This application claims priority to foreign French patent application No. FR 1600504, filed on Mar. 25, 2016, the disclosure of which is incorporated by reference in its entirety.
The present invention relates to a secondary radar able to detect targets at high elevation.
Air traffic control radars do not generally cover all the elevational angles lying between the direction of the horizon and the zenith. The non-covered zone above the radar antenna's phase centre forms a cone that is called the silence cone. This silence cone can affect several air traffic control radar functions.
“En-route” radars are characterized by a very long range in the direction of their maximum radiation. Their installation at high-altitude sites, by freeing them from obstacles of the relief, guarantees their ability to exploit this low-elevation range capability. For these radars, the silence cone may be deemed too large (for example, the cruising altitude of commercial flights (FL 330) corresponds to an elevation angle of 25° at 25 km). The silence cone may also pose problems for an airport radar. Indeed, in both cases the silence cone induces gaps:
Conventionally, in principle the antennas of air traffic control radars, also called ATC radars, are therefore antennas of LVA (Large Vertical Aperture) type having four objectives:
The antennas of the civil air traffic control (ATC) sector exhibit a cosecant squared radiation pattern, on account of their adaptation to aerial surveillance: such a pattern makes it possible to distribute in the vertical plane the energy radiated in a single exploration of the azimuthal quantum. This radiation pattern makes it possible to obtain a received signal of relatively constant amplitude for a target describing a constant-altitude trajectory.
For a cosecant squared pattern such as this and in a zone traversed according to a constant-altitude trajectory, the antenna gain G varies substantially as the square of the cosecant of the angle of elevation i.e. G(β)˜cosec2 β, that is to say that the variation of this gain compensates the closing-in effect so as to preserve a constant received signal level over this part of the trajectory. Moreover, it is not useful to perform surveillance of the airspace at an altitude greater than the aircraft flight ceiling.
In practice, the silence cone 20 is envisaged rather as a degree of freedom for the design of the antenna. In particular the requirements would pertain rather to a guaranteed fading beyond about 50° of elevation.
The current antennas used in the ATC world are therefore clearly not made to deal with targets in the silence cone.
Consequently, the system level solution for alleviating this state of affairs, which is common to ATC radars, consists in using dual radar coverage. These 2 radars being fairly close together make it possible to each ensure detection in the silence cone of the other.
An aim of the invention is in particular to alleviate this drawback. For this purpose, the subject of the invention is a secondary radar able to detect a target at high elevation in the silence cone, equipped with a main antenna having three radiation patterns, a sum pattern, a difference pattern and a pattern assigned to a control function, corresponding to the said antenna, the said radar furthermore comprising:
The said antenna of the auxiliary antennal device is for example of boom type.
The position of the sum pattern of the said antenna of the auxiliary antennal device is for example adjusted in elevation and in gain with respect to the pattern of the said main antenna by altering respectively the inclination of the said antenna and the coefficient of coupling between these two antennas.
The steepness of the flanks of the sum pattern of the said antenna of the auxiliary antennal device is for example adjusted by altering the number of elevational elements.
The position of the control pattern ensured by the said rear element is for example adjusted in elevation by altering the inclination of the said rear element in a vertical plane.
The said main antenna is for example composed of an antenna of LVA type, with wide vertical aperture, and of a rear radiating element.
Other characteristics and advantages of the invention will become apparent with the aid of the description which follows offered in relation to appended drawings which represent:
The MSSR cabinet 3 comprises an RF unit 31 for transferring the RF signals of the transmitter 33 to the Σ, Δ, Ω patterns of the antenna 1 and, reciprocally these patterns to the receiver 34. Each cabinet 3 comprises:
Conventionally, the MSSR cabinet 3 can also include the redundant resources common to the primary and secondary processings, in particular:
The cabinet also comprises the redundant interfaces 39 with the client links. The ancillary functions allow management of the radar by the client by exhibiting the supervision, the blip offsets and tracks and the parametrizations of the primary PSR, secondary SSR/S Mode and offset functions.
In S mode mainly the dynamic management of aircraft is controlled by:
The kit comprises at least one boom antenna 41 (comprising few elements, typically from 1 to 3 radiating elements height-wise), which may be of small dimension width-wise, for example 2 to 4 metres, a rear radiating element 42 and coupling means 43. The boom antenna 41 is coupled to the SSR antenna 1 (of standard LVA type) on the same existing access ports by the coupling means 43.
No modification is necessary at the level:
The invention is therefore simple and economical to implement.
The boom antenna 41 is fixed above the SSR antenna 1, with the same orientation, more precisely oriented forwards of the SSR antenna 1, it is inclined with respect to that of the SSR antenna 1.
The SSR antenna 1 is conventionally composed of an array of radiating bars 51. This antenna 1, of LVA type, may be a standard antenna of the ATC market for SSR surveillance, operating with three radiation patterns: sum, difference and control.
A radiating element 12, situated at the rear of the frontal panel consisting of the radiating bars, makes it possible to perform a control function for the SSR mode/S Mode, in particular as regards the geographical situation of the transponders picked up.
The boom antenna 41 is for example a boom antenna often employed as IFF antenna for military radars therefore possessing the same types of radiation pattern as the main antenna 1 of LVA type: sum, difference and control.
Preferably it comprises at least two elevational elements so that the zero gain value is close to its main lobe, by causing a steepening of the flanks on either side of the main lobe as illustrated by the sum pattern 63 of the boom antenna 41 presented in
The antenna 41 is inclined in a vertical plane so as to orient its maximum gain in the silence cone and to guarantee a minimization of its gain both just above 90° of elevation and also below 40°.
It also comprises a radiating element 42 situated at the rear, dedicated to its control pattern Ω 66 illustrated by
The coupling means 43 carry out the coupling of the three patterns, sum Σ, difference Δ and control Ω, of the boom antenna, with a coupling coefficient typically equal to 25 dB (to be adjusted according to the value of the maximum gain of the pattern 63 of the sum pathway of the boom antenna 41), with the three patterns, sum Σ, difference Δ and control Ω, of the SSR antenna 1, with the aim of guaranteeing a maximum gain of the sum pattern in the silence cone of the order of 20 dB below the sum gain plateau of the SSR antenna (plateau extending from 20° to 40° of elevation as illustrated by
As shown by these patterns, an objective is to ensure a minimum gain of the order of 35 to 40 dB below the maximum even at 90° of elevation (aircraft at high elevation necessarily being close together distance-wise, the antenna gain required for their detection is markedly smaller than that for long-range aircraft, typically 35 to 40 dB). This objective is obtained by inclining the boom antenna 41, the effect of this being to translate its elevational patterns, and in particular its sum pattern (translation along the abscissa axis). The value of the coefficient of coupling between the boom antenna 41 and the SSR antenna 1, by altering the gain, makes it possible moreover to adjust the patterns along the ordinate axis. The adjusting of the position of the patterns is thus supplemented by a translation along the ordinate axis.
The value of the coupling coefficient is thus defined, both:
The zone 64 of gain equivalence of the sum pathways between the SSR antenna 1 and the boom antenna 41 is typically situated around 55° of elevation. Beyond this value of elevation, the gain 63 of the boom antenna takes over from the gain 61 of the SSR antenna 1 to ensure the desired minimum gain for the sum pathway up to the zenith. It may be verified that the level transmitted on the pattern of the sum pathway 63 of the boom antenna 41 is much greater than the level of the pattern of the control pathway 62 of the SSR antenna 1 guaranteeing that targets at high elevation of 60° to more than 90° respond to the interrogations of the radar. The control pathway 62 associated with the rear element 12 of the SSR antenna 1 conventionally allows the blocking of the transponders receiving interrogations through the leaks of the sum radiation pattern 61 of the antenna for elevations of 90° to 180°.
Preferably the sum radiation pattern 63 of the boom antenna must not be too wide so as not to disturb the radiation pattern 61 of the main antenna outside of the silence cone. The control pathway 66 associated with the radiating element 42, situated at the rear of the boom antenna 41, makes it possible to avoid receiving target responses beyond the elevation at 90°, flagged by a dash 65 in
The signals transmitted by the radar via the rear element 42 thus allow the blocking of the transponder of a target when the main antenna 1 is in the direction opposite to the azimuth of this target. The radiation pattern and the orientation of this radiating element 42 are adapted for this purpose, in particular an optimal setting ought to make it possible to block the transponder onwards of 91°.
Around the zone 64 of equivalence of the gains of the sum pathways of the SSR antenna 1 and of the boom antenna 41, the phase-wise uncontrolled recombining of the signals may induce detection losses over a span of the order of +/−5°, i.e. from +50° to +60°, elevation-wise in the example of this
Number | Date | Country | Kind |
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1600504 | Mar 2016 | FR | national |