Aerospace and Electronic Systems Magazine October 2017 - 58

One-On-One With Hugh Griffiths

Lorenzo: You said Moonbounce... That's interesting! Can you
say more on that?
Hugh: For moonbounce (at 432 MHz and 1.3 GHz) we built a 6
m dish. That taught me a lot about real engineering, since in order
to receive the very weak echoes, every part of the whole system
had to work properly. But we were able to receive echoes from our
transmissions (the delay to the Moon and back is about 2 seconds),
and to communicate with other similarly-equipped stations in other
countries (Figure 3A).
Lorenzo: It seems that you were a radar engineer even before
getting an engineering degree! So, what did you study during
college?
Hugh: My undergraduate degree was in Physics at Oxford University. I had won a scholarship to support my studies, and studying at Oxford was a wonderful experience. When I graduated in
1978 I joined the Plessey company, working at the Roke Manor
research lab, on adaptive antennas, mostly for communications applications. In those days (the late 1970s) these were all analog, and
digital techniques were only just starting to be considered. I was
lucky in that pretty much from the first day I had my own project
that I was responsible for.
Lorenzo: Very interesting: did you publish this work?
Hugh: Yes. My first paper was published at an IEE Antennas and
Propagation Conference in 1981, on a four-channel airborne adaptive array system1.
But by then I had become interested in the possibility of studying for a Ph.D., and I was also attracted by the bright lights of
London. In my work at Roke Manor I had read some publications
on circular antenna arrays, and I had found out that one of the leading figures in that subject was Professor DEN Davies of University
College London (UCL), and met him at the Antennas and Propagation Conference in 1981. As a result, in January 1982 I joined UCL
as a Research Assistant.
Lorenzo: What research did you pursue at UCL?
Hugh: I was fortunate enough to have the freedom to work on
three topics in parallel. First was the circular array work that had
attracted me to UCL in the first place. Circular arrays have some
interesting properties that allow direction finding, null steering
and pattern synthesis over the full 360° of azimuth and over very
broad bandwidths. Second was some work on satellite-borne radar altimeters. These had been developed to make measurements
of ocean surface height, wave height and wind speed, but had
also produced interesting data over land and ice sheet surfaces.
The European Space Agency were developing their ERS-1 satellite, and wanted to know how the design of its radar altimeter
1

Griffiths, H.D., 'A four-element VHF adaptive array processor';
Proc. 2nd IEE Intl. Conference on Antennas and Propagation, York;
IEE Conf. Publ. No. 195 Part I, pp185-189, 13-16 April 1981.

might be optimized to measure ice sheet elevation, and hence to
study the effects of global warming. It was this work that I wrote
up for my Ph.D. thesis.
The third topic was bistatic radar.
Lorenzo: Oh, Nice! That's definitely your preferred topic!
Hugh: Yes indeed. We developed a bistatic receiver that hitchhiked off a UHF Air Traffic Control radar at Heathrow airport. The
key part of this was synchronization of the receiver to the scan and
PRF of the transmitter, which was achieved by 'flywheel' clocks
at the receiver. I also developed a digital beamforming array for
pulse chasing, and a coherent MTI scheme using stable close-in
clutter echoes to provide a phase reference. My first journal paper
described this2, and it won a Premium Award.
That work really fascinated me, and laid the foundations for
much of the work that I have pusued in my career (Figure 3B).
Lorenzo: Who was your supervisor during this period?
Hugh: My Ph.D. supervisor, Professor DEN Davies, had a wonderful knack of being able to understand any problem within just
a few minutes, and was always able offer valuable advice. He
went on to become Vice-Chancellor of the University of Loughborough, and then Chief Scientific Adviser to the UK Ministry
of Defence. I also had the privilege of working with Professor
Alex Cullen, who was one of the foremost engineers in the world
in microwaves and antennas. Both of these were very influential
in my career.
Following on from that, we had the idea of trying to exploit television transmissions as the basis of radar. We built a
system - which worked, but not very well, for reasons we now
understand. Firstly, the analog TV waveform has strong ambiguities associated with the 64 μs line repetition rate. This results
in range ambiguities at (in monostatic terms) 9.6 km intervals.
There are also ambiguities corresponding to the frame scan rate
of 25 Hz. These effects, plus the fact that the amplitude modulation of the vision carrier never actually reduces to zero, mean
that the analog television signal is far from ideal as a radar signal. The paper that we published on this work3 was the first in
the open literature on what is now called Passive Radar, and has
been quite highly cited.
Not long after that I started collaborating with Chris Baker,
who was then working at the Royal Signals and Radar Establishment (RSRE) at Malvern in the UK. We have worked on many topics together for more than twenty years, and published more than
a hundred papers and books together - including the third edition
of the Stimson's Introduction to Airborne Radar book and (most
recently) An Introduction to Passive Radar.

Griffiths, H.D. and Carter, S.M., 'Provision of moving target indication in an independent bistatic radar receiver'; The Radio and Electronic Engineer, Vol.54, No.7/8, pp336-342, July/August 1984.
Griffiths, H.D. and Long, N.R.W., 'Television-based bistatic radar'; IEE Proc., Vol.133, Pt.F, No.7, pp649-657, December 1986.

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OCTOBER 2017

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