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

Lead Research Organisation: University of St Andrews
Department Name: Physics and Astronomy

Abstract

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.

Planned Impact

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".

Publications

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Donaldson C (2018) CNC Machined Helically Corrugated Interaction Region for a THz Gyrotron Traveling Wave Amplifier in IEEE Transactions on Terahertz Science and Technology

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McElhinney P (2017) An Output Coupler for a W-Band High Power Wideband Gyroamplifier in IEEE Transactions on Electron Devices

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Zhang L (2017) Optimization and Measurement of a Smoothly Profiled Horn for a W-Band Gyro-TWA in IEEE Transactions on Electron Devices

 
Description In this collaborative grant with Strathclyde University, St Andrews developed, constructed and tested a mm-wave radar and associated test rig suitable for testing a next generation very high power (multi-kW) wideband amplifier operating at 94 GHz - for cloud profiling radar and magnetic resonance applications. This radar work has now been published. Unfortunately there were delays in the development of the the amplifier at Strathclyde (due to very late delivery of components by external companies). A year after the grant finished, the amplifier was shown to work with the intended state-of-the-art power bandwidth products - and this key advance has been published by Strathclyde in an important paper. However, to demonstrate very high impact applications, a suitable (highly specialised) power supply is required to improve the repetition rate of the device. One of the key work packages within the grant was to integrate the amplifier with a suitable antenna structure and low return loss vacuum window. St Andrews initially provided the design of a high performance corrugated feed horn (with minor modifications by Strathclyde) and Strathclyde designed the vacuum window. This device met specification in terms of its optical performance, but proved not to be "high vacuum" compatible, due to the electroforming process involved in the manufacture of the feed horn. St Andrews subsequently designed a high performance smooth feedhorn, (with minor modifications from Strathclyde) to overcome this problem . This solved the vacuum problem and produces high quality antenna patterns and has now been published.

In the meantime, the radar has been adapted to demonstrate its use for low a low power cloud radar application (which was one of the original major applications) as part of an IAA EPSRC project and is currently undergoing field trials (and key design aspects published in a separate paper).
Exploitation Route The new high power amplifier technology, being developed at Strathclyde, would open up new fields in magnetic resonance and high resolution radar imaging (e.g. of space debris) or for very high bandwidth communications (if they can integrate with a suitable power source). This remains a medium risk / high reward piece of research. At St Andrews we have made modifications to the radar (using EPSRC IAA funding) and have field trials are ongoing using the radar with the aim of demonstrating that cloud radar measurements can be made using (much cheaper) solid-state sources using FMCW techniques. This work looks very promising and is still ongoing. Unfortunately main results have been delayed due to a regulator failing leading to the failure of several devices which have just been replaced.
Sectors Aerospace, Defence and Marine,Chemicals,Electronics,Manufacturing, including Industrial Biotechology,Security and Diplomacy

 
Description A number of companies have previously expressed interest in developing the amplifier technology at Strathclyde (which had technical/collaborative input) from St Andrews. The first demonstration of the amplifier technology last year should accelerate this process as there are strong potential applications in communications, magnetic resonance and radar. The radar that was developed at St Andrews for testing that instrument has been modified for use as a lower power FMCW cloud radar (using STFC IAA funding) and is currently installed on top of the Napier Astronomy building at St Andrews taking data, with the specific aim of commercialisation. During the grant St Andrews and Strathclyde working on feed horn (antenna) design. That work has since been expanded and taken forward at St Andrews and led to the development of new types of broadband and compact high performance feeds. These new designs directly helped a collaborative partner Thomas Keating win contract for various satellite systems including a NASA sponsored CUBESAT project to detect hurricanes. The system is due to be launched this year.
First Year Of Impact 2018
Impact Types Economic