna for transmitting transmission microwave pulses from the solid-state microwave source; and said microwave receiver, wherein the pulse generator is the sampling frequency of the microwave reference signal controls and represents the gate control unit for switching the gate through. In this case it consists of the Receiving antenna received, originating from a distant target object received signal from reflections of the

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Transmitting antenna transmitted transmission signal to the moving object.

The previously developed Doppler radar arrangements, which are either pulse-modulated or keyed or a Use continuous wave transmission signal and are miniaturized or non-miniaturized, use a in their receiver Continuous wave reference signal. However, it can be shown that the use of a keyed mixer reference signal with a gate, a filter and an integrator as in the radar arrangement according to the invention, the total direct current power consumption the radar assembly is significantly reduced, as will be explained in more detail below, without the Detection properties are deteriorated.

In this way, the radar arrangement according to the invention can be fed by a battery, for. B. by a Battery that is constantly recharged by a solar cell.

The transmit, receive and reference signal pulses can be of equal or unequal length and the same spacing exhibit. A typical value for the pulse length is 0.1-10 / US and the pulse spacing is 0.1-10 ms, so that

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the duty cycle is between 10 and 10 ^J.

The reference signal generator for generating the pulse-modulated microwave reference signal is preferably the via a microwave source of the radar arrangement connected to the mixer. But it can also be through a additional solid-state microwave source operating as a separate local oscillator, however is scanned by the pulse generator.

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The mixer can be implemented by a conventional silicon Schottky barrier layer or have a solid-state oscillator which also works as a signal source and reference signal generator.

In the simplest case, the integrator is a capacitor and the gate is preferably constructed using CMOS technology.

It is particularly advantageous if the mixer output signal is filtered through a high pass filter.

Finally, it is convenient to use the output of the integrator to be connected to a narrowband filter amplifier that supports the Doppler frequency component of the integrator output signal filters, wherein a comparator compares the output signal of the narrow band filter with a threshold signal and a Display unit generates a display signal when the comparator detects the presence of a signal above the noise level.

The invention will now be explained in more detail with reference to the drawing. Show it:

1 shows the block diagram of a miniature Doppler radar arrangement;

FIGS. 2a, 2b and 2c show signals for explaining the operating mode of the radar arrangement according to FIG. 1;

3 shows the typical course of the noise figure as a function of the mixer differential frequency a Doppler radar array; and

Flg. 4 shows the block diagram of a further miniature D oppler radar arrangement.

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The radar arrangement according to Flg.l has a transmission electron oscillator 1, which is periodically sampled by a pulse generator. During the duration of the impulses (which are typically 1 ais long and 1 ms apart) the oscillator 1 generates a microwave signal (with a typical frequency of 10 GHz) which is fed into a transmitting antenna is fed in and emitted from this aimed at a (not shown) moving target in the free space. The reflection signals reflected from the moving target are picked up by a receiving antenna 7, which can have the same structure as the transmitting antenna 5. The received signal is mixed in a mixer diode 9 with a reference signal which is generated by part of the oscillator 1 gated signal is shown. The output signal of the Mixer diode 9 consists of pulses, which are controlled by pulses from the pulse generator 3 gate 11 in a Integrator 13 are fed. The output signal of the Integrator 13 is through a narrow band filter amplifier 15 filtered and fed into a comparator 17, where it is compared with a threshold voltage V- will. When the output of the Fi It er amplifier 15 is above the threshold voltage Vm, the comparator generates an output signal which a display unit 19 switches through.

2a shows the sampled transmission signal with the amplitude T, which is transmitted by the transmission antenna 5. FIG. 2b shows the corresponding sampled signal V _mlx at the mixer diode 9. The mixer diode 9 receives a voltage pulse made up of two components for a specific duration of each transmission pulse. A component represented by a horizontal dashed line in Fig. 2b is fixed and originates only from the reference signal pulse. The other

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Component that is additively superimposed on the fixed component, is variable and is generated by mixing the reference signal with the reflection signal. This mutable Component oscillates in amplitude with the difference or Doppler frequency. With this consideration it is assumed that that the reflected received signal or reflection signal before the end of the transmission pulse, d. H. within 1 / US.

FIG. 2c shows the pulses V _mix on a compressed time scale, these pulses appearing as narrow lines L. The amplitude scale is stretched in this illustration so that it can be seen that the envelope curve E fluctuates sinusoidally with the Doppler frequency (a typical value is 30 Hz).

The gate 11 switches with each pulse V. in such a way that the signal applied to the integrator 13 only has pulses, but not pulse pauses. Thus, each pulse fed into the integrator 13 is a sample of the sinusoidal envelope curve E according to FIG. 2c. The integrator 13 integrates these sampled values and stores them until the arrival of the next pulse, which is indicated by dashed lines in FIG. 2c. The integrator 13 thus generates a continuous electrical output signal which changes sinusoidally with the Doppler frequency. Non-Doppler components are filtered out by the filter amplifier 15. The comparator 17 compares the amplitude of the filtered low-frequency _{signal with the threshold value V T} , which is set higher than the presumed noise level, so that the display unit 19 only responds to target objects which cause a signal above a predetermined value.

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Although the pulse generator 3 in Flg. 1 is presented as a single unit, it consists of a practical one Made up of a pulse clock generator, a gate and a battery, the gate being generated by logic pulses from the Clock is switched on and the battery voltage is applied to the oscillator 1. The logic impulses of the clock also switch the gate or gate 11 through. The clock and the gate 11 can be in standard CMOS technology be constructed. The pulse generator gate can, for example, be an avalanche transistor or MOS transistor (e.g. of the Siliconix VMP 1 type).

The oscillator 1 is preferably an electronic component with a high degree of efficiency (15 to 20 %) , as described, for example, in GB-PS 1 450 998 and in DT-OS 2620980.5. The electronic component in the first-mentioned patent specification has an active indium phosphide and a cathode made of a silver-galium-oxygen alloy. The electronic component described in the laid-open specification also has an active indium phosphide layer, but the cathode has a zone or layer, e.g. B. a Schottky barrier layer, and between this zone and the active layer, a narrow n ⁺ layer.

The oscillator 1, the mixer 9, the antenna 5 (and the antenna 7, if this is different) can in one single (not shown) housing are housed, through which the coupling of the mixer reference signal at the same time from the oscillator 1 into the mixer 9. As examples of such a unit, the selenium Doppler radar modules CL 8960 and CL 8920 from Mullard called. In the first-mentioned unit are the oscillator 1

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and the mixer 9 arranged in two adjacent open waveguides which act as antennas 5 and 7. the Coupling between the oscillator and mixer is established by direct coupling between the waveguides. In the second unit are the oscillator, the mixer and a single antenna connected to three inputs of a microwave ferrite circulator. The coupling between oscillator and mixing is done by a scatter signal in the circulator.

The filter amplifier 15 is preferably a very low power programmable amplifier, e.g. B. of the type LM 4250 from the US company National Semiconductor.

In the simplest case, the integrator 15 is a capacitor of size 2000 pF.

The display unit can, for example, by a Liquid crystal panel, a light emitting diode, a counter or a high frequency transmitter for the transmission of a display signal to a remote recipient. At the input of the display unit, an RC filter (not shown) with a certain time constant is expediently connected, which filters out unwanted signals that are triggered by momentary movements of objects that do not belong to the object to be examined can be traced back.

As already mentioned, by keying the. Mixer, z. B. the mixer diode 9 according to Fig.l in the inventive Radar arrangement of the total DC power consumption and the mean microwave power generated by the radar arrangement can be reduced without the Detektlons properties deteriorate. The reason for this is as follows: The one shown in FIG. 3 on a logarithmic scale

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Noise figure for a typical Doppler radar arrangement with beat signal reception and a continuous wave mixer reference signal changes at difference frequencies below a critical frequency represented by a point W approximately inversely proportional to the difference frequency that the mixer detects (this difference frequency can be the Doppler frequency itself or the Doppler frequency superimposed with an intermediate frequency). Above the frequency W, the noise figure runs horizontally to to a point U, above which the noise figure characteristic curve has a finite slope. The point W is depending on the mixer between 10 kHz and 1 MHz, the point U, which is not exactly defined in practice) is around 100 MHz.

As commercially available miniature Doppler radar arrays detect relatively low target object speeds and the difference frequencies are thus low whose noise figure is very high, which is shown in FIG. 3 by the point X.

If, however, the mixer reference signal is sampled as in the arrangement according to FIG. 1, the noise figure represented by point X does not apply, but an average noise figure which corresponds to point Y. - In this example, a comb structure in the spacing of pulse repetition frequency and with a located - based envelope, wherein the first minimum

at the inverse pulse duration (typically 1 MHz). This spectrum, which is the Fourier _w transformed of the pulse signal shown in FIG. 2b, is transmitted via gate 11, which is opened synchronously with this signal and thus represents an adapted or "Matohed" filter for the sampled mixer signal. The total noise figure becomes

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thus considerably reduced compared to the case in which the mixer reference signal is a continuous wave signal. The associated reduction in input DC power at the same detection properties can be several orders of magnitude. Since the noise figure of the mixer is very low Frequencies is very high, as FIG. 3 shows, a high-pass filter 10 can also be inserted between the mixer 9 and the gate 11 to improve the overall noise power whose corner frequency is approximately at the frequency W.

It can be shown that the radar arrangement according to FIG. 1 has an average direct current power of only about 0.3 mW with a 1 kHz pulse train of pulses of length 1 / US at 10 GHz for sufficient detection of slowly moving target objects in the close range -transmission electron arrangement with 20 % efficiency is sufficient. The rest of the circuitry of the radar arrangement requires comparable power. This means that the radar system can be continuously fed for three years from a mercury battery with a capacity of 1.5 Ah.

Another advantage of the radar arrangement according to FIG. 1 relates to the interference between two radar arrangements which are on work in the same place, d. H. feed in mutually undesirable signals. This problem is very difficult with commercial miniature Doppler continuous wave radars to report and complex frequency modulation devices are required in the radar systems to keep mutual interference or disturbance as small as possible. In contrast, in the radar arrangement according to Flg.l the probability of interference with other identical radar arrangements is very low, since the duty cycle of the

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Impulses is very low (a typical value is 10). In addition, the transmission pulses of such radar arrangements consistently out of phase and the reflected received pulses are recorded coherently. Even in case that one arrangement detects an undesired pulse emitted by another arrangement is the phase of the next unwanted pulse randomly compared to the sampling frequency of the receiving radar arrangement. Consequently would be the output of filter 15 for this next Impulse simply create additional noise. The noise power can be increased by widening the bandwidth of the radar array can be minimized by simply changing the frequency of the oscillator 1.

It can be shown that the frequency change of a 1 / US microwave pulse for a target object in the area of 10 m without any significant deterioration in the signal-to-noise ratio may be 5 MHz. This frequency stability can be easily implemented by conventional waveguide circuit arrangements achieve.

In modification of the radar arrangement according to Fig.l can also a separate or local transmission electronic oscillator (not shown) used to generate the sampled mixer reference signal, the local oscillator is sampled by the pulse generator 3 at the same time as the oscillator.

The speed of the target object can be determined simply by measuring the frequency of the output signal from the filter 15 to be determined.

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For the description of the radar arrangement according to Pig.l was assumed to be the time for one at a moving target reflected and received signal (this time is calculated from half the propagation speed, multiplied by the target object distance) is less than the microwave pulse length and is typically 1 / US. This means that a desired target object resolution is achieved by limiting the target distance; with a 1 / us pulse the distance is 150 m. In order to detect target objects at a greater distance, the arrangement according to FIG. 1 can be modified in such a way that the opening of the gate 11 and the keying of the mixer 9 by the reference signal by a delay unit or by a second pulse from the source 1, which is switched through to the mixer 9 only when the transmitting antenna is blocked, is delayed will.

FIG. 4 shows a further modification of the radar arrangement according to FIG. 1. This radar arrangement is expanded in such a way that direction information about the target object can be obtained. Instead of a single detector channel which, according to FIG. 1, has the mixer 9, the gate 11, the integrator 15 and the filter amplifier 15, two channels a and b are provided in the radar arrangement according to FIG the additions a and b are provided. In this arrangement, the reflected received signal detected by the receiving antenna 7 is split into two signals by a differential ring transformer 25 which also rotates the phase of one of the two signals. One signal is fed into a mixer 9a without a phase change, while the other signal is fed into the mixer 9a with a relative + 90 ° phase change

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another mixer 9b arrives. Similarly, sampled reference signals of the oscillator 1 are obtained without a phase shift and with a 90 ° phase shift via a differential ring transformer 27 into the mixers 9a and 9b fed in. The Doppler signal is acquired separated in channels a and b, in the same way as already described with reference to FIGS. 1, 2 and 3 by opening gates 11a and 11b at the same time. The output signal of one of the two filters 15 * z. B. the filter 15 »(see. Fig.4) is as in the arrangement fed into the comparator 17 and the display unit 19 according to FIG. The output signals of both Filters 15a and 15b are also mixed in a phase detector 29, the output signal of which has two parallel Comparators 31 and 35 are fed to the display units Control 33 and 37.

The output of the phase detector 29 is a Direct current signal, the sign of which, according to known theoretical considerations, depends on the direction of the detected Target object. When this output signal is positive and greater than a threshold V, the comparator controls 31 displays the display unit 33 to show an approach of the target object. When the output is negative and is greater than a threshold V_, the display unit 37 is activated by the comparator 35; this means that the target object is moving away.

Miniature Doppler radar assemblies according to the invention can be used in the following applications:

(1) Microwave intrusion alarm arrangements (e.g. for Shops) with a single microwave transmission beam;

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(2) Microwave barriers (ζ. B. for a factory), consisting of several microwave intrusion alarm arrangements, the beams of which overlap and define a "security fence";

(3) Vehicle speedometer j

(4) vehicle counter;

(5) toll booth tax orders;

(6) Revolution counter when testing the vehicle;

(7) anti-collision assemblies;

(8) traffic regulation;

(9) traffic light control;

(10) Railway speedometers and position detectors (especially for future passenger trains);

(11) railway metering point switch;

(12) yard speed control;

(13) Diagnostic facilities, ζ. B. for material testing of turbine blades;

(14) grinding wheel peripheral speed measurements;

(15) steel mills;

(16) bucket speed measurements;

(17) bridge vibration detection;

(18) Mooring of large ships, especially tankers;

(19) respiratory monitoring in animals and humans;

(20) He Im radars;

(21) people counter;

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(22) anti-collision systems for cranes;

(23) elevator controls;

(24) automatic lighting;

(25) plug-in runway monitoring;

(26) boat and ship radar and speedometer;

(27) rate of climb indicator; and

(28) altimeter.

Although the microwave receiver according to the invention in primarily used as a miniature Doppler radar receiver it can also be used in analog systems. For example, it can act as a receiver in a microwave communications system (e.g. for speech transmission). In this case it is from the target object originating received signal a z. B. with the information amplitude-modulated signal from a remote transmitter. Here must have a reference signal local oscillator and the gate connection, for example by receiving radio command pulses can be synchronized from a central control unit or by a servo tracking device. One such an arrangement is advantageous in a very noisy environment where. hearing protection (e.g. through helmets) is necessary is.

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Claims (9)

Claims Doppler radar arrangement for transmitting one on one Moving target directed pulse-modulated signal, for receiving a reflection signal of the moving target and to Mixing of the reflection signal with a local oscillator signal in such a way that a Doppler signal can be determined, marked by a solid-state microwave source (1); a pulse generator (3) for periodically sampling the solid-state microwave source (1) in such a way that microwave signal pulses are generated; a transmitting antenna (5) for transmitting the microwave signal pulses; a receiving antenna (7) for receiving reflected Microwave signal pulses; a reference signal generator for generating a sampled reference signal; a mixer (9) for mixing the sampled reference signal with the microwave signal pulses reflected from the moving target; on simultaneously with the output pulses of the mixer (9) pulse-like switchable gate (11); and one integrating the output pulses of the mixer (9) Integrator (13) for generating the Doppler signal (Fig.l). 2. Doppler radar arrangement according to claim 1, characterized in that the solid-state microwave source (1) for generating the sampled reference signal is connected via a shunt path to the mixer (9) (Fig.l). 709830/0729 GRWWNAL INSPECTED 3. Doppler radar arrangement according to claim 1, characterized through a narrow band filter amplifier (15) and one Comparator (17) for detecting a Doppler signal lying above a noise level (FIG. 1). 4. Doppler radar arrangement according to claim 1, characterized by a display unit (19) for displaying the over one Noise level lying and by the comparator (17) detected Doppler signal (Pig.l). 5. Doppler radar arrangement according to claim 1, characterized by a time delay between the transmitted microwave signal pulses and the signal pulses fed into the mixer (9) to determine the detection range for the Enlarging moving target. 6. Doppler radar arrangement according to claim 1, characterized by a high-pass filter (18) for filtering the output pulses the mixer (9) (Fig.l). 7. Doppler radar arrangement according to claim 1, characterized by the microwave source (1) and a separate one through solid-state microwave reference signal generator gated by the pulse generator (3) (Flg.l). 8. Doppler radar arrangement according to claim 1, characterized in that the mixer (9) is an oscillator, which is also used as a reference signal generator gated by the pulse generator (3) works (Fig. 1). 9. Doppler radar arrangement according to claim 1, characterized in that that the mixer (9) is a diode (Fig. 1). 709830/0729