GB2026808A

GB2026808A - Improvements in or relating to secondary-radar systems

Info

Publication number: GB2026808A
Application number: GB7920598A
Authority: GB
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1978-06-20
Filing date: 1979-06-13
Publication date: 1980-02-06
Also published as: FR2429435B1; DE2826902A1; FR2429435A1; DE2826902B2; NL7904844A; DE2826902C3; IT7923611A0; GB2026808B; IT1121414B

Abstract

In an arrangement for eliminating "fruit" interferences in a secondary- radar system using same-channel operation, the interrogating station is characterised by the use of an additional item of information (mark), in that the information, forms a part of the interrogation which causes a specific response signal to be emitted in the response device (transponder). in order to better suppress the reception of undesired responses in the interrogating station which results from the same-channel operation and at the same time to keep the outlay for the analysis of the mark as low as possible, a plurality of specific responses are made available in the transponder, from which, in dependence upon the mark of the particular received interrogation, in accordance with a calculating rule, a specific response code is selected and/or a conversion into another response code is carried out. Simultaneously to the interrogation the interrogating station response receiver is prepared in accordance with the same calculating rule for the reception of the selected response code. The calculating rule may change with time.

Description

SPECIFICATION Improvements in or relating to secondary-radar systems The invention relates to secondary-radar systems designed for operating on a common channel frequency and incorporating an arrangement for eliminating "fruit" interferences, by the use of an additional item of information, a mark, which characterises the interrogating station in that the information in the relevant pulse telegram forms a part of the interrogation which controls the emission of a specific response signal in the response device.

One arrangement of this kind is described in the German Patent 1,801,850.

In the aforementioned known arrangement the pulse telegram which is used to characterise the interrogating station, and which can consist of additional marking bits, is transferred, as an address component, into the response signal of the response device. The associated increase in the quantity of information to be transmitted results in a lengthening of the response signal.

This produces an increased garbling danger, due to possible overlapping of the response signals. An increase in the fault quota must also be expected in the analysis of extended pulse telegrams of this kind, as the response signal which is characterised by additional marking bits can be simulated by a random combination of one or more marking bits and part of the identification information of the interrogated station, and can trigger a faulty display.

One object of the present invention is to provide a system giving a further improvement in the elimination of "fruit" interferences.

The invention consists in a secondary-radar system for operating on a common channel and with means for eliminating "fruit" interference by the use of an additional mark item of information, said mark characterising the interrogating station and the information transmitted as a pulse telegram forming part of the interrogating which controls the emission of a specific response signal in the responder, the supply of a plurality of items of response-identification information in the form of a response code being made available in the responder and an analysis circuit being provided, which reacts in dependence upon the mark of the particular received interrogation signal in accordance with a calculating rule and makes a specific selection from the response codes and/or converts the response code, and that simultaneously to the interrogation means in the responder receiver in the interrogating station prepare for the reception of the selected response code in accordance with the same calculating rule.

Simpie coincidence checking merely analyses those response signals which conform with the response code selected in the interrogating station. In an arrangement constructed in accordance with the invention systems in which identification information changes over a period of time can be used, and it is immaterial whether the information changes between the interrogation code and the response code in accordance with a fixed time plan or whether the response information must first be derived from the interrogation.

In an advantageous development the additional mark information which is included in the interrogation signal as a pulse telegram can make a selection from the response code addresses of the responder device which have been established via the normal assignment. It is equally possible to reconvert the contents of the response information so that the responder mark is contained in the response information selected by the special interrogation mark. The calculating rule can consist of a programme which is either fixed, or changes over a period of time, and for example can contain a fixed assignment.

The responder signal can be formed by arranging the stages provided in the responder device for the analysis of the identification information and for the preparation of the response to be logic-linked to one another via a device, for example, a micro-computer which is fed with external guide parameters, e.g. a calculating rule.

The invention will now be described with reference to the drawings, in which: Figure 1 is a block schematic circuit diagram of a part of the transponder of one exemplary embodiment of the invention; and Figure 2 illustrates schematically further details of the stage 2 of Figure 1.

The signals obtained from the input of the transponder shown in Figure 1 are fed via a logic circuit to pass via a stage 1 for the analysis of the identification information to be fed to a stage 3 for the formation of a response signal, which signal is transmitted via an output A to a following circuit for preparation for the responder transmitter stage.

The functions of the two stages 1 and 3 are logic-linked to one another by a stage 2, whose circuit is arranged between the two aforementioned stages and which is referred to here as an "assignment stage." The assignment stage 2 can consist, for example, of a microcomputer which is fed with a guide parameter via an input F, which serves as calculating rule.

The marking information contained in an interrogation pulse telegram of a ground station is separated from the remainder of the interrogation signal and input into the stage 2 at F as an additional guide value. For example, by means of a set of calculating programme, the marking information can select one of the response code addresses which have already been established via the normal assignment. On the other hand, it would also be possible to convert the contents of.

the response information. In that case the mark of the response is contained in the response information specially selected by the mark of the interrogation.

Figure 2 is a block schematic diagram that illustrates an exemplary arrangement for the further formation of the stage 2 of Figure 1. A received signal supplied to an input selects a response code which is determined in accordance with a time flow established by a pulse generator output from a response address store 21. The response code is converted into a new response code in a stage 23 by means of a computer stage 22 which is influenced by a guide parameter (e.g.

a mark). Via a store 24 the new response code then supplies the response identification information which is emitted from the transponder.

The practical effects of the use of the arrangement corresponding to the invention consist in that in the transponder an interrogating station which does not transmit any additional marking information triggers those responses which are likely on the basis of the assignment, established by the system, of interrogation-response signals. On the other hand, interrogation containing an additional marking information can trigger responses which result from the system's own assignment and also from a calculating rule with the marking information of the interrogation in the transponder. As the same calculation is carried out in the response receiver of the ground station, the response code which is to be analysed is known here.

If a very large number of ground stations are operating in one area, the probability of "fruit" interferences can be kept negligible by the use of a correspondingly large code supply.

Claims

1. A secondary-radar system for operating on a common channel and with means for eliminating "fruit" interference by the use of an additional mark item of information, said mark characterising the interrogating station and the information transmitted as a pulse telegram forming part of the interrogation which controls the emission of a specific response signal in the responder, the supply of a plurality of items of responseidentification information in the form of a response code being made available in the responder and an analysis circuit being provided, which reacts in dependence upon the mark of the particular received interrogation signal in accordance with a calculating rule and makes a specific selection from the response codes and/or converts the response code, and that simultaneously to the interrogation means in the responder receiver in the interrogating station prepare for the reception of the selected response code in accordance with the same calculating rule.

2. A system as claimed in Claim 1, in which the calculating rule consists of a programme which is fixed, or changes over a period of time.

3. A system as claimed in Claim 1 or Claim 2, in which a fixed assignment is used as a calculating rule.

4. A system as claimed in any preceding Claim, in which the additional mark information which is included in a pulse telegram in the interrogation signal causes a selection from the response code addresses established via the normal assignment

5. A system as claimed in any one of Claims 1 to 3, in which the mark included in the interrogation causes the response code of the responder determined via the normal assignment to be converted into a new response code.

6. A system as claimed in any preceding Claim, in which stages are provided in the responder for the analysis of the identification information and for the preparation of the response, which stages are logic-linked to one another via an assignment device such as a micro-computer which is fed with external guide parameters, e.g. a calculating rule.

7. A system as claimed in any preceding Claim, in which the identification information is changed over in a given period of time.

8. A secondary radar system as claimed in Claim 1, substantially as described with reference to Figures 1 and 2.