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Radar apparatus

Radar apparatus description/claims

This application is based on and incorporates herein by reference Japanese Patent Application No. 2005-224636 filed on Aug. 2, 2005.

The present invention relates to a radar apparatus.

There are various types of radar apparatus for detecting a distance and a direction of an object with respect to the radar apparatus. A frequency modulated continuous wave (FMCW) radar apparatus is a radar apparatus that continuously transmits a frequency-modulated radar signal to the object and detects the distance or a relative velocity of the object based on the transmitted radar signal reflected from the object.

In one method for detecting the direction of the object, a transmitting means for transmitting a radar signal mechanically turns and scans the transmitted radar signal reflected from the object. In another method that uses a digital beam forming (DBF) algorithm, the transmitting means is fixed and an antenna having multiple elements arranged in an array receives the transmitted radar signal. The received radar signal is digitally processed and the direction of the object is detected based on the digital signal. Specifically, in the DBF algorithm, an angular spectrum is generated based on the received radar signal on each of the elements and a peak of the angular spectrum is detected. The direction of the object is estimated based on the peak of the angular spectrum.

In a beamformer algorithm as the DBF algorithm, the angular spectrum is generated such that amplitudes of the received signal at a given time are connected as shown in FIGS. 10A and 10B. A multiple signal classification (MUSIC) algorithm is known as a high-resolution direction of arrival (DOA) estimation algorithm.

In the DOA estimation algorithm, correlation matrices are calculated, eigenvalue expansions are performed on each of the correlation matrices, the angular spectrum is calculated from eigenvectors of the correlation matrices, and the direction of the object is calculated based on the angular spectrum.

A FMCW radar apparatus disclosed in U.S. Pat. No. 6,121,917 corresponding to JP-A-H11-133142 detects the direction of the object by using the beamformer algorithm. In the FMCW radar apparatus, a fast Fourier transform (FFT) is applied to the received wave signal to obtain a peak frequency of a distance power spectrum. Then, the beamformer algorithm is applied to only the peak frequency component of the received signal so that the amount of calculation required to detect the direction of the object is reduced.

However, when the beamformer algorithm is used in the radar apparatus, resolution of the radar apparatus depends on the number of elements arranged in the array. Therefore, the radar apparatus using the beamformer algorithm needs to be increased in size to obtain high resolution.

The high-resolution DOA estimation algorithm such as the MUSIC algorithm achieves the high resolution without an increase in the number of the elements. In the DOA estimation algorithm, the resolution may be increased by reducing noise with summation of the received signal with respect to time. The summation is performed such that a present angular spectrum calculated in a present process and a previous angular spectrum calculated in a previous process are summed up.

However, when the object moves, a frequency corresponding to the distance changes between in the previous process and in the present process. Therefore, the DOA estimation algorithm needs to be applied to all the frequency components of the received signal on each process to calculate the angular spectrum, and the calculated angular spectrum needs to be stored in a memory. The calculation of the angular spectrum requires an eigenvalue expansion that requires a lot of calculation. Therefore, when the angular spectrum is calculated on each frequency component, the amount of calculation is significantly increased. In the DOA estimation algorithm, the high resolution results in a significant increase in the amount of calculation.

In view of the above-described problem, it is an object of the present invention to provide a radar apparatus that achieves a high resolution without a significant increase in the amount of calculation.

A radar apparatus uses a DOA estimation algorithm performed at a predetermined time interval to detect an object. The radar apparatus includes a transmitting means that transmits a wave signal to the object, a receiving means that receives the transmitted wave signal reflected from the object, a beat signal generation means that generates a plurality of beat signals based on the received wave signal, a correlation matrix generation means that calculates a plurality of correlation matrices based on the beat signals with respect to each frequency component of the beat signals, an addition means that calculates a plurality of addition correlation matrices, a storing means that stores at least a portion of a plurality of previous correlation matrices calculated by the correlation matrix generation means at a previous time, a detection means that detects at least one frequency component of the beat signals, the frequency component satisfying a predetermined condition, an extraction means that extracts an extraction matrix from the addition correlation matrices, the extraction matrix corresponding to a frequency component closest to the frequency component detected by the detection means, and a direction calculation means that calculates a direction of the object with respect to the radar apparatus based on the extraction matrix. The receiving means includes a plurality of elements arranged in an array and each of the beat signals generated by the beat signal generation means corresponds to each of the elements. The addition means calculates the addition correlation matrices by adding the correlation matrices calculated by the correlation matrix generation means to the previous correlation matrices stored by the storing means.

In a conventional DOA estimation algorithm, correlation matrices are generated from beat signals. Then, angular spectrums are calculated from each eigenvector of each of the correlation matrices. The storing means stores the angular spectrums as previous information and the angular spectrums are used in a next process to reduce noise.

In the DOA estimation algorithm used in the radar apparatus, a position of the object (i.e., a frequency component indicating a presence of the object) is estimated from the beat signals and then an angular spectrum corresponding to the position is calculated. Correlation matrices calculated in a present process and previous correlation matrices calculated in a previous process are summed up to reduce noise. In the radar apparatus, therefore, the storing means stores the correlation matrices as the previous information, not the angular spectrums.

For example, in a MUSIC algorithm, the amount of calculation required to calculate the correlation matrices is about one-thirteenth the amount of calculation required to calculate MUSIC spectrums. Because the radar apparatus uses the correlation matrices instead of the angular spectrums to reduce the noise, a significant increase in the amount of calculation can be prevented. Thus, the radar apparatus achieves a high resolution without the significant increase in the amount of calculation.

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