A transmission signal generator produces N transmission pulses for every transmission period from N (N: an integer of 2 or more) kinds of transmission code sequences and (N×M) (M: an integer of 2 or more) kinds of orthogonal code sequences, the transmission pulses being obtained by multiplying transmission codes of the N kinds of transmission code sequences, with selected N orthogonal codes of the (N×M) kinds of orthogonal code sequences. In one transmission period, a radio transmitter converts the N transmission pulses to high-frequency signals, and transmits the signals through a transmission antenna. The (N×M) kinds of orthogonal code sequences are code sequences which satisfy a predetermined mathematical expression in M transmission periods.
1. A radar device comprising:
a transmission signal generator which produces N transmission pulses for every transmission period from N (N: an integer of 2 or more) kinds of transmission code sequences and (N×M) (M: an integer of 2 or more) kinds of orthogonal code sequences, the transmission pulses being obtained by multiplying transmission codes of the N kinds of transmission code sequences, with selected N orthogonal codes of the (N×M) kinds of orthogonal code sequences; and
a radio transmitter which, in one transmission period, converts the N transmission pulses to high-frequency signals, and transmits the signals through a transmission antenna,
wherein the (N×M) kinds of orthogonal code sequences are code sequences which satisfy an expression (1) in M transmission periods; and
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wherein CNM is an orthogonal code which is multiplied with an N-th transmission code in an M-th transmission period.
2. The radar device according to claim 1 , wherein the transmission signal generator includes:
a transmission code storage which stores the N kinds of transmission code sequences;
an orthogonal code storage which stores the (N×M) kinds of orthogonal code sequences; and
an orthogonal code multiplier which multiplies transmission codes of the N kinds of transmission code sequences with N orthogonal codes which are used in the M-th transmission period in the (N×M) kinds of orthogonal code sequences.
3. The radar device according to claim 1 , further comprising:
a radio receiver which receives, through a reception antenna, reflected wave signals that are obtained by reflecting the N transmission pulses from a target, and which produces N baseband reception pulses;
N correlation calculators which calculate correlation values between the N transmission pulses in which the N orthogonal codes are multiplied, and the N reception pulses; and
a coherent adder which adds together the correlation values that are calculated over the M transmission periods.
4. The radar device according to claim 1 , further comprising:
a radio receiver which receives, through a reception antenna, reflected wave signals that are obtained by reflecting the N transmission pulses from a target, and which produces N baseband reception pulses;
(N−1) delaying devices which provide amounts of delay corresponding to from a time difference of transmission timings of first and second transmission pulses of the N transmission pulses, to a time difference of transmission timings of the first and N-th transmission pulses, to (N−1) reception pulses of the N reception pulses;
an adder which adds together the (N−1) reception pulses to which the amounts of delay are provided, and the one reception pulse to which the amounts of delay are not provided;
a correlation calculator which calculates correlation values between the N transmission pulses in which the N orthogonal codes are multiplied, and an output of the adder; and
a coherent adder which adds together the correlation values that are calculated over the M transmission periods.
5. The radar device according to claim 4 , wherein the correlation calculator calculates the correlation values by using a result of addition of codes of the N transmission pulses as a correlation coefficient.
6. The radar device according to claim 1 , further comprising:
a transmission timing controller which, for every M transmission periods, outputs a transmission timing control signal for changing intervals of transmission timings of at least two transmission pulses of the N transmission pulses,
wherein the transmission signal generator changes intervals of transmission timings of at least two transmission pulses of the N transmission pulses, based on the transmission timing control signal.
7. The radar device according to claim 1 , further comprising:
a transmission beam controller which outputs N times in one transmission period a transmission beam control signal indicating different main beam directions of the N transmission pulses in the transmission period,
wherein the radio transmitter transmits the N transmission pulses while switching the main beam directions based on the transmission beam control signal.