ARMMS reaches out to encourage youth
At the 2012 April ARMMS RF & Microwave Society Meeting, held near Oxford, UK, Robert Smith of Cardiff University and Stephen Russell of Glasgow University both received newly introduced Young Engineer Prizes, intended to recognise and encourage engineers beginning their career in RF & Microwave technology. The meeting was a complete sell-out, and the record number of delegates saw the two young engineers take to the presenter’s podium alongside acknowledged experts in the field who described their work in detail.
Robert Smith’s work is on the push-pull configuration at microwave frequencies. He described a 20 W amplifier operating from 250 MHz to 3.1 GHz, having both good efficiency and linearity. The ‘waveform engineering’ design technique, allowed the optimum drain voltage waveform to be synthesised. Stephen Russell spoke on transistors fabricated from diamond, which have achieved the highest yet reported cut-off frequency of 55 GHz for a 50 nm device. He explained the difficulties of fabrication and the potential benefits of diamond as a semiconductor.
Techniques to achieve both good linearity and high efficiency in cellular radio power amplifiers were addressed by Ray Pengelly of Cree RF & Microwave. He explained the possible configurations based on GaN HEMTS; envelope tracking, Doherty and Chereix arrangements. He drew the slightly controversial conclusion that Doherty is the optimum arrangement, as the overall efficiency of ET is degraded by the power loss in the switching DC supply.
‘Diffusion of Innovation’ was the term applied to the work of David McLaughlin of the University of Massachusetts-Amherst. Small scale X-band weather radars to probe the lower atmosphere that achieve a $200,000 price point are being developed. In this implementation, 64 one-Watt transmitters and antenna elements are phase steered in the azimuth plane, with a mechanical tilt mechanism. Antenna pattern performance is adequate to greatly improve local weather forecasting.
The Steve Evans-Pughe memorial prize for best paper was presented to Charles Suckling of Triquint, for his paper on the thermal modelling of GaN devices. He showed that the thermal resistance of the Silicon Carbide (SiC) material under the active GaN varies with temperature. Careful finite element modelling of the heat paths showed that a 20°C increase in the base temperature resulted in a 30°C increase in channel temperature. Device reliability is directly dependent on managing the channel temperature.
Alongside the conference, twenty exhibitors displayed their latest products, with strong representation from the test and measurement sector, alongside amplifier, connector and semiconductor manufacturers. There was also the opportunity to network, and more, during the Society Dinner.