Radar imaging apparatus, imaging method, and program thereof

A radar imaging apparatus, comprising:

• a transmission unit configured to generate a transmission signal by spreading carrier waves using a transmission spreading code;
• a transmission antenna which radiates the transmission signal as radiation waves;
• a plurality of receiving antennas each of which receives reflected waves which are the radiation waves reflected from an object;
• a delay code generation unit configured to repeat, for M scan periods, scan processing of sequentially generating N delay codes in a scan period for scanning N range gates having mutually different distances from the radar imaging apparatus, the N delay codes being the same as the transmission spreading code and corresponding to the distances, M being an integer equal to or greater than two, and N being an integer equal to or greater than two;
• a plurality of despreading units corresponding to the respective receiving antennas and each configured to despread, by sequentially using the N delay codes, the reflected waves received by a corresponding one of the receiving antennas;
• a plurality of demodulators corresponding to said respective despreading units and each configured to perform, using the carrier waves, quadrature demodulation of the reflected waves despread by a corresponding one of said despreading units, and generate demodulated signals Rij corresponding to the reflected waves received by a corresponding one of said receiving antennas, i being an integer from one to N, and j being an integer from one to M;
• a storage unit configured to store, in association with a delay time in said delay code generation unit and a scan period, the demodulated signals Rij generated by each of said demodulators;
• a memory control unit configured to (i) repeatedly write, in said storage unit, for the M scan periods, the N demodulated signals R1j to RNj corresponding to the mutually different distances corresponding to the N delay codes in said delay code generation unit and a single scan period, and (ii) sequentially read out, from said storage unit, a group of the M demodulated signals Ri1 to RiM corresponding to same distances and mutually different scan periods;
• a Doppler frequency detection unit configured to detect, for each of said demodulators, a Doppler frequency component, a phase, and an intensity by performing frequency analysis on the M demodulated signals Ri1 to RiM read out by said memory control unit and corresponding to the same distances, the Doppler frequency component being a frequency component representing a difference between the reflected waves and the carrier waves in each of the range gates, and the phase and the intensity corresponding to the Doppler frequency component;
• and
• a direction estimation unit configured to estimate a direction of the object by (i) calculating, from the detected phase corresponding to each of said demodulators, a phase difference between said demodulators and (ii) detecting, from the calculated phase difference, a direction of arrival of the reflected waves in each of the range gates.