Communications: directive radio wave systems and devices (e.g. – Directive – Beacon or receiver
Reexamination Certificate
1998-10-13
2001-11-06
Blum, Theodore M. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Beacon or receiver
C342S156000
Reexamination Certificate
active
06313795
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
Priority is claimed with respect to German application No. 197 44 692.2 filed in Germany on Oct. 10, 1997, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
The invention is based on a direction-finding method for determining an incident direction of a high-frequency electromagnetic signal with respect to a predeterminable primary direction of an antenna arrangement including at least two receiving antennas spaced apart a known distance for receiving the incident signal, wherein a phase difference is determined between the output signals of the receiving antennas and the incident direction of the signal is determined from the phase difference.
A method of this type is known per se, particularly in so-called interferometer direction finders. These are based on the use of at least two (receiving) antennas specified for a predeterminable frequency range, such as the high-frequency (HF) range. The antennas possess a predeterminable directional pattern, for example a so-called forward characteristic. That is, each antenna has a maximum receiving range of 180° in, for example, the azimuth plane (parallel to the earth's surface) It is useful to orient the primary receiving directions of all antennas essentially parallel to one another, resulting in a common primary receiving direction. If a mono-frequency HF signal, for example, is incident at such an antenna arrangement from a direction other than the primary receiving direction, differences in transit times occur at the individual antennas, from which associated phase differences can be determined. The searched receiving direction (incident direction) of the HF signal (HF wave) can basically be determined from this phase difference between the received signals of two antennas.
SUMMARY OF THE INVENTION
It is an object of the invention to improve on a method of the generic type first mentioned above to permit a high measuring precision with a high angular resolution and a high reaction speed.
The above and other objects are accomplished according to the invention by a direction-finding method for determining an incident angle (&thgr;) of a high-frequency electromagnetic signal in a system including at least two receiving antennas spaced apart by a known distance (D) for receiving the incident signal, the method including steps of:
(a) converting output signal of each antenna into an intermediate-frequency signal having a predeterminable intermediate frequency;
(b) converting the intermediate-frequency signals into a corresponding digital signals;
(c) converting the digital signals into the frequency domain through a Fourier transformation;
(d) measuring a phase-difference in the frequency domain between the frequency domains signals associated with the antennas yielding a phase difference (&Dgr;&phgr;);
(e) performing a phase-sequence analysis in the frequency domain for determining phase differences for temporally-successive Fourier intervals continuously within a predeterminable measuring period;
(f) determining from the phase differences of step (e) an estimated value for signal frequency (f) within the discrete Fourier spectrum; and
(g) determining an incident angle (e) from the phase difference (&Dgr;&phgr;) and the signal frequency (f) according to the formula:
&thgr;=arcsin[c
0
·&Dgr;&phgr;/(2
&pgr;·f·D
)]
where
c
0
=speed of light.
A first advantage of the invention is that it is not necessary to determine the frequency of the incident signal (wave). Thus, a so-called broadband receiver advantageously having a predeterminable, short transient period can be used. This is because a long transient period causes a disadvantageous reduction in the reaction time of the measurement method.
A second advantage is that the method of the invention is largely independent of intentional and/or unintentional disturbances and environmental conditions, for example a further incident signal that is virtually identical to the signal to be evaluated.
A third advantage is that it is possible to perform a simultaneous measurement of a plurality of identical or different signals having different signal frequencies.
A fourth advantage is that a high aging stability can be attained for an arrangement operated in accordance with the invention. The measurement results can be advantageously reproduced, because so-called drift is avoided.
Further advantages ensue from the following detailed description considered in conjuction with the accompanying drawings.
REFERENCES:
patent: 4626859 (1986-12-01), Stansfield
patent: 4876549 (1989-10-01), Masheff
patent: 5497161 (1996-03-01), Tsui
patent: 5559518 (1996-09-01), DiDomizio
patent: 5568154 (1996-10-01), Cohen
patent: 4421571 A1 (1996-01-01), None
Herrmann Franz
Schuster Manfred
Blum Theodore M.
Daimler-Benz Aerospace AG
Kinberg Robert
Spencer George H.
Venable
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