Transferred electron oscillators at mm wave frequencies and their characterisation using quasi-optical techniques.
A study of high frequency millimetre wave oscillators is performed operating at Wband
and above, using test bench equipment designed and constructed in St. Andrews.
Octave tuneable oscillators have been designed, constructed, and used to characterise
developmental Gunn dervices, as well as to provide ideal oscillators for test bench
measurement systems. These oscillators have been sold to many millimetre-wave
laboratories throughout Britain. The operation, optimisation and characterisation of these
oscillators is described in detail, and various non-linear effects are explained and modelled
successfully. The wideband tuneability and matching has also allowed evaluation of new
developmental Gunn devices to accurately determine the optimum operating frequency
range of the devices. This was part of a developmental program by GEe Hirst and MEDL
which has now produced state of the art GaAs Gunn oscillators at 94GHz.
Much of the characterisation of the oscillators is performed using novel quasioptical
techniques, which has allowed low loss accurate performance at these very high
frequencies. Several quasi-optical techniques are described and the design, manufacture
and evaluation of many optical components are given. In particular, the frequency and
harmonic content of the oscillators was determined using a Martin-Puplett Interferometer
which utilised a frequency counting technique. This enabled easy wideband measurements
to be performed with much greater accuracy than traditional cavity wavcmeters. In
addition, a state of the art noise bench has been designed and constructed for operation at
W-band and above, that utilises a novel open resonator to effect a very high Q suppression
filter. The system has been shown to make noise measurements at much lower power
levels and with greater sensitivity than comparable systems.