Conventional microwave and millimetre-wave oscillators produce sinewave output at a chosen frequency. These sinewaves can then have their amplitude, frequency, or phase modulated to produce a pattern which permits them to carry information. The oscillators can also be used as ‘local oscillators’ to drive the mixers which is used in most radio receivers to detect signals as they arrive and convert the information to lower frequency which are easier to amplify and measure.
The St-Andrews MM-Wave Group have over ten years experience in making ‘conventional’ sinewave oscillators for the 50 - 150 GHz range. These are based upon a type of device called a Gunn Diode which exhibits a weird property called ‘negative resistance’ which causes it to oscillate when placed in a suitable circuit and provided with d.c. input power.
Around 1992 we began developing novel ‘semi chaotic’ oscillators. These produce an output waveform which seems like wideband noise, but behaves in a predictable way. In effect, it replaces the conventional sinewave with a ‘noise like’ output, but this can be used in all the same ways as a conventional oscillator. It does, however, have a number of advantages over normal sinewave oscillators. The main advantages being:
- The output can be used as a very high-rate pseudo-random number generator
- The output covers a wide bandwidth
When used as a pseudo-random number generator the device acts as if it were creating over a billion random numbers per second. This is potentially very useful in encrypted signalling. The wide bandwidth means the signals it produces are relatively immune to various kinds of interference as the transmitted information is ‘spread out’ over a very wide bandwidth. Hence these devices have many applications and are proving to be of great interest. They also represent one of the first practical applications of the study of Chaos.
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University of St. Andrews, St Andrews, Fife KY16 9SS, Scotland.