TECHNICAL FIELD

The present invention relates to a multiple input multiple output (hereinafter, referred to as MIMO) radar device.

BACKGROUND ART

Conventionally, there has been known a technique in which a plurality of transmission antennas transmit transmission signals different from each other, receive reflection signals formed by reflection of the transmission signals off an object, and thereby forms a MIMO beam. Note that formation of the MIMO beam corresponds to formation of a transmission beam and formation of a reception beam with respect to a reception signal.

A MIMO beam pattern obtained by forming the MIMO beam matches a transmission/reception product beam that is a product of a transmission beam pattern from a transmission antenna and a reception beam pattern from a reception antenna. In a conventional MIMO beam pattern, a transmission angle of a reflection signal (hereinafter, referred to as DOD angle) and an arrival angle of the reflection signal (hereinafter, referred to as DOA angle) are the same as each other, and it is assumed that the reflection signal is a directly propagated reflection signal.

For example, Patent Literature 1 describes a method for reducing side lobes of a MIMO beam pattern using a window function in order to reduce unnecessary reflection signals due to direct propagation (hereinafter, referred to as direct propagation clutters) included in a reception signal of a MIMO radar device.

CITATION LIST

Patent Literatures

Patent Literature 1: JP 2016-90432 A

SUMMARY OF INVENTION

Technical Problem

A reception signal of an actual MIMO radar device also includes an unnecessary reflection signal due to multipath propagation (hereinafter, referred to as multipath clutter) in addition to the direct propagation clutter.

However, the radar device described in Patent Literature 1 cannot reduce multipath clutters included in a reception signal disadvantageously because the multipath clutters are not considered.

The present invention solves the above problem, and an object of the present invention is to provide a radar device capable of reducing direct propagation clutters and multipath clutters included in a reception signal.

Solution to Problem

A radar device according to the present invention includes N transmission signal generating units, wherein N indicates two or more, N transmission antennas, M reception antennas, wherein M indicates two or more, M matched filter banks, a correlation matrix calculating unit, a diagonal load processing unit, a window function calculating unit, a window function applying unit, and a beam forming unit. The N transmission signal generating units generate transmission signals different from each other. The N transmission antennas are connected to the N transmission signal generating units one by one, and transmit transmission signals. The M reception antennas receive reflection waves of the transmission signals transmitted from the N transmission antennas, the reflection waves being formed by reflection off an object. The M matched filter banks are connected to the M reception antennas one by one, and each output a reception signal vector that is an output of a matched filter using the transmission signal generated by each of the N transmission signal generating units as a replica of the matched filter. The correlation matrix calculating unit calculates an unnecessary signal correlation matrix using a steering vector of an unnecessary signal defined on the basis of a DOD angle of the unnecessary signal and a DOA angle of the unnecessary signal. The diagonal load processing unit performs diagonal load processing on the unnecessary signal correlation matrix calculated by the correlation matrix calculating unit using a diagonal load amount, and calculates an unnecessary signal correlation matrix after the diagonal load processing. The window function calculating unit calculates a window function for obtaining a side lobe characteristic that reduces unnecessary signals on the basis of the unnecessary signal correlation matrix after the diagonal load processing, calculated by the diagonal load processing unit. The window function applying unit multiplies the reception signal vector output from the M matched filter banks by the window function calculated by the window function calculating unit, and outputs a reception signal vector to which the window function is applied. The beam forming unit forms a MIMO beam on the basis of the reception signal vector output from the window function applying unit and a beam directivity angle.

Advantageous Effects of Invention

According to the present invention, a window function is derived on the basis of a principle of suppressing reflection signals belonging to a subspace of a space defined by steering vectors of direct propagation clutters and multipath clutters to be reduced. By using this window function, the radar device can reduce direct propagation clutters and multipath clutters included in a reception signal.

