A radar includes a transmission section, a heterodyne reception section, a power supply section and a detection section. The transmission section emits a transmission wave to a target. The heterodyne reception section receives a reflected wave from the target. The power supply section supplies power to the reception section. A switching frequency of the power supply section is in synchronization with a local oscillation frequency of the reception section. The detection section determines that the switching frequency is out of synchronization with the local oscillation frequency when a certain peak frequency existing in an output signal of the reception section before a transmission state of the transmission section is changed still exists in the output signal of the reception section after the transmission state of the transmission section is changed.

In a radio wave radar system using a two-frequency CW modulation method, it is possible to detect a distance between a host vehicle and a forward vehicle and to realize a stable ACC following travel, even in a condition in which the relative speed is 0. By combining the two-frequency CW modulation method with the frequency pulse CW modulation method, that is, by using combination with the two-frequency CW method when the relative speed occurs and the frequency pulse CW method when the relative speed is close to 0, even if the relative speed is 0, the IF signal obtained from the reflected wave from the forward vehicle can be generated to detect the existence of the ACC target vehicle, so that it is possible to realize a stable ACC following travel.

A high-frequency oscillation apparatus wherein an oscillation signal output from a voltage controlled oscillator (VCO) is transferred through a transfer line to a resonator and the resonator is excited. The resonator is coupled with a second transfer line and an RF signal having a level corresponding to the frequency of the oscillation signal is transferred through the second transfer line. When the resonant frequency of the resonator is set to a frequency higher than the oscillation-frequency modulation range of the VCO, the oscillation frequency and the RF-signal level have one-to-one correspondence. A detector detects the RF signal and outputs to a control section. The control section compensates a control voltage signal applied to the VCO according to the detected-signal level, and outputs the control voltage signal to the VCO to compensate the oscillation signal of the VCO.

An FM-CW radar apparatus capable of detecting a stationary object, in particular, an overbridge, located above the road ahead in a simple manner uses a traveling wave antenna as a transmitting antenna, and includes a means for varying, in upward and downward directions the projection angle of a combined beam pattern of a transmitted wave radiated from the traveling wave antenna, and an overbridge is detected by varying the projection angle of the combined beam pattern in the upward direction using the varying means. Further, a phase shifter for varying the projection angle of the beam pattern in upward/downward directions by controlling the phase of the radio wave to be transmitted or received is provided on either a transmitting antenna or a receiving antenna or on a transmitting/receiving antenna, and an overbridge is detected by controlling the phase shifter and varying the projection angle of the beam pattern in the upward direction.