Communications: directive radio wave systems and devices (e.g. – Directive – Beacon or receiver
Reexamination Certificate
1999-10-28
2001-08-07
Issing, Gregory C. (Department: 3661)
Communications: directive radio wave systems and devices (e.g.,
Directive
Beacon or receiver
C342S434000
Reexamination Certificate
active
06271791
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to radio-signal direction finding. The invention may be used, for example, for controlling an antenna array such that the antenna array provides an antenna pattern that is directed to a radio-signal source.
BACKGROUND ART
Radio-signal direction finding can be carried out as follows. There are two antennas at different locations. Both antennas receive a signal from a source whose direction has to be determined. The direction is calculated on the basis of a phase difference between the signal received by the one antenna and the signal received by the other antenna. This principle of radio-signal direction appears to be described in the Electronic Engineers' Handbook, 4
th
edition, by D. Fink et al. (ISBN 0-07-021077-2), section 29.3.1.1.1, page 29.82.
SUMMARY OF THE INVENTION
It is an object of the invention to provide radio-signal direction finding at relatively modest cost.
The invention takes the following aspects into consideration. It will often not be possible to determine the direction in which the source of a radio signal is located, by directly measuring a phase difference between two antennas. The reason for this is that, in practice, an antenna will not exclusively receive a radio signal from the source whose direction has to be determined. It may also receive radio signals from other sources. These unwanted radio signals will diminish the precision with which the direction can be determined, or may even make it impossible to determine the direction.
A possible solution is to suitably process each antenna signal, which often is a mixture of various radio signals, so as to suppress unwanted radio signals. Accordingly, a pair of phase-detection input signals will be obtained. The phase difference between the pair of phase-detection input signals is measured and the direction is determined on the basis of the phase difference measured. This solution requires a radio-signal processor for each antenna. Each radio-signal processor will be functionally equivalent to a receiver and will thus be relative complex. Consequently, the solution described in this paragraph is relatively expensive.
According to the invention, a switchable antenna-coupler switches from one antenna being coupled to a radio-signal input, to another antenna being coupled to the radio-signal input. A radio-signal processor processes a radio signal which is present at the radio-signal input so as to obtain a phase-detection input signal. A phase-change detector detects a phase change in the phase-detection input signal due to the switching from the one antenna to the other antenna. A calculator calculates the direction in which the source of the radio signal is located on the basis of the phase change. Accordingly, the invention allows a sufficiently precise phase-difference measurement with one radio-signal processor only. Thus, the invention allows direction finding at relatively modest cost.
Another advantage of the invention relates to the following aspects. A radio-signal processor introduces some phase shift. The phase shift will vary due to temperature changes, aging and component spread. In principle, these phase-shift variations will not affect the phase-change due to the switching from the one antenna to the other antenna. Since, according to the invention, the direction is calculated on the basis of this phase change, the invention allows a relatively good precision in direction finding.
The invention and additional features, which may be optionally used to implement the invention to advantage, are apparent from and elucidated with reference to the drawings described hereinafter.
REFERENCES:
patent: 3813672 (1974-05-01), Weisser
patent: 4647935 (1987-03-01), Helbing
patent: 4719469 (1988-01-01), Beier et al.
patent: 4978963 (1990-12-01), Thorpe
patent: 5497161 (1996-03-01), Tsui
patent: 0373604A1 (1990-06-01), None
By D. Fink et al, “Electronic Engineers” Handbook, 4thEdition, (ISBN 0-07-021077-2), Section 29.3.1.1.1, pp. 29.82.
Halajian Dicran
Issing Gregory C.
U.S. Philips Corporation
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