SECONDARY RADAR SYSTEM

• US 3,772,688 A
• Filed: 07/12/1971
• Issued: 11/13/1973
• Est. Priority Date: 07/17/1970
• Status: Expired due to Term

• Current Assignee: Johny Abram Smit, Wim Bernard Samuel Maria Kneefel
• Original Assignee: Johny Abram Smit, Wim Bernard Samuel Maria Kneefel
• Inventors: Smit, Johny Abram, Kneefel, Wim Bernard Samuel Maria
• Primary Examiner(s): Hubler, Malcolm F.
• Application Number:
  US05/161,676
• Time in Patent Office: 855 Days
• Field of Search: 343/6.5R,6.5LC
• US Class Current: 342/43
• CPC Class Codes: G01S 13/78 discriminating between different kinds of targets, e.g. IFF-radar, i.e. identification of friend or foe G01S13/75, G01S13/79 take precedence

Abstract

A primary and secondary radar system utilizing a common directional scanning antenna are located in an interrogator in order to obtain navigational information and identity for each of the interrogated transponders of the objects of interest. Selected objects are interrogated by a specific address for each object transponder, in a sequence determined by the position of the objects with respect to the interrogator. The desired information is obtained from each transponder reply which occur only at the moment of interrogation from the scanning directional antenna.

Claims

1. A secondary radar system comprising at least one interrogator and a plurality of responder beacons cooperating therewith, means for coupling said interrogator in time and angle to a primary radar system by means of a common directive scanning antenna, said responder beacons being either stationary mounted or mounted in mobile objects, said system further characterized in that for obtaining the desired data, such as bearing and distance, of a number of selected objects together with an object identification during one searching sweep, said interrogator includes means adapted for calling the selected objects one by one in a predetermined sequence by transmitting an address different for each responder beacon (2) by means of a transmission code, said transmission code being reconstructible after channel distortion and suitable for asynchronous transmission, and means in each said responder beacon responsive to having been called with its address and having recognized same for emitting a short pulse (22) at a carrier wave frequency other than the carrier wave frequency of the radar pulse (20) of the primary radar system only at the moment said beacon is scanned by said primary radar pulse.

2. A secondary radar system according to claim 1, wherein said interrogator comprises both an address encoding means in which the addresses of responder beacons to be called during one searching sweep are stored in calling sequence, and a calculating means for calculating the positions of the selected objects from the obtained bearings and distances, so as to compose an address sequence for a next searching sweep, characterized in that said address encoding means (6) is connected to a channel encoding means (5) for converting the address code to said transmission code, and that said responder beacon comprises a decoding and recognition means (15) for decoding and recognizing the received transmission signal and generating a short response pulse (22) after recognition thereof, as soon as an AND gate (16) is opened by said primary radar pulse (20).

3. A secondary radar system according to claim 2, characterized in that for asynchronously transmitting the transmission code said code is provided with an appropriate prefix and a freerunning clock generator (152) is coupled to said decoding and recognition means (15), and that for suppressing pulse prolongation due to over-excitation or reflections of more remote objects an automatic gain control (144, 141, 142) is provided in the amplifier (14) of said responder beacon (2), said gain control being adapted to be actuated and to start up during the decoding of the prefix before the actual address is received.