GB2553542A - Method and apparatus for receiving a continuous radar wave - Google Patents

Abstract

A method of processing a received radar return comprising at least a first spectral component in a first sub-bandwidth and a second spectral component in a second sub-bandwidth, the method comprising steps of: filtering the received signal by separately filtering out the first sub-bandwidth and the second sub-bandwidth so as to respectively obtain a first signal related to the first spectral component and a second signal related to the second spectral component; obtaining separately, from the first signal and the second signal, a first beat frequency signal and a second beat frequency signal respectively; and mixing the first beat frequency signal and the second beat frequency signal so as to obtain a mixed signal. Before filtering the received signal the received signal may be mixed with a carrier signal to remove the carrier signal from the received signal. The signal processing method overcomes the problem of increased resolution due to reduced bandwidths when the frequency modulation is split into sub-bands.

Description

(54) Title of the Invention: Method and apparatus for receiving a continuous radar wave

Abstract Title: Processing sub-bandwidths of FMCW radar returns by mixing beat frequencies to maintain resolution.

(57) A method of processing a received radar return comprising at least a first spectral component in a first sub-bandwidth and a second spectral component in a second sub-bandwidth, the method comprising steps of: filtering the received signal by separately filtering out the first sub-bandwidth and the second sub-bandwidth so as to respectively obtain a first signal related to the first spectral component and a second signal related to the second spectral component; obtaining separately, from the first signal and the second signal, a first beat frequency signal and a second beat frequency signal respectively; and mixing the first beat frequency signal and the second beat frequency signal so as to obtain a mixed signal. Before filtering the received signal the received signal may be mixed with a carrier signal to remove the carrier signal from the received signal. The signal processing method overcomes the problem of increased resolution due to reduced bandwidths when the frequency modulation is split into sub-bands.

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METHOD AND APPARATUS FOR RECEIVING A CONTINUOUS RADAR WAVE

FIELD OF THE INVENTION

The invention relates to the field of continuous wave radars, in particular the reception of a signal comprising at least a first spectral component in a first subbandwidth and a second spectral component in a second sub-bandwidth.

BACKGROUND OF THE INVENTION

Radar technologies may be classified based on their mode of operation. A pulse radar apparatus emits pulses with a typical duration in the lower microsecond ps range and receives a reflected echo off an object. In this case, the propagation time of the pulse is used to determine the distance to the object.

A frequency modulated continuous wave (FMCW) radar apparatus emits continuous signals, and may be used to measure the speed of a moving objet or the distance to an object, moving or stationary.

A frequency modulated continuous waveform (FMCW) scheme may be used to transmit a signal, the frequency of which is modulated or “swept” across a frequency bandwidth. An FMCW signal is defined as a continuous signal that has a frequency varying up and/or down over a fixed period of time, the frequency variation being determined by a modulating signal.

With respect to pulse radar apparatuses, those that employ FMCW are more cost-effective since the detection mechanisms use a beat frequency (e.g., the frequency difference between the transmitted and the reflected signal), rather than the frequency of the transmitted signal.

A Stepped Frequency Continuous Wave (SFCW) radar is a particular case of FMCW radar wherein the frequency of the transmitted signal is changed in discrete steps, using a sequence of non-modulated frequencies.

Range resolution is defined as the ability of a radar apparatus to distinguish between two or more targets on the same bearing but at different ranges - the lower the range resolution, the better the performance of the radar. The range resolution estimated by the radar depends directly on the size of the bandwidth BW of the transmitted signal; thus larger bandwidths BW provide improved range resolution but require more time to perform frequency sweeps across the band. In addition, it is difficult to generate linear sweeps (i.e., regular frequency evolutions over time) across a large bandwidth BW of frequencies.

Figures 1A, 1B are graphs of transmitted and reflected sweep signals. An upsweep signal US is defined as a frequency sweep FS with an instantaneous frequency increasing from a minimum frequency Fmin to a maximum frequency Fmax (thus Fmax > Fmin) during a sweep duration TS. In contrast, a downsweep signal DS is defined as a frequency sweep FS with an instantaneous frequency decreasing from the maximum frequency Fmax to the minimum frequency Fmin during the sweep duration TS.

Figure 1A shows a transmitted upsweep signal TUS of increasing frequency sweep FS over a bandwidth BW for a sweep duration TS. Figure 1B shows a transmitted downsweep signal TDS of decreasing frequency sweep FS over a bandwidth BW for a sweep duration TS. Each bandwidth BW of frequencies extends from the minimum frequency Fmin to the maximum frequency Fmax.

Respective reflected signals RUS, RDS (upsweep or downsweep signals) are reflected back by a target, such as a moving or stationary object, and are received by the apparatus after a delay related to the distance between the apparatus and the target. A beat frequency FB corresponds to the difference, at a given time, between the frequency of the transmitted signal TS and the reflected signal RS; in order to digitally process this signal, an analog to digital ADC converter samples the signal with a sampling frequency of at least double the beat frequency FB.

As previously stated, when considering the specifications of radar systems, in particular those dedicated to range measurement, one important specification is range resolution. For radar systems based on FMCW waves with a single upsweep or downsweep as shown in Figures 1A, 1B, the obtained range resolution RES is given by the following equation:

RES = c/(2*BW) [equation 1] wherein c is the speed of light (3x10^Λ8 m/s) and BW is the bandwidth of the signal used for the range resolution.

Figures 2A, 2B, 2C are graphs of transmitted and reflected sweep signals, each signal characterized by a plurality of contiguous frequency upsweep signals with respect to time T. In these examples, only two contiguous frequency upsweep signals are shown, but the number may be higher.

The use of a plurality of contiguous frequency sweep signals, with respect to a single frequency sweep as shown in Figures 1A, 1B, allows the same bandwidth BW to be covered by a reduced sweep duration TS/2, an increased bandwidth 2*BW to be covered by the same sweep duration TS, or the same bandwidth BW to be covered by the same sweep duration TS but with a reduced beat frequency FB (that is to say, a reduced slope of the “frequency F vs. time T” curve). It may be noted that two or more of these above effects may be obtained by using more than two contiguous frequency sweep signals, for example by using four signals to cover the increased bandwidth 2*BW at the reduced sweep duration TS/2.

In the example of Figure 2A, the same bandwidth BW is divided into two subbandwidths SB1, SB2 (or “sub-bands”) of frequencies and swept by frequency sweeps FS over a reduced sweep duration TS/2. The sub-band SB1 extends from the minimum frequency Fmin to a frequency Fm (here a mid-point frequency between Fmin and Fmax), and the sub-band SB2 extends from the frequency Fm to the maximum frequency Fmax. A first transmitted spectral component TSC1 (here an upsweep, but could be a downsweep indifferently) is generated and transmitted in the sub-band SB1, and a second transmitted spectral component TSC2 (also an upsweep) is generated and transmitted in the sub-band SB2. First and second reflected spectral components RSC1, RSC2 (also upsweeps) are received and processed in the respective sub-bands SB1, SB2. Again, it may be noted that upsweeps are shown here, but could equally be downsweeps, or an alteration of upsweeps and downsweeps.

In the example of Figure 2B, the bandwidth is increased by two times 2*BW, is divided into two sub-bands SB1 and SB2, and is swept by frequency sweeps FS over the same sweep duration TS. The sub-band SB1 extends from the minimum frequency Fmin to a new frequency Fm’ (the maximum frequency Fmax of Figure 1A), and the sub-band SB2 extends from the new frequency Fm’ to a new maximum frequency Fmax’ (Fmax’ being two times the maximum frequency Fmax of Figure 1A). Corresponding transmitted spectral components TSC3, TSC4 are performed simultaneously (with reflected spectral components RSC3, RSC4), without overlap or gap in frequencies, thus allowing an increased bandwidth 2*BW to be swept over a same sweep duration TS.

In the example of Figure 2C, the same bandwidth BW is here divided into two sub-bands SB1 and SB2, and swept by frequency sweeps FS over a same sweep duration TS. The sub-bandwidth SB1 extends from the minimum frequency Fmin to a frequency Fm (here a mid-point frequency between Fmin and Fmax), and the sub-band SB2 extends from the frequency Fm to the maximum frequency Fmax. Corresponding transmitted spectral components TSC5, TSC6 are performed simultaneously (with reflected spectral components RSC5, RSC6), without overlap or gap in frequencies, thus allowing a same bandwidth BW to be swept over the same sweep duration TS. However, as the slope of the lines frequency F versus time T is decreased (due to the plurality of sweeps), the beat frequency FB is also decreased.

It may be noted that though only two spectral components TSC1, TSC2; TSC3, TSC4; TSC5, TSC6 are shown in Figures 2A, 2B, 2C, there may be a greater number of spectral components (upsweeps or downsweeps), such as 3, 4, or more simultaneously generated and transmitted (and thus reflected, received, and processed), depending on the configuration of the apparatus, as will be described below. In this case, the frequency Fm is not necessarily at the mid-point between the frequencies Fmin, Fmax, but may be for example at every third, every fourth, etc. of the total frequency (bandwidth) range.

Figure 3 represents a conventional continuous wave radar apparatus 100 capable of generating, transmitting, receiving, and processing a signal composed of a plurality Μ (M > 2) of simultaneous spectral components, such as shown in Figure 2, based on the apparatus disclosed by van Genderen et al. in the article “A multi frequency radar for detecting landmines: design aspects and electrical performance”.

The apparatus 100 comprises a transmitter 110 and a receiver 130. The transmitter 110 comprises a Base Signal Generator BSG 111, a plurality of frequency sweep generating lines 112-m (m being the index from 1 to M of the line, here only two lines are shown 112-1 and 112-2) one for each sub-bandwidth (related to SB1, SB2 of the Figures 2) of frequencies to be swept, a carrier frequency local oscillator 113, an adder ADD 114, an amplifier 115, and an antenna 116. Each frequency sweep line 112-m comprises a local oscillator 121, a first mixer 122, a filter 123, and a second mixer 124.

The generator 111 is configured to generate a continuous wave signal (e.g., FM-CW) S1 with a frequency Fsw. The generator 111 may be a Voltage Controlled Oscillator (VCO) or a Direct Digital Synthesizer (DDS).

The local oscillator 121 of a line 112-m is configured to generate a signal S2m at a determined base frequency Fbase that will be used by the first mixer 122 to transpose the continuous wave signal S1 with frequency Fsw from the generator 111 to an intermediate frequency signal S3 corresponding to a sub-bandwidth of frequencies of the whole bandwidth BW of frequencies. For example, with reference to Figure 2A, the oscillator OS1 of line 112-1 generates a signal S2-1 with a base frequency Fbase equal to Fmin, and the oscillator OS2 of line 112-2 generates a signal S2-2 with a base frequency Fbase equal to Fm (the mid-point frequency in the case of two sub-bands). The first mixer 122 combines the signal S2 (S2-1 or S2-2) at the base frequency Fbase (Fmin or Fm, depending on the generating line) and the continuous wave signal S1 at frequency Fsw, generating an intermediate signal S3 comprising, at each time, a first spectral component corresponding to the sum (Fbase + Fsw) of the spectral component of the continuous wave signal S1 and the spectral component of the base frequency signal S2, and a second spectral component corresponding to the difference (Fbase - Fsw) between the spectral component of the continuous wave signal S1 and the spectral component of the base frequency signal S2, the sum and the difference also known as the image frequencies.

The filter 123 filters out one spectral component (the sum or the difference) from the intermediate frequency signal S3, that is to say, either the upper sub-band SB2 (Fbase + Fsw) or the lower sub-band SB1 (Fbase - Fsw), supplying a filtered intermediate frequency signal S4 comprising the retained spectral component.

The carrier signal CS local oscillator 113 generates a carrier signal S5 with a carrier frequency FC to be used as carrier for the radio transmission of a transmitted signal TS. The second mixer 124 of each line 112-m receives on input the filtered intermediate frequency signal S4 (Fbase + Fsw or Fbase - Fsw) and the carrier signal S5, and transposes the filtered intermediate frequency signal S4 at the carrier frequency FC to be used for the transmission, suppling a signal S6 on output.

The output signals S6 (from each line 112-m) are filtered and summed by the adder 114, which supplies on output a summed signal S7 comprising the transposition of the simultaneous frequency sweep signals in each sub-band SB1, SB2, covering the desired range of frequencies and thus the entire bandwidth BW.

The signal S7 from the adder 114 is then amplified by the amplifier 115 and supplied to the antenna 116 for transmission as the transmitted signal TS.

The receiver 130 comprises an antenna 131, a Low Noise Amplifier 132, a mixer 133, and a plurality M of frequency sweep detecting lines 134-m (m being the same index from 1 to M as of the frequency sweep generating lines 122-m, here detecting lines 134-1 and 134-2) one associated with each sub-bandwidth (related to

SB1, SB2 of the Figures 2) swept by the transmitter, each frequency sweep detecting line 134-m comprising a first filter 141, a first mixer 142, a second filter 143, a second mixer 144, and an analog to digital converter (ADC) 145.

The antenna 131 receives a reflected signal RS, which is amplified by the amplifier 132 before being supplied as a signal S11 on input to the mixer 133, which also receives on input the carrier signal S5 supplied by the carrier signal CS local oscillator 113 of the transmitter 110. The mixer 133 extracts a plurality of spectral components associated with a plurality of sub-bandwidths (related to SB1, SB2...) from the reflected signal RS, with respect to the carrier frequency FC of the carrier signal S5, which are supplied as a signal S12 to each frequency sweep detecting line 134-m.

The first filter 141 of each line 134-m removes an unwanted frequency image (or “unwanted spectral component”) generated by the mixer 133 and extracts the subbandwidth (related to SB1, SB2....) of interest for the line as a signal S13. For each detecting line, the resulting signal is then supplied on input to the first mixer 142, which also receives on input the signal S2 (S2-1 or S2-2) with the base frequency Fbase supplied by the corresponding local oscillator 121 of the transmitter 110. The first mixer 142 extracts the signal S2 (S2-1 or S2-2) from the sub-bandwidth of the reflected signal S13, and supplies an extracted baseband signal S14. The extracted signal S14 is then filtered by the second filter 143, which removes the spectral components related to the sum of the frequencies of input signals. The filtered extracted signal is supplied as a signal S15 to the second mixer 144, which also receives on input the continuous wave signal S1 supplied by the sweep source 111 of the transmitter 110.

The second mixer 144 performs a multiplication of the filtered extracted signal S15 with the frequency sweep signal S1, and supplies an extracted beat frequency FB signal S16 for the concerned sub-bandwidth and a beat frequency image which is removed by a filter (not shown here). The beat frequency signal S16 is then supplied to the ADC converter 145 for conversion to digital form for digital signal processing (not shown in Figure 3), and is supplied on output as a signal S17. A processor is configured to convert the signal in the frequency domain using a Fast Fourier Transform (FFT) or a Discrete Fourier Transform (DFT) and to determine frequencies with the highest magnitudes. The range of the target may then be determined as described above in relation with equation 1.

Classical signal processing performed on the output signals S17 provides range resolution for FMCW radars as given by the equation 1 above. The receiver 130 provides two range estimations based on the computation of the two reflected signals

S13 having spectral components comprised in the sub-bands SB1 and SB2, each subbandwidth having a bandwidth of BW/2 (in the case the number of generating lines M being greater than two, then each sub-band would have a bandwidth of BW/M). Although the transmitted signal TS, which is a combination of two frequency sweeps, sweeps the entire bandwidth BW, the range resolution of each output signal S17 is equal to c/BW.

Though the use of a plurality of upsweep of downsweep signals as shown in Figures 2A, 2B, 2C has certain advantages (decreased sweep duration, increased bandwidth, or decreased beat frequency), it also has the disadvantage of decreasing the range resolution.

It may therefore be desired to improve the range resolution for a plurality of transmitted and received signals.

SUMMARY OF THE INVENTION

The present invention has been devised to provide improved range resolution for a radar apparatus comprising a plurality of transmitted and received signals.

Embodiments of the invention relate to a method of receiving, by a radar apparatus, a signal comprising at least a first spectral component in a first subbandwidth and a second spectral component in a second sub-bandwidth, the method comprising the steps of:

- filtering the received signal by separately filtering out the first sub-bandwidth and the second sub-bandwidth so as to respectively obtain a first signal related to the first spectral component and a second signal related to the second spectral component;

- obtaining separately, from the first signal and the second signal, a first beat frequency signal and a second beat frequency signal respectively; and

- mixing the first beat frequency signal and the second beat frequency signal so as to obtain a mixed signal.

According to one embodiment, the method further comprises, before filtering the received signal, a step of mixing the received signal with a carrier signal so as to obtain a signal wherein the carrier signal has been removed.

According to one embodiment, the method further comprises, after the step of filtering the received signal, the steps of:

- mixing separately each of the first signal and the second signal with a first base frequency and a second base frequency respectively so as to extract a first base frequency signal from the first signal and a second base frequency signal from the second signal respectively;

- filtering separately the first base frequency signal and the second base frequency signal so as to remove unwanted spectral components; and

- mixing separately the filtered first base frequency signal and the filtered second base frequency signal with a continuous wave signal so as to obtain the first beat frequency signal and the second beat frequency signal respectively.

According to one embodiment, the method further comprises, after the step of filtering the mixed signal, the steps of:

- mixing separately each of the first signal and the second signal with a third signal characterized by an instantaneous frequency composed of the first spectral component and the second spectral component, the spectral components evolving over time within the sub-bandwidths and symmetrical with respect to a central frequency, wherein one spectral component is generated based on an image frequency related to the other spectral component, so as to obtain the first beat frequency signal and the second beat frequency signal, wherein the third signal is a function of the received signal; and

- filtering separately each of the first beat frequency signal and the second beat frequency signal so as to remove an unwanted image signal.

According to one embodiment, the method further comprises a step of separately converting the first beat frequency signal and the second beat frequency signal from analog to digital form before mixing the first beat frequency signal and the second beat frequency signal together.

According to one embodiment, the method further comprises a step of converting the first beat frequency signal and the second beat frequency signal are converted from analog to digital form after mixing the first beat frequency signal and the second beat frequency signal together.

According to one embodiment, the received signal comprises a plurality N of spectral components in a plurality N of sub-bandwidths, so that a plurality N of beat frequency signals are obtained, wherein N is greater than two, and the method further comprises a step of mixing the beat frequency signals together in a plurality of N-1 mixing steps.

According to one embodiment, the plurality N is an even number greater than 2.

According to one embodiment, the method further comprises a step of amplifying the received signal before mixing the received signal with the carrier signal.

According to one embodiment, the method further comprises a step of selecting at least one of the beat frequency signals or the mixed signal for processing.

According to one embodiment, the method further comprises a step of determining a range value corresponding to the distance between a target and the radar apparatus, and wherein the step of selecting the selected signal for processing is based on the determined range value.

According to one embodiment, the method further comprises the steps of:

- determining a signal resolution for the mixed signal and one of the first or second beat frequency signals;

- determining a resolution to apply, based on the determined range value;

- comparing the resolution to apply with each of the signal resolutions; and

- selecting one of the signals for processing.

According to one embodiment, the method further comprises the steps of:

- adding the mixed signal with one of the first or second beat frequency signals so as to obtain an added signal;

- converting the added signal to a digital form by means of an analog to digital converter; and

- filtering the converted signal based on a determined range value.

Embodiments of the invention also relate to a radar receiver apparatus configured to receive a signal comprising at least a first spectral component in a first sub-bandwidth and a second spectral component in a second sub-bandwidth, the receiver apparatus comprising:

- a filter configured to filter the received signal by separately filtering out the first sub-bandwidth and the second sub-bandwidth so as to respectively obtain a first signal related to the function of the first spectral component and a second signal related to the function of the second spectral component;

- circuitry for obtaining, from the first signal and the second signal, a first beat frequency signal and a second beat frequency signal respectively; and

- a mixer to mix the first beat frequency signal and the second beat frequency signal so as to obtain a mixed signal.

According to one embodiment, the receiver apparatus further comprises an antenna configured to receive the signal and a mixer arranged between the antenna and the filter, the mixer being configured to mix the received signal with a carrier signal so as to obtain a signal wherein the carrier signal has been removed.

According to one embodiment, the receiver apparatus further comprises, further comprising, after the filter:

- a mixer configured to mix separately each of the first signal and the second signal with a first base frequency and a second base frequency respectively so as to extract a first base frequency signal from the first signal and a second base frequency signal from the second signal respectively;

- a filter configured to filter separately the first base frequency signal and the second base frequency signal so as to remove unwanted spectral components; and

- a mixer configured to mix separately the filtered first and second base frequency signals with a continuous wave signal so as to obtain the first beat frequency signal and the second beat frequency signal respectively.

According to one embodiment, the receiver apparatus further comprises, after the filter:

- a mixer configured to mix separately each of the first signal and the second signal with a third signal characterized by an instantaneous frequency composed the first spectral component and the second spectral component, the spectral components evolving over time with the sub-bandwidths and symmetrical with respect to a central frequency, wherein one spectral component is generated based on an image frequency related to the other spectral component, so as to obtain the first beat frequency signal and the second beat frequency signal, wherein the third signal is a function of the received signal; and

- a filter configured to filter separately each of the first beat frequency signal and the second beat frequency signal so as to remove an unwanted image signal.

According to one embodiment, the receiver apparatus further comprises an analog to digital converter configured to convert separately from analog to digital form each of the first beat frequency signal and the second beat frequency signal before they are supplied to the mixer.

According to one embodiment, the receiver apparatus further comprises an analog to digital converter configured to convert from analog to digital form the first beat frequency signal and second beat frequency signal after they have been mixed together by the mixer.

According to one embodiment, the receiver apparatus is configured to process a received signal comprising a plurality N of spectral components in a plurality N of frequency sub-bands, so that a plurality N of beat frequency signals are obtained, wherein N is greater than two, and wherein a plurality of N-1 mixers are supplied to mix together the beat frequency signals.

According to one embodiment, the plurality N is an even number greater than 2.

According to one embodiment, the receiver apparatus further comprises an amplifier configured to amplify the received signal before it is supplied to mixer that mixes the received signal with the carrier signal.

According to one embodiment, the receiver apparatus further comprises a means for selecting at least one of the beat frequency signals or the mixed signal for processing.

According to one embodiment, the receiver apparatus further comprises a processor configured to determine a range value corresponding to the distance between a target and the radar apparatus, and wherein the step of selecting the selected signal for processing is based on the determined range value.

According to one embodiment, the processor is further configured to:

- determine a signal resolution for the mixed signal and one of the first or second beat frequency signals;

- determine a resolution to apply, based on the determined range value;

- compare the resolution to apply with each of the signal resolutions; and

- select one of the signals for processing.

According to one embodiment, the receiver apparatus further comprises:

- an adder to add the mixed signal with one of the first or second beat frequency signals so as to obtain an added signal;

- an analog to digital converter configured to convert the added signal to a digital form; and

- a filter to filter the converted signal based on a determined range value.

Embodiments of the invention also relate to a radar apparatus substantially as hereinbefore described with reference to, and as shown in Figures 4, 5, 6, 8, and 10.

BRIEF DESCRIPTION OF THE DRAWINGS

Other particularities and advantages of the invention will also emerge from the following description, illustrated by the accompanying drawings, in which:

Figures 1 (1A, 1B), previously described, are graphs of the spectra of transmitted and reflected FMCW signals with respect to time,

Figures 2 (2A, 2B, 2C), previously described, are graphs of the spectra of FMCW signals composed of a plurality of contiguous frequency upsweep signals according to various implementations,

Figure 3, previously described, shows a conventional continuous wave radar apparatus capable of generating and processing a plurality of simultaneous frequency sweep signals, such as those shown in the Figures 2,

Figure 4 shows a continuous wave radar apparatus with a receiver according to one embodiment of the invention,

Figure 5 shows a continuous wave radar apparatus with a receiver according to another embodiment of the invention,

Figure 6 shows a continuous wave radar apparatus with a transmitter and a receiver according to an embodiment of the invention,

Figures 7 (7A, 7B, 7C) show the spectra of transmitted and received signals, transmitted and received by an apparatus according to Figure 6,

Figure 8 shows a continuous wave radar apparatus with a transmitter and a receiver according to yet another embodiment of the invention,

Figures 9 (9A, 9B, 9C) respectively show the range, the resolution, and the bandwidth with respect to time from the radar apparatus to a target,

Figure 10 shows the receiver portion of a continuous wave radar apparatus according to another embodiment of the invention,

Figure 11 is a flowchart of a method of selecting the appropriate mode of operation according to one embodiment, and

Figure 12 is a flowchart of a method of selecting the appropriate mode of operation according to another embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Embodiments of the invention relate to a continuous wave radar apparatus with improved range resolution with respect to known apparatuses, obtained by mixing the signals on output of the detecting lines of the receiver. Implementations of the invention also allow receiving and processing a signal that can be performed over an increased bandwidth, in a shorter amount of time, and/or with reduced sampling frequencies, as desired while providing a range resolution corresponding to the total bandwidth swept.

The following equations 2A, 3A, 4A relate to the context illustrated by Figure 2A, where a transmitter transmits a signal comprising, at each time, two spectral components (from a continuous wave signal S1 having a bandwidth BW/2), offering a reduced sweep duration TS/2 (with respect to the conventional sweep duration TS).

With reference again to the receiver 130 of Figure 3, two range estimations are provided based on computations of the two signals output by the mixers 144. As each sub-bandwidth SB1, SB2 has a bandwidth of BW/2, the range resolution of each signal output by the mixers 144 is equal to:

RES = c/[2*(BW/2)] = c/BW [equation 2A]

The proposed invention enables the expected range resolution (of equation 1) to be recovered, that is to say that which is expected when sweeping a bandwidth BW, by the mixing of the signals, thus:

RES = c/[2*(BW/2)] [from the first line] MIX c/[2*(BW/2)] [from the second linej], [equation 3A] wherein MIX is the mixing operator, providing:

RES = c/(2*BW) [equation 4A]

The following equations 2B, 3B, 4B relate to the context illustrated by Figure 2B, where a transmitter transmits a signal comprising, at each time, two spectral components (from a continuous wave signal S1 having a bandwidth BW), offering an increased bandwidth swept 2*BW (with respect to the conventional bandwidth BW).

Wth reference again to the receiver 130 of Figure 3, two range estimations are provided based on computations of the two signals output by the mixers 144. As each sub-bandwidth SB1, SB2 has a bandwidth of BW, the range resolution of each signal output by the mixers 144 is equal to:

RES = c/(2*BW) [equation 2B]

The proposed invention enables the expected range resolution (of equation 1) to be recovered, that is to say that which is expected when sweeping a bandwidth 2*BW, by the mixing of the signals, thus:

RES = [c/(2*BW) [from the first line] MIX c/2*(BW) [from the second linej] [equation 3B] wherein MIX is the mixing operator, providing:

RES = c/[2*(2*BW)j [equation 4B]

As a reminder, a lower range resolution is preferable, thus the value in the denominator should be as high as possible. Conventional FMCW radar apparatus perform continuous frequency sweeps FS (up-sweeps US or down-sweeps DS) across their entire bandwidth BW during a certain time TS, as shown in Figures 1A, 1B. The signals related to these frequency sweeps FS are transmitted over the air, usually after transposition (modulation) to a carrier frequency FC.

Some FMCW radar apparatus generate simultaneous continuous frequency sweep signals across sub-bands (SB1, SB2...), the entire bandwidth (BW, 2*BW...) being swept by the combination of the continuous frequency sweep signals, as shown in the Figures 2.

It is one of the objectives of the proposed invention to achieve the optimal range resolution, that is to say, the range resolution related to the entire bandwidth BW swept by a combination of continuous frequency sweep signals.

Embodiments of the present invention enable optimal range resolution to be obtained for a received signal comprising several spectral components. Several transmitting and receiving schemes based on the combination of continuous frequency sweep signals may be used. Generally, the schemes described below (in relation with the Figures 2 previously described) lead to reduced range resolution when implemented with known architectures. However, these same schemes provide improved range resolution when implemented with a radar apparatus, in particular a receiver apparatus, according to embodiments of the invention.

The different schemes may be summarized as follows:

1) reduced sweep duration TS (Figure 2A),

2) increased bandwidth BW (Figure 2B), and

3) reduced (i.e. improved) beat frequency by reduction of the slope of the curve “frequency vs. time” (Figure 2C).

Concerning the first point (reduction of the sweep duration TS):

- the frequency supplied by an oscillator (such as oscillator 121 of Figure 3) is a function of its control voltage and it is dependent on the oscillator components. As a matter of fact, the speed of the frequency change is limited by the oscillator components. When the sweep frequency is large (a large bandwidth BW is swept), a certain sweep duration TS is required. By dividing the large bandwidth BW into simultaneously swept sub-bandwidths allows the sweep duration TS to be reduced (TS/2 for two sub-bands, TS/4 for four sub-bands, etc.);

- linearity of the frequency supplied by an oscillator with respect to its control voltage is important to obtain accurate measurements. The larger the bandwidth BW, the more difficult it is to design an oscillator (121) with high linearity. By dividing the large bandwidth BW into simultaneously swept sub-bands, the bandwidth BW swept by the oscillator is reduced and its linearity is easier to achieve;

- reducing the sweep duration TS provides improved measurement accuracy since the entire bandwidth BW is swept with more stable targets: target context (position, orientation, speed) evolutions are reduced when the sweep duration TS is reduced. For a given bandwidth BW, a shorter sweep duration TS corresponds to a faster scanning of the scene, and so it improves real-time tracking of mobile targets;

- for a given Pulse Repetition Frequency PRF, defined as the number of repeated signals during a given amount of time, reducing the sweep duration TS increases the remaining time before the next sweep, thus providing more time for the signal processing of received signals RS;

- for a given PRF, reducing the sweep duration TS increases the remaining time before the next transmission, thus allowing the radio resources to be shared, limiting interferences with other radars working at the same carrier frequency in the vicinity.

Concerning the second point (increasing the bandwidth BW), when a “combination” of continuous frequency sweep FS signals is used to increase the total bandwidth, for example to 2*BW (with respect to the prior art of Figures 1A, 1B, and as shown in Figure 2B), the range resolution is improved since it is directly dependent on the bandwidth BW; that is to say RES = c/[2*(2*BW)]. The range resolution is thus improved by two for a same sweep duration TS.

Concerning the third point (reduction of the slope of the curve “frequency vs. time”), when a same bandwidth BW is swept over a same sweep duration TS by a plurality of continuous frequency sweep signals, the slope of the curve is reduced, allowing the constraints for the design of the oscillator to be relaxed. That is to say, an oscillator may be configured to be able to change the frequency of its output signal in a given time, for example switching from 10 MHz to 20 MHz may require more than 10 ps (microseconds).

A “set-up time” or “switching time” is necessary for an oscillator to switch from producing one frequency to producing another frequency. Assuming for example that the switching time is 10 ps, if the oscillator has to sweep from 5 to 100 MHz by steps of 5 MHz each for a total of twenty steps, the total time to sweep the frequency range of 5 MHz to 100 MHz will require 10 ps * 20 = 200 ps.

If a sweep duration TS of 100 ps is desired for the same frequency range (5 to 100 MHz), the oscillator switching time must be reduced from 10 ps to 5 ps, which creates constraints on the oscillator design. However, by employing two continuous frequency sweep signals, one oscillator may sweep from 5 to 50 MHz, and one oscillator may sweep from 55 to 100 MHz, each oscillator using steps of 5 MHz but only for a total of ten steps each, such that the total time for each oscillator to sweep its frequency range (5 to 50 MHz or 55 to 100 MHz) will require 10 ps * 10 = 100 ps. The desired sweep duration TS may therefore be achieved without having to increase the constraints on the oscillator design, which enables the cost of the oscillator to be reduced and/or to its performances (such as linearity, phase noise) to be improved.

Figure 4 shows a continuous wave radar apparatus 100’ according to one embodiment of the invention.

The apparatus 100’ comprises a conventional transmitter 110 and a receiver 130’. The transmitter 110 is essentially the same as that shown in Figure 3, and comprises a Base Signal Generator BSG 111, a plurality of frequency sweep FS generating lines 112-m (m being the index from 1 to M of the line, here only two lines are shown 112-1 and 112-2) one for each sub-bandwidth (related to SB1, SB2....) to be swept, a carrier frequency local oscillator 113, an adder 114, an amplifier 115, and an antenna 116. Each frequency sweep line 112-m comprises a local oscillator 121, a first mixer 122, a filter 123, and a second mixer 124.

The receiver 130’ essentially corresponds to the conventional receiver 130 shown in Figure 3, and to that end comprises an antenna 131, a Low Noise Amplifier 132, a mixer 133, and a plurality M of frequency sweep detecting lines 134-m (m being the same index from 1 to M as of the frequency sweep generating lines 122-m, here detecting lines 134-1 and 134-2) one associated with each sub-bandwidth (related to SB1, SB2...) swept by the transmitter, each frequency sweep detecting line 134-m comprising a first filter 141, a first mixer 142, a second filter 143, a second mixer 144, and an analog to digital converter (ADC) 145.

The receiver 130’ further comprises a mixer 135 arranged on output of the frequency sweep detecting lines 134-m, and receives on input the signals S17 (S17-1,

S17-2) supplied by each detecting line (134-1, 134-2 respectively). The mixer 135 mixes, in the digital domain, the input signals and supplies an output signal S18.

As described in relation with equations related to Figure 2A, if the generator 111 generates a signal S1 having a bandwidth BW/2, the signals S17-1, S17-2 provide range data with a resolution equal to c/(BW), such that the output signal S18 provides range data with a resolution equal to c/(2*BW) due to the mixing by the mixer 135, which is twice as precise as that supplied by the conventional receiver 130.

The mixing of the two signals (S17-1, S17-2) supplied by the receiver provides a mixed signal S18, the spectrum of which presents an amplitude peak for a given frequency proportional to 4*k*R, wherein k is a constant determined from the parameters of the transmitter and R is the range value corresponding to the distance between the radar and a detected target, instead of 2*k*R for each of the signals S17-1, S17-2. That is to say, the mixing of the signals S17-1, S17-2 allows the recovery of the entire bandwidth BW, since:

RES = c/BW [for line 134-1] MIXc/BW [for the line 134-2]

RES = c/(2*BW) for the output signal S18, rather than only half the resolution if each signal S17-1, S17-2 is analyzed separately.

As described in relation with equations related to Figure 2B, if the generator 111 generates a signal S1 having a bandwidth BW, the signals S17-1, S17-2 provide range data with a resolution equal to c/(2*BW), such that the output signal S18 provides range data with a resolution equal to c/[2*(2*BW)] due to the mixing by the mixer 135, which is twice as precise as that supplied by the conventional receiver 130. As previously stated, the mixing of the two signals (S17-1, S17-2) supplied by the receiver provides a combined signal S18, the spectrum of which presents an amplitude peak for a given frequency proportional to 4*k*R, wherein k is a constant determined from the parameters of the transmitter and R is the range value corresponding to the distance between the radar and a detected target, instead of 2*k*R for each of the signals S17-1, S17-2. That is to say, the mixing of the signals S17-1, S17-2 allows the recovery of the entire bandwidth, since:

RES = c/(2*BW) [forline 134-1] MW c/(2*BW) [for the line 134-2]

RES = c/[2*(2*BW)] for the output signal S18, rather than only half the resolution if each signal S17-1, S17-2 is analyzed separately.

Figure 5 shows a continuous wave radar apparatus 100” according to another embodiment of the invention.

The apparatus comprises a conventional transmitter 110 and a receiver 130”. The transmitter 110 is essentially the same as that shown in Figure 3, and comprises a Base Signal Generator BSG 111, a plurality of frequency sweep generating lines 112m (m being the index from 1 to M of the line, here only two lines are shown 112-1 and 112-2) one for each sub-bandwidth (related to SB1, SB2....) to be swept, a carrier frequency FC local oscillator 113, an adder 114, an amplifier 115, and an antenna 116. Each frequency sweep line 112-m comprises a local oscillator 121, a first mixer 122, a filter 123, and a second mixer 124.

The receiver 130” essentially corresponds to the conventional receiver 130 shown in Figure 3, and to that end comprises an antenna 131, a Low Noise Amplifier 132, a mixer 133, and a plurality M of frequency sweep detecting lines 134”-m (m being the same index from 1 to M as of the frequency sweep generating lines 122-m, here detecting lines 134”-1 and 134”-2) one associated with each sub-bandwidth (related to SB1, SB2...) swept by the transmitter.

With respect to the detecting lines 134-m shown in Figures 3 and 4, the detecting lines 134”-m do not comprise the analog to digital converter 145. Thus, each frequency sweep detecting line 134”-m only comprises a first filter 141, a first mixer 142, a second filter 143, and a second mixer 144.

The receiver 130” further comprises a mixer 136 arranged on output of the frequency sweep detecting lines 134”-m, and an analog to digital converter 137, rather than the analog to digital converter 145 being arranged within the detecting lines 134-m (as illustrated by Figure 4). The mixer 136 receives on input the signals S16 (S16-1, S16-2) supplied by each detecting line (134”-1, 134”-2 respectively), in particular on output of the second mixers 144. The mixer 136 mixes, in the analog domain, the input signals and supplies an output signal S19 to the analog to digital converter 137, which converts the signal S19 into a digital signal S20. Like the receiver 130’ described in relation with Figure 4, if the generator 121 generates a continuous wave signal S1 having a bandwidth BW/2 (in relation with equations related to Figure 2A), the receiver 130” also supplies an output signal S20 comprising range data with a resolution equal to c/(2*BW), which is twice as precise as the conventional receiver 130.

If the generator 121 generates a continuous wave signal S1 having a bandwidth BW (in relation with equations 2B, 3B, 4B related to Figure 2B), the receiver 130” also supplies an output signal S20 comprising range data with a resolution equal to c/[2*(2*BW)], which is twice as precise as the conventional receiver 130.

The decision to implement the apparatus 100’ or 100” may be based on available signal processing capabilities (easier to perform the mixing of the signals in the analog domain or in the digital domain) and parts cost.

Figure 6 shows a continuous wave radar apparatus 200 according to one embodiment of the invention, capable of generating, transmitting, receiving, and processing a signal composed of a set of a first spectral component and a second spectral component, the first spectral component evolving over time within an upper band of frequencies and the second spectral component evolving over time within a lower band of frequencies, the evolution over time of the first and second spectral components being symmetric with respect to a central frequency Fcen, that is to say, mirrored one and the other with respect to the central frequency, as shown in Figures 7.

The apparatus comprises a transmitter 210 and a receiver 230. The transmitter 210 comprises a Base Signal Generator BSG 211, at least one frequency sweep FS signal generating line 212-n (n being the index of the line from 1 to N, here N is equal to 1, thus a single generating line 212-1), a carrier frequency local oscillator 213, an amplifier 215, and an antenna 216. The line 212-n (212-1) comprises a local oscillator 221, a first mixer 222, and a second mixer 223 comprising a filter configured to remove an unwanted spectral component.

The generator 211 is configured to generate a continuous wave signal S21 with a frequency Fsw, which may be an upsweep US (increasing frequency values over a bandwidth BW for a period of time TS), a downsweep DS (decreasing frequency values over a bandwidth BW for a period of time TS), a combination of sweeps such as a saw tooth wave, or another frequency modulation such as a sinusoid modulation. The generator 211 may be a Voltage Controlled Oscillator (VCO) or a Direct Digital Synthesizer (DDS).

The local oscillator 221 of a line 212-n is configured to generate a sinusoidal signal S22 with a central frequency Fcen used by the first mixer 222 as the central frequency above and below which the frequency sweep Fsw of the continuous wave signal S21 from the generator 211 is transposed. That is to say, the central frequency

Fcen separates two sub-bandwidths SB1, SB2 of the entire bandwidth BW to be swept, a “lower band” SB1 below the central frequency Fcen and an “upper band” SB2 above the central frequency Fcen. Thus, the lower band SB1 extends from a minimum frequency Fmin to the central frequency Fcen, which is here the mid-point Fm between the minimum frequency Fmin and the maximum frequency Fmax, and the upper band SB2 extends from the central frequency Fcen to the maximum frequency Fmax. Each sub-band SB1, SB2 corresponds to the bandwidth BW swept by the generator 211, which is then doubled.

In other words, the first mixer 222 combines the central frequency Fcen signal

522 and the frequency sweep Fsw, generating a signal S23 characterized by an instantaneous frequency which is composed of a set of two spectral components, one spectral component evolving over time within an upper band of frequencies and another spectral component evolving over time within a lower band of frequencies. One spectral component corresponds to the sum (Fcen + Fsw) of the spectral component of the first signal and the spectral component of the second signal, and another spectral component corresponds to the difference (Fcen - Fsw) between the spectral component of the first signal and the spectral component of the second signal, the first and second components being also known as the image frequencies. In contrast with the conventional transmitter shown in Figures 3, 4 and 5, the apparatus according to embodiments of the invention does not comprise a filter (equivalent to the filter 123) to filter out either the sum or the difference signal.

The carrier signal CS local oscillator 213 generates a carrier signal S24 with a carrier frequency FC to be used as carrier for the radio transmission of a transmitted signal TS. The second mixer 223 of the line 212-n (212-1) receives on input the signal

523 (i.e., the signal characterized by an instantaneous frequency composed of a set of two spectral components, one spectral component evolving over time within an upper band of frequencies and another spectral component evolving over time within a lower band of frequencies) and the carrier signal S24, and transposes the signal S23 at the carrier frequency FC.

A transposed output signal S25 is obtained on output of the mixer 223 and is supplied on input to the amplifier 215, which amplifies the signal S25 and supplies it to the antenna 216 for transmission as the transmitted signal TS. A filter (not shown in Figure 6) is associated with the mixer 223 and is configured to remove an unwanted image frequency related to the mixing of signals S23 and S24 by the mixer 223. The transmitter 210 is not limited to one line 212-n, but can comprise a plurality of lines, which would be combined in an adder (equivalent to the adder 114) as shown in

Figures 3 and 4.

The receiver 230 comprises an antenna 231, a Low Noise Amplifier 232, a mixer 233, a set of 2*N (N being the number of signal generating lines, here N = 1) frequency sweep detecting lines 234-nb (n being the index n of the line, b being the reference of the type of band U or L corresponding to the upper band or to the lower band respectively) for every sub-bandwidth generated by the transmitter, and a mixer 235. Each detecting line 234-nb is associated with a sub-bandwidth (related to SB1, SB2...) swept by the transmitter, each frequency sweep detecting line 234-nb comprising a first filter 241, a first mixer 242, a second filter 243, and an analog to digital converter 244. Here, as the transmitter 210 only had one generating line 212-n, the receiver only has two detecting lines 234-1U, 234-1L.

The antenna 231 receives a reflected signal RS (i.e. the transmitted signal as reflected back to the apparatus from a target), which is amplified by the amplifier 232 before being supplied as an amplified reflected signal S31. The mixer 233 receives on input the amplified reflected signal S31 and the carrier signal S24, and supplies on output a signal S32 comprising the frequency sub-bands (upper and lower), the carrier signal S24 and higher frequency bands generated by the mixer 233 having been extracted.

The signal S32 comprising the frequency sub-bands is supplied to each detecting line 234-1U, 234-1L. The first filter 241 of each line 234-1U, 234-1L extracts a signal S25 comprising the frequency sub-band, upper or lower respectively, of interest for the line. A resulting signal S33 is then supplied on input to the first mixer 242 of the line. The first mixer 242 also receives on input the signal S23 supplied on output of the mixer 222 of the transmitter 210, and supplies on output a beat frequency signal S34 as well its image. The beat frequency signal S34 is then filtered by the second filter 243, which removes the beat frequency image (or “unwanted image signal”), and supplies a single beat frequency signal S35. The beat frequency signal S35 is then supplied to the ADC converter 244 for conversion to digital form for digital signal processing, which supplies on output a digital signal S36-b (S36-U, S36-L) of the line to the mixer 235.

The mixer 235 receives on input the signals S36 (S36-U, S36-L) supplied by each detecting line (234-1U, 234-1L respectively). The mixer 235 mixes, in the digital domain, the input signals and supplies an output signal S37. As described in relation with equations 2A, if the generator 211 generates a signal F21 having a bandwidth

BW/2, the signals S36-U, S36-L provide range data with a resolution equal to c/(BW), such that the output signal S37 provides range data with a resolution equal to c/(2* BW), which is twice as precise as that supplied by the conventional receiver 130.

As described in relation with equation 2B, if the generator 211 generates a signal S21 having a bandwidth BW (which is then doubled by the image frequencies), the signals S36-U, S36-L provide range data with a resolution equal to c/(2*BW), such that the output signal S37 provides range data with a resolution equal to c/[2*(2*BW)], which is twice as precise as that supplied by the conventional receiver 130.

As a possible alternative (not shown), a mixer receives on input the beat frequency signals (equivalent to signal S35-1 from detecting line 234-1 and signal S352 from detecting line 234-2). The mixer mixes, in the analog domain, the beat frequency signals and supplies an output signal which is then supplied to an ADC converter for conversion to digital form for digital signal processing.

Figures 7 (7A, 7B, 7C) show the spectra of transmitted and received signals, transmitted and received by an apparatus according to Figure 6. It should be noted that the transposition to the carrier frequency FC, though present, is not represented in these figures. With respect to the prior art shown in Figure 1A, these embodiments respectively provide the same bandwidth BW to be covered by a reduced sweep duration TS/2, an increased bandwidth 2*BW to be covered by the same sweep duration TS, or the same bandwidth BW to be covered by the same sweep duration TS but with a reduced beat frequency FB (reduced slope of the “frequency F vs. time T” curve), similarly to the graphs shown in Figures 2 (2A, 2B, 2C).

Figure 7A shows a transmitted downsweep spectral component TDSC7 and a transmitted upsweep spectral component TUSC7, both signals being mirrored (or symmetrical) with respect to the central frequency Fcen, as well as a reflected downsweep spectral component RDSC7 and a reflected upsweep spectral component RUSC7. The sweep duration is divided by two (TS/2), since the same bandwidth BW is explored in half the time. The beat frequency FB remains unchanged. Since the signals on output of the receiving lines are mixed, the range resolution is improved. It may be noted here that though an upsweep is shown in sub-band SB1 and a downsweep is shown in sub-band SB2, an upsweep could be shown in sub-band SB2 and a dowsweep shown in sub-band SB1, as one is merely the mirror of the other.

Figure 7B shows a transmitted downsweep spectral component TDSC8 and a transmitted upsweep spectral component TUSC8, both signals being mirrored with respect to the central frequency Fcen, as well as a reflected downsweep spectral component RDSC8 and a reflected upsweep spectral component RUSC8. Since an increased bandwidth 2*BW is explored over a same sweep duration TS, and the signals on output of the receiving lines are mixed, the range resolution is doubly improved. The beat frequency FB remains unchanged.

Figure 7C shows a transmitted downsweep spectral component TDSC9 and a transmitted upsweep spectral component TUSC9, both signals being mirrored with respect to the central frequency Fcen, as well as a reflected downsweep spectral component RDSC9 and a reflected upsweep spectral component RUSC9. The sweep duration (TS) and the bandwidth (BW) remain unchanged, but the slope of the lines “frequency F vs. time T” are reduced (here divided by two). Since the signals on output of the receiving lines are mixed, the range resolution is improved.

As shown in the Figures 7, the spectral components begin at opposite ends of the bandwidth (minimum frequency Fmin and maximum frequency Fmax) and converge to meet at the midpoint, the central frequency Fcen at the end of the sweep duration (one cycle), but could equally begin at the central frequency Fcen and diverge to opposite ends of the bandwidth (minimum frequency Fmin and maximum frequency Fmax). After the completion of the first cycle, a second cycle may be begun. In the case where the same types of signals are used, that is to say a sequence of converging signals or a sequence of diverging signals, between the end of a cycle and the beginning of the next cycle, there are sharp up and down ramps between the successive transmitted and received sweeps. However, if a converging cycle is followed by a diverging cycle, followed by a converging cycle, and so forth, there are no sharp up and down ramps.

Figure 8 shows a continuous wave radar apparatus 300 according to another embodiment of the invention. The apparatus 300 comprises a transmitter 310 and a receiver 330. The transmitter 310 comprises a Base Signal Generator BSG 311, at least one frequency sweep FS signal generating line 312-p (p being the index of the line from 1 to P, here P = 1, thus a single line 312-1) capable of generating two sets of spectral components, a carrier frequency local oscillator 313, an amplifier 315, and an antenna 316. The line 312-1 comprises a plurality Q of local oscillators 321-q (q being the index of the oscillator from 1 to Q, here Q = 2 for two oscillators 321-1, 321-2), first mixers 322-1, 322-2, and a second mixer 323 comprising a filter configured to remove an unwanted spectral component.

The generator 311 is configured to generate a continuous wave signal S41 with a frequency Fsw. The generator 411 may be a Voltage Controlled Oscillator (VCO) or a Direct Digital Synthesizer (DDS).

The first local oscillator 321-1 is configured to generate a sinusoidal signal S42-1 with a frequency F1. This frequency F1 is used by the mixer 322-1 as the central frequency Fcen above and below which the frequency sweep Fsw of the continuous wave signal S41 from the generator 311 is transposed, supplying a signal S43-1 on output. The second local oscillator 321-2 is configured to generate a sinusoidal signal

542- 2 with a frequency F2. This frequency F2 is used by the mixer 322-2 as the central frequency Fcen above and below which the signal S43 supplied from the mixer 322-1 is transposed, supplying a signal S43-2 on output.

The carrier signal CS local oscillator 313 generates a carrier signal S44 with a carrier frequency FC to be used as carrier for the radio transmission of a transmitted signal TS. The mixer 323 of the line 312-1 receives on input the signal S43-2 and the carrier signal S44, and transposes the signal S43-2 at the carrier frequency FC to be used for the transmission, supplying a signal S45 on output. The amplifier 315 receives the signal S45, amplifies it, and supplies it to the antenna 316 for transmission as the transmitted signal TS.

A filter (not shown in Figure 8) is associated with the mixer 323 and is configured to remove an unwanted image frequency related to the mixing of signals

543- 2 and S44 by the mixer 323.

The receiver 330 comprises an antenna 331, a Low Noise Amplifier 332, a mixer 333, a set of 2*P*Q (here four) frequency sweep FS detecting lines 334-pqb (q being the index q of the corresponding oscillator 321-q of the transmitter, b being the reference of the type of band U or L corresponding to the upper band or to the lower band respectively) for every generating line 312-p of the transmitter, a plurality Q of first mixers 335-q, and at least one second mixer 336.

Each detecting line 334-qb is associated with a sub-bandwidth (related to SB1, SB2...) swept by the transmitter, each frequency sweep detecting line 334-qb comprising a first filter 341, a first mixer 342, a second filter 343, and an analog to digital converter 344.

Here, as the transmitter 310 only had one generating line 312-1 with two oscillators 321-1, 321-2, the receiver has four detecting lines 334-1U, 334-1L, 334-2U, 334-2L, two first mixers 335-1, 335-2, and one second mixer 336.

The antenna 331 receives a reflected signal RS (i.e. the transmitted signal TS as reflected back to the apparatus from a target), which is amplified by the amplifier 332 before being supplied as an amplified reflected signal S51. The mixer 333 receives on input the amplified reflected signal S51 and the carrier signal S44, and supplies on output a signal S52 comprising the frequency sub-bands, the carrier signal S44 and higher frequency bands generated by the mixer 333 having been extracted.

The signal S52 comprising the frequency sub-bands is supplied to each detecting line 334-qb (334-1U, 334-1L, 334-2U, 334-2L). The first filter 341 of each line 334-qb extracts a signal S53 comprising the frequency sub-band of interest for the line. A resulting signal S53 is then supplied on input to the first mixer 342 of the line. The first mixer 342 also receives on input the signal S43-2 supplied on output of the mixer 322-2 of the transmitter 310, and supplies on output a beat frequency signal S54 as well its image. The beat frequency signal S54 is then filtered by the second filter 343, which removes the beat frequency image, and supplies a single beat frequency signal S55. The beat frequency signal S55 is then supplied to the ADC converter 345 for conversion to digital form for digital signal processing, which supplies on output a digital signal S56-qb of the line to the first mixer 335-q.

The mixer 335-q receives on input a set of signals S56 supplied by the detecting lines relating to the same index q. The first mixer 335-q mixes, in the digital domain, the input signals and supplies an output signal S57-q to the second mixer 336, which then mixes the signal to supply an output signal S58.

The above embodiments improve the range resolution by mixing the signals obtained from each sub-band sweep, the resolution being improved by a factor equal to the number of sub-bands; i.e. a factor of two for two sub-bands, a factor of four for four sub-bands, etc. This resolution improvement is obtained from the multiplication of the beat frequency FB by an equivalent factor, hence an increased beat frequency. The increased beat frequency at a given sampling frequency defined by the analog to digital converter, modifies the maximum target distance detectable by the radar.

It may be desired to optimize resolution (RES) or range (RNG), when processing a received signal composed of a plurality of sub-signals sweeping non overlapping sub-bandwidths, by selecting the appropriate mode (defined by a given beat frequency FB) according to the estimated distance without changing the hardware components (in particular the local oscillators and the analog to digital converters).

The selection between modes allows, for a given distance to a target, either:

- to have improved resolution RES but with a shorter range RNG; or

- to have a longer range RNG but with diminished resolution RES.

The modes, providing a choice between high resolution RES or long range RNG, implement the same analog to digital converter. For a sampling frequency below 200 KHz it is possible to use a low-cost analog to digital converter dedicated to audio.

The following description and the accompanying figures relate to this aspect of the invention.

Figures 9 (9A, 9B, 9C) respectively show the range RNG, the range resolution RES, and the bandwidth BWwith respect to time Ti.

Figure 9A illustrates a scenario wherein, as a target T moves from a distance zero (close to the radar apparatus) to a distance max (far from the radar apparatus) over time Ti, the range RNG correspondingly increases from a minimum value RNGmin to a maximum value RNGmax3.

Figure 9B illustrates the evolution of the range resolution value within the same scenario. The higher the range, the higher the range resolution value. In other words, as the target T moves away from the radar apparatus (from distance zero to distance max), the range resolution RES correspondingly increases from a low resolution RESbest (which corresponds to the best resolution value) to a high resolution RESworst (which corresponds to the worst resolution value).

Figure 9C shows the evolution of the bandwidth BW of the signal, depending on the number of sub-bands selected for processing. The number of sub-bands available for selection may be one sub-band 1SB, two sub-bands 2SB, or four subbands 4SB when implemented with respect to the apparatus 300 shown in Figure 8, wherein the bandwidth of the transmitted signal is fixed at four sub-bands 4SB.

Thus, the received signal comprises four sub-bands 4SB, of which only one sub-band 1SB, two sub-bands 2SB, or all four sub-bands 4SB may be selected for processing, depending on the desired mode, as will be described in further detail with respect to Figure 10. The total number J of sub-bands available is here 4, with the index j (from 1 to J) indicating the number of sub-bands selected, here 1, 2 or 4. The total number J is equal to 2^ΛΙ_, wherein L is an index derived from the number of subbands, and is a positive integer. For example, in the case of two sub-bands, L is equal to 1; in the case of four sub-bands, L is equal to 2, and so forth. A total of D modes Md are defined; d being an index of a selected mode from 1 to D, here equal to 3, providing modes M1, M2, M3.

Mode M3 [M(D)] thus utilizes one sub-band SB1, provides the high resolution RESworst, and has a high range RNG3 extending from the range RNGmax2 to the range RNGmax3 (the maximum range values being described below in more detail with repect to equation 7).

Mode M2 [M(D-1)] utilizes two sub-bands SB2, provides an intermediate resolution RESinter (equal to the maximum resolution RESmax divided by two), and has a medium range RNG2 extending from the range RNGmaxI to the range RNGmax2.

Mode M1 [M(D-2)] utilizes four sub-bands SB4, provides the low resolution RESbest, and has a low range RNG1 extending from the minimum range RNGmin to the range RNGmaxI.

The following equations refer to the embodiment illustrated by Fig. 7B. However, the skilled person can easy adapt them to the embodiments illustrated by Figures 7A, 7C.

The beat frequency FB, when mixing J sub-bands SB (for example on output of the mixer 235 of Figure 6) is provided by the following equation:

FB = (2*J*BW*RT)/(c*TS) [equation 5] wherein c is the speed of light (3*10⁸ m/), BW is the bandwidth of a sub-band

SB in Hertz, TS is the sweep duration in seconds, RT is the range (distance) to the target T in meters, and J is the total number of sub-bands available (2, 4, 8...) and is equal to 2^ΛΙ_, wherein L is a positive integer.

For a given sampling frequency SF, and from the Nyquist/Shannon sampling theorem, the maximum detected beat frequency FBmax is given by the following equation:

FBmax = SF/2 [equation 6]

From equations 5 and 6 (solving for the range RT of equation 5 by substituting in SF/2 of equation 6 for FB), the maximum range RNGmax is given by the following equation:

RNGmax = (c*TS*SF)/[4*J*BW] [equation 7] wherein again, c is the speed of light, TS is the sweep duration, SF is the sampling frequency, J is the total number of sub-bands available (2, 4, 8...) and is equal to 2^ΛΙ_, and BW is the bandwidth of each sub-band (for example,SB1 or SB2 of

Figure 7B).

From equations 5 and 7, the range resolution RES is given by the following equation:

RES = c/(2*J*BW] [equation 8] wherein again, c is the speed of light, J is the total number of sub-bandsavailable (2, 4, 8...) and is equal to 2^AL, and BW is the bandwidth of each sub-band.

As a reminder, a lower value for the range resolution is preferable, thus the value in the denominator should be as high as possible.

Taking the case of four sub-bands, and as illustrated in respect with Figures 9, the equations 7 and 8 may be defined with respect to the mode d (M1, M2, M3...) as follows:

RNGmaxd = (c*TS*SF)/[4*2^A(D-d)*BW] [equation 9]

RESd = c/[2*2^A(D-d)*BW] [equation 10] wherein D is the total number of modes available (here D = 3), and d is the index of the mode selected (here d = 1, 2, or 3).

Applying equations 9 and 10 for each mode povides the following range and resolution values:

- Mode M1 :

RNGmaxI = (c*TS*SF)/(4*2^A(3-1)*BW) = (c*TS*SF)/(4*4*BW) [equation 9.1]

RES1 = c/[2*(2^A(3-1)*BW] = c/(2*4*BW) [equation 10.1] (It may be noted that here the value RES1 corresponds to the value RESbest of Figure 9B).

- Mode M2 [mode M(D-1)]:

RNGmax2 = (c*TS*SF)/(4*2^A(3-2)*BW) = (c*TS*SF)/(4*2*BW) [equation 9.2]

RES2 = c/[2*(2^A(3-2)*BW] = c/(2*2*BW) [equation 10.2] (It may be noted that here the value RES2 corresponds to the value RESinter of Figure 9B).

- Mode M3 [mode M(D)]:

RNGmax3 = (c*TS*SF)/(4*2^A(3-3)*BW) = (c*TS*SF)/(4*BW) [equation 9.3]

RES3 = c/[2*(2^A(3-3)*BW] = c/[2*BW] [equation 10.3] (It may be noted that here the value RES3 corresponds to the value RESworst of Figure 9B).

It should be noted that other apparatuses could implement more or fewer modes Md. For example, the apparatus of 200 of Figure 6 comprises only two subbands available for processing, thus providing only two modes: a first mode M1 comprising the mixed signal of two sub-bands (signal S37), and a second mode M2 comprising only one sub-band (signal S36).

An apparatus with for example eight sub-bands would provide four modes, corresponding to one sub-band M4, two sub-bands M3, four sub-bands M2, and eight sub-bands M1.

Figure 10 shows the receiver portion 430 of a continuous wave radar apparatus 400 according to another embodiment of the invention. The apparatus 400 is similar to the apparatus 300 of Figure 8, with like references 3XX, 4XX indicating like features, the transmitter portion not being shown here for reasons of dimensioning of the Figure.

The receiver 430 differs from the receiver 330 in that it further comprises a computing block CB 437 arranged on output of the mixer 436 (equivalent mixer 336). The computing block 437 is for example a processor and receives on one input the signal S58 supplied on output of the mixer 436, on one input one of the signals S57, and on one input one of the signals S56.

Signal S56 corresponds to mode M3 since the signal of a single sub-band is used, signal S57 corresponds to mode M2 since the signals of two sub-bands are used, and signal S58 corresponds to mode M1 since the signals of four sub-bands are used. Furthermore, it may be noted that the signal S56 used on input of the computing block 437 may be any one of the four signals S56 supplied on output of the detecting lines 434, and the signal S57 used on input of the computing block 437 may be any one of the two signals S57 supplied on output of the mixers 435. Likewise, all of the signals S56 and all of the signals S57 may be supplied on input of the computing block 437, for example for redundancy reasons. The signals S56, S57, S58 are hereinafter refered to as selection signals SSd (SS3, SS2, SS1) respectively.

It may be noted that the analog to digital converter 445 may be arranged in front of the mixer 435 or after the mixer 435, indifferently, as described for example in relation with Figures 4 and 5. If the analog to digital converter 445 is arranged in front of the mixer 435, the “mixer” corresponds to a multiplication performed by a digital signal processor DSP or by a field-programmable gate array FPGA. If the analog to digital converter is arranged after the mixer 435, the “mixer” is an analog mixer (discreet component).

The computing block 437 is configured to apply a selection algorithm, as described below in relation with Figures 11, to select the appropriate mode to be used according to the current target range.

Figure 11 shows a method 1100 of selecting the appropriate mode of operation according to one embodiment. The method 1100 comprises the steps 1101 to 1106, and is implemented by the computing block 437, and is generalized to work for 2^A(D-1) frequency sweeps, D being the number of modes available.

In step 1101, the method is initialized.

In step 1102, the mode Md with the highest range (thus the worst resolution) is selected, here mode M3 [M(D)] providing the range RNG given above in equation 9.3, and the resolution RES given above in equation 10.3.

In step 1103, the range (distance) RT to the target T is measured by the transmission and reception of a signal to the target T.

In step 1104, the mode Md having a range interval comprising the measured target range RT is determined, for example according to the table below.

Range	Mode
RNG1 (RNGmin to RNGmaxI)	Mode 1
RNG2(RNGmax 1 to RNGmax2)	Mode 2
RNGD (RNGmax(D-l) to RNGmaxD)	Mode D

In step 1105, the selection signal SSd corresponding to the determined mode Md is selected. For instance, if in step 1104 the target range RT is determined to be comprised within the interval RNG1 (RNGmin < RT < RNGmaxI), then in step 1105 the selection signal SS1 corresponding to mode M1 is selected, for example signal S58 of Figure 10, and so forth, in order to determine the ideal resolution for the range.

In step 1106, the fourrier transform of the the selection signal SSd is computed.

In step 1107, the beat frequency FBd present in the signal SSd is determined.

In step 1108, the range RNG corresponding to the determined beat frequency FB is estimated according to equation 5, solving for the target range RTd when using mode Md:

RTd = (FB*c*TS)/[2*2^A(D-d)*BW] [equation 11] again, FB is the beat frequency, c is the speed of light, TS is the sweep duration, D is the total number of modes available, d is the index of selected mode, BW is the bandwidth of a sub-band, and RTd is the target range in meters measured when using the mode Md.

In an alternative embodiment to that shown in relation with Figure 10, the computing block CB 437 is replaced by an adder (or summer) that receives the selection signals SSd {S56(M3), S57(M2), S58(M1)} on input, and supplies on output a summed signal ZS on output. The summed signal ZS is then supplied to an analog to digital converter that converts the summed signal ZS to its digital format. Frequency filtering in the digital domain may then be applied to filter out the unwanted frequency (or frequencies), depending on a calculated target range value, calculated by a processor for example. This method is now described in further detail in relation with Figure 12.

Figure 12 shows a method 1200 of selecting the appropriate mode of operation according to another embodiment. The method 1200 comprises the steps 1201 to 1207, and is implemented by an adder as described above.

In step 1201, the method is initialized.

In step 1202, the selection signals SSd are received on input.

In step 1203, the sum ZS of the signals SSd is calculated.

In step 1204, the fourrier transform of the sum ZS is computed.

In step 1205, the beat frequencies FB present in the fourrier transform of the sum ZS are determined, for a total of (D-d+1) beat frequencies, D being the total number of modes available, d being the index of the selected mode, thus providing for example 3-2+1 = 2 beat frequencies for mode M2.

In step 1206, the highest beat frequency FBmax of the determined beat frequencies FB is selected in order to get the best resolution.

In step 1207, the target range RT is calculated from the beat frequency FBmax by means of equation 11 above.

In step 1208, the appropriate mode Md is selected.

In another embodiment, not shown, instead of a computing block or an adder receiving the selection signals SSj, a simple switch may be implemented, to switch between two or more modes depending on a control signal relating to a calculated target range RT, calculated by a processor for example.

It may be understood that the transmitters and receivers may be extended by any number of generating and receiving lines, as necessary. For example, in order to obtain more than four spectral components transmitted and received, the transmitter 310 may either have additional generating lines 312-p and an adder to add the outputs from each line, or else an oscillator and a mixer can be added to the generating line 312-1 for each additional pair of spectral components. The receiver may then have additional receiving lines.

For systems based on the combination of a higher number of continuous frequency sweep signals, for example a plurality N, N being greater than two, further mixers are supplied, for example, for a system with four simultaneous continuous sweep signals N=4, the number of mixers corresponds to the number of simultaneous frequency bands swept minus one, N-1, thus three mixers, with a same number of mixing steps. Further, the number N is preferably an even number.

With respect to the apparatus 300 of Figure 8, an increased number of subbandwidths generated by the transmitter 310 increases the complexity of the receiver 330 accordingly. For example, if the transmitter 310 had two generating lines 312, each with two local oscillators 321, there would be a total of eight detecting lines 334, four first mixers 335, two second mixers 336, and a third mixer to supply the output signal. If the transmitter 310 had four generating lines 312, each with two local oscillators 321, there would be a total of sixteen detecting lines 334, eight first mixers 335, four second mixers 336, two third mixers, and one fourth mixer, and so forth. Wth respect to the apparatus 200 of Figure 6, if the transmitter 210 has two generating lines 212, then the receiver 230 would have four detecting lines 234, two first mixers 235, and one second mixer. If the transmitter 210 has four generating lines 212, then the receiver 230 would have eight detecting lines 234, four first mixers 235, two second mixers, and one third mixer.

Wth respect to the apparatuses 100’, 100” of Figures 4 and 5, if the transmitter 110 has four generating lines 112, then the receiver 130’, 130” would have four detecting lines 134, 134”, two first mixers 135, 136, and one second mixer. If the transmitter 110 has eight generating lines 112, then the receiver 130’, 130” would have eight detecting lines 134, 134”, four first mixers 135, 136, two second mixers, and one third mixer, and so forth.

It may be noted that though the transmitters 110, 210, 310 and the receivers 130’, 130”, 230, 330, 430 have been disclosed as being integrated within a single apparatus (housing), they may also be integrated in separate apparatus (housings) coupled together. Also, the signal connections between the transmitter and the receiver may vary in number, depending on the branches for different paths, and so forth.

Furthermore, in some embodiments, the continuous wave signal (S1, S21, S41) may be a stepped frequency continuous wave (SFCW) signal.

In some embodiments, the mixer 122, 222, 322 may be a harmonic mixer, configured to supply sum and difference frequencies at a harmonic multiple of one of the inputs. The output signal then contains frequencies such as (k*Fbase + Fsw), (k*Fbase - Fsw), (k*Fcen + Fsw), (k*Fcen - Fsw) where k is an integer. For example, a continuous wave signal supplied to the input of the harmonic mixer is transformed into a downsweep and an upsweep for the first occurrence of k (centered on Fbase or Fcen). The upsweep is then replicated without overlap for the frequencies above the frequency Fcen, Fbase and corresponding to the other occurrences of k, that is k = 2, 3, 4, etc.... and the downsweep is also replicated without overlap for the frequencies below the frequency Fcen, Fbase and again corresponding to the other occurrences of k, that is k = 2, 3, 4, etc....

It may be noted that alternatively, the frequency of the continuous wave signal Fsw (instead of Fbase or Fcen) could be multiplied by the integer k. For example, a continuous wave signal (upsweep or downsweep) supplied to the input of the harmonic mixer may be transformed into a downsweep and an upsweep for the first occurrence of k (centered on Fbase or Fcen), and then the ensemble of upsweep and downsweep is replicated along the frequency band and corresponding to the other occurrences of k, that is k = 1, 3, 5, etc. In this case, the values of k are odd numbers in order to prevent overlaps of the frequency sweeps at the output of the harmonic mixer. Such an embodiment may be implemented by a common oscillator and a plurality of harmonic mixers multiplying only by k, wherein the outputs are summed, or harmonic mixers such that the output is composed of the multiple harmonics.

It may be noted that though in the preceeding it has been described that the carrier signal S5, S24, S44, the continuous wave signal S1, and the local oscillator signal S2, S23, S43-2 are generated by the transmitter and applied to the receiver for the use thereby, one or more of these signals could be independently generated by the receiver. Likewise, the signals could be generated in a separate entity (that is to say, not within the transmitter strictly speaking) and supplied to both the transmitter and the receiver.

Furthermore, though it has been described that the transmitted signal comprises at each time a first spectral component and a second spectral component, the received signal also comprising at each time a first spectral component and a second spectral component, all of these spectral components (that is to say, the first and second components for each time) are not necessarily processed by the receiver, as needed. For example, only every other set of spectral components could be processed, every third set, etc.

Finally, the signals may have their frequencies shifted with respect to one another (e.g., due to the Doppler effect). For example, with respect to Figure 6, signal S23 and the signal S33 (after reception, amplification, mixing, and filtering of the received signal RS) applied to the mixer 242 may be two different signals, thus having different spectral components. Therefore, physically speaking, signal S33 may be considered as a function of signal S23, thus S33 = f1 (S23), f1 being a shifting function, or, mathematically speaking, signal S23 may be considered as a function of signal S33, thus S23 = f2(S33), f2 being a shifting function that is the inverse of function f1.

Certain aspects of the invention are set forth below.

Aspect 1. A method of:

- generating and transmitting, by a radar transmitter apparatus, a transmitted signal comprising at least a first spectral component in a first sub-bandwidth and a second spectral component in a second sub-bandwidth, and

- receiving, by a radar receiver apparatus, a received signal by reflection of the transmitted signal, the received signal comprising at least the first spectral component in the first sub-bandwidth and the second spectral component in the second subbandwidth, the method comprising the steps of:

- generating a signal for transmission comprising the first spectral component in the first sub-bandwidth and the second spectral component in the second subbandwidth;

- transmitting the signal;

- receiving the transmitted signal as the received signal;

- filtering the received signal by separately filtering out the first sub-bandwidth and the second sub-bandwidth so as to respectively obtain a first signal related to the first spectral component and a second signal related to the second spectral component;

- obtaining separately, from the first signal and the second signal, a first beat frequency signal and a second beat frequency signal respectively; and

- mixing the first beat frequency signal and the second beat frequency signal so as to obtain a mixed signal.

Aspect 2. The method according to aspect 1, further comprising the steps of:

- before transmission, modulating the first and second spectral components with a carrier signal, and

- after reception of the signal and before filtering the received signal, mixing the received signal with the carrier signal so as to obtain a signal wherein the carrier signal has been removed.

Aspect 3. The method according to one of aspects 1 or 2, wherein the step of generating the signal for transmission comprises the step of generating a third signal characterized by an instantaneous frequency composed of the first spectral component and the second spectral component, the spectral components evolving over time within the sub-bandwidths and symmetric with respect to a central frequency, wherein one spectral component is generated based on an image frequency related to the other spectral component, wherein the third signal is a function of the received signal.

Aspect 4. The method according to aspect 3, wherein the generating step comprises the steps of:

- generating a continuous wave signal;

- generating at least one central frequency signal;

- mixing the continuous wave signal and the central frequency signal so as to obtain a signal comprising, for each instant:

the first spectral component corresponding to the sum of the continuous wave signal and the central frequency signal, and the second spectral component corresponding to the difference between the continuous wave signal and the central frequency signal.

Aspect 5. The method according to aspect 4, wherein the continuous wave signal is a stepped frequency continuous wave signal.

Aspect 6. The method according to aspect 4, wherein a plurality of sets of symmetrical spectral components, each centered on a different central frequency, are generated and transmitted simultaneously

Aspect 7. A radar apparatus comprising:

- a transmitter configured to generate and transmit a transmitted signal comprising at least a first spectral component in a first sub-bandwidth and a second spectral component in a second sub-bandwidth, and

- a receiver configured to receive a received signal by reflection of the transmitted signal, the received signal comprising at least the first spectral component in the first sub-bandwidth and the second spectral component in the second subbandwidth, the transmitter comprising:

- circuitry for generating a signal for transmission comprising the first spectral component in the first sub-bandwidth and the second spectral component in the second sub-bandwidth; and

- an antenna configured to transmit the signal; the receiver comprising:

- an antenna configured to receive the transmitted signal as the received signal;

- a filter configured to filter the received signal by separately filtering out the first sub-bandwidth and the second sub-bandwidth so as to respectively obtain a first signal related to the first spectral component and a second signal related to the second spectral component;

- circuitry for obtaining separately, from the first signal and the second signal, a first beat frequency signal and a second beat frequency signal respectively; and

- a mixer to mix the first beat frequency signal and the second beat frequency signal so as to obtain a mixed signal.

Aspect 8. The apparatus according to aspect 7, wherein:

- the transmitter further comprises a local oscillator configured to generate a carrier signal, the transmitted signal being modulated with the carrier signal, and

- the receiver further comprises a mixer arranged between the antenna and the filter, the mixer being configured to mix the received signal with the carrier signalsignal so as to obtain a signal wherein the carrier signal has been removed.

Aspect 9. The apparatus according to one of aspects 7 or 8, wherein the circuitry for generating the signal for transmission comprises a frequency sweep signal generating line configured to generate a signal characterized by an instantaneous frequency composed of the first spectral component and the second spectral component; the spectral components evolving over time within the sub-bandwidths and symmetric with respect to a central frequency, wherein one spectral component is generated based on an image frequency related to the other spectral component.

Aspect 10. The apparatus according to aspect 9,

- further comprising a base signal generator configured to generate a continuous wave signal; and

- wherein the frequency sweep signal generating line comprises:

- at least one local oscillator configured to generate the central frequency signal;

- at least one first mixer configured to mix the continuous wave signal and the central frequency signal so as to obtain a signal comprising, at each time:

- the first spectral component corresponding to the sum of the continuous wave signal and the central frequency signal, and

- the second spectral component corresponding to the difference between the continuous wave signal and the central frequency signal.

Aspect 11. The apparatus according to aspect 10, wherein the base signal generator is configured to generate the continuous wave signal as a stepped frequency continuous wave signal.

Aspect 12. The apparatus according to aspect 9, further configured to generate and transmit a plurality of sets of symmetrical spectral components, each centered on a different central frequency.

Although the present invention has been described hereinabove with reference to specific embodiments, the present invention is not limited to the specific embodiments, and modifications which lie within the scope of the present invention will be apparent to a person skilled in the art. In particular different features from different embodiments may be interchanged, where appropriate. Many further modifications and variations will suggest themselves to those versed in the art upon making reference to the foregoing illustrative embodiments, which are given by way of example only and which are not intended to limit the scope of the invention as determined by the appended claims.

Claims (26)

1. A method of receiving, by a radar apparatus, a signal comprising at least a first spectral component in a first sub-bandwidth and a second spectral component in a second sub-bandwidth, the method comprising the steps of:

- filtering the received signal by separately filtering out the first sub-bandwidth and the second sub-bandwidth so as to respectively obtain a first signal related to the first spectral component and a second signal related to the second spectral component;

- obtaining separately, from the first signal and the second signal, a first beat frequency signal and a second beat frequency signal respectively; and

- mixing the first beat frequency signal and the second beat frequency signal so as to obtain a mixed signal.

2. The method according to claim 1, further comprising, before filtering the received signal, a step of mixing the received signal with a carrier signal so as to obtain a signal wherein the carrier signal has been removed.

3. The method according to one of claims 1 or 2, further comprising, after the step of filtering the received signal, the steps of:

- mixing separately each of the first signal and the second signal with a first base frequency and a second base frequency respectively so as to extract a first base frequency signal from the first signal and a second base frequency signal from the second signal respectively;

- filtering separately the first base frequency signal and the second base frequency signal so as to remove unwanted spectral components; and

- mixing separately the filtered first base frequency signal and the filtered second base frequency signal with a continuous wave signal so as to obtain the first beat frequency signal and the second beat frequency signal respectively.

4. The method according to one of claims 1 or 2, further comprising, after the step of filtering the mixed signal, the steps of:

- mixing separately each of the first signal and the second signal with a third signal characterized by an instantaneous frequency composed of the first spectral component and the second spectral component, the spectral components evolving over time within the sub-bandwidths and symmetrical with respect to a central frequency, wherein one spectral component is generated based on an image frequency related to the other spectral component, so as to obtain the first beat frequency signal and the second beat frequency signal, wherein the third signal is a function of the received signal; and

- filtering separately each of the first beat frequency signal and the second beat frequency signal so as to remove an unwanted image signal.

5. The method according to one of claims 1 to 4, further comprising a step of separately converting the first beat frequency signal and the second beat frequency signal from analog to digital form before mixing the first beat frequency signal and the second beat frequency signal together.

6. The method according to one of claims 1 to 4, further comprising a step of converting the first beat frequency signal and the second beat frequency signal are converted from analog to digital form after mixing the first beat frequency signal and the second beat frequency signal together.

7. The method according to one of claims 1 to 6, wherein the received signal comprises a plurality N of spectral components in a plurality N of sub-bandwidths, so that a plurality N of beat frequency signals are obtained, wherein N is greater than two, and the method further comprises a step of mixing the beat frequency signals together in a plurality of N-1 mixing steps.

8. The method according to claim 7, wherein the plurality N is an even number greater than 2.

9. The method according to claim 2, further comprising a step of amplifying the received signal before mixing the received signal with the carrier signal.

10. The method according to claim 1, further comprising a step of selecting at least one of the beat frequency signals or the mixed signal for processing.

11. The method according to claim 10, further comprising a step of determining a range value corresponding to the distance between a target and the radar apparatus, and wherein the step of selecting the selected signal for processing is based on the determined range value.

12. The method according to claim 11, further comprising the steps of:

- determining a signal resolution for the mixed signal and one of the first or second beat frequency signals;

- determining a resolution to apply, based on the determined range value;

- comparing the resolution to apply with each of the signal resolutions; and

- selecting one of the signals for processing.

13. The method according to claim 11, further comprising the steps of:

- adding the mixed signal with one of the first or second beat frequency signals so as to obtain an added signal;

- converting the added signal to a digital form by means of an analog to digital converter; and

- filtering the converted signal based on a determined range value.

14. A radar receiver apparatus configured to receive a signal comprising at least a first spectral component in a first sub-bandwidth and a second spectral component in a second sub-bandwidth, the receiver apparatus comprising:

- a filter configured to filter the received signal by separately filtering out the first sub-bandwidth and the second sub-bandwidth so as to respectively obtain a first signal related to the function of the first spectral component and a second signal related to the function of the second spectral component;

- circuitry for obtaining, from the first signal and the second signal, a first beat frequency signal and a second beat frequency signal respectively; and

- a mixer to mix the first beat frequency signal and the second beat frequency signal so as to obtain a mixed signal.

15. The receiver apparatus according to claim 14, further comprising an antenna configured to receive the signal and a mixer arranged between the antenna and the filter, the mixer being configured to mix the received signal with a carrier signal so as to obtain a signal wherein the carrier signal has been removed.

16. The receiver apparatus according to one of claims 14 or 15, further comprising, after the filter:

- a mixer configured to mix separately each of the first signal and the second signal with a first base frequency and a second base frequency respectively so as to extract a first base frequency signal from the first signal and a second base frequency signal from the second signal respectively;

- a filter configured to filter separately the first base frequency signal and the second base frequency signal so as to remove unwanted spectral components; and

- a mixer configured to mix separately the filtered first and second base frequency signals with a continuous wave signal so as to obtain the first beat frequency signal and the second beat frequency signal respectively.

17. The receiver apparatus according to one of claims 14 or 15, further comprising, after the filter:

- a mixer configured to mix separately each of the first signal and the second signal with a third signal characterized by an instantaneous frequency composed the first spectral component and the second spectral component, the spectral components evolving over time with the sub-bandwidths and symmetrical with respect to a central frequency, wherein one spectral component is generated based on an image frequency related to the other spectral component, so as to obtain the first beat frequency signal and the second beat frequency signal, wherein the third signal is a function of the received signal; and

- a filter configured to filter separately each of the first beat frequency signal and the second beat frequency signal so as to remove an unwanted image signal.

18. The receiver apparatus according to one of claims 14 to 17, further comprising an analog to digital converter configured to convert separately from analog to digital form each of the first beat frequency signal and the second beat frequency signal before they are supplied to the mixer.

19. The receiver apparatus according to one of claims 14 to 17, further comprising an analog to digital converter configured to convert from analog to digital form the first beat frequency signal and second beat frequency signal after they have been mixed together by the mixer.

20. The receiver apparatus according to one of claims 14 to 19, configured to process a received signal comprising a plurality N of spectral components in a plurality N of frequency sub-bands, so that a plurality N of beat frequency signals are obtained, wherein N is greater than two, and wherein a plurality of N-1 mixers are supplied to mix together the beat frequency signals.

21. The receiver apparatus according to claim 20, wherein the plurality N is an even number greater than 2.

22. The receiver apparatus according to claim 15, further comprising an amplifier configured to amplify the received signal before it is supplied to mixer that mixes the received signal with the carrier signal.

23. The receiver apparatus according to claim 14, further comprising a means for selecting at least one of the beat frequency signals or the mixed signal for processing.

24. The receiver apparatus according to claim 23, further comprising a processor configured to determine a range value corresponding to the distance between a target and the radar apparatus, and wherein the step of selecting the selected signal for processing is based on the determined range value.

25. The receiver apparatus according to claim 24, wherein the processor is further configured to:

- determine a signal resolution for the mixed signal and one of the first or second beat frequency signals;

- determine a resolution to apply, based on the determined range value;

- compare the resolution to apply with each of the signal resolutions; and

- select one of the signals for processing.

26. The receiver apparatus according to claim 24, further comprising:

- an adder to add the mixed signal with one of the first or second beat frequency signals so as to obtain an added signal;

- an analog to digital converter configured to convert the added signal to a digital form; and

5 - a filter to filter the converted signal based on a determined range value.

24 08 17

Intellectual

Property

Office

Application No: GB1615207.6

26. The receiver apparatus according to claim 24, further comprising:

- an adder to add the mixed signal with one of the first or second beat frequency signals so as to obtain an added signal;

- an analog to digital converter configured to convert the added signal to a digital form; and

- a filter to filter the converted signal based on a determined range value.

27. A radar apparatus substantially as hereinbefore described with reference to, and as shown in Figures 4, 5, 6, 8, and 10.

Amendments to the claims have been filed as follows:

24 08 17

1. A method of receiving and processing, by a radar apparatus, a signal comprising at least a first spectral component in a first sub-bandwidth and a second

5 spectral component in a second sub-bandwidth, the method comprising the steps of:

- filtering the received signal by separately filtering out the first sub-bandwidth and the second sub-bandwidth so as to respectively obtain a first signal related to the first spectral component and a second signal related to the second spectral component;

10 - obtaining separately, from the first signal and the second signal, a first beat frequency signal and a second beat frequency signal respectively; and

- mixing the first beat frequency signal and the second beat frequency signal so as to obtain a mixed signal.

15 2. The method according to claim 1, further comprising, before filtering the received signal, a step of mixing the received signal with a carrier signal so as to obtain a signal wherein the carrier signal has been removed.

3. The method according to one of claims 1 or 2, further comprising, after the

20 step of filtering the received signal, the steps of:

- mixing separately each of the first signal and the second signal with a first base frequency and a second base frequency respectively so as to extract a first base frequency signal from the first signal and a second base frequency signal from the second signal respectively;

25 - filtering separately the first base frequency signal and the second base frequency signal so as to remove unwanted spectral components; and

- mixing separately the filtered first base frequency signal and the filtered second base frequency signal with a continuous wave signal so as to obtain the first beat frequency signal and the second beat frequency signal respectively.

4. The method according to one of claims 1 or 2, further comprising, after the step of filtering the mixed signal, the steps of:

- mixing separately each of the first signal and the second signal with a third signal characterized by an instantaneous frequency composed of the first spectral

35 component and the second spectral component, the spectral components evolving

24 08 17 over time within the sub-bandwidths and symmetrical with respect to a central frequency, wherein one spectral component is generated based on an image frequency related to the other spectral component, so as to obtain the first beat frequency signal and the second beat frequency signal, wherein the third signal is a function of the

5 received signal; and

- filtering separately each of the first beat frequency signal and the second beat frequency signal so as to remove an unwanted image signal.

5. The method according to one of claims 1 to 4, further comprising a step of 10 separately converting the first beat frequency signal and the second beat frequency signal from analog to digital form before mixing the first beat frequency signal and the second beat frequency signal together.

6. The method according to one of claims 1 to 4, further comprising a step of 15 converting the first beat frequency signal and the second beat frequency signal are converted from analog to digital form after mixing the first beat frequency signal and the second beat frequency signal together.

7. The method according to one of claims 1 to 6, wherein the received signal 20 comprises a plurality N of spectral components in a plurality N of sub-bandwidths, so that a plurality N of beat frequency signals are obtained, wherein N is greater than two, and the method further comprises a step of mixing the beat frequency signals together in a plurality of N-1 mixing steps.

25 8. The method according to claim 7, wherein the plurality N is an even number greater than 2.

9. The method according to claim 2, further comprising a step of amplifying the received signal before mixing the received signal with the carrier signal.

10. The method according to claim 1, further comprising a step of selecting a selected signal comprising at least one of the beat frequency signals or the mixed signal in order to select an appropriate mode of operation.

24 08 17

11. The method according to claim 10, further comprising a step of determining a range value corresponding to the distance between a target and the radar apparatus, and wherein the step of selecting the selected signal is based on the determined range value.

12. The method according to claim 11, further comprising the steps of:

- determining a signal resolution for the mixed signal and one of the first or second beat frequency signals;

- determining a resolution to apply, based on the determined range value;

10 - comparing the resolution to apply with each of the signal resolutions; and

- selecting the selected signal.

13. The method according to claim 11, further comprising the steps of:

- adding the mixed signal with one of the first or second beat frequency signals 15 so as to obtain an added signal;

- converting the added signal to a digital form by means of an analog to digital converter; and

- filtering the converted signal based on a determined range value.

20 14. A radar receiver apparatus configured to receive and process a signal comprising at least a first spectral component in a first sub-bandwidth and a second spectral component in a second sub-bandwidth, the receiver apparatus comprising:

- a filter configured to filter the received signal by separately filtering out the

25 first sub-bandwidth and the second sub-bandwidth so as to respectively obtain a first signal related to the function of the first spectral component and a second signal related to the function of the second spectral component;

- circuitry for obtaining, from the first signal and the second signal, a first beat frequency signal and a second beat frequency signal respectively; and

30 - a mixer to mix the first beat frequency signal and the second beat frequency signal so as to obtain a mixed signal.

15. The receiver apparatus according to claim 14, further comprising an antenna configured to receive the signal and a mixer arranged between the antenna

24 08 17 and the filter, the mixer being configured to mix the received signal with a carrier signal so as to obtain a signal wherein the carrier signal has been removed.

16. The receiver apparatus according to one of claims 14 or 15, further 5 comprising, after the filter:

- a mixer configured to mix separately each of the first signal and the second signal with a first base frequency and a second base frequency respectively so as to extract a first base frequency signal from the first signal and a second base frequency signal from the second signal respectively;

10 - a filter configured to filter separately the first base frequency signal and the second base frequency signal so as to remove unwanted spectral components; and

- a mixer configured to mix separately the filtered first and second base frequency signals with a continuous wave signal so as to obtain the first beat frequency signal and the second beat frequency signal respectively.

17. The receiver apparatus according to one of claims 14 or 15, further comprising, after the filter:

- a mixer configured to mix separately each of the first signal and the second signal with a third signal characterized by an instantaneous frequency composed the

20 first spectral component and the second spectral component, the spectral components evolving over time with the sub-bandwidths and symmetrical with respect to a central frequency, wherein one spectral component is generated based on an image frequency related to the other spectral component, so as to obtain the first beat frequency signal and the second beat frequency signal, wherein the third signal is a function of the

25 received signal; and

- a filter configured to filter separately each of the first beat frequency signal and the second beat frequency signal so as to remove an unwanted image signal.

18. The receiver apparatus according to one of claims 14 to 17, further

30 comprising an analog to digital converter configured to convert separately from analog to digital form each of the first beat frequency signal and the second beat frequency signal before they are supplied to the mixer.

19. The receiver apparatus according to one of claims 14 to 17, further

35 comprising an analog to digital converter configured to convert from analog to digital

24 08 17 form the first beat frequency signal and second beat frequency signal after they have been mixed together by the mixer.

20. The receiver apparatus according to one of claims 14 to 19, configured to 5 process a received signal comprising a plurality N of spectral components in a plurality N of frequency sub-bands, so that a plurality N of beat frequency signals are obtained, wherein N is greater than two, and wherein a plurality of N-1 mixers are supplied to mix together the beat frequency signals.

10 21. The receiver apparatus according to claim 20, wherein the plurality N is an even number greater than 2.

22. The receiver apparatus according to claim 15, further comprising an amplifier configured to amplify the received signal before it is supplied to mixer that

15 mixes the received signal with the carrier signal.

23. The receiver apparatus according to claim 14, further comprising a means for selecting a selected signal comprising at least one of the beat frequency signals or the mixed signal in order to select an appropriate mode of operation.

24. The receiver apparatus according to claim 23, further comprising a processor configured to determine a range value corresponding to the distance between a target and the radar apparatus, and wherein the step of selecting the selected signal is based on the determined range value.

25. The receiver apparatus according to claim 24, wherein the processor is further configured to:

- determine a signal resolution for the mixed signal and one of the first or second beat frequency signals;

30 - determine a resolution to apply, based on the determined range value;

- compare the resolution to apply with each of the signal resolutions; and

- select the selected signal.