GB2212021A

GB2212021A - Radio frequency generator

Info

Publication number: GB2212021A
Application number: GB8726084A
Authority: GB
Inventors: Kevin Christopher Byron; Peter George Hale
Original assignee: STC PLC
Current assignee: STC PLC
Priority date: 1987-11-06
Filing date: 1987-11-06
Publication date: 1989-07-12
Anticipated expiration: 2007-11-06
Also published as: GB2212021B; GB8726084D0

Abstract

An airbourne decoy arrangement e.g. for deployment for an aircraft comprises a mode linked semiconductor laser 11 whereby an optical carrier modulated with a radio frequency signal is generated and transmitted via an optical fibre link 13 to a decoy target 12, where the modulation is recoverved from the carrier and broadcast via antenna 14. <IMAGE>

Description

RADIO FREQUENCY GENERATOR This invention relates to radio frequency generators, and in particular to an arrangement for the remote generation of radio frequency signals.

A number of techniques have been described for tne remote generation of radio frequency signals e.g. in tine construction of decov targets for airborne missiles.

aar.iculGr problems are involved when the decoy target is to be displayed from an aircraft. FIrstly, conventional wire coupling between tb.e aircraft and decoy target can permit radiative ioss of wire guided signals and t:us reveal tne true position of the aircraft. Secondly, the weight and power requirements of conventional systems renders them unsuitable for aircraft use.

The object of the present invention is to minimise or to overcome these disadvantages.

According to the invention there Is provided an arrangement for remote generation and radiation of radio fiequency signals, the systems including a base station and one or more remote stations eac coupled to the base stations via an optical path, and wherein the radio frequency is transmitted from the base station to the remote station or stations as a modulation on an optical carrier.

According to the invention there is further provided a decoy arrangement for deployment from an aircraft, the arrangement including mode locked laser whereby, in use, an optical carrier modulated wlth a radio frequency signal is generated, = de@@y target provided with an oscillator whereby, ir. use, radio frequency signals are broadcast in synchronism w-th the modulation, and an optical waveguide connection between the laser and decoy target whereby, in use, the radio frequency signals are broadcast from a position remote from the aircraft.

The term radio frequency as employed herein is understood to include radar frequencies.

An embodiment of the invention will now be describe with reference to the accompanying draings in wnich : - Figure 1 is a schematic drawir: of an aircraft deployed decoy arrangement; Figure 2 shows the aircraft-mounted portion of the decoy arrangement of Figure t; and Figure 3 shows the decoy target possitior. of the arrangement of Figure 1.

Referring to Figure 1, the eco arrangement incudes an aircraft mounted transmitter unt 11 linked to a decoy target 12 via an optical fibre 13. The target 12 is adapted to be deployed from the aircraft, and for this purpose the optical fibre 13 may be provide with a supporting plastics strain member is formes from an aramid fibre.

An optical carrier wave modulated with a radio frequency signal is transmitted from the transmitter unit 11 via the optical fibre 13 to the decoy target 12 where the modulation is recovered from the carrier and broadcast as a radio signal via antenna 14. The broadcast signal may. be continuous or it may comprise a series of fishes.

Figure 2 shows the details of the aircraft mounted transmitter unit. Typically the transmitter comprises a mode locked semiconductor laser 21. Mode locking may be achieved by anti-relflection coating the facets and/or by angling the facets at the Brewster angle, and adding an external cavIty. Advantageously the external cavity is provided by a fibre stub 22 the length (L) o which stub determines the mode locked repetition rate. The repetition rate 'f, is given b the expression: f = C 2 L where C is the velocity of light.For example, a 10cr external cavity is equivalent to a repetition rate f of 1.5 G=z. The laser 21 can also be driven et frequencies corresponding to multiples of the cavity length so that a choice of frequencIes can be generated.

Figure 3 shows in schematic fror the decoy target portion of the arrangement. Modulates light received from the transmitter unit via fibre 13 is fed to photodetector 31 whereby demodulation of the optical signal is effected to recover the radio frequency signal. The photodetector 31 is adjunct to or forms part of an oscillator 32 tuned to the frequency of the radio signal. Advantageously the oscillator 32 is a regenerative oscillator. Oscillation is thus maintained in synchronism with the radio frequency signal. In some applications the oscillator 32 may also include a quench circuit 33 whereby the oscillator output comprises a series of signal bursts or pulses.

The output of the oscillator 3; is couple to the antenna 14 whereby the radio frequency signal is broadcast, e.g. to provide a eco radar echo tc an intelligent airbourne missile.

Power from the oscillator may be provided via the optical fibre link and stored in a capacitor (not shown). Alternatively, or in addition, power may be supplied from a battery 34. As the duty time of the oscillator is short, this battery can be small and light.

It will be appreciated that, as the signal between the deploying aircraft anc decoy target is carried by an optical linkr there is nc leakage of radio frequency radiation from this link. The optical link is thus invisible to radar and does not reveal tne true position of the deploying aircraft.

It will also be appreciated that the arrangement describe herein is not limited to aircraft use but can also, with minor modification, be adapted for deployment from a land vehicle or a machine vessel.

Claims

CLAlYS

1. An arrangement for remote generation and radiation of radio frequency signals, the systems including a base station and one or more remote stations each coupled to the base stations via an optical path, and wherein the radio frequency is transmitted from the base station to the remote station or stations as a modulation on an optical carrier.

2. A decoy arrangement for deployment from an aircraft, the arrangement including a mode locked laser whereby, in use, an optical carrier modulated with a radio frecuency signal is generated, a deco target provided with an oscillator whereby, in user radio frequency signals are broadcast in synchronsr with the modulation, and an optical waveguide connection between the laser anc decoy target whereby, in use, the radio frequency signals are @@oa@@@st from a position remote from he aircraft.

3. A decoy arrangement as claimec 1n C air 2, wherein the mode-locked laser is provided wit: an external cavity comprising c fibre stub.

z. k decoy arrangement as claimed in Claims 2 and 3, wherein the optical waveguide connection is provided with a plastics film strain member.

5. -. A decoy arrangement substantially as described herein with reference to and as shown in the accompanying drawings.