Communications: radio wave antennas – Antennas – Balanced doublet - centerfed
Patent
1980-11-10
1983-09-13
Tubbesing, T. H.
Communications: radio wave antennas
Antennas
Balanced doublet - centerfed
343 5NQ, 343 77, 343113R, G01S 348
Patent
active
044045611
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a radar system comprising an antenna including a reflector and two vertically mounted receiving elements for forming almost coinciding, substantially cosecant-squared beam patterns, and two receiving channels connected to the receiving elements.
A radar apparatus having two partially coinciding beams is known from the Dutch patent application No. 76.12575 corresponding to U.S. Pat. No. 4,136,341. In this patent application the reflector in cooperation with a first receiving element is described as forming a substantially cosecant-squared beam pattern, while the reflector in cooperation with a second receiving element forms a beam pattern that substantially coincides with the most elevated part of the substantially cosecant-squared beam pattern. With such an antenna the radar system described in the cited patent application ensures practically clutter-free reception.
SUMMARY OF THE INVENTION
The present invention has for its object to utilize the radar system set forth in the opening paragraph for determining the angle of elevation of detected targets. The radar system is characterized in that a phase measuring circuit is connected to the two receiving channels for measuring the phase difference .DELTA..phi. between the signals received by the two receiving elements, and that a transformation unit is incorporated for converting the measured phase difference .DELTA..phi. into the elevation angle .epsilon. at which the target is situated.
The invention is based on the surprising effect that, with a suitably selected reflector and arrangement of the receiving elements, a clear phase difference .DELTA..phi. manifests itself over a considerable angle of elevation .epsilon.. For example with a long-range radar, where the radar frequency is in the L band, an unambiguously measured phase difference .DELTA..phi. corresponds with an elevation .epsilon. between 0.degree. and 40.degree., if the phase centers of the receiving elements are spaced 35 cm-45 cm apart.
The determination of the elevation by phase measurement has been known from prior art for a long time. Radar interferometers of this kind are used in air traffic approach systems. With these systems a plurality of receiving elements are employed, and the elevation angle is determined by interferometric means. Because these systems do not include a reflector, they lack the high gain which is necessary to integrate them in radar systems suitable for long-range operation.
If the radar system according to the invention is subject to clutter, faulty measurements will be made and incorrect elevation angles will be obtained. For this reason it is desirable to equip the radar system with conventional MTI circuitry. To retain the phase information in the received signals quadrature phase detectors are employed.
It will be clear that the present invention is applicable in the most diversified active, passive, pulse- and and continuous-wave radar systems, and that the phase measuring circuit may be used in all kinds of conventional embodiments.
BRIEF DESCRIPTION OF THE DRAWING
A preferable embodiment will now be described with reference to the accompanying FIGURE which schematically illustrates a radar system in accordance with the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In the FIGURE, 1 represents a pulse radar transmitter, 2 an antenna, and 3 and 4 two receiving channels. Antenna 2 consists of a reflector 5 and two vertically mounted radiating elements 6 and 7, of which element 6 functions as transmitting and receiving element and element 7 as receiving element only. The radar pulses generated in transmitter 1 are emitted via a circulator 8 and antenna 2. The echo signals are received by antenna 2 and are converted to i.f. signals in receiving channels 3 and 4. These channels are connected to quadrature phase detectors 9 and 10. Each of detectors 9 and 10 consists of two phase detectors, 11, 12 and 13, 14 respectively, and a 90.degree. phase shifter, 15 and 16 respectively, so that phase detectio
REFERENCES:
patent: 3049702 (1962-08-01), Schreitmueller
patent: 3281840 (1966-10-01), Feten
patent: 3495249 (1970-02-01), Downie
patent: 3761927 (1973-09-01), Amoroso, Jr.
patent: 3766556 (1973-10-01), Amoroso, Jr.
Mulder Willem
van Rooyen Gerrit
Zwarts Johan M. C.
Hollandse Signaalapparaten B.V.
Kraus Robert J.
Tubbesing T. H.
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