| 摘要 |
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. |
