Since the St Andrews mm-wave group started in the 1980s, we have had a keen interest in low noise mm-wave sources. In particular, we have done a lot of work evaluating GaAs and InP Gunn diodes and oscillator circuits. A great deal of work was done by Dr Graham Smith, the present group leader, in conjunction with the semiconductor group at GEC’s Hirst Research Centre (which ultimately became e2v technologies) assessing the performance of novel Gunn diode structures, such as the graded-gap injector design.

Using our quasi-optical Martin-Puplett spectromter we have the ability to measure the spectrum of oscillators in the 60-600GHz range, which is useful for examining harmonic output. One of the key parameters which is of interest to us is the phase noise content of oscillators. Dr Smith developed a very high performance quasi–optical phase noise measurement system, commissioned by the UK’s National Physical Laboratory, which sets the standard for this type of measurement at mm-wave frequencies.

One of the key developments which enabled the group to study Gunn diode performance was the development of a wideband mechanically tuned oscillator block, based on the successful design of Carlstrom. We have manufactured many of these oscillators and have sold them to groups world wide. An example can be seen below.