The disclosed technique includes transmitting a signal intermittently according to a transmission cycle having a predetermined transmission period and a non-transmission period; receiving the signal reflected from a target with reception antennas; and detecting the target from the reflected signal. A high-frequency transmission signal attenuated during the transmission period and a receipt signal received during the non-transmission period are combined together. A correlation value between a reference transmission signal and the receipt signal in the combined signal is calculated, and the amount of phase shift in an arbitrarily selected reception antenna is calculated from the correlation value of a reference reception antenna, and the correlation values of the other reception antennas. The phase component of the correlation value of the arbitrarily selected reception antenna is corrected on the basis of the amount of phase shift.
1. A radar device for transmitting a high-frequency transmission signal intermittently in a transmission cycle having a predetermined transmission period and a non-transmission period, receiving a signal reflected by a target by using a plurality of reception antennas, and detecting the target based on the reflected signal, the radar device comprising:
a transmission signal generator which generates a transmission signal in baseband;
a RF transmitter which converts the transmission signal generated by the transmission signal generator into a high-frequency transmission signal;
a directional coupler which distributes the high-frequency transmission signal converted by the RF transmitter in accordance with a predetermined signal power ratio;
a level adjuster which adjusts the high-frequency transmission signal distributed by the directional coupler to a predetermined level;
a signal combiner which combines a signal output from the level adjuster and a reception signal received by the reception antennas;
a RF receiver which converts the signal combined by the signal combiner into a reception signal in the baseband;
a reference transmission signal generator which generates a reference transmission signal the same as the transmission signal generated by the transmission signal generator;
a correlation value calculator which calculates a correlation value between the reference transmission signal generated by the reference transmission signal generator and the reception signal converted by the RF receiver;
a phase shift quantity calculator which calculates a phase shift quantity in arbitrary one of the reception antennas based on the correlation value in a reference reception antenna which is specific one of the reception antennas and the correlation value in any one of the other reception antennas; and
a phase corrector which corrects a phase component of the correlation value in the arbitrary reception antenna based on the phase shift quantity calculated by the phase shift quantity calculator.
2. The radar device according to claim 1 , further comprising:
a first switch which changes the reception antennas sequentially and selects a single reception antenna from the reception antennas,
wherein the signal combiner combines the signal output from the level adjuster and a reception signal received by the single reception antenna selected by the first switch in the transmission period.
3. The radar device according to claim 2 , further comprising:
a switch controller which controls the first switch in sync with the transmission cycle of the transmission signal generated by the transmission signal generator.
4. The radar device according to claim 3 , wherein the level adjuster attenuates the high-frequency transmission signal output from the directional coupler to such a degree that the high-frequency transmission signal becomes sufficiently higher than the reception signal in the transmission period.
5. The radar device according to claim 3 , further comprising:
an A/D converter which converts the reception signal converted by the RF receiver into digital data.
6. The radar device according to claim 3 , further comprising:
a timing controller which notifies of a timing of completion of changing of the reception antennas by the switch controller through the first switch,
wherein the phase shift quantity calculator calculates a phase shift quantity in any one of the other reception antennas based on the correlation value in the reference reception antenna and the correlation value in any one of the other reception antennas calculated by the correction value calculator based on the notification of the timing by the timing controller.
7. The radar device according to claim 6 , further comprising:
a storage which stores the correlation value having the phase component corrected by the phase corrector with respect to each of the reception antennas; and
an arrival angle and distance estimator which calculates an arrival angle of the target and a distance to the target based on the correlation value stored in the storage.
8. The radar device according to claim 7 , further comprising:
a second switch which switches whether inputting of the high-frequency transmission signal attenuated by the level adjuster to the signal combiner is blocked or not,
wherein the reception signal received by each of the reception antennas includes a crosstalk signal that is the transmitted high-frequency transmission signal coming to each of the reception antennas;
wherein the correlation value calculator calculates the correlation value in each of the reception antennas in the timing of arrival of the crosstalk signal due to blocking inputting of the attenuated high-frequency transmission signal to the signal combiner by the second switch; and
wherein the phase shift quantity calculator calculates intersystem phase error from each of the reception antennas to the first switch based on the phase component of the correlation value calculated by the correlation value calculator in the timing of arrival of the crosstalk signal and the phase shift quantity in each of the reception antennas in the timing of completion of changing of the reception antennas.
9. The radar device according to claim 8 , further comprising:
a reference phase storage which stores the intersystem phase error calculated by the phase shift quantity calculator as a reference phase value with respect to each of the reception antennas,
wherein the correlation value calculator calculates the correlation value in each of the reception antennas in the timing of arrival of the crosstalk signal which comes to the reception antenna;
wherein the phase shift quantity calculator calculates the phase shift quantity in the reception antenna based on the phase component of the correlation value in the reception antenna in the timing of arrival of the crosstalk signal and the reference phase value stored in the reference phase storage; and
wherein the phase corrector corrects the phase component of the correlation value in the reception antenna calculated by the correlation value calculator based on the phase shift quantity calculated by the phase shift quantity calculator.
10. The radar device according to claim 6 , further comprising:
a second switch which switches whether inputting of the high-frequency transmission signal attenuated by the level adjuster to the signal combiner is blocked or not,
wherein the switch controller controls the second switch so that whether inputting of the high-frequency transmission signal to the signal combiner is blocked or not, is switched in accordance with a cycle of sequentially changing the reception antennas.
11. The radar device according to claim 6 , further comprising:
an intersystem fixed phase error storage which stores intersystem fixed phase error from each of the reception antennas to the first switch,
wherein the phase shift quantity calculator corrects the phase shift quantity in any one of the other reception antennas inclusive of the intersystem fixed phase error stored in the intersystem fixed phase error storage.
12. The radar device according to claim 2 , further comprising:
a switch controller which controls the transmission signal changer to change the signal combiner units sequentially in sync with the transmission cycle of the transmission signal generated by the transmission signal generator.
13. The radar device according to claim 1 , wherein the signal combiner includes a plurality of signal combiner units each of which combines the signal output from the level adjuster and a reception signal received by corresponding one of the reception antennas; and
the radar device further comprising:
a transmission signal changer which selects one of the signal combiner units and inputs the signal output from the level adjuster to the selected signal combining unit.