The design of radio frequency (RF) components for cellular mobile communications (Impact Case Study 1)
Submitting InstitutionUniversity of Leeds
Unit of AssessmentElectrical and Electronic Engineering, Metallurgy and Materials
Summary Impact TypeTechnological
Research Subject Area(s)
Engineering: Electrical and Electronic Engineering
Technology: Communications Technologies
Summary of the impact
Research at the University of Leeds underpinned the development and
manufacture of RF filter
technology by Radio Design Ltd, including the 3G `Universal RF
Combiner Unit' with sales of
>£18M (40,000 units) since 2008, which led to the company's Queen's
Award for Enterprise
(Innovation) in 2011. This technology was subsequently improved
specifically for the 2012 London
Olympics for shared use by all five cellular operators, and has now been
further developed, again
using Leeds research, for 4G systems (with >£4.2M sales in 2013). Leeds
contributed directly to ~75% of Radio Design's products, and its
expansion from 11 employees in
2008 to 150 employees today. Leeds-designed RF filters have also been
widely utilized by other
manufacturers, with estimated annual international sales of tens of
millions of pounds since 2008.
In parallel, Leeds research on the physical modelling and design of pHEMT
switches has been
used since 2008 by RFMD (UK) Ltd (previously Filtronic
Compound Semiconductors), who supply
all major mobile phone manufacturers — over 2 billion pHEMT switches are
used worldwide, with
RFMD's estimated sales exceeding £250M since 2008.
The University of Leeds has a long-standing international reputation
dating back to the 1970s for
the development and exploitation of RF components. Much of our research in
this field over the
last 35 years has been in partnership with Filtronic Components Ltd,
which was founded by
Rhodes from the University in 1977 and floated as Filtronic PLC
in 1994, as well as with a number
of companies that have arisen directly from Filtronic.
Here, we focus on two areas of Leeds research, and their impact
post-2008: the development of
dielectric filters (Hunter, Rhodes, Pollard); and, the accurate
physical modelling of semiconductor
devices, leading to the design of high breakdown voltage power transistors
In 1998, Leeds started a new research activity, led by Hunter, on
the development of dielectric
resonator filters for the rapidly expanding mobile communications market.
This work, in
collaboration with Filtronic Comtek Ltd, led to a new method of
realizing cross-couplings using non-resonant
nodes, the latter being needed to produce zeros in the filter transfer
function. A new
class of patented dual-mode filters resulted, where each
dielectric resonator supports two
orthogonal resonant modes ; hence an eight pole filter requires only
four dielectric resonators,
leading to a significant and commercially important 50% reduction in size
and mass (Hunter and
Rhodes, `Dual TM Mode Composite Resonator' US Patent 6,414,571 B1,
As cellular networks became deployed more widely, there was a need for
filters with bandwidths of <1 MHz at centre frequencies of 1 GHz for
base stations. Leeds
therefore conducted research into the synthesis of filters with
significant dissipation loss and non-uniform
Q filters were patented (Rhodes and Hunter, `Reflection mode filter
and method with a
constant loss offset' US Patent 6,448,872 B2, priority 28/02/2001). This
new technique took low-Q
structures into account, avoiding any reduction in skirt selectivity and
was then extended to
transmission-mode filters with elimination of the requirement for a
Based on this research, Leeds received funding from two TSB projects with
TWI (Cambridge) to
develop filter designs (`Adept-Sip' Ref. 461348, £398,401,
1/05/2006-31/10/2009; and `PPM2' Ref.
475416, £325,000, 1/06/08-31/11/11), as well as consultancies with the
Centre for Electromagnetic Remote Sensing to underpin applications in the
More recently, with the development of LTE and 4G systems by cellular
radio operators, there has
been the need to develop directional channel combining filters. To respond
to this, and working
with Radio Design Ltd, Leeds developed a theoretical synthesis
technique for the design of
directional filters for 4G power combining systems (`Apparatus for
allowing radio frequency
selectivity and method of use thereof', Patent Application No.
GB1222019.0, priority 7/12/12).
These filters enable very high selectivity to be achieved in a small
physical size .
The quality of this underpinning research is exemplified by: Hunter's
FIEEE in 2007; election by the
Board of Directors to General Chair of the 2011 European Microwave week;
award of an RAEng
Research Chair in 2012 (co-funded by Radio Design Ltd) on the
`Theory and design of filters for
mobile communication systems'; and, FREng in 2013.
In addition to developing filter technology for cellular base station
application, from the early 1990s
Leeds research also tackled the increasing need for more efficient, and
linear, microwave power
amplifiers for handsets and base stations. Led by Snowden, Leeds
focused on the accurate
physical modelling of semiconductor devices, initiallydesigning
heterojunction bipolar transistors (HBTs)  (with the modelling
incorporated into commercial CAD
suites, such as Agilent ADS). This led to the design of high breakdown
transistors, resulting in a seven-fold increase in breakdown voltage
pseudopmorphic high electron mobility transistors (pHEMTs) in 2001 .
This device technology
underpinned the establishment of Filtronic's volume manufacturing
facility  at Newton Aycliffe
in 2000 — the world's largest 150 mm GaAs wafer facility at the time.
The quality of this underpinning research is exemplified by Snowden's
award of: the 2004 RAEng
Silver Medal; FRS in 2005; knighthood in 2012; and the 2012 European
Outstanding Career Award. Ref. 4 received the 1999 International
IEEE Microwave Prize — only
the second UK recipient in 43 years.
Ian Hunter (Senior Research Fellow, 01/08/1998-31/08/2001; Reader,
and Professor, 01/06/2003-present).
Roger Pollard (Lecturer, 01/09/1974-30/09/1985; Senior Lecturer,
Professor, 01/08/1998- 30/09/2010, when he retired). Pollard also served
as Head of the School
of Electronic and Electrical Engineering (1999-2002), and inaugural Dean
of the Faculty of
Christopher Snowden (Professor, 01/07/1983-05/04/2005, when he left to
become CEO of
Filtronic Compound Semiconductor). Snowden also served as Head of the
School of Electronic
and Electrical Engineering (1995-1998).
David Rhodes (Professor, 01/04/1975-31/12/1993; Industrial Professor,
when he retired).
References to the research
 I C Hunter, J D Rhodes and V Dassonville, `Dual-mode
filters with conductor-loaded
dielectric resonators', IEEE Transactions on Microwave Theory and
Techniques 47, 2304-2311
(1999). DOI: 10.1109/22.808975.
 A C Guyette, I C Hunter and R D Pollard, `The
design of microwave bandpass filters using
resonators with nonuniform Q', IEEE Transactions on Microwave Theory
and Techniques 54,
3914-3922 (2006). DOI: 10.1109/TMTT.2006.884627.
 I C Hunter, E Musonda, R Parry, M Guess, and M Meng,
`Transversal directional filters for
channel combining', Proceedings of the IEEE MTT-S International
Seattle, WA (2013), in press, and distributed electronically at conference
 C M Snowden, `Large-signal microwave characterization of
AlGaAs/GaAs HBTs based on a
Physics-Based Electrothermal Model', IEEE Transactions on Microwave
Techniques 45, 58-71 (1997). DOI: 10.1109/22.552033.
 W Batty, C E Christoffersen, A J Panks, S David
and C M Snowden, `Electrothermal CAD
of power devices and circuits with fully physical time-dependent compact
of complex nonlinear 3-D systems', IEEE Transactions on Components and
Technologies 24, 566-590 (2001). DOI: 10.1109/6144.974944.
 M F O'Keefe, J S Atherton, W Bösch, P Burgess,
N I Cameron and C M Snowden, `GaAs
pHEMT-based technology for microwave applications in a volume MMIC
environment on 150-mm Wafers', IEEE Transactions on Semiconductor
376-383 (2003). DOI: 10.1109/TSM.2003.815631.
Leeds researchers in bold.
Outputs 1-2, 4-6 are all published in internationally leading
peer-reviewed archival journals, and
are recognised internationally in terms of originality, significance and
rigour. Outputs 1, 2, and 4
are particularly highlighted to underpin the impact described in this case
Details of the impact
Much of our research in microwave/millimetre-wave frequency components
with its translation and impact post-2008, has been in partnership with Filtronic
or companies that
have arisen from Filtronic. In October 2006, Filtronic
sold the majority of its wireless infrastructure
division, Filtronic Comtek, to Powerwave (USA), with key
staff from the filters division forming a
new company Radio Design Ltd in August 2007. In March 2008, Filtronic
Semiconductor's GaAs business was sold to RF Micro Devices Inc.,
and the facility (RFMD (UK)
Ltd) became the largest volume manufacturer of GaAs devices in
Europe. In August 2008,
Filtronic sold its defence business to Teledyne Technologies
Inc., forming Teledyne Defence Ltd.
In this case study, we focus on the creation of impact post-2008 of two
areas of Leeds research:
the development of RF filters principally through Radio Design Ltd,
and the design and
manufacture of high breakdown voltage power transistors through RFMD
(UK) Ltd. However, all
the companies discussed above derived from Filtronic PLC and were
all underpinned by Leeds
research and researchers post-1993 — Filtronic Wireless, Filtronic
Broadband, RFMD (UK), Radio
Design Ltd and Teledyne Defence Ltd between them had >500
employees and a total turnover of
~£80M in the most recent financial year [A].
Radio Design Ltd designs and manufactures single-band and
multi-band RF filters and combiners
for cellular radio systems, focusing on: inter-operator and technology
sharing; tower mounted
amplifiers; interference reduction; and, the provision of test equipment.
It has grown from 11 staff
in 2008, to 70 staff and sales of £8.7M in 2010, to 150 staff and sales of
£14.7M in 2012, with `75%
of the company's products derived directly from underpinning research at
the University of Leeds'
[B]. Its original (2007) 30,000 sq ft, manufacturing facilities in
Shipley, Yorkshire have expanded to
include 10,000 sq ft facilities in India (December 2008), and 20,000 sq ft
in China (March 2012).
Markets include the UK, Ireland, Scandinavia, Eastern and Western Europe,
China, India, and
recently the USA [B].
As examples of the uptake and exploitation of Leeds research by Radio
Design Ltd, our
development of non-uniform Q filters led to the company's 3G
Universal Combiner Unit, with
sales of >40,000 dual-channel units (total value £18M) from 2008 and
creation of >50 jobs; this
resulted in the company's Queen's Award for Enterprise (Innovation) in
2011 [B]. Based on the
success of this product, Radio Design Ltd were contracted to
design and build 35 power combiners
(each costing ~£35k) to enable all five cellular operators to share a
common antenna system at the
2012 London Olympics, removing the need for multiple cellular base
stations. Leeds' subsequent
development in 2012 of 4G power combining technology in
conjunction with Radio Design Ltd
has already led to sales in 2013 of 6,000 units (average cost: £700/unit)
to cellular radio operators
for use in LTE and 4G systems (with anticipated sales going forward of
18,000 units in 2014 and
35,000 units in 2015, leading directly to the creation of a further 50
Leeds' development of miniaturized filters has, however, not only
led to the growth and success of
Radio Design Ltd, but also the "tens of thousands of dielectric
resonator filters ... manufactured by
Filtronic and subsequently Powerwave ... for use in US cellular radio
infrastructure, which has been
widely utilised in the period 2008-2013" [B]. Furthermore,
the technology "is now used by many
manufacturers of filters, and I would estimate that there have been
sales since 2008 of tens of
millions of pounds" [B]. Bespoke filters were also designed by Leeds
for Selex Galileo, who have
integrated these filters into new designs for wideband defensive airborne
radar [C]. (Owing to
defence implications a definitive statement on how many £30M fighter
aircraft have adopted this
technology is not available. Indicative sales are of 500 units (two
filters per unit) [C]).
In parallel with the above, between 2008-2013 RFMD (UK) Ltd at
Newton Aycliffe produced
pHEMT switches for all major mobile phone manufacturers, based on the
initial Leeds research on
the design of high breakdown voltage power transistors, which was
first commercialized from
2005 through Filtronic Compound Semiconductors (CEO: Snowden) [D]
— "I therefore anticipate
that during the period 2008-2013 over 2 billion pHEMT switches have been
produced and used, all
originating from the Newton Aycliffe site and all deriving from
Professor Snowden's initial research
on the modelling of semiconductor devices. This corresponds to sales in
excess of £250M" [D].
[text removed for publication].
In 2013, RFMD (UK) Ltd sold the volume manufacturing facility established
at Newton Aycliffe to
Compound Photonics, with the planned creation of an additional 200 jobs
[figure removed for publication]
Figure 1 [text removed for publication]
Our close relationship with Filtronic led to Hunter's appointment
at Leeds in 1998 as a part-time
Senior Research Fellow (full-time from 2001) from his position as Fellow
Engineer at Filtronic, with
the objective of building research collaborations through PhD studentships
(12 based at Leeds, 3
in Filtronic), and research grants. Filtronic also funded
an undergraduate degree programme and
a Masters degree programme at Leeds, with total sponsorship of over £1M.
The impact of this
support, and the strength of our underpinning research, is evidenced by
the number of former PhD
students who held/have taken up senior positions in the UK and overseas
over the period 2008-2013,
including: Christoph Ernst (PhD awarded 2000), currently head of R&D
microwave components European Space Agency, Noordwijk, Netherlands;
(2003), senior research engineer, Filtronic; Ben Senior (2003) and Michael
Guess (2012) filter
designers, Radio Design Ltd, Shipley, UK; Andrew Guyette (2006), Research
Engineer at Naval
Research Labs, Washington DC, USA; Alaa Abunjaileh (2007), antenna
Stevenage, UK; Emika Sandhiya (2007), MMIC designer, SELEX Galileo, UK.
Sources to corroborate the impact
[A] `Company Financials for Filtronic Wireless, Filtronic
Broadband, RFMD(UK), Radio Design
Ltd and Teledyne Defence Ltd', www.duedil.com,
accessed 28 October 2013.
[B] Testimonial from the Managing Director, Radio Design Ltd (formerly
Filtronic), Shipley, West Yorkshire, 20 September 2013.
[C] Testimonial from the Principal Microwave Engineer, SELEX Galileo Ltd,
13 July 2012.
[D] Testimonial from the Chairman, Isotek Oil and Gas, Leeds, West
Yorkshire, 27 September
2013 (former Chairman of Filtronic).
[E] [text removed for publication].
[F] `Compound Photonics buys Newton Aycliffe RFMD factory', 25 July 2013,
accessed 24 October 2013.