Vehicle-detecting apparatus using electromagnetic wave

Claim 2

A vehicle-detecting apparatus, comprising, in combination: a high-frequency section including antenna means for radiating an electromagnetic wave and for receiving a reflected wave from vehicles and means for detecting a Doppler-shifted component in terms of amplitude contained in said reflected wave; a low-frequency section, including: circuit means for selectively amplifying only a part of said Doppler-shifted component which is within a particular range; means means for wave-shaping said amplified signal component; and a timesetting circuit, including first circuit means for converting converting a plurality of shaped signals from a wave-shaping circuit into a smaller number of count signals, means extending the duration time of said plurality of shaped signals, and second circuit means operatively connected to said first circuit means for converting at least one shaped signal from said wave-shaping circuit into a larger number of count signals and means for dividing said at least one shaped signal, the number of said count signals being nearly representative of the actual number of vehicles passing through an effective range of a radiated beam of electromagnetic waves from said antenna; and fail-safe circuit means monitoring said low-frequency section and supplying an output signal to said low frequency section upon detection of an abnormal operation of said high-frequency section.

Claim 3

A vehicle-detecting apparatus according to claim 1, wherein said Doppler-shift detecting means includes means applying said reflected wave to an active element and means for mixing a portion of said reflected wave with a portion of said radiated signal.

Claim 4

A vehicle-detecting apparatus according to claim 1, wherein said Doppler-shift detecting means includes means applying said reflected wave to an active element and means for mixing a portion of said reflected wave with a portion of said radiated signal.

Claim 5

A vehicle-detecting apparatus as set forth in claim 1, characterized in that said fail-safe circuit includes a gate circuit for sending an artificial signal at a frequency of a commercial power source to said low-frequency section in the event of a power failure in said high frequency section detected in terms of a variation in the bias voltage of either one of a frequency-multiplying active element and an oscillation active element in said high-frequency section.

Claim 6

A vehicle-detecting apparatus comprising a high frequency section including a high-frequency oscillator circuit, an antenna for radiating an output of said high frequency oscillator circuit toward a ground surface and for receiving a radio wave reflected by a moving vehicle on the ground surface and a detector circuit for detecting a Doppler-shifted frequency component in the received wave; a low-frequency section including a bandpass amplifier circuit for selectively amplifying a component lying within a predetermined frequency band of said Doppler-shifted frequency component, a detector circuit for detecting only an amplitude of an output of said bandpass amplifier circuit, a wave-shaping circuit for producing a constant-amplitude output for a waveform having a varying amplitude greater than a predetermined value in an output of said detector circuit and producing zero output for a wave form having an amplitude smaller than said predetermined value, time-setting circuit means including a time-setting circuit A for holding an output of said wave-shaping circuit for a predetermined time to prevent a plurality of count outputs from being produced by a single vehicle and a time-setting circuit B for dividing, at every predetermined time interval, a single output of long duration of said wave-shaping circuit produced when a plurality of vehicles successively pass to simulate the number of passing vehicles, and an output circuit for controlling the output of said wave-shaping circuit by said time-setting circuit means to deliver a signal as an output Thereof; and a fail-safe circuit for monitoring the operation of said high-frequency section to produce an artificial signal having a substitutive frequency corresponding to said Doppler-shifted frequency when said high-frequency section becomes inoperative, thereby simulating the passing of vehicles in succession, and to send the artificial signal to said low-frequency section, thereby maintaining the operation of said vehicle-detecting apparatus in a state of detecting a predetermined number of passing vehicles by utilizing said time-setting circuit B.

Claim 7

A vehicle-detecting apparatus comprising a high frequency section including a high-frequency oscillator circuit, an antenna for radiating an output of said high frequency oscillator circuit toward a ground surface and for receiving a radio wave reflected by a moving vehicle on the ground surface and a detector circuit for detecting a Doppler-shifted frequency component in the received wave; a low-frequency section including a bandpass amplifier circuit for selectively amplifying a component lying within a predetermined frequency band of said Doppler-shifted frequency component, a detector circuit for detecting only an amplitude of an output of said bandpass amplifier circuit, a wave-shaping circuit for producing a constant-amplitude output for a waveform having a varying amplitude greater than a predetermined value in an output of said detector circuit and producing zero output for a wave form having an amplitude smaller than said predetermined value, time-setting circuit means including a time-setting circuit A for holding an output of said wave-shaping circuit for a predetermined time to prevent a plurality of count outputs from being produced by a single vehicle and a time-setting circuit B for dividing, at every predetermined time interval, a single output of long duration of said wave-shaping circuit produced when a plurality of vehicles successively pass to simulate the number of passing vehicles, and an output circuit for controlling the output of said wave-shaping circuit by said time-setting circuit means to deliver a signal as an output Thereof; and a fail-safe circuit for monitoring the operation of said high-frequency section to produce an artificial signal having a substitutive frequency corresponding to said Doppler-shifted frequency when said high-frequency section becomes inoperative, thereby simulating the passing of vehicles in succession, and to send the artificial signal to said low-frequency section, thereby maintaining the operation of said vehicle-detecting apparatus in a state of detecting a predetermined number of passing vehicles by utilizing said time-setting circuit B.

Claim 8

A vehicle-detecting apparatus as defined in claim 4, wherein said detector circuit in said high frequency section for detecting the Doppler-shifted frequency component includes means to supply a part of a transmission output produced by a high-frequency oscillator circuit comprising an active element and a Doppler-shifted frequency wave received by said active element through said antenna and to detect by utilizing a nonlinear characteristic of said active element.

Claim 9

A vehicle-detecting apparatus as defined in claim 4, wherein said fail-safe circuit comprises a gate disposed in an output circuit of an oscillator of a predetermined frequency within the Doppler frequency band, said gate being opened by a reduction in a bias voltage of an active element.

Claim 10

A vehicle-detecting apparatus as defined in claim 6, wherein a voltage source of a commercial line frequency 50 Hz. or 60 Hz. is utilized in place of said oscillator of a predetermined frequency within the Doppler frequency band.