EP1608998A1

EP1608998A1 - Compact low power consumption microwave distance sensor obtained by power measurement on a stimulated receiving oscillator

Info

Publication number: EP1608998A1
Application number: EP04711353A
Authority: EP
Inventors: Martin Vossiek; Martin Nalezinski; Andreas Kornbichler
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2003-03-31
Filing date: 2004-02-16
Publication date: 2005-12-28
Also published as: JP2006515424A; WO2004088354A1; US20060220947A1; DE10314557A1

Abstract

The invention relates to a pulse radar that comprises a receiving oscillator whose transient response is influenced by a received return.

Description

description

Compact microwave distance sensor with low power consumption through power measurement on a stimulated local oscillator

Pulse radar sensors are often used to measure distances with microwaves. The methods and arrangements for the construction and operation of pulse radar sensors exist in a variety of forms and have long been e.g. known from US 3,117,317, US 4,132,991 and US 4,521,778. Pulse radar sensors are used as level sensors in industrial measurement technology, as parking aids or near-distance sensors in motor vehicles to avoid collisions, to map the surroundings and to navigate autonomous vehicles and transport systems such as Robots and conveyor systems.

Pulse radar sensors usually work in the listed areas of application at center frequencies of approx. 1 GHz to 100 GHz with typical pulse lengths of 100 ps to 20 ns. Because of the large bandwidth, such sensors have been referred to as ultra-wideband (UWB) radar for some time. Common to almost all pulse radar sensors is that the pulse signals have such a large bandwidth that they cannot be recorded and processed directly with the usual methods of signal detection, but must first be converted to a lower frequency. For this purpose, almost all known pulse systems use the so-called sequential scanning method. With this principle, which is already known from early digital sampling oscilloscopes, the measurement signal is sampled over several measurement cycles, the sampling times being shifted sequentially from cycle to cycle.

US Pat. No. 3,117,317, US Pat. No. 4,132,991 and US Pat. No. 4,521,778 describe the circuitry implementation of sequential sampling in such a way that a transmit pulse with a specific one Repetition frequency CLK-Tx (clock transmission) is transmitted and its echo is sampled with a scanning gate with a repetition frequency CLK-Rx (clock reception). If the frequencies of the transmission sequence and the scanning sequence differ slightly, the two shift

Follow each other slowly in their phase. This slow relative shift of the sampling point at the time of transmission causes a sequential sampling process.

FIG. 1 shows a known embodiment of a pulse radar with sequential sampling, which operates according to the prior art. The output signal of a continuously operated oscillator is divided into a transmit and a receive path. These two signals are switched through for a brief moment via the switches SW-Tx / SW-Rx with the clock CLK-Tx / CLK-Rx, whereby two cyclic pulse sequences s _Tx (t) and Sτ _x (t) are generated with a slightly different clock rate , The pulse train s _Tx (t) is transmitted via the antenna ANT-Tx. The pulse sequence Sκχ (t) is fed to the first gate of the mixer MIX, which acts as a scanning gate. The

At its second gate, the mixer is fed with the received signal reflected by the object TARGET1 and the object TARGET2. The pulse train received is mixed in the mixer MIX into the low-frequency baseband. The resulting sampling pulse sequence is smoothed by a bandpass filter and thus results in the low-frequency measurement signal s _m (t).

As FIG. 2 shows, it is also known to use a common antenna for transmitting and receiving instead of separate antennas as in FIG. 1, the transmitting and

Received signals are separated from each other, for example by a circulator or directional coupler.

If measurements are carried out with the conventional radar topology according to FIGS. 1 and 2 with sequential sampling, the following disadvantages result: In the case in which the measurement signal s _m (t) is recorded as a real value, the amplitude of the echo pulse changes as a function of the specific phase between the transmit and receive signal. If the TARGET2 object moves, the one belonging to this object "wobbles"

Pulse envelope as shown in FIG. 3 (labeled TARGET2) as a function of the instantaneous reflection phase given by the respective distance of the moving object TARGET2 between the values + A and -A, with the

The position of the pulse envelope is shifted according to the change in location. The envelope between these extremes disappears completely. If the object to be measured reflects a phase in which the pulse envelope disappears, the object is not recognized. A complex value acquisition of the measurement signal s _m (t) can be used to calculate a non-"wobbling" pulse envelope curve according to FIG. 6 from the real and the imaginary part of the measurement signal by forming an amount. However, it is the complex value acquisition, ie the use of two Mixers and the evaluation of two signals Re {S _m (t)} and Im {s _m (t)} are necessary.The switches SW-Tx / SW-Rx allow only a limited switching contrast, which means that one signal is always emitted and a Doppler signal can be seen between the pulse envelopes. In addition, the continuous wave signal emitted can be problematic in the sense of the secondary transmissions approved by the authorities. The oscillator HFO is always switched on and used up

Electricity. In battery-operated applications, this means a reduced battery life. To generate the pulses, an oscillator and two switches, which are difficult to design, are required for the HF. An arrangement according to FIG. 4 solves some of the problems mentioned. The function essentially corresponds to that of the arrangement of FIG. 1, the pulse sequences in this case being achieved by briefly switching on the signal sources HFO-Tx / HFO-Rx by a fast voltage pulse from PO-Tx / PO-Rx can be reached. Here too, the resulting pulse trains have slightly different clock rates CLK-Tx / CLK-Rx.

To achieve a good signal-to-noise ratio

(SNR) of the measurement signal is crucial that the oscillators PO-Tx / PO-Rx are in a deterministic, that is to say in a non-stochastic, phase relationship to one another over all pulses of a sequence. A deterministic relationship arises when the pulse signals that the

Switch on pulse oscillators HFO-Tx / HFO-Rx, very rich in harmonic components in the frequency band of

High frequency oscillators are. The harmonics mean that the oscillators do not oscillate stochastically, but in relation to the voltage pulses PO-Tx / PO-Rx with a rigid, characteristic initial phase. The output signals of the two oscillators are therefore also in a deterministic phase and time relationship to one another, predetermined by the transmission signal sequence and the scanning signal sequence.

The advantages of the arrangement in FIG. 4 are:

- The system has a significantly lower current consumption than that of Figure 1, since the high-frequency oscillators are switched off most of the time of a measuring cycle.

The system no longer has complex high-frequency switches.

However, it is disadvantageous: - It also requires a great deal of effort to generate sufficiently strong, fast, harmonic-rich voltage pulses. If the harmonics are very weak, the start-up phase is also influenced by other interfering signals, the measurement signal amplitude is noisy and jittery. To determine the distance from the measurement signal, the envelope curve usually has to be determined. This usually requires a very high amplification of the low-frequency measurement signal, which is also difficult to ensure.

In another technical field, namely that of the transponder, it is known from US Pat. No. 5,630,216 that an oscillator is influenced not only in its phase, but also in its speed of oscillation, by an injected signal of a similar frequency. This effect is used for a very low-power demodulation of a received AM code signal. However, this amplification effect is not suitable for a coherent measurement method like the one described above. ^•

The object of the present invention is to show systems which fulfill the task of the radar arrangements described in a different and improved form.

This object is achieved by the inventions specified in the independent claims. Advantageous refinements result from the dependent claims.

Accordingly, an arrangement or device has transmission means for generating and transmitting an electromagnetic signal, and reception means for receiving an echo of the transmitted electromagnetic signal. The receiving means have a receiving oscillator whose transient response, in particular the transient period and thus the average power output, can be influenced by the strength, in particular the amplitude, of the received reflection of the transmitted electromagnetic signal. So the local oscillator is like this wired that it can be excited and / or stimulated by reflection of the transmitted electromagnetic signal, whereby a measurement signal depending on the strength, in particular amplitude, of the reflection of the transmitted electromagnetic signal can be generated.

For this purpose, the arrangement preferably has a detector by means of which the average power of the local oscillator can be measured.

It is also advantageous if the arrangement is designed for pulse operation in the transmission and / or reception branch, in that the transmission means and / or reception means have means for periodically switching on and off. In particular, the arrangement can have means for periodic input and output

Turn off the local oscillator at a clock rate.

In a particularly cost-effective and space-saving manner, the local oscillator can be connected in such a way that it also functions as a local oscillator for generating the electromagnetic signal to be transmitted.

Alternatively, the arrangement can have a second oscillator, which functions as a transmission oscillator for generating the electromagnetic signal to be transmitted.

The arrangement is in particular an arrangement for distance measurement, a radar, preferably a pulse radar.

To detect a measurement signal, it can have a mixer in which a first partial measurement signal and a second partial measurement signal are added, in particular a mixer with two diodes, the diodes being used with the same polarity, that is to say in parallel, and the measurement signal being formed as the sum of two partial measurement signals or where the diodes are used with opposite polarity, ie anti-parallel and the measurement signal is formed by the difference between the two partial signals. The advantage of using such a symmetrical mixer is the doubling of the measurement signal amplitude and its particularly good transmission properties, which are particularly desirable for the low-attenuation transmission of the transmission signal and the excitation of the local oscillator by a received signal.

In the case of a measuring method, in particular for measuring distance,

- generates and transmits an electromagnetic signal using transmission means,

receive a reflection, that is to say an echo of the transmitted electromagnetic signal, with reception means which have a reception oscillator,

- The transient response, in particular the transient period and thus the average power output, of the local oscillator is influenced by the strength, in particular amplitude, of the reflection of the transmitted electromagnetic signal.

Advantageous configurations of the method result analogously to the advantageous configurations of the arrangement.

Further advantages and features of the invention result from the description of exemplary embodiments. It shows:

Figure 1 A pulse radar according to the prior art; Figure 2 shows a second pulse radar according to the prior art;

3 shows a measurement carried out with the pulse radar according to FIG. 1 or the pulse radar according to FIG. 2; Figure 4 shows a third pulse radar according to the prior art; 5 shows an arrangement with transmitting means and receiving means;

FIG. 6 shows a measurement carried out with the arrangement according to FIG. 5; Figure 7 shows an alternative arrangement with transmission means and

Receiving means; FIG. 8 shows an alternative arrangement with transmitting means and receiving means; 9 shows a mixer which can be used in the arrangements.

Arrangements are described below which avoid the disadvantages of the systems of FIGS. 1, 2 and 4.

As already mentioned, an oscillator is in its

Start-up behavior is influenced not only in its phase, but also in its start-up speed by an injected signal of a similar frequency. A periodically switched on and off oscillator then swings faster under the influence of a received signal of a similar frequency than without this signal. The greater the amplitude of the received signal at the switched oscillator, the shorter its settling time and the longer the oscillator vibrates during a predetermined switch-on time.

If the output signal of a switched oscillator, which has been stimulated by a received signal, is fed to a detector DET with a subsequent low pass, the detector in this arrangement functions as a power meter which measures the average power output of the stimulated oscillator. If the oscillator is stimulated by an AM reception signal, the mean output power of the oscillator fluctuates depending on the signal amplitude of the stimulating reception signal that is present at the oscillator. The measurement signal S _m (t) thus represents a highly amplified image of the AM received signal.

In the present case, the amplification effect with a switched oscillator is used to implement a very simple distance radar with extremely low power consumption using the sequential sampling method. A corresponding radar system is shown in FIG. 5. This radar system has a transmit oscillator HFO-Tx, which is periodically switched on briefly using a fast switch PO-Tx with a clock rate CLK-Tx. Typical operating times are 100 ps - 20 ns, typical clock rates 0.1 - 10 MHz. The signal is transmitted via a diplexer DIP, which is designed as a circulator in the case shown, reflected on an object, received again via the diplexer DIP and reaches a reception oscillator HFO-Rx in the form of a detector DET

Local oscillator, which is switched on and off via a switch PO-Rx with a clock rate CLK-Rx. In the case where, for example, through practically unavoidable coupling from the receiving antenna via detector DET to the local oscillator HFO-Rx, signal components of the reflected

Received signal at the time the local oscillator HFO-Rx is connected to it, these signals, as described above, cause the oscillator to oscillate faster than when the oscillator swings out of the noise. In a distance measurement, echoes of different strengths arrive in accordance with the reflector scenario over time. Received signals of different strengths thus reach the local oscillator HFO-Rx via antenna ANT, diplexer DIP and detector DET. The strength of the reflection at the time of switching on is shown as the mean duty cycle of the oscillator, that is to say as the mean oscillator power. The detector DET forms the pulse envelope curve shown in FIG. 6 from this mean oscillator power.

The advantages of this system topology and measurement method are as follows:

- After the measurement signal s _m (t) is generated not coherently by mixing but by power detection, the "wobbling" of the signal amplitude as a function of the phase of the reflection is also eliminated for a moving reflector TARGET2. The measurement signal does not have to be generated with complex values for this.

Typical reflections lead to measurement signal amplitudes in the range of a few hundred millivolts, in contrast to mixed signals which are typically a few ten millivolts in a coherent system. Without additional circuitry in the HF range, amplifier stages of 20-30 dB in the LF range can be saved. - The radar system works with extremely low power consumption.

At HF frequencies, only two oscillators are required to generate the pulses. For the content of harmonics in the voltage pulses generated by the switches, there are not the high requirements as for the voltage pulses of the switches SW-Rx or SW-Tx for the arrangement in FIG. 4.

A particularly simple embodiment of the radar system provides

Figure 7 shows: The oscillator HFO operates both as a transmitter oscillator as well as stimulated local oscillator which is both turned on by the switch PO-Tx at the clock rate CLK-Tx, is referred to as also switched on by the switch PO-Rx with the ^■ clock rate CLK-Rx. Alternatively, it can

Switching on can also be carried out by an arrangement as in FIG. However, this requires a switch that can achieve extremely fast pulse repetition rates.

It is advantageous but not mandatory if the detector DET in the system of FIGS. 7 and 8 is more symmetrical

Mixer based on a 90 ° hybrid (see, for example, A. Maas: "The RF and Microwave Circuit Design Cookbook", Artech House 1998, pp. 107-109), as shown in FIG. 9 with a special feature. The special feature exists in that the two diodes, as in a frequency doubler, are used with the same polarity, that is in parallel, and the measurement signal is nevertheless a sum of the two partial signals S _m i (t) and Ξ _m2 (t) is formed or the diodes are used with opposite polarity, i.e. antiparallel, and the measurement signal is formed by the difference between the two partial signals. The measurement signal amplitude is doubled in comparison to an arrangement with only one diode or the tapping of only one partial signal s _m ι (t) or Sπ _ώ Ct). The advantage of using a symmetrical mixer according to FIG. 9 is furthermore its particularly good transmission properties, which are particularly desirable for the excitation of the oscillator by a received signal.

In contrast to the mixer presented here, the measurement signal is formed in a conventional mixer by either using the two diodes in anti-parallel and the

Partial signals are added or the diodes are used in parallel and the two partial signals are subtracted. In contrast to a conventional mixer, the diodes in the mixer presented here are not adapted to be low-reflection, but deliberately high-resistance and therefore reflective

(typ. 100 Ω - 100 kΩ in a 50 Ω system). If necessary, a series resistor R can be connected in series with the diodes in order to achieve the high resistance.

In addition to the advantages that have already been mentioned for the system according to FIG. 5, this system also has to be very simple. Only an RF oscillator is required to generate the pulses.

configurations:

- With the radar sensor described, instead of using the method of sequential sampling, all other methods for distance measurement common for pulse radars can also be used. For example, the radar system can only be made sensitive for a predetermined range in which the two clock rates CLK-Tx and CLK-Rx are identical. are and are offset from one another by a time period which corresponds to the signal transit time between the sensor and the distance range to be monitored. In this operating mode, the system could, for example, serve as a very cost-effective limit switch (e.g. in industrial level measurement technology as overflow or underflow protection) or as a type of radar barrier (e.g. for counting / detecting people and vehicles or for detecting objects on assembly lines) be used.

Likewise, the clocks CLK-Tx and CLK-Rx do not have to be regularly shifting the clocks to each other to generate a complete distance profile, but a series of samples can also be used according to any scheme (e.g. stochastic or coded)

Generate object scene and then correctly assign and assign the distance measuring points to each other in an evaluation unit. Other methods of operating the radar are conceivable. Instead of the circulator according to FIG. 5, the transmission

Reception separation also take place via a directional coupler or are completely dispensed with. In the latter case, the antenna can be connected via a simple stub line. However, a significantly poorer performance in distance measurement is to be expected, since direct crosstalk from the transmit path to the receive path or signals reflected on the stub act like a very close reflector. The range of uniqueness of the radar, as is customary with pulse radars, is determined by the pulse repetition rate. Reflected pulses that arrive at the radar sensor only after the next transmission pulse has been transmitted are interpreted as very close reflectors. Since the average received energy determines the S / N, it is desirable to select a high pulse repetition rate and inevitably to make the uniqueness range as small as possible. - The magnitude of the duty cycle of CLK-Tx and CLK-Rx must be in the range of Q oscillation periods of the oscillators HFO-Tx / HFO-Rx, where Q represents the loaded quality of the resonator in the oscillator. Otherwise the oscillator cannot swing up to its maximum amplitude during the switch-on time. In this respect, the resonator should have the lowest possible quality. In contrast to many pulse radar sensors (such as that in FIG. 4), it is not necessary that the switch-on pulse vibrate particularly steeply and generate harmonics in the high-frequency range.

Due to the particularly simple and inexpensive construction, the radar arrangements are outstandingly suitable for all cost-sensitive applications. Worth mentioning in particular are the short-range sensors around vehicles (vehicle parking aid, automotive blind spot, automotive airbag, pre-crash, robot navigation, generally as sensors for autonomous vehicles), the short-range sensors in vehicles (seat occupancy control, intrusion detectors, windows - Sunroof pinch protection) and the entire area of industrial distance sensors and the area of house sensors (monitoring of windows, doors, rooms and boundaries).

Claims

claims

1. Arrangement with transmitting means for transmitting a signal and with receiving means for receiving a reflection of the transmitted signal, the receiving means one

Have local oscillator, characterized in that the transient response of the local oscillator can be influenced by the reflection of the transmitted signal.

2. Arrangement according to claim 1, characterized in that the settling time and / or the average power output of the local oscillator can be influenced by the reflection of the transmitted signal.

3. Arrangement according to one of the preceding claims, characterized in that the power of the local oscillator is measurable.

4. Arrangement according to one of the preceding claims, characterized in that the arrangement has means for, in particular periodic, switching the receiving oscillator on and off at a clock rate.

5. Arrangement according to one of the preceding claims, characterized in that the local oscillator also functions as a local oscillator for generating the signal to be transmitted.

6. Arrangement according to one of the preceding claims, characterized in that the arrangement has a second oscillator which functions as a transmission oscillator for generating the signal to be transmitted.

7. Arrangement according to one of the preceding claims, characterized in that the arrangement is an arrangement for distance measurement.

8. Arrangement according to one of the preceding claims, characterized in that the arrangement is a radar, in particular a pulse radar.

9. Arrangement according to one of the preceding claims, characterized in that the arrangement for detecting a measurement signal has a mixer in which a first partial measurement signal and a second partial measurement signal are added.

10. Arrangement according to one of the preceding claims, characterized in that the arrangement for detecting a measurement signal has a mixer with two diodes, the diodes being used with the same polarity and the measurement signal being formed as the sum of two partial measurement signals, or with the diodes having opposite polarity are used and the measurement signal is formed by the difference between the two partial signals.

11. Vehicle, building or industrial plant comprising an arrangement according to one of the preceding claims.

12. Measuring method, in particular for distance measurement, in which

a signal is generated and transmitted with transmission means, a reflection of the transmitted signal is received with reception means which have a reception oscillator,

- The transient response of the local oscillator is influenced by the reflection of the transmitted signal.