Communications: directive radio wave systems and devices (e.g. – Directive – Beacon or receiver
Reexamination Certificate
1999-03-23
2001-08-21
Gregory, Bernarr E. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Beacon or receiver
C342S432000, C342S444000, C342S445000
Reexamination Certificate
active
06278406
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a direction finder with an array antenna, for measuring the incoming angles of plural incident signals to the array antenna in multipath environments such as urban spaces or indoors. The present invention also relates to a device for processing measurement results for the direction finder.
The MUSIC method or ESPRIT method is known as an algorithm for measuring the incoming angles of plural radio signal with no correlation that are received by an array antenna. These algorithms, which can provide excellent resolution and precision, compared with, for example, the conventional Fourier conversion method or the beam scanning method, have been widely applied to direction finders. However, the algorithm cannot accurately perform a specific value resolution because the factorial of a covariance matrix of a signal received by an array antenna is degenerated when correlative signals such as multipath waves are handled. This means that the incoming angle cannot be measured.
An approach of overcoming the above-mentioned drawback, is the movement averaging method In this method a matrix created by dividing a covariance matrix into plural matrix groups with equal orders, as shown in
FIG. 3
, is decomposed into specific values, and the factors of the divided matrix groups added together. Such a method is disclosed in the literature, “On Spatial Smoothing for Direction of Arrival Estimation of Coherent Signals”, IEEE Trans on ASSP Vol. 33(4), 1985. In order to apply the movement averaging method, it is essential that the covariance matrix is in a Vandermode format. In the array antenna for a direction finder, the antenna elements are arranged at regular intervals. The received phase response (a) must be expressed as shown by the following formula (1):
a=−
exp(
jnkd
sin &thgr;) (1)
where n is the number of an antenna element; k is a wave number; d is an element spacing; and &thgr; is an incoming angle.
However, the movement averaging method cannot be applied to an actual array antenna because the received phase response (a) is not linearly expressed as shown by the formula (1) due to the mutual coupling between antenna elements even when antenna elements are arranged at regular intervals. Many literatures disclose the technique of measuring the incoming directions of plural correlative signals using the above-mentioned movement averaging method. In any of the techniques, the incoming angle is measured by spatially moving a sole antenna element at regular intervals to avoid the interference of the mutual coupling. Any trouble does not occur even when an antenna element is spatially moved in a static environment such as indoor environment limiting no measurement time. However, the conventional technique is impractical in the case when the antenna element is mechanically moved in outdoor mobile communication environments where the propagation condition momentarily changes, in consideration of the measurement time.
SUMMARY OF THE INVENTION
The present invention is made to solve the above-mentioned problems.
This invention provides a direction finder that can measure the incoming angles of plural correlative signals using the respective signals received by antenna elements configuring an array antenna.
Furthermore, the invention provides a direction finder which does not require the spatial movement of the antenna elements and can be applied to outdoor mobile communication environments.
The invention also provides a direction finding method for measuring the incoming angles of plural correlative signals using the respective signals received by antenna elements configuring an array antenna.
The invention also provides a measurement result processing method suitable for a direction finder.
The objective of the present invention is achieved by a direction finder comprising an array antenna including plural antenna elements arranged at regular intervals in a straight line or in a plane state; a receiver for receiving a signal received with each of the antenna elements in the array antenna and then outputting demodulated signal groups; a front end processor for multiplying the demodulated signal groups to be chronologically obtained by an inverse matrix of a coupling coefficient matrix of the array antenna and then outputting time series signal groups; and a signal processing unit for obtaining a covariance matrix in response to output signal groups from the front end processor, subjecting the covariance matrix to a movement averaging process, and then resolving the result into specific values to obtain an incoming azimuth.
Furthermore, according to the present invention, a measurement result processing device obtains a mutual coupling matrix by normalizing a measurement result of an array element pattern containing a mutual coupling with a measurement result of an element pattern of a sole antenna element not containing a mutual coupling and then expanding the resultant normalized pattern in a Fourier series.
In the direction finder according to the present invention, the coupling coefficient matrix of the array antenna is obtained by normalizing a measurement result of an array element pattern containing a mutual coupling with a measurement result of an element pattern of a sole antenna element not containing a mutual coupling and then expanding the resultant normalized pattern in a Fourier series.
In a direction finder according to the present invention, a movement averaging process can performed by multiplying a time series signal group by an inverse matrix of a coupling coefficient matrix of an array antenna to remove received signal components due to a mutual coupling between antenna elements, the time series signal group being obtained by demodulating a signal received with the array antenna, the array antenna being formed of plural antenna elements arranged at regular intervals, and by making the covariance matrix of a received signal group in a Vandermonde format.
In the direction finder according to the present invention, the signal processing unit comprises a covariance matrix creating unit for creating a covariance matrix from a snapshot in a time series signal group from which a mutual coupling is removed, a movement averaging unit for obtaining a movement average matrix by moving in parallel from the covariance matrix, a specific value resolving unit for resolving a specific value from a movement average matrix, a wave number estimating unit for judging a wave number based on a specific value obtained through the specific value resolving step, and a MUSIC spectrum plotting unit.
In the direction finder according to the present invention, the movement averaging unit divides a covariance matrix obtained with a linear array antenna into sub-array matrixes and then adds the sub-array matrixes.
In the direction finder according to the present invention, the specific value resolving unit obtains N specific values &lgr;i (i=1 to N) by resolving a movement-averaged covariance matrix into specific values.
In the direction finder according to the present invention, the wave number estimation processing unit estimates a wave number from a distribution of specific values.
Furthermore, according to the present invention, a direction finding method comprises the steps of multiplying a time series signal group by an inverse matrix of a coupling coefficient matrix of an array antenna to remove received signal components due to a mutual coupling between antenna elements, the time series signal group being obtained by demodulating a signal received with the array antenna, the array antenna being formed of plural antenna elements arranged at regular intervals; and making the covariance matrix of a received signal group in a Vandermonde format, whereby a movement averaging process is performed.
Moreover, according to the present invention, a measurement result processing method comprises the steps of normalizing a measurement result of an array element pattern containing a mutual coupling with a measurement result
Gregory Bernarr E.
NEC Corporation
Ostrolenk Faber Gerb & Soffen, LLP
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