Communications: directive radio wave systems and devices (e.g. – Determining direction – Low angle processing
Patent
1987-07-02
1989-01-03
Tubbesing, T. H.
Communications: directive radio wave systems and devices (e.g.,
Determining direction
Low angle processing
342149, G01S 1348
Patent
active
047960310
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a radar system for precisely measuring an angle of elevation of a target with a low elevation angle over a surface of a sea where a strong mirror reflection wave exists.
BACKGROUND ART
Conventionally, for a precise measurement of an angle of a target, (1) a voltage which becomes greater as the target in the radiation beam of a radar antenna shifts from a direction of the beam center to the peripheral section, namely, the angle error voltage has been measured and the magnitude of the measured value has been used.
As methods to generate such a voltage, there have used a monopulse method in which the sum pattern and the difference pattern are generated in the antenna, a conical scan method in which the radiation beam is successively rotated about the direction of the antenna axis, and a lobe switching method in which the radiation beam in the angle measuring plane is successively deflected with the center located at the direction of the antenna axis.
In this specification, we use the term "beam" to refer to a radio wave which, not only when emitted but also when received, has a particularly strong intensity in a specific direction.
Moreover, as other precise measurement methods, there have been (2) a method in which a plurality of antennas are located in the angle measuring plane with the distance therebetween each being slightly different from each other and the reception phase differences between the respective antennas are measured to obtain the angle and (3) a method, as described in the Japanese Patent Laid-Open No. 60-46477, in which two beams are formed with the oriented directions thereof being slightly shifted from each other in the vertical direction, the direction of the antenna axis at which these two beams intersect each other is set to be oriented to the middle point of the target and the image thereof, and the phase difference between the received waves (the composite wave of the direct wave and the indirect wave) associated with these two beams are measured, thereby the determining the height of the target with a low elevation angle.
However, in the methods of (1) and (2), in a case where the target with a low elevation angle exists over a relatively calm sea and the antenna beam includes the target and the image thereof generated by the surface of the sea, the interference between the direct wave from the target and the indirect wave(mirror reflection wave) passing the surface of the sea makes it impossible to correctly measure the angle. The third method involves disadvantages in that high accuracy is obtained only when reflection coefficient k of the surface of a sea is nearly equal to 1, and many ambiquities are obtained together with the true height of a target as the ratio of the antenna height to the wavelength increases.
To remove these problems, according to the present invention, there is provided a radar system having means wherein two beams are formed with the oriented directions thereof slightly shifted from each other in the vertical direction by use of an antenna, the direction of the antenna axis at which these two beams inersect each other is set to be oriented to the middle point of the target and the image thereof by use of a direction adjusting mechanism the phase differences between the received waves associated with these two beams are measured with respect to two frequencies, and the actual height of the target is determined from two sets of heights calculated based on the phase differences, each set including a plurality of heights, thereby measuring the height of the target with a low elevation angle (low elevation angle measurement).
In the present invention, the antenna axis is caused to aim at the mid point between a target and the image thereof. The resultant wave of a direct wave and an indirect wave is received through two beams, and then is processed through a predetermined procedure on the basis of the phase difference between these two beams. Therefore the radar system is still capable of eliminating influen
REFERENCES:
patent: 3229283 (1966-01-01), Hefter et al.
patent: 3618093 (1971-11-01), Dickey, Jr.
patent: 3795913 (1974-03-01), Kosowsky et al.
patent: 4110754 (1978-08-01), Endo
patent: 4219816 (1980-08-01), Schenkel et al.
P. R.: "Accurate Tracking of Low Elevation Targets over the Sea with a Monopulse Radar", Radar Present & Future, (date unknown), pp. 160-165.
Hellner Mark
Mitsubishi Denki & Kabushiki Kaisha
Tubbesing T. H.
LandOfFree
Radar system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Radar system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Radar system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2170891