Communications: directive radio wave systems and devices (e.g. – Radar transponder system – Iff or sif
Reexamination Certificate
2001-01-05
2003-04-08
Sotomayor, John B. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Radar transponder system
Iff or sif
C342S013000
Reexamination Certificate
active
06545632
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to systems and methods providing a capability for IFF transponder and interrogator functions in addition to ESM/ECM functions, and in particular but not exclusively to such systems and methods for aircraft. Such systems and methods may also find applications in other vehicles for land, air, sea or space use.
2. Discussion of Prior Art
For Air Traffic Control (ATC) purposes, civil and military aircraft are required to be fitted with Identify Friend or Foe (IFF) transponders. These transponders reply automatically, with information such as height, speed, aircraft identification code, when they receive a Radio Frequency (RF) request from a ground station—usually located at airports.
In times of conflict this identity reporting is used to prevent fratricide and to aid friendly assets in gaining a picture or awareness of the battlespace. In order to prevent enemy forces from exploiting this identity reporting, the interrogation signals are coded or, in the case of more modern systems, encrypted.
A transponder is also required to satisfy civil air traffic control requirements; in this case there are no requirements for coding or encryption other than that the transponder replies with the identify of the aircraft and its current altitude. Military IFF transponders are capable of operating in the civil ATC modes. An emergency mode is also provided which will enable the transponder to act as a distress beacon in the event of pilot ejection or similar emergencies.
A transponder comprises a transmitter/receiver unit, upper and lower transmit/receive antennas and a control unit, as exemplified in
FIG. 1
of the accompanying drawings. By international accord, they operate on a transmit frequency band centred on 1090 MHz and a receive frequency band centred on 1030 MHz, and in each case the bandwidth is normally less than 10 MHz.
The military purpose of IFF is identification of friendly aircraft by the use of identification codes on the transmission and reply. In this case, called IFF ‘Interrogation’, an aircraft can be requested by either a ground station, land/sea vehicle or another aircraft fitted with an Interrogator to reply to a coded request for identification. Only friendly aircraft who know the code of the day can provide the correct response to the Interrogation. On most fighter aircraft the IFF Interrogator, which requires extra ‘black boxes’ and antennas to those of the IFF Transponder, is often enacted by mounting the IFF Interrogator antennas on the main nose radar dish. In this way, when an aircraft is detected by that radar, it can be selectively interrogated by the directional nose radar dish, without broadcasting the interrogating aircraft's position through the omnidirectional transmissions typical of Transponder systems.
FIG. 2
of the accompanying drawings illustrate a typical such arrangement.
All modern military aircraft have either a Radar Warning Receiver (RWR) or a more capable RWR called Electronic Support Measures (ESM). The purpose of both is to receive, identify and classify RF emissions received at the aircraft; to notify the crew of the direction from which the RF signals came; and, if classified as a ‘threat’, to enable or initiate appropriate crew warnings and counter measures. Such countermeasures can include RF Electronic Countermeasures (ECM or ‘jammers’). Most military aircraft especially fighters and bombers, and including helicopters, have ECM capability, either podded (carried under a wing) or internal to the fuselage.
FIG. 3
of the accompanying drawings gives a block diagram of a typical fighter ESM/ECM system.
An ESM receiver is essentially a sensitive radio receiver which is rapidly scanned over a wide range of frequencies in order to detect radar signals incident on the aircraft; detected signals are analysed on a pulse by pulse basis to determine, by comparison with a stored library of emitter characteristics, the source of the radar signals. The antenna arrangement associated with the ESM receiver enables the direction from which the signals are arriving to be measured.
The information derived by the ESM receiver is presented graphically to the crew and, if a threat emitter is detected, may be used to cue a jammer or electronic countermeasures (ECM) system to disrupt the operation of the threat. The ECM system consists of an RF transmitter and associated antennas which can be tuned to the frequency of the detected threat and can transmit a variety of complex signals generated by a “techniques generator”. More recent ECMs are capable of directing the jamming signal towards the threat system in order to maximise their effectiveness.
There is a potential operational problem associated with an IFF transponder as described above due to the fact that transponder signals are broadcast in all directions. The scenario should be considered where a first aircraft is operating covertly and emitting no radio signals in order to minimise the likelihood of an enemy detecting its presence. Another friendly asset, possibly a coalition aircraft or surface based radar, interrogates the first aircraft with a valid IFF signal and its transponder broadcasts its identity thus alerting the enemy to its presence. It should be noted that the enemy do not have to decode the transponder signal in order to detect its presence and, possibly, its bearing. This problem could be averted by the first aircraft suppressing the operation of its transponder; however, this may incur the risk of engagement by the “friendly” asset and negates the value of having an IFF system in the first place.
SUMMARY OF THE INVENTION
We have designed a system in which the IFF Transponder and Interrogator functionality are subsumed within the ESM/ECM equipment. The ESM is used to detect and decode IFF interrogations and to use the associated ECM to transmit the appropriate reply, preferably in the direction of the interrogator. As the replies can be directed specifically towards the interrogator, spurious emissions are minimised, thereby assisting in keep the presence of the aircraft covert. The functionality associated with the IFF decoder and an encryption computer are also preferably incorporated into the ESM and ECM equipment, as well as appropriate interfaces for receiving cryptography information and a control panel.
This system provides significant benefits as a result of the removal of the IFF Transponder and Interrogator boxes and antennas, both for the manufacture of the aircraft and the operator. The system benefits from reduced weight, volume, power and cooling requirements, and cost. The initial and life cycle costs of the aircraft may be reduced, and the system may provide improved aircraft reliability. The aircraft maintenance effort required may also be reduced. The system also provides substantial tactical advantages. Thus the system assists in reducing the electronic signature of the aircraft, giving it improved survivability because of reduced detectability by opposing ground/airborne threat radars. The system also releases space on existing aircraft for other function and/or performance improvements.
Accordingly, in one aspect, this invention provides a radar system for a station, said system comprising:
at least one antenna means for passing signals in the radio frequency waveband;
Identify Friend or Foe (IFF) transponder means for receiving and responding to requests from a remote transmitter via said antenna means;
IFF interrogator means for selectively interrogating in use a remote transmitter via said antenna means;
Radar Warning receiving (RWR) means for processing radio frequency emissions received by said antenna means to identify potential threats; and
Electronic Countermeasure (ECM) means for generating electronic countermeasures signals and for passing said signals to said antenna means for transmission.
The arrangement preferably includes control means for controlling the passage of signals between said IFF transponder means, said IFF interrogator means, said RWR means, said ECM mea
Lyons Geoffrey
Pywell Michael
BAE Systems plc
Nixon & Vanderhye P.C.
Sotomayor John B.
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