GB2433664A

GB2433664A - Arrangement for determining the angle of incidence of an electromagnetic wave

Info

Publication number: GB2433664A
Application number: GB0619633A
Authority: GB
Inventors: Joerg Schoebel
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2005-12-20
Filing date: 2006-10-04
Publication date: 2007-06-27
Anticipated expiration: 2026-10-04
Also published as: FR2895089B1; ITMI20062433A1; GB0619633D0; GB2433664B; FR2895089A1; DE102005060875A1

Abstract

An arrangement for determining the an angle of incidence of an electromagnetic wave is disclosed comprising, a transmission unit 102 for emitting an electromagnetic wave in a primary emission direction towards a target object, at least two reception units 101a,101b for receiving the electromagnetic wave reflected by the target object, and an evaluation instrument (500, Fig.6) for evaluating reception signals of the reception units 101a, 101b, so as to obtain the angle of incidence of the electromagnetic wave with respect to the boresight of the transmission unit 102 and therefore an angular position of the target object with respect to the boresight of the transmission unit 102. The evaluation device (500,Fig.6) is divided into an angle determination instrument (300,Fig.6) and a selection instrument (400,Fig.6) for selecting a correct side of the boresight of the possible angles of incidence of the electromagnetic wave.

Description

1 2433664

Description Title

Method and device for signal processing with an angle determination by means of microwave motion sensors The present invention relates in general to signal processing methods and devices for angle determination by means of microwaves. In particular, the present invention relates to a recording device for recording an angle of incidence of an electromagnetic wave which has been emitted by a transmission unit in a primary emission direction towards a target object. At least two reception units are provided for receiving the electromagnetic wave, which receive the electromagnetic wave reflected by the target object and convert it into at least one intermediate frequency signal. This intermediate frequency signal is converted into at least a first and second recording signal by means of a converter instrument, and an evaluation instrument evaluates the first and second recording signals so as to obtain the angle of incidence of the electromagnetic wave with respect to the primary emission direction of the transmission unit and therefore an angular position of the target object with respect to the primary emission direction of the transmission unit.

Prior Art

As shown for example in Fig. 1, motion detectors for detecting persons or their movements conrise a combination of microwave sensors and passive infrared sensors PIR. The microwave sensor device in this case has a radiofrequency source which typically delivers a continuous wave signal 0.

The RF source is represented as an oscillator OSZ, which typically operates in the GHz range. The radiofrequency signal 0 is fed to a splitting instrument A, which on the one hand generates a transmission signal Tx and on the other hand delivers a local oscillator signal 0 for the mixing of a reception signal Rx in a mixer M. The reception signal Rx mixed with the local oscillator signal 0 is output from the mixer M as an intermediate frequency signal ZF, optionally with in-phase and quadrature components, to an evaluation unit E. The reception signal Rx obtained as a function of the transmission signal Tx may be Doppler-shifted according to the motions of a target object Z. The motions are represented by velocity components and Vj in Fig. 1. Infrared radiation IR from the target object 2 is furthermore received by means of an infrared sensor PIR. A corresponding PIR signal is likewise fed to the evaluation unit AE, which then combines the signals obtained from the microwave part with those of the infrared part by a conventional method and outputs an alarm signal AS.

Microwave sensors are often designed so that the Doppler effect can be utilised. In the simplest case, such sensors are constructed with a radiofrequency (RF) continuous wave (CW) source, the output signal of which is split between a first antenna, the transmission antenna, and the local oscillator (LO) input of a mixer. In many cases the continuous wave source can be switched off, so that inactive periods of the sensor operation can be implemented.

The signal of a second antenna, the so-called reception antenna, is fed to the signal input of the mixer. A corresponding Doppler signal is available at the output of the mixer. For a reflection back to the sensor system of the signal emitted by the stationary sensor system to a moving object, the Doppler frequency f of the Doppler signal is given by the following equation: Af -2 v f/c where c -the velocity of light, I -frequency of the transmission signal (typically 10 GHZ) and v -velocity of the target object (a positive value here indicates a velocity direction towards the sensor system, and a negative value indicates a velocity direction away from the sensor system). The velocity of the target object typically lies in a range of from 0.1 to 3 rn/s (0.36 to 10.8 km/h), which gives a Doppler frequency of between 6.7 and 200 Hz.

In order to identify the motion direction (towards the sensor instrument or away from it), it is necessary to be able to detect the in-phase and quadrature components of the mixing product which are known to the person skilled in the art. A so-called IQ mixer is employed for this purpose, in which case it is possible to use "single-sideband" signal processing which yields the sign of the Doppler frequency.

In the case of digitised evaluation, a Fourier transformation is carried out in a digital evaluation unit so that two signals are obtained according to the following relations: S1 -Fourier transform of s1(t); S0 -Fourier transform of s0(t) The components s and s referred to in the above equation represent the mixing product of the reception signal s(t) with the local oscillator signals for a 900 phase difference, here represented as cos( t) and sin(et) respectively. The resulting single-sideband spectrum is given by: S33 -S1 -j'S0.

In order to improve the operating behaviour of microwave-based motion detectors, it has been proposed in the prior art to provide a functionality extending beyond the known object detection and optionally velocity and distance determination, by also determining the angular position of one or more objects. As disclosed in DE 102 34 291 Al, a plurality of antennas are provided on the reception side for this purpose. This approach, however, has the disadvantage that radiofrequency and low-frequency/baseband signal processing has to be provided for each reception path. Particularly for motion detectors in alarm systems, this inexpediently leads to high costs. It is furthermore proposed in DE 102 34 291 Al to provide switching between a plurality of reception antennas, so that only one signal processing path is necessary. EP 0987561 A2 describes a holographic switching concept, switching being carried out between a plurality of transmission and reception antennas.

Kederer, W.; Detlefsen, J.: Direction of arrival (DOA) determination based on monopulse concepts, 2000 Asia-Pacific Microwave Conference, 3-6 Dec. 2000, pages 120-123, describes a method for angle determination by means of a plurality of beam lobes or antenna elements in a reception path, with a transmission antenna irradiating the recording region.

Advantages of the Invention The object of the invention is to provide a recording device for recording an angle of incidence of an electromagnetic wave, which avoids the disadvantages of the prior art and allows efficient and cost-effective angle evaluation.

This object is achieved according to the invention by a recording device having the features of Patent Claim 1.

The object is furthermore achieved by a method as specified in Patent Claim 8.

Further configurations of the invention can be found in the dependent claims.

It is an essential concept of the invention to design an evaluation instrument for the evaluation of recording signals so that the evaluation instrument is divided into an angle determination instrument for determining possible angles of incidence of the electromagnetic wave with respect to the primary emission direction of the transmission unit, and a selection instrument for selecting a correct one of the possible angles of incidence of the electromagnetic wave with respect to the primary emission direction of the transmission unit. In particular, it is expedient to provide a separation of the magnitude-related angle determination and the right/left discrimination in a microwave motion sensor which is based on "digital" beam shaping.

In accordance with the method according to the invention, two possible angle values are expediently determined first from the digitised baseband signals in the time domain.

Right/left discrimination is subsequently or simultaneously carried out in the frequency domain. In particular, the advantage of the method according to the invention is that an accurate angle determination no longer has to be carried

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out in the frequency domain, so that a "coarse" Fourier transformation with few sampling values is sufficient. The number of sampling values is advantageously just 2 to 64.

It is furthermore very advantageous that the method according to the invention entails a small memory requirement and allows short cycle times of the angle calculation. Such short cycle times are achieved by the short duration of the sampling and by a small calculation outlay. An angle determination is therefore expediently less sensitive to interference overall, because the object can be plausibilised over a plurality of cycles before the alarm triggering takes place.

The recording device according to the invention for recording an angle of incidence of an electromagnetic wave essentially comprises: a) a transmission unit for emitting an electromagnetic wave in a primary emission direction towards a target object; b) at least two reception units for receiving the electromagnetic wave reflected by the target object and for converting the received electromagnetic wave into at least one intermediate frequency signal; c) a converter instrument for converting the at least one intermediate frequency signal into at least a first and a second recording signal; and d) an evaluation instrument for evaluating the first and second recording signals so as to obtain the angle of incidence of the electromagnetic wave with respect to the primary emission direction of the transmission unit and therefore an angular position of the target object with

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respect to the primary emission direction of the transmission unit. The evaluation device furthermore comprises an angle determination instrument for determining possible angles of incidence of the electromagnetic wave with respect to the primary emission direction of the transmission unit by means of the first and second recording signals, and a selection instrument for selecting a correct one of the possible angles of incidence of the electromagnetic wave with respect to the primary emission direction of the transmission unit by means of the first and second recording signals.

Furthermore, the method according to the invention for recording an angle of incidence of an electromagnetic wave essentially comprises the following steps: a) emitting an electromagnetic wave in a primary emission direction towards a target object by means of a transmission unit; b) receiving the electromagnetic wave reflected by the target object by means of at least two reception units; c) converting the received electromagnetic wave into at least one intermediate frequency signal by means of the at least two reception units; d) converting the at least one intermediate frequency signal into at least a first and a second recording signal by means of a converter instrument, and e) by means of an evaluation instrument, evaluating the first and second recording signals so as to obtain the angle of incidence of the electromagnetic wave with respect to the primary emission direction of the transmission unit and therefore an angular position of the target object with respect to the primary emission direction of the transmission unit, the evaluation by means of the evaluation instrument comprising: ci) determining possible angles of incidence of the electromagnetic wave with respect to the primary emission direction of the transmission unit from the first and second recording signals by means of an angle determination instrument; and e2) selecting a correct one of the possible angles of incidence of the electromagnetic wave with respect to the primary emission direction of the transmission unit from the first and second recording signals by means of a selection instrument.

Advantageous refinements and improvements of the respective subject-matter of the invention can be found in the dependent claims.

According to a preferred refinement of the present invention, the angle determination instrument comprises a beam shaping instrument for forming sum signals and difference signals as beam-shaped signals from the first and second recording signals. The beam-shaped signals are advantageously fed to the subsequent processing instruments in the angle determination instrument.

According to yet another preferred refinement of the present invention, the beam-shaped signals are fed both to the angle determination instrument 300 and to the selection instrument 400. The beam shaping instrument is expediently contained as a separately identifiable block in the evaluation instrument.

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According, to yet another preferred refinement of the present invention, the transmission unit for emitting the electromagnetic wave in the primary emission direction and the at least two reception units for receiving the electromagnetic wave reflected by the target object and for converting the received electromagnetic wave into at least one intermediate frequency signal are designed for continuous wave operation. According to yet another preferred refinement of the present invention, it is advantageous to design the transmission unit and the at least two reception units for pulsed operation or modulated operation.

According to yet another preferred refinement of the present invention, the recording device for recording an angle of incidence of the electromagnetic wave comprises at least two transmission units for emitting at least two electromagnetic waves in a common primary emission direction and a reception unit for receiving the electromagnetic waves reflected by the target object and for converting the received electromagnetic waves into at least one intermediate frequency signal.

According to yet another preferred refinement of the present invention, the recording device for recording an angle of incidence of the electromagnetic wave comprises at least two transmission units for emitting at least two electromagnetic waves in a common primary emission direction and at least two reception units for receiving the electromagnetic waves reflected by the target object and for converting the received electromagnetic waves into at least one intermediate frequency signal.

It is furthermore advantageous for a determination of possible angular positions of the target object with respect to the primary emission direction of the transmission unit from the first and second recording signals to be carried out by means of the angle determination device in the time domain.

According to another preferred refinement of the present invention, a selection of a correct one of the possible angular positions of the target object with respect to the primary emission direction of the transmission unit from the first and second recording signals is carried out, by means of the selection device in the frequency domain.

It is advantageous to employ a maximum value of a magnitude of the beam-shaped sum signal for establishing the primary emission direction. A minimum value of the magnitude of the beam-shaped difference signal of a difference between the first recording signal and the second recording signal may furthermore be employed for establishing the primary emission direction.

It is furthermore possible to employ a phase change of the beam-shaped difference signal for establishing the primary emission direction. The phase change of the beam-shaped difference signal is expediently 180 .

According to yet another preferred refinement of the present invention, a correct one of the possible angular positions of the target object with respect to the primary emission direction of the transmission unit is selected in the selection instrument on the basis of the beam-shped signals, which are determined from the first and second recording signals.

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Drawings Exemplary embodiments of the invention are represented in the drawings and explained in more detail in the following

description.

In the drawings: Fig. 1 shows the recording device for a target object with a combination of a microwave sensor and passive infrared sensor according to the prior art; Fig. 2 shows a block diagram of a circuit arrangement for a recording device to record an angle of incidence of an electromagnetic wave with analogue signal evaluation to illustrate the principles of the present invention; Fig. 3(a) shows a reception signal power as a function of a direction angle, sum and difference signals being plotted in one diagram; Fig. 3(b) shows a reception signal phase as a function of a direction angle for a sum signal and a difference signal according to Fig. 3(a).

Fig. 4(a) shows a block diagram of a recording device for recording an angle of incidence with digital beam shaping having separate mixers for each reception branch to explain the principles of the present invention; Fig. 4(b) shows the arrangement shown in Fig. 4(a), the separate mixers for each reception branch being replaced by a selector switch between the

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reception antennas, to explain the principles of the present invention; Fig. 5 shows a block diagram of a recording device according to the invention for recording an angle of incidence of an electromagnetic wave with digital processing and two reception branches with IQ mixers; Fig. 6 shows an overall block diagram of the recording device according to the invention according to a preferred exemplary embodiment of the present invention; and Fig. 7 shows an overall block diagram according to a further exemplary embodiment of the present invention.

In the figures, references which are the same denote identical or functionally equivalent components or steps.

Description of the Exemplary Embodiments

Fig. 2 shows an outline block diagram to illustrate the mode of operation of the present invention. In order to be able to carry out an angle evaluation of a received microwave signal, at least two antenna elements are conventionally used. To illustrate the principles of the present invention, Fig. 2 shows analogue signal evaluation.

An oscillator signal 0 is fed by a splitting instrument A on the one hand to mixers M in lhe two reception signal branches and on the other hand to a transmission antenna 108. The signal reflected by a target object (not shown in Fig. 2), i.e. an electromagnetic wave, strikes the reception units lOla, lOib at a particular angle.

The reception units lOla, lOib have respective reception antennas 109a and 109b. The reception signals El and E2 are fed to a coupler, which is preferably designed as a 180 coupler. The sum S and difference signals D are mixed with the local oscillator signal 0 in the mixers N, in order to obtain corresponding intermediate frequency signals ZF which are processed further in a post-processing instrument (not shown). In the analogue beam shaping illustrated in Fig. 2, a number of beam lobes are formed by a group antenna via a beam-shaping element. The beam-shaping element is designed for example as a coupler, a Rotman lens, a Butler matrix or a Blass matrix, and has a plurality of inputs coinciding with the beam lobes.

The beam lobes are designed 80 that they present different azimuthal directions, and so that an overlap occurs between neighbouring beam lobes. In the overlap region of the beam lobes, it is possible to determine the azimuthal angle position of a target object from the amplitude or power ratios of the signals in neighbouring beam lobes. An evaluation of the phases of the signals or a combined evaluation of amplitudes (or powers) and phases may furthermore take place. To this end, for example, signals with their respective magnitudes and phases may be represented as complex numbers (phasors) and fed to a complex-value functional adaptation of the relation of the azimuthal angles for taking ratios of the complex-value reception signals.

In principle, a particularly simple angle determination is possible with the aid of the monopulse method. In this case two antenna elements at a spacing of approximately one half the free-space wavelength are used, via which two beam

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lobes are formed by tapping and adding the signals of the antenna elements on the one hand in-phase (sum beam lobe) or antiphase (difference beam lobe). Such sum and difference signals, which are based on the sum or difference beam lobes, can be generated with the aid of the coupling instrument K. It is furthermore possible to switch between the output signals of the coupler, in order to economise on a mixer and baseband path. This has the disadvantage that additional losses would occur in the reception path owing to the coupler and optionally the selector switch, however, which reduce their sensitivity and range.

It should be pointed out that in an extension of a radiofrequency front-end of a microwave-based recording device for recording an angle of incidence of an electromagnetic wave, it is also possible to use more than two antenna elements with frequency conversion and evaluation of the reception signals to determine the azimuthal angle position of a target object. The phase difference q between the signals of the antenna elements, which is due to the delayed incidence of the electromagnetic wave as a function of the azimuth angle e, is finally used for the angle evaluation in each case.

Figs 3(a) and 3(b) respectively show a reception signal power 114 and a reception signal phase 115 as a function of a direction angle (azimuth angle) 113. The sum signal 305a respectively comes from the sum beam lobes, whereas the difference signal 305b comes from the difference beam lobes.

In the exemplary embodiment shown in Fig. 3, the beam characteristic of two patch elements at a spacing of one half the free-space wavelength was obtained from an analytical model, the elements respectively being exposed to the same amplitude and phase (sum beam lobe) and to the same amplitude but in antiphaae (difference beam lobe). A phase change of 180 occurs at the zero crossing of the power (with an angle of 0 (azimuth angle equal to zero)) in the phase profile of the difference beam lobe.

The angle of the target object, from which the electromagnetic wave emitted by the transmission antenna 108 (see Fig. 2) is reflected towards the reception antennas 109a, 109b (see Fig. 2), is given by the ratio of the signals in the sum and difference beam lobes while observing the phase of the difference beam lobes with respect to the phase of the sum beam lobes.

The signals in so-called "digital" beam shaping, and here particularly the phase differences, of individual elements or groups of antenna elements are processed and evaluated separately, as illustrated in Fig. 5. In contrast to the arrangement shown in Fig. 2, the mixing processes in the reception units lOla and lOib are fully separated from each other here so that intermediate frequency signals can be obtained separately from each other. The recording device shown in Fig. 5 for recording an angle of incidence of an electromagnetic wave is constructed from a transmission unit 102 and two reception units lOla, bib. The transmission unit comprises a transmission antenna 108 on which a transmission signal 106 is sent out. The transmission signal 106 is obtained from an oscillator 103, the oscillator signal being fed via a splitter unit 110 on the one hand to the transmission antenna 108 and on the other hand to the two reception units lOla, bib.

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It should be pointed out, although this is not illustrated in the figures, that more than two reception units may be used for receiving the electromagnetic wave and for evaluating an angle of incidence of the electromagnetic wave. It is furthermore possible that the recording device for recording an angle of incidence of the electromagnetic wave may comprise at least two transmission units 102 for emitting at least two electromagnetic waves in a common primary emission direction, in which case only a single reception unit lOla is provided for receiving the electromagnetic waves reflected by the target object and for converting the received electromagnetic waves into at least one intermediate frequency signal. The transmission units are connected alternately to the instrument for splitting the oscillator signal, for example via a selector switch.

It is furthermore possible that the recording device for recording an angle of incidence of the electromagnetic wave may comprise at least two transmission units 102 for emitting at least two electromagnetic waves in a common primary emission direction, and at least two reception units for receiving the electromagnetic waves reflected by the target object and for converting the received electromagnetic waves together into at least one intermediate frequency signal.

Fig. 4 (a) shows a device according to the invention respectively having a transmission unit 102 and two reception units lOla, lOib. n oscillator signal 104 is fed to the splitting instrument 110 and is further used as a transmission signal 106, which is fed to the transmission antenna 108, and a local oscillator signal which is fed to mixers lila, ilib. The signals received by the reception antennas 109a, 109b are fed as reception signals 107a and 107b respectively to the mixers lila or 11Th. An intermediate frequency signal 112a, 112b output from the mixers after the mixing is then fed to a converter device described below with reference to Figs 6 and 7.

Fig. 4(b) shows a recording device which corresponds in its essential components to those of Fig. 4(a), with the exception that the two mixers lila, ilib are replaced by a single mixer 111 which outputs a single intermediate frequency signal 112. In order to further process the reception signals 107a and 107b of both reception units lOla, 10Th, which are received by the respective reception antenna units 109a, 109b, a selector switch U is provided which alternately connects signals of one of the two reception units lOla, lOib through to the mixer.

Fig. 5 shows in more detail the arrangement represented in Fig. 4(a), IQ mixers lila, lllb and ilic, illd respectively being represented in the arrangement shown in Fig. 5. In order to derive IQ signals, the oscillator signal 104 is mixed directly with the respective reception signals lO7a, 107b in a mixer lila or illb in order to generate an I signal, whereas a Q signal 8 is obtained by mixing the oscillator signal 104 phase-shifted in a retardation unit 105a or 105b with the reception signals 107a, 107b. The output signals s, s and x2, s are therefore available as output signals of the first and second reception units lOla and i0lb for evaluation in a converter instrument 200 (described below with reference to Figs 6 and 7).

The way in which the transmission/reception device 100 explained in Fig. 5 interacts with the other blocks, i.e. with a converter instrument 200, an angle determination instrument 300, an evaluation instrument 500 and a beam shaping instrument 600 Csee Figs 6 and 7 below), of the recording device according to the invention for recording an angle of incidence of an electromagnetic wave will now be described below.

The advantage of so-called "digital" beam shaping is that it requires a smaller construction. Digital beam shaping is furthermore substantially more flexible and better performing in the evaluation; in particular, the possibilities of resolving multi-target scenarios, i.e. a plurality of targets in a range cell, are in principle available with high-resolution methods when a correspondingly greater number of antenna elements or reception devices are used. The distinguishability of target objects in multi-target scenarios is restricted in purely analogue beam shaping to the width of the beam lobes, i.e. targets which lie closer together in angle than the width of a beam lobe inexpediently cannot in principle be separated from one another with analogue beam shaping.

In order to avoid ambiguities, the spacing of the antenna elements mustbe of the order of magnitude of one half the free-space wavelength (comparably with the occurrence of higher diffraction orders in group antennas or in optical gratings).

When a phase evaluation of the reception signals is used for the angle determination, which in particular is the case with digital beam shaping, then it is necessary to use an IQ mixer in order to obtain a phase reference of the mixing signal with respect to the local oscillator, and therefore correctly determine the sign of a recorded

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Doppler frequency. With the single-sideband spectrum described above, a phase difference of two Doppler-frequency lines is obtained according to the following Relation (1): c ci -c2 for the lines 6(af)e' (1) where e3 denotes a phase factor. The phase q is composed of components which depend on the range and the azimuthal angulation. From a phase difference of the signals of two neighbouring reception antennas according to Relation (1) above, it is possible to determine the angulation 0 according to the following relation: 1t Açl 0 = arcsini-.--i (2) La 2zJ With a spacing of the phase centres of the two reception antennas.

When the switching between the individual reception antennas 109a, 109b, .. is used, then the switching between the antenna elements must take place so rapidly that the range component of the phase changes only in a negligible way.

It should be pointed out that the oscillator 103 shown in Fig. 5 (radiofrequency oscillator) is designed in the simplest case as a continuous wave (CW) source. The radiofrequency oscillator 103 may furthermore be operated cyclically, in order to reduce an energy consumption. It is moreover also possible for the principle according to the invention to be applied to modulated (in particular pulse-or pulse-Doppler-radar or FSK-modulated) recording systems.

The recording principle of the device according to the invention will now be described with reference to Figs 5 and 6. An oscillator signal 104 generated by the oscillator 103 is split into a transmission signal 106 and a local oscillator signal 104. The reception signals are mixed with the local oscillator signal 104 in EQ mixers lila-hid.

The IQ mixers may, for example be implemented by a phase retardation of 90 in the supply of the local oscillator signal 104, i.e. by retardation units 105a, 105b. It is furthermore possible to provide the use of a 90 hybrid instrument. Although this is not illustrated in Fig. 5, the phase retardation may furthermore be introduced into the reception path (above the mixers lila-hid in Fig. 5). The mixers lila-hid themselves are designed as push-pull mixers in a preferred embodiment of the present invention, for example with the use of 90 or 1800 coupling instruments.

A particularly advantageous configuration is a single-diode mixer, since in this case a cost saving is obtained over the aforementioned mixing instruments. When a moving target object lies in the recording region of the transmission/ reception instrument, signal components at one or more Doppler frequencies occur on the mixer outputs. The signal components in the region of the oscillator frequency of the oscillator signal 104, generated by the oscillator 103, and the higher mixing products and harmonics occurring in the mixers lila-hid are suppressed at the mixing outputs by suitable RE' decoupling and filtering (see Fig. 6 below).

The baseband signals Sj, z2, s obtained are Lowpass filtered in filter units 202a-202d, which are designed as lowpass filters, after the corresponding signals have been amplified in respective (optional) amplifiers 201a-201d (Fig. 6).

A conversion of the analogue signal into digital signals is subsequently carried out in the converter units 203a-203d (AID) according to a sampling rate 204, which is fed to the respective converter units 203a-203d. The signal paths of the signals s and s respectively comprise an adaptation unit 205a and 205b. Subsequently, i.e. after such multiplication by (-j) in the adaptation units 205a, 205b, the signals output by the converter units 203a-203d are combined or added in respective combination units 206a, 206b. Here, the signals corresponding to the signals a,. and sc = are combined in the combination unit 206a, whereas the signals corresponding to the signals 3x2 and s are combined in the combination unit 206b.

As a consequence of the combination process, the combination units 206a and 206b respectively output first and second recording signals 207a or 207b for the further processing. The first and second recording signals 207a, 207b are fed to an evaluation instrument 500.

Occurrence of artefacts or aliasing" is avoided by the ].owpass filtering of the baseband signals. Signal frequencies of typical perturbation cases are furthermore optionally suppressed. The sampling rate 204 is provided as a constant time period At, and is determined by the highest occurring Doppler frequency and the characteristic of the baseband filter (anti-aliasing filter). The sampling rate At typically lies in a range of from 1 to 2.5 milliseconds (ma), which corresponds to a sampling frequency of from 400 to 1000 Hz. The resolution of the spectrum is obtained from this as:

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1/(NAt) (2a) The duration of a scan is dictated by the required frequency resolution, the following table showing typical resolutions in the range of from 1 to 3 Hz: t-2.5nis t-2ms t=lzns Duration Af-lHz N-400 N-500 N-1000 is Af2Hz N-200 N-250 14-500 0.5s AI3Hz 14-133 N-167 14=333 O.33s In order to be able to cover a range interval of typically from 0.5 to 25 m, the data must comprise a dynamic range in amplitude of (25/0.5)2 2500. The digitise1 I and Q signals sampled in this way correspond to complex time signals at the corresponding sampling times tj according to the following Equation (3): Sj(tj) = Si(tj) -j'S01(tj) (3) S2(tj) -S12(tj) -j'S(ta) The sign of the quadrature component is given by the phase relation of the I and Q signals. It changes when, for example, Q is defined as leading before I. Such complex time signals contain the full phase-frequency information, that is to say in particular the information about whether the Doppler frequency is positive or negative, i.e. whether the target object is moving towards the sensor or away from it.

Both the (at least two) recording signals coming from the at least two reception units lOla-lOib, i.e. the first recording signal 207a and the second recording signal 207b, are fed in a first exemplary embodiment of the present a invention directly to a selection instrument 400 which is arranged in the evaluation instrument 500. The selection instrument will be described in detail below.

The first and second recording signals 207a, 207b are furthermore fed to an angle determination instrument 300 arranged in the evaluation instrument 500. The angle determination instrument 300 in a first exemplary embodiment of the present invention comprises a beam shaping instrument 600, which makes it possible to form sum and difference signals 305a or 305b which were explained with reference to Fig. 3 from the first and second recording signals 207a, 207b. Such sum and difference signals 305a, 305b now provide the opportunity to record an angle of incidence of an electromagnetic wave * Beam shaping at a digital level in the time domain is advantageously carried out with the digitised complex time signals. A particularly simple embodiment is achieved by providing two reception units lOla, lOib, so that it is possible to carry out simmting and differencing of the two signals derived with reference to Equation (3) above.

It should be pointed out here that, although this is not explained in the present description, more than two reception units lOla, lOib may be provided so that more than two recording signals 207a, 207b can then be processed in the evaluation instrument 500. The sum and difference signals 305a or 305b resulting from the above equation are calculated as shown in Equation (4) below: Ss(tj) -si(tj) + 52(t,) (4) S,(tj) -Sj(tj) -52(tj) From the complex time signals of the beam lobes as obtained by Equation (4) above, a magnitude formation or a peak value detection or another form of rectification is now carried out, a time average furthermore being formed. One efficient method of averaging is the sliding average according to Equation (5) below.

m(tj) a*m(tj_1) + b(S(tj)j (5) moxr,(tj) -a*moxp,.(tj_i) + b ISDIpt(tj) I a + b -1 Such averaging carried out according to Equation (5) above entails only an extremely small memory requirement.

It is now possible to calculate two angle values from the average values m and The magnitude formation and averaging according to Equation (5) above is carried out in the angle determination instrument 300 of the evaluation instrument 500 by means of respective magnitude formation units 302a, 302b and respective averaging units 303a, 303b.

The sum signal 305a obtained and the difference signal 305b obtained are then fed to a calculation unit 304, from which it is directly possible to obtain the angle 8 which corresponds to an angle of incidence of the electromagnetic waves reflected by the target object (azimuth angle).

The ratio./m1 is now formed in order to calculate the azimuth angle, and an interpolation of the measured response curves i.e. the angle profile is performed over the ratio As an alternative, it is also possible to store the ratios m./m1 with associated angle values in a table, intermediate values being interpolated. It is therefore possible to determine the angle magnitude of the azimuth angle, but not the information about which side the angle lies Ofl (Cf. Fig. 3(a)), i.e. no conclusion is possible about whether the angle lies "right or left" of 0'.

An asyimnetry of the ratio m/in as a function of the azimuth angle of the target object may occur owing to the structures of the antennas, manufacturing toleranceB, phase and amplitude differences of the signal paths etc. For a ratio mam/mn, the angle determination instrument 300 then respectively delivers two possible azimuth angles with respectively different magnitudes, which lie on the right and left of a primary emission direction. The primary emission direction does not necessarily lie at 00, but is known for example from calibration measurements.

A "right" or "left" identification cannot be provided by the angle determination instrument 300. In order to provide such discrimination, the evaluation instrument 500 furthermore comprises a selection instrument 400 which operates in the frequency domain.

The advantage of the sliding time average carried out in the angle determination instrument 300, however, consists on the one hand in a low memory requirement and on the other hand in a flexible adjustment possibility for the averaging time. For example, the averaging time may be selected to be greater than typical sampling time periods for a Fourier transformation which will be explained below

with reference to the description of the selection

instrument 400. It is therefore possible to average out short-term perturbations and fairly fast effects, which permits an azimuth angle determination which is overall insensitive to perturbations. It is furthermore expedient that the output signal of the sliding average Ce) is provided continuously, in contrast for example to Fourier-transformed data which are only ever available at the end of a sampling time period.

This allows a high flexibility in the post-processing of the signals and the azimuth angle determined therefrom. A Fourier transformation over sliding sampling windows which respectively overlap has the substantial disadvantage that the memory requirement and computation time are increased.

When more than two beam lobes or more than two reception units lOla, lOib are used, the beam lobe with the greatest average signal value must be determined first, the neighbouring beam lobe with the next highest average signal value then being recorded. An angle determination is then similarly carried out between these two. Ambiguities again occur here as well, i.e. there are for example two angle values at which the signal amplitudes in the two beam lobes are equal. The identification of a correct angle is carried out in a similar way to a right-left discrimination for sum/difference beam lobes with the aid of the phase difference, as will be described below.

The selection instrument 400 which is contained in the evaluation instrument 500 respectively has successively connected windowing units 401a and 401b and transformation units 402a or 402b for each signal point, i.e. the signal path for a signal which comes from the reception unit lOla and the signal path for a signal which comes from the reception unit lOib, i.e. the first and second recording signals 20la and 207b. As will be described below, a right/ left determination R/L is then carried out in a discrimination unit 403 which is supplied with the signals transformed into the frequency domain output by corresponding transformation units 402a and 402.

Real objects generate not just a narrow Doppler frequency line, but a broad spectrum of Doppler frequency components (due for example to persons who have different motion rates of the torso, arms and legs when running). These different frequencies are again found in the "single-sideband" Doppler spectrum. The significant frequency lines are identified, for example, by a maximum search above a threshold. An angle determination according to the aforementioned Relation (2) is carried out for all frequency lines. When a plurality of objects with different velocities occur at different angular positions, it is possible to carry out the angle determination for all frequency components in the Doppler spectrum.

It is furthermore necessary to ensure that only the influences of an object motion are actually contained in a line (in a frequency "bin") of the Doppler spectra of the baseband signals, in order to avoid falsifying the angle determination. In particular, the angle determination via the phase difference according to Relation (2) above is sensitive to perturbation. For example, a running person can generate positive and negative Doppler frequencies simultaneously, for example when a person's body moves forward towards the microwave sensor while an arm swings back. The resolution 6f of the Fourier transformation must therefore be sufficiently good.

The present invention now resolves this problem by the aforementioned division of the evaluation instrument into an angle determination instrument 300 (described above) and a selection instrument 400, which must merely deliver a

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right/left discrimination. This offers substantial advantages, since the selection instrument 400 and therefore the evaluation instrument 500 as a whole can be siinpli fied.

The transformations from the time domain to the frequency domain to be carried out in the transformation units 402a and 402b, Fourier transformations in the preferred exemplary embodiment, can therefore be constructed very simply so that the arithmetic functions of the Fourier transformation can be produced on lower-cost microcoritroflers. This expediently leads to a 8inlplification and cost reduction of the entire evaluation instrument of the recording device according to the invention. By the windowing units 401a, 401b which precede the transformation units 402a and 402b, for instance, it is possible to image a comparatively short excerpt of the digitised complex time signals. A rectangular window is used in the simplest case, i.e. a temporal excerpt of the signal is simply selected. Other windowing functions may furthermore advantageously be used in order to suppress the subsidiary maxima in the spectrum (in the Doppler frequency spectrum), for example Hanining, Hanning, Kaiser, Techebycheff windows, etc. The sections generated in this way are subsequently Fourier-transformed in the transformation units 402a, 402b.

The temporal excerpt which is provided by the upstream windowing units 401a, 401b is in this case so short that, for example, two complex time signals can be processed in a cost-effective microcontroller. A typical order of magnitude is N -2 to 64 sample values. Resolution of all Doppler components is therefore no longer possible, because the frequency resolution f (see Equation (2a) above) is selected to be so coarse that Doppler components of several parts of the target object generally lie within a frequency line of width AZ. Expediently, according to the method according to the invention, a more detailed resolution of the Doppler components in the frequency spectrum is now no longer actually necessary, because the angle determination can be carried out in a separate angle determination instrument 300.

A frequency line in the output signals of the first and second reception units lOla, lOib, which is representative of the target object, is determined. To this end, for example, the line with the greatest amplitude may be selected or, for example, the same frequency line representative of moving objects is always selected.

A right/left discrimination is carried out with the aid of the phase difference between this frequency line in the spectra of the signals of the antenna elements. Only the sign of the phase difference needs to be determined in this case, and this sign can be determined reliably enough even with a coarse frequency resolution AZ (Relation (2a) above).

When there are more than two beam lobes, discrimination can be carried out between primary and secondary lobes with the aid of the phase difference. Furthermore, it is also possible to derive a comparatively rough angle estimate from the phase difference, for example according to Equation (2) above. This may be employed for a consistency check with respect to a match between the signals output by the angle determination instrument 300 and the selection instrument 400.

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Fig. 7 describes a further exemplary embodiment according to the present invention. Components which are the same as in Fig. 6 are denoted by identical references, and will not be explained again here in order to avoid an overlapping description. In contrast to the circuit arrangement shown in Fig. 6, the beam shaping instrument 600 is no longer designed as a component of the angle determination instrument 300, but, as an individually identifiable unit, separately precedes both the angle determination instrument 300 and the selection instrument 400. The effect of this is that beam-shaped signals, i.e. the sum and difference signals 305a and 305b, are fed to the selection instrument.

This provides the advantage that a phase difference of 180 is already formed between positive and negative angles in a narrow angle range around 0 . This phase difference can be detected extremely reliably and accurately, as explained above with reference to Fig. 3(b).

In the arrangements shown in Figs 6 and 7, an angle determination is respectively carried out in the time domain in a separate angle determination instrument 300, whereas a right/left determination is carried out in the frequency domain in a separate selection instrument 400.

With respect to the conventional recording device for recording an angle of incidence of an electromagnetic wave as represented in Fig. 1, reference is made to the

introduction of the description.

Claims

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Claims 1. Recording device for recording an angle of incidence of an electromagnetic wave, having: a) a transmission unit (102) for emitting an electromagnetic wave in a primary emission direction towards a target object; b) at least two reception units (lOla, lOib) for receiving the electromagnetic wave reflected by the target object and for converting the received electromagnetic wave into at least one intermediate frequency signal (112a, 112b): C) a converter instrument (200) for converting the at least one intermediate frequency signal (112a, 112b) into at least a first and a second recording signal (207a, 20Th); and d) an evaluation instrument (500) for evaluating the first and second recording signals (207a, 207b) so as to obtain the angle of incidence of the electromagnetic wave with respect to the primary emission direction of the transmission unit (102) and therefore an angular position of the target object with respect to the primary emission direction of the transmission unit (102); characterised in that the evaluation device (500) comprises e) an angle determination instrument (300) for determining possible angles of incidence of the electromagnetic wave with respect to the primary emission direction of the transmission unit (102) by means of the first and second recording signals (207a, 207b); and f) a selection instrument (400) for selecting a correct one of the possible angles of incidence of the electromagnetic wave with respect to the primary emission direction of the

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transmission unit (102) by means of the first and second recording signals (207a, 207b).

2. Device according to Claim 1, characterised in that the angle determination instrument (300) comprises a beam shaping instrument (600) for forming sum signals (305a) and difference signals (305b) as beam-shaped signals from the first and second recording signals (207a, 20Th).

3. Device according to Claim 1, characterised in that a beam shaping instrument (600) for forming sum signals (305a) and difference signals (305b) as beam-shaped signals from the first and second recording signals (207a, 207b) is provided in the evaluation instrument (500) so that the beam-shaped signals (305a, 305b) can be fed both to the angle determination instrument (300) and to the selection instrument (400).

4. Device according to Claim 1, characterised in that the transmission unit (102) for emitting the electromagnetic wave in the primary emission direction and the at least two reception units (lOla, lOib) for receiving the electromagnetic wave reflected by the target object and for converting the received electromagnetic wave into at least one intermediate frequency signal (112a, 112b) are designed for continuous wave operation (CW).

5. Device according to Claim 1, characterised in that the transmission unit (102) for emitting the electromagnetic wave in the primary emission direction and the at least two reception units (lOla, lOib) for receiving the electromagnetic wave reflected by the target object and for converting the received electromagnetic wave into at least one intermediate frequency signal (112a, 112b) are designed for pulsed operation or modulated operation.

6. Device according to Claim 1, characterised in that the recording device for recording an angle of incidence of the electromagnetic wave comprises: a) at least two transmission units (102) for emitting at least two electromagnetic waves in a common primary emission direction; and b) a reception unit (lOla) for receiving the electromagnetic waves reflected by the target object and for converting the received electromagnetic waves into at least one intermediate frequency signal (112a, 112b).

7. Device according to Claim 1, characterised in that the recording device for recording an angle of incidence of the electromagnetic wave comprises at least two transmission units (102) for emitting at least two electromagnetic waves in a common primary emission direction and at least two reception units (lOla, lOib) for receiving the electromagnetic waves reflected by the target object and for converting the received electromagnetic waves into at least one intermediate frequency signal (112a, 112b).

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8. Method for recording an angle of incidence of an electromagnetic wave, having the following steps: a) emitting an electromagnetic wave in a primary emission direction towards a target object by means of a transmission unit (102); b) receiving the electromagnetic wave reflected by the target object by means of at least two reception units (lOla, lOib); C) converting the received electromagnetic wave into at least one intermediate frequency signal (112a, 112b) by means of the at least two reception units (lOla, lOib); d) converting the at least one intermediate frequency signal (112a, 112b) into at least a first and a second recording signal (207a, 207b) by means of a converter instrument (200); and e) by means of an evaluation instrument (500), evaluating the first and second recording signals (207a, 207b) so as to obtain the angle of incidence of the electromagnetic wave with respect to the primary emission direction of the transmission unit (102) and therefore an angular position of the target object with respect to the primary emission direction of the transmission unit (102); characterised in that the evaluation step e) comprises the following substeps:

ci) determining possible angles of incidence of the electromagnetic wave with respect to the primary emission direction of the transmission unit (102) from the first and second recording signals (207a, 20Th) by means of an angle determination instrument (300); and e2) selecting a correct one of the possible angles of incidence of the electromagnetic wave with respect to the primary emission direction of the transmission unit (102)

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from the first and second recording signals (207a, 207b) by means of a selection instrument (400).

9. Method according to Claim 8, characterised by the following further steps: a) forming sum signals (305a) and difference signals (305b) from the first and second recording signals (207a, 207b) by means of a beam shaping instrument (600) provided in the evaluation instrument (500), in order to obtain beam-shaped signals; and b) feeding the beam-shaped signals (305a, 305b) both to the angle determination instrument (300) and to the selection instrument (400).

10. Method according to Claim 8, characterised in that a determination of possible angular positions of the target object with respect to the primary emission direction of the transmission unit (102) from the first and second recording signals (207a, 207b) is carried out by means of the angle determination device (300) in the time domain.

11. Method according to Claim 8, characterised in that a selection of a correct one of the possible angular positions of the target object with respect to the primary emission direction of the transmission unit (102) from the first and second recording signals (207a, 207b) is carried out by means of the selection device (400) in the frequency domain.

12. Method according to Claim 9, characterised in that a maximum value of a magnitude of the beam-shaped sum signal (305a) is employed for establishing the primary emission direction.

13. Method according to Claim 9, characterised in that a minimum value of the magnitude of the beam-shaped difference signal (305b) is employed for establishing the primary emission direction.

14. Method according to Claim 9, characterised in that a phase change of the beam-shaped difference signal (305b) is employed for establishing the primary emission direction.

15. Method according to Claim 14, characterised in that the phase change of the beam-shaped difference signal (305b) for establishing the primary emission direction is 180 degrees.

16. Method according to Claim 9, characterised in that a correct one of the possible angular positions of the target object with respect to the primary emission direction of the transmission unit (102) is selected in the selection instrument (400) on the basis of the beam-shaped signals (305a, 305b).

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17. Method according to Claim 10, characterised in that a determination of possible angular positions of the target object with respect to the primary emission direction of the transmission unit (102) from the first and second recording signals (207a, 207b) by means of the angle determination instrument (300) involves a rectification or peak value detection.

18. Method according to Claim 17, characterised in that a determination of possible angular positions of the target object with respect to the primary emission direction of the transmission unit (102) from the first and second recording signals (207a, 207b) by means of the angle determination instrument (300) involves a sliding average, in which an average value determined in a chronologically preceding recording cycle and one or more signal values recorded chronologically afterwards are added together by using individual weighting factors.

19. Recording device substantially as hereinbefore described with reference to the accompanying drawings.

20. Method substantially as hereinbefore described with reference to the accompanying drawings.