Method for calibrating a MIMO radar sensor for motor vehicles

1. A method for calibrating an antenna diagram of a multiple input, multiple output (MIMO) radar sensor having N tx transmitting antenna elements and N rx receiving antenna elements, comprising:

before commissioning of the radar sensor:

storing an antenna diagram that associates with each of a plurality of several angles θ a respective control vector a(θ) that is made up of a transmitting control vector a tx (θ) and a receiving control vector a rx (θ);

after commissioning:

performing a radar measurement to localize an object;

checking whether the localized object is a single target or a multiple target;

if the localized object is a single target:

performing a single input, multiple output (SIMO) measurement with each of the transmitting antenna elements;

estimating the angle θ of the object based on the measurement results;

calculating a first comparison variable, dependent on the components of the transmitting control vector a tx (θ), for each transmitting antenna element;

calculating a second comparison variable, dependent on the results of the SIMO measurements, for each transmitting antenna element; and

correcting the transmitting control vector a tx (θ) on the basis of a known relationship between the first and second comparison variables for each transmitting antenna element.

2. The method as recited in claim 1 , wherein the following relationships are used to correct the transmitting control vector a tx (θ):

a tx,n (θ)/ a tx,1 (θ)= y n (θ)/ y 1 (θ)

where a tx,n (θ) are the components of the transmitting control vector a tx (θ), a tx,1 (θ) is any one of those components, and the variables y n (θ) for all n=1 . . . N tx are defined by

y i (θ)= a rx H (θ) xi

where a rx H (θ) is the vector Hermitian-conjugated with the receiving control vector a rx (θ) and xi is a vector whose components indicate complex amplitudes of signals that were transmitted by the i-th transmitting antenna element and were received by the N rx receiving antenna elements.

3. The method as recited in claim 1 , wherein the following relationships are used to correct the transmitting control vector a tx (θ):

a tx,n (θ)/ a tx,1 (θ)=(1/ N rx ) Σ k ( x n,k /x 1,k )

where a tx,n (θ) are the components of the transmitting control vector a tx (θ), a tx,1 (θ) is any one of those components, and the variables x n,k indicate complex amplitudes of signals that were transmitted by the n-th transmitting antenna element and were received by the k-th receiving antenna element.

4. A method for calibrating an antenna diagram of a multiple input, multiple output (MIMO) radar sensor having N tx transmitting antenna elements and N rx receiving antenna elements, the method comprising:

before commissioning of the radar sensor:

storing an antenna diagram that associates with each of a plurality of several angles θ a respective control vector a(θ) that is made up of a transmitting control vector a tx (θ) and a receiving control vector a rx (θ),

after commissioning:

performing a radar measurement to localize an object;

checking whether the localized object is a single target or a multiple target;

if the localized object is a single target:

performing a multiple input, single output (MISO) measurement with each of the transmitting antenna elements;

estimating the angle θ of the object based on the measurement results;

calculating a first comparison variable, dependent on the components of the receiving control vector a rx (θ), for each receiving antenna element;

calculating a second comparison variable, dependent on the results of the MISO measurements, for each receiving antenna element; and

correcting the receiving control vector a rx (θ) on the basis of a known relationship between the first and second comparison variables for each receiving antenna element.

5. The method as recited in claim 4 , wherein the following relationships are used to correct the receiving control vector a rx (θ):

a rx,n (θ)/ a rx,1 (θ)= x′ n (θ)/ x′ 1 (θ)

where a rx,n (θ) are the components of the receiving control vector a rx (θ), a rx,1 (θ) is any one of those components, and the variables x′ n (θ) for all n=1 . . . N rx are defined by)

x n 1 (θ)=Σ i a tx,i *(θ) xi n

where a tx,i (θ) is the i-th component of the transmitting control vector a tx (θ) and xi is a vector whose components indicate complex amplitudes of signals that were transmitted by the i-th transmitting antenna element and were received by the N rx receiving antenna elements.

6. The method as recited in claim 4 , wherein the following relationships are used to correct the receiving control vector a rx (θ):

a tx,n (θ)/ a tx,1 (θ)=(1/ N rx )Σ k ( x n,k /x 1,k )

where a rx,n (θ) are the components of the receiving control vector a rx (θ), a rx,1 (θ) is any one of those components, and the variables x k,n indicate complex amplitudes of signals that were transmitted by the k-th transmitting antenna element and were received by the n-th receiving antenna element.