Communications: radio wave antennas – Antennas – Balanced doublet - centerfed
Patent
1981-07-17
1984-08-21
Wilbur, Maynard R.
Communications: radio wave antennas
Antennas
Balanced doublet - centerfed
343379, G01S 956
Patent
active
044673264
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method and an arrangement in the receiver of a radar beacon which is intended to respond to radar pulses from vessels within a certain radial distance from the beacon. The carrier frequency of the transmitted radar pulses from a certain vessel differ from the carrier frequency of the radar pulses from another vessel. The radar beacon then transmits as a response to the received radar pulses a signal which consists of one or several pulses with the same carrier frequency as those received and with a certain duration back to the transmitting vessel, for indicating information about the position of the beacon.
BACKGROUND ART
Radar beacons of the so called sweep frequency type are heretofore known which provide responding signals to a vessel whereas the frequency of the sweeping responding signal coincides with the frequency of the signal transmitted from the vessel. Such a technique has a certain delay of the responding signal of the magnitude 1-2 minutes which, however, is not considered to be fully satisfying by, among others, the shipping authorities. Another disadvantage of previously known radar beacons is that they under certain circumstances they also respond to signals originating from the side lobes of the vessel antenna. This implies ambiguity concerning the position of the beacon when this position is indicated on the indicator of the vessel. The useful range of the radar beacon will then be limited to the position of such vessels which are situated outside a critical area within which radar pulses originating from the side lobes are also so strong that the radar beacon respond.
DISCLOSURE OF THE INVENTION
The principles of the method and the arrangement or apparatus of the present invention are based on the observation that the probability that two (or more) vessels transmit radar pulses with the same carrier frequency is small. By detecting and storing the frequency of the received pulses in the receiver of the radar beacon and, after that, comparing the frequencies and the signal strength, it can be determined whether or not a transmitted pulse originates from a side lobe of the antenna system of the vessel radar, and thus whether or not a responding signal should be transmitted back. The arrangement also makes it possible for the radar beacon to give a response to a transmitted radar pulse from a certain vessel a short time after that the carrier frequency of the received radar pulse is detected by the receiver. The response then consists of a signal with the same frequency as the radar pulse transmitted from the vessel.
An object of the present invention is thus to provide a method and apparatus included in the receiver of a radar beacon which receives radar pulses transmitted from a vessel with a certain carrier frequency and which prevents that beacon's response to radar pulses which originate from the side lobes of the antenna system of the vessel, but transmits responding signals only for the radar pulses which originate from the main lobe of the antenna system.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be more fully described with reference to the accompanying drawing in which FIG. 1 schematically shows the position of three vessels in relation to a radar beacon whose receiver contains the arrangement according to the present invention.
FIG. 2 shows a schematic diagram of the time variation of the received signal strength for the vessels shown in FIG. 1.
FIG. 3 shows a block diagram of the part of the radar beacon receiver in which the arrangement according to the invention is included.
FIG. 4 shows a block diagram of a comparator included in the arrangement.
FIG. 5 shows a block diagram of the frequency memory included in the arrangement.
FIGS. 6a-6b show diagrams of certain waveforms which appear in the arrangement according to FIG. 3.
DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
In FIG. 1, the positions of three vessels F1, F2, F3 are schematically shown in relation to a radar beacon R. Each vessel
REFERENCES:
patent: 2824301 (1958-02-01), Levell et al.
patent: 3007156 (1961-10-01), Barber
patent: 3934251 (1976-01-01), Spratt
Charas Philip M.
Gustavsson Per-Olof G.
Morwing Bo A.
Gordon M. R.
Telefonaktiebolaget L M Ericsson
Wilbur Maynard R.
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