An 11 GHz FET oscillator with a stable Ba Ti 0 resonator has been developed for the local oscillator of a sate?lP?e TV front-end. It has excellent frequency and amplitude stability, low noise and high efficiency. An original amplitude control provides the means for optimisation of the mixer drive.A generalised circuit analysis will be presented which optimises the osclllation conditions whilst avoiding parasitic frequencies. Complete measurements will be given.
INTRODUCTIONThe oscillator was developed as a local oscillator for a receiver front-endat 12 GHz. The required specifications included good frequency stability, amplitude stability (with electronic level control), low noise and high efficiency.
The performance of MESFET mixers used as down-converters from frequencies around 8 GHz to an intermediate frequency of 1 GHz is presented. Several possible mixer configurations have been considered and preliminary results are described involving the use of the MESFET in single as well as double device circuits.Experimental results concern the devices single sideband. noise figures and associated values of small signal conversion gain. Large signal saturation is discussed and results of third order intermodulation product are described.A single sideband noise figure of 7.8 dB associate with a gain of 8 dB at 7 GHz has been measured from a mixer using a single transistor.
A 12 GHz receiver front-end has been designed and realised which uses field-effect transistors for each of the three major functions of r.f. preamplifier, mixer and local oscillator. In each of these functions, the FET presents its particular advantages of low noise figure as an amplifier, a conversion gain as a mixer and a relatively high efficiency as an oscillator. An overall noise figure of 4 dB should be possible in production quantities. The structure and overall system performance will be described.
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