Communications: directive radio wave systems and devices (e.g. – Radar ew – Detection of surveilance
Reexamination Certificate
2000-04-11
2003-01-14
Gregory, Bernarr E. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Radar ew
Detection of surveilance
C342S195000
Reexamination Certificate
active
06507308
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a microwave detector, and in particular relates to an improved microwave detector structure capable of detecting very faint detection target microwave signals even when such microwave signals are buried within circuit noise.
2. Description of the Prior Art
Microwave detectors which generate an alarm upon detecting the specific microwave signals emitted by radar type speed measurement devices are known in the prior art. In general, such microwave detectors employ various heterodyne type reception systems to detect target microwave signals from the microwaves picked up by the antenna.
In microwave detectors equipped with heterodyne reception systems, the antenna output (reception signal) and the local oscillator output undergo frequency mixing in a mixer, and then after the intermediate frequency signal obtained by such mixing is amplified to an appropriate level, a signal process is carried out to convert detection target microwave signals into prescribed signals.
Namely, after carrying out frequency mixing and amplifying a desired band signal with an intermediate frequency amplifier, the intermediate frequency signal obtained thereby will have either a peak waveform when target microwave frequency signals are received, or a faint noise waveform when no target microwave frequency signals are received.
Accordingly, by detecting the peak waveform with a wave detector and outputting a digital pulse when the level of the peak waveform reaches or exceeds a prescribed threshold value, such arrangement makes it possible to output pulses only when detection target microwave signals are received, and this forms the basis of the detection process. Further, in the case where amplification is carried out with an amplifier having an amplification factor large enough to create noise saturation, the noise component will alternately appear as positive and negative high frequency signals, but when a detection target microwave frequency signal is received, the noise saturation will continue in either its positive or negative state without change, and this enables a pulse having a prescribed width to be outputted.
Incidentally, because the oscillation frequency of normal local oscillators repeatedly sweeps the frequency band occupied by the detection target microwave frequency, in the case where a single detection target microwave frequency signal is present, the intermediate frequency signal will output two peaks having a desired spacing. In this connection, the determination of whether or not such spacing forms a prescribed spacing is used as a means for judging whether or not a real microwave signal from a detection target is present.
Now, in order to accurately determine whether the received microwave signal is a real detection target microwave signal or a false signal, a signal in which the detection characteristics (i.e., S-curve characteristics) accurately reappear is inputted into a microcomputer, but because this signal that is inputted into the computer must have a cycle rate that is two-times or higher than the frequency of the S-shaped waveform, an excessive load will be placed on the circuit. In this connection, because the S-shaped waveform is not a sine wave, the signal described above generally uses a frequency as high as possible.
Further, because the reproducibility of the S-shaped waveform has a huge effect on the resolution of an A/D converter, the signals inputted into the microcomputer require the use of a high performance device such as a DSP or the like. Furthermore, because the amount of memory required depends on the resolution of the A/D converter, high resolution requires a large amount of memory. Moreover, the provision of elements needed to satisfy such requirements leads to high costs, and this makes it difficult to construct accurate microwave detectors.
On the other hand, there is another type of microwave detector known in the prior art, in which the oscillation frequency of the local oscillator carries out a sweeping operation until a detection target microwave frequency signal is detected, whereupon the oscillation frequency of the local oscillator is switched from a sweeping mode to a fixed frequency mode (i.e., a sweep stop is carried out).
In this way, in the case where a real microwave signal from a detection target is received, because the detection of the microwave signal will continue without alteration of the frequency state, by measuring the amount of time the sweep was temporarily suspended, the microwave detector can be arranged to use such time measurements as a base for judging whether or not a real microwave signal from a detection target has been received. In the case where random microwave signals such as noise or the like is received by this type of microwave detector, because such random signals will immediately disappear upon fixing the oscillation frequency of the local oscillator (i.e., upon stopping the sweep), the fixed state of the local oscillator will be released to allow the local oscillator to return to a sweeping mode. Accordingly, the local oscillator will be released from the fixed state (sweep suspension state) before the prescribed time interval has elapsed, and this makes it possible to prevent false alarms. An example of a microwave detector which uses this basic principle is disclosed in Japanese Laid-Open Patent Application No. HEI 7-35845.
Now, because this detection method only involves measuring the sweep suspension time interval, there is no need to carry out complicated waveform processing operations, and this makes it possible to construct a microwave detector having a relatively simple structure. However, in the case where a very faint microwave signal is received, such signal will become buried in the circuit noise. As a result, even when such faint microwave signal is a real microwave signal from a detection target, the sweep suspension state of the local oscillator will be released before the prescribed time interval has elapsed. Further, if the sweep suspension time is simply shortened in order to increase sensitivity, there will also be an increased risk of malfunctions due to degradation of the pulse characteristics and the like.
Further, when faint detection target microwave signals are received, the resulting output level may be relatively larger than the noise level, but the weak level of such faint microwave signals makes it difficult to accurately discriminate the case where a faint detection target microwave signal is present from the case where there is just noise with no microwave signals.
SUMMARY OF THE INVENTION
With a view toward overcoming the problems of the prior art described above, one object of the present invention is to provide a low-cost microwave detector which can carry out a highly sensitive detection of faint detection target microwave signals using a simple structure to enable accurate detections with few false alarms. Further, another object of the present invention is to make it possible to detect faint detection target microwave signals using a simple arithmetic processing portion and a small capacity memory.
One way to achieve the objects of the present invention is to construct a microwave detector from a heterodyne-type reception portion equipped with an antenna for picking up microwave signals, a local oscillator for repeatedly carrying out a sweep operation, and a mixer for frequency mixing the output from the antenna with the output from the local oscillator, wherein the heterodyne reception portion outputs detected wave signals based on the output from the mixer; a digital processing portion which receives the detected wave signals outputted from the reception portion, wherein the digital processing portion is designed to output a High pulse when the level of the detected wave signals reaches or exceeds a prescribed reference level, and a Low pulse when the level of the detected wave signals is below the reference level; a sweep control portion for controlling the sweep operation of the loca
Kajita Yuichi
Ono Hisao
Marger & Johnson & McCollom, P.C.
Yupiteru Industries Co., Ltd.
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