Arrangement for detecting objects in a region to be monitored

• US 5,774,045 A
• Filed: 05/19/1997
• Issued: 06/30/1998
• Est. Priority Date: 07/18/1994
• Status: Expired due to Fees

• Current Assignee: Siemens AG
• Original Assignee: Siemens AG
• Inventors: Lubbe, Bodo, Helma, Hans
• Primary Examiner(s): Lefkowitz, Edward
• Application Number:
  US08/776,461
• Time in Patent Office: 407 Days
• Field of Search: 340/436, 340/568, 340/572, 342/42, 342/44, 342/361, 342/362
• US Class Current: 340/436
• CPC Class Codes: B61L 29/00 Safety means for rail/road crossing traffic
• CPC Class Codes: F16P 3/147 using electro-magnetic technology, e.g. tags or radar
• CPC Class Codes: G01S 13/04 Systems determining presence of a target based on relative movement of target G01S13/56
• CPC Class Codes: G01S 13/34 using transmission of continuous, frequency-modulated waves while heterodyning the received signal, or a signal derived therefrom, with a locally-generated signal related to the contemporaneously transmitted signal
• CPC Class Codes: G01S 13/755 using delay lines, e.g. acoustic delay lines
• CPC Class Codes: G01S 13/76 wherein pulse-type signals are transmitted
• CPC Class Codes: G01S 13/82 wherein continuous-type signals are transmitted
• CPC Class Codes: G01S 7/025 involving the transmission of linearly polarised waves
• CPC Class Codes: G01S 7/026 involving the transmission of elliptically or circularly polarised waves
• CPC Class Codes: H01Q 1/3225 Cooperation with the rails or the road
• CPC Class Codes: H01Q 3/46 Active lenses or reflecting arrays

Abstract

A transmitter/receiver unit and a reflector unit are installed at opposite ends of a region to be monitored. The reflector unit consists of a receiving antenna whose signal is sent to a surface wave transit time element via a Wilkinson divider or a circulator. The signal returned from the latter is sent by the Wilkinson divider or the circulator to an amplifier that supplies a transmitting antenna, which in turn sends the signal back to the transmitter/receiver unit. Objects in the field of the beam cause a change in amplitude of the reflected signal, so the object can be detected with the help of an analyzer unit, namely an amplitude discriminator in the simplest case. The signals may be pulsed radar signals. It is advantageous, however, to use frequency-modulated signals corresponding to FMCW radar, so the frequency difference between the transmitted and reflected signal can also be used as a criterion for objects present in the monitored region in addition to using the amplitude of the reflected signal. The present invention can be used for monitoring railroad crossings.

Claims

1. A system for detecting an object in a region to be monitored comprising:

a transmitter unit located on a side of the region;

a reflector unit located on a side of the region opposite the side on which the transmitter is located, the reflector unit including a transit time element;

a receiver unit located on a side of the region opposite the side on which the reflector unit is located; and

an analyzer unit coupled to the receiver unit, wherein;

the transmitter unit transmits a signal to the reflector unit,

the reflector unit reflects to the receiver unit the signal received from the transmitter unit after a period of time determined by the transit time element,

the analyzer unit analyzes the signal received by the receiver unit, the analyzer analyzing at least one of a transit time and an amplitude of the received signal,

the reflector unit includes a reflector receiving antenna coupled to the transit time element via a directional separating filter which provides a signal returning from the transit time element to an amplifier which drives a reflector transmitting antenna, and

a coupling between the reflector receiving antenna and the reflector transmitting antenna is smaller than a gain of the amplifier.

2. The system of claim 1, wherein the signal transmitted by the transmitter unit to the reflector unit has a different polarization than the signal reflected by the reflector unit to the receiver unit.

3. The system of claim 2, wherein the signal transmitted by the transmitter and the signal reflected by the reflector unit are polarized linearly with an angle of 90°

relative to one another.

4. The system of claim 1, wherein the signal transmitted by the transmitter and the signal reflected by the reflector unit are circularly polarized.

5. The system of claim 1, wherein the signal transmitted by the transmitter is pulsed.

6. The system of claim 1, wherein the transit time element is a surface wave element.

7. The system of claim 1, wherein:

the signal transmitted by the transmit unit is frequency modulated,

the receiver unit forms a differential signal with a frequency difference between the signal transmitted and the signal reflected and having an amplitude that corresponds to an amplitude of the reflected signal, and

the receiver unit generates a status signal when the amplitude of the differential signal changes by more than a predetermined amount.

8. The system of claim 7 comprising a plurality of receiver units arranged with a spatial separation between them so that the receiver units receive a reflected beam of the transmitter unit, wherein a heterodyne signal is frequency modulated in the same way as the signal transmitted by the transmitter unit.

9. The system of claim 1, wherein:

a spectral analysis of the received signal is performed in the receiver unit, and

a status signal is generated if a characteristic quantity of a spectrum of the received signal differs by more than a predetermined amount from a normal value.

10. The system of claim 1, wherein:

a power of the transmitter unit is altered,

a status signal is delivered when operation is error-free, and

the system is monitored for the occurrence of a status signal.