Novel Gyro-TWA Amplifier for High Power mm-wave Radar Remote Sensing

Modelling the global climate accurately, and developing tools which can predict the weather more reliably, is of fundamental importance us all. To improve the quality of atmospheric models we need increasingly widespread and more sensitive measurements of atmospheric constituents. In particular, clouds play an enormous role in the earth's atmospheric processes but currently they are still relatively poorly understood, partly due to a lack of measured data, and this lack of data means that atmospheric computer simulations are of limited validity. As global warming takes effect, this can result in more moisture in the atmosphere, increasing the frequency of extreme weather events. Thus, improving our ability to measure clouds is an important goal for climate researchers. Radars which operate with millimetre wavelengths are ideally placed to measure clouds, ice particles, aerosols and volcanic ash since their operating wavelength is appropriate to the scale of these atmospheric constituents. However, current millimetre wave cloud profiling radars, which are usually ground based and use narrow frequency band high power pulse amplifiers, have limited ability to detect the most tenuous ensembles of very fine particles, especially at very high altitudes, where their interaction with solar radiation is highly significant. Furthermore, the limited sensitivity of earlier generations of cloud profiling radars tended to mean they measured slowly and only looked in a single direction, usually vertically upwards. This limited view of clouds then fails to capture their true three dimensionality and dynamic behaviour. The next generation of cloud profiling radars will scan their beam around in space to reveal cloud structure and record the temporal evolution of cloud masses, but this requires increased transmit power.

The aim of our project is to demonstrate a new class of high power, wideband millimetre wave amplifier, called a gyro-TWA, which offers a ten-fold increase in available bandwidth and a five-fold increase in available peak power over the amplifiers used in current cloud profiling radars. This will lead to greater radar sensitivity, enabling measurement of smaller or more tenuous particulates, with finer resolution, at longer ranges or in a shorter timescale. The technology also has the potential to be applied to the ground based mapping of space debris, a major consideration for all orbiting systems including environmental monitoring satellites. The proposal is a collaboration between two major millimetre wave groups at the University of Strathclyde and the University of St Andrews who collectively have decades of experience and vibrant international reputations in the development of high power millimetre wave sources, radars, instrumentation and components, plus a strong track record in commercialisation, industrial collaboration, and delivering on project objectives. The gyro-TWA represents a core technology that is likely to lead to UK leadership in the field of high power millimetre wave radar.

Commercial: In time, once this technology has been proven, we have the potential to make the UK leaders in high power wideband millimetre wave amplifiers and associated systems. There is a global market for high power millimetre wave radar systems covering remote sensing applications, as is the focus of this call, but also for space debris detection, tracking radar, synthetic aperture radar (SAR) and surveillance applications. Numerous millimetre wave cloud profiling radars operating at either 35 or 94GHz are currently deployed throughout the world in support of meteorological observations (e.g. Helmholtz-Zentrum, Geestacht, GE; STFC Chilbolton Observatory, UK; Cesar Observatory, Cabauw, NL; SIRTA, Palaiseau, FR; NICT, Japan) with the majority being deployed by the US Atmospheric Radiation Measurement (ARM) program at about 15 sites. The ARM program has recently invested $30M+ upgrading cloud radars, which cost >$1M per system. Beyond radar, there is a significant market in magnetic resonance spectroscopy instrumentation in which very fast (ns or sub-ns) high power millimetre wave pulses are used to manipulate electron spins. The wideband, high power capabilities of the gyro-TWA will dramatically enhance the sensitivity of both Electron Paramagnetic Resonance (EPR) and Nuclear Magnetic Resonance (NMR), via Dynamic Nuclear Polarisation (DNP), which are predominantly applied to biological investigations. Existing EPR and DNP systems cost up to $5M/system and with ~300 research systems operating world-wide this equates to a $billion industry. The ultimate commercial potential can be assessed through the pervasive deployment of conventional NMR systems. All together these represent a substantial potential market. Our Project Partners and other established collaborators are very well placed to capitalise on these markets given their track record and experience. Note that the benchmark for high power millimetre wave amplifiers as used in cloud radars and EPR/DNP spectrometers is the extended interaction klystron (EIKA) which typically cost >$200k per tube and modulator.

Environmental: Clouds have a profound impact on the Earth's climate. Millimetre wave radars bridge an observational gap in Earth's hydrological cycle by adequately detecting clouds and precipitation thus offering a unique and more holistic view of the water cycle in action. We aim to develop a unique high power 5kW, broadband 10%, short wavelength (3.2mm) cloud radar that has excellent sensitivity to small cloud droplets and ice crystals at high altitudes and provides measurements of their reflectivity and Doppler velocity. This millimetre wave radar will be an important tool in characterising the properties of clouds via detailed cloud and precipitation process studies and monitoring activities that strive to improve our understanding of cloud processes. The observation and monitoring of clouds, aerosols and precipitation is critical to understanding the earth's atmosphere and a vital prerequisite for the validation of global climate models.

Societal: In the long term, improved remote sensing of the atmosphere will lead to more accurate climate models and weather forecasting. This has obvious direct societal benefits including better understanding of climate change, improved flood risk assessment, understanding and mitigation of the effect of atmospheric pollution and aviation on atmospheric radiation balance. We will convey to the public the exciting results of our work and its implications for society via St Andrews' highly successful outreach programme "Millimetre Waves: Vision for the Future".