Communications: directive radio wave systems and devices (e.g. – Clutter elimination
Reexamination Certificate
2002-12-18
2004-09-28
Lobo, Ian J. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Clutter elimination
C342S018000, C342S202000, C342S203000
Reexamination Certificate
active
06798375
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a radar device including means for generating a carrier signal with a carrier frequency f
T
, means for generating pulses with a pulse repetition frequency f
PW
, means for distributing the carrier signal to a transmission branch and a receiving branch, means for delaying the pulses, means for modulating the carrier signal in the transmission branch using the delayed pulses and for generating a reference signal, means for mixing the reference signal in the receiving branch with a received signal, and means for integrating the mixed signal. The present invention also relates to a method of suppressing the interference in a radar device including the steps: generating a carrier signal having a carrier frequency f
T
, generating pulses having a pulse repetition frequency f
PW
, distributing the carrier signal to a transmission branch and a receiving branch, generating the pulses, modulating the carrier signal in the transmission branch using the undelayed pulses, modulating the carrier signal in the receiving branch using the delayed pulses and generating a reference signal, mixing the reference signal in the receiving branch with a received signal, and integrating the mixed received signal.
BACKGROUND INFORMATION
Radar devices and methods according to the related art are used, for example, in short-range sensing systems in motor vehicles. They are used, for example, to prevent accidents or to detect objects in a blind spot of a motor vehicle.
FIG. 1
shows a schematic view of the basic structure of a radar device of the related art. A local oscillator (LO)
110
generates a carrier frequency f
T
. This carrier frequency is distributed by a power divider
116
to a transmission branch and a receiving branch. In addition to carrier frequency f
T
, a pulse generator
112
provides a pulse repetition frequency f
PW
to modulate the carrier frequency. In the transmission branch, this modulation occurs using switch
120
, to which the carrier frequency is applied and which is switched with the pulse repetition frequency. The signal thus generated is emitted by a transmitting antenna
136
. A modulation also occurs in the receiving branch. However, the pulses of the pulse repetition frequency are delayed by a delaying device
118
for the purpose of this modulation. These delayed pulses are used to modulate carrier frequency f
T
by operating switch
122
, to which the carrier frequency is also applied. In this way, a reference signal S
R
is made available in the receiving branch. This reference signal is mixed in a mixer
124
with a received signal received via receiving antenna
134
. The output signal of mixer
124
is supplied to an integrating means
126
, for example, a low-pass filter and an amplifier. The signal thus generated is supplied to a signal analyzer and controller
138
, preferably after analog/digital conversion. Signal analyzer and controller
138
now determines the delay of delaying device
118
, which is varied between a value &Dgr;t
min
and &Dgr;t
max
. For example, the delay may be varied by a microcontroller or by a digital signal processor. It is also conceivable that special hardware is used for this purpose. If the transit time of the radar pulses, which as a rule is equal to twice the transit time between the target and antenna, is identical to the delay, the amplitude of the output signal of mixer
126
is at its maximum. A correlation receiver is thus available via which the distance to the target and the radial speed between the target and antenna may be inferred from the delay set by controller
138
. By way of example,
FIG. 1
shows only the formation of the in-phase (I) signal. The quadrature (Q) signal is formed in an analogous manner by mixing with the carrier frequency, which is 90° out of phase.
It is basically desirable to suppress interference signals originating from highly varied sources. The use of additional modulation of the microwave signal to separate the signal components reflected by the targets from interference signals has already been described. Such methods in particular suppress interference by other uncoded transmitters, broadcast transmitters for example, or noise.
However, radar devices are also subject to noise resulting from parasitic effects which are essentially independent of the effect of other radar sensors. Thus, for example, switches
120
,
122
in
FIG. 1
have in reality a finite ratio between the resistances in the off or on condition R
off
/R
on
. In addition, undesirable emissions or bridging of the carrier frequency arise from the local oscillator, for example, to the reference input of the mixer. This means that an approximately continuous leakage signal having the carrier frequency and low amplitude is transmitted in the transmission pauses between the radar pulses. This leakage signal in particular is also present irrespective of the delay set in the reference branch and is mixed with the received signal. As a result of this and other parasitic effects, an interference signal is received in addition from targets located outside the distance range (range gate) momentarily set by the delay in the reference signal. If such “undesirable” targets have a large backscattering cross-section or they are within short range of the sensor, then the interference signal amplitude may be on the order of magnitude of the desired signal amplitude or exceed it and consequently result in measurement errors.
It is possible to improve the R
off
/R
on
ratio and accordingly reduce the interference signal amplitude by using, for example, several switches linked in series. However, this increases the technical complexity and consequently the costs.
SUMMARY OF THE INVENTION
According to a first embodiment, the present invention builds on a radar device of the related art by providing means for binary phase shift keying (BPSK) modulation of the carrier signal. BPSK modulation of the carrier signal may be used to integrate interference signals with constantly alternating signs in the subsequent integration while the desired signal is integrated with a constant sign. The interference signals are suppressed in this manner.
According to a second embodiment, the present invention builds on a radar device of the related art by providing means to switch the polarity of the received signal. In this manner, the subsequent integration suppresses the interference signals to a great extent while the desired signals are further processed.
Preferably, means are provided for BPSK modulation of the carrier signal in the transmission branch. In this variant, the carrier signal in the receiving branch may be supplied to the mixer as a reference signal without BPSK modulation. However, modulation takes place in the receiving branch so that the information necessary for the interference signal suppression is present there.
However, it may also be advantageous to provide means for BPSK modulation of the carrier signal in the receiving branch. In this case, a BPSK-modulated carrier signal is used as a reference signal while the transmitted signal is transmitted unmodulated. The information necessary for the interference signal suppression is contained in the carrier signal in the receiving branch.
It is useful in particular if the BPSK modulation results in a switchover of the phase angle for half a period T
PW
of pulse repetition frequency f
PW
. In this way, the phase of the modulated carrier signal is switched between 0° and 180° after each half period. This periodic switchover of the phase angle advantageously ensures that the interference signals are integrated with a constantly alternating sign while the desired signal is integrated with a constant sign. Referring to two periods in each case, a pulse is generated in the transmission branch in each of the first and second half periods T
PW
and in the receiving branch in each of the first and fourth half periods. The process is repeated after every two periods.
For effective interference signal suppression, it is advantageous in particular
Lobo Ian J.
Robert & Bosch GmbH
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