RF Interference Mitigation Service
Expert advice for the deployment of complex RF systems
IntelligentInsight
Radio Frequency Interference Mitigation Service
The Electromagnetic (EM) spectrum is a scarce resource that is essential to modern life.
In many RF bands there is severe overcrowding which causes interference, reducing the
benefits of the communications system, and results in increased operating costs.
This trend is only set to increase as ever more use is made
of the EM spectrum. The busy bands where the problems
of overcrowding are well known, such as the 400 MHz and
800 MHz modem/microphone bands, are indicators of what
could happen in other bands.
The problem is escalated by new and diverse uses of the
radio spectrum which increase the number of signals that
can cause interference. Some of this interference can be
sporadic or seasonal, making it more difficult to monitor.
CURRENT AND EMERGING
INTERFERENCE PROBLEMS
• Co-channel Interference
An example of this is continental interference from
Europe affecting telemetry links on the east coast of
England, and interference to Freeview TV from 4G
systems.
• Fundamental Overload
Interference can be caused by overloading due to
nearby large signals (perhaps mobile and fleeting). Such
interference causes saturation of the receiver front end
and reduces the effective sensitivity of the receiver.
• Receiver Inter-modulation
In the presence of large signals, often a significant distance
away in frequency, some receivers suffer from intermodulation problems (i.e. inadvertent mixing products
falling in band). Sources of potential interference are
radio controlled traffic management systems, aircraft
communications, police/fire radio and ship/maritime radio.
• Poor Network Deployment
A poorly designed network can lead to unfavourable
signal propagation conditions.
Roke have the experience and expertise to help
in these problem areas. We have the analytic tools,
Inter-modulation Interference (IMI) experience and
unique mitigation technology to assist clients who
have RF interference problems.
INTERFERENCE MITIGATION SERVICE
Roke is the UK’s premier supplier of interference cancellation
technology with equipment deployed in both military and
commercial equipment. Our service comprises:
1. Planning and design advice
2. Analysis and modelling – propagation models through
to detailed modelling using HFSS
3. Monitoring and diagnostics – direction finding and signal
counting using superresolution technology
4. Mitigation design, manufacture, fitting and testing
– antenna layout, antenna selection, filtering, screening
and cancellation
MONITORING AND DIAGNOSTICS
It is important that signal monitoring is conducted
to have a full understanding of the sources of
interference. Our N-channel receiver equipment
is ideal for such diagnostic work in complex multisignal environments.
• Monitor and record co-channel signal data
for separation and offline analysis
• Direction finding capability which allows the
direction of the signals to be determined
• Data collection can be started remotely when
interference actually occurs.
Case Studies
CASE STUDY:
FILTER IMPLEMENTATION
Where high power wideband transmitters are installed on
military vehicles there is often a need to provide filtering to
protect important reception bands but with minimal impact
on the noise figure. These filters also have to survive the
power levels coupled from the transmitter, and to perform
with low levels of Passive Intermodulation (PIM) if receivers
are to be adequately protected.
Roke has considerable experience in this area and has
developed many cavity and resonator coupled filter solutions
designed to protect sensitive bands from high power
adjacent signals. Our filtering solutions have been fitted to
many defence applications.
CASE STUDY:
INTERFERENCE CANCELLATION
Telemetry systems used by the public utility companies to
monitor outlying installations are subject to interference from
continental Europe.
Following an investigation
by Ofcom, it was concluded
that the main source of this
interference was from the
CDMA450 networks in Europe,
Interference Cancellation Unit
and that it was particularly
serious in the south-east corner of the UK between the
months of April and October. The interference happens
because the CDMA450 base station’s transmit frequencies
that overlap with the telemetry receive frequencies and
during the summer months atmospheric ducting cause these
signal to propagate to the UK.
Roke worked closely with the client to help mitigate the
effect of this continental interference to their telemetry
links. The work resulted in the development of interference
cancellation equipment which successfully mitigated the
interference by coherently cancelling the interference signal
in the antenna feeder. The equipment has since been used
for similar applications in other frequency bands.
In recent years interference mitigation technology has moved
to fully digital implementations, with both temporal and
spatial filtering. This technology has been proven in fixed and
mobile applications, where dynamic changes can be readily
compensated for.
CASE STUDY:
ANTENNA DESIGN AND POSITIONING
Mast top space is at a premium and everyone wants to
mount antennas at the highest point to achieve 360°
coverage. However, on most radio towers and high buildings
the zenith is not always available and compromises are
required. Antennas then have the effects of the structure to
contend with, beam shapes can become distorted and there
is a risk of blind arcs in the antenna coverage. In many
cases this risk and compromise is unacceptable (where the
communications channel is critical) and the antenna
performance must be guaranteed.
By utilising an array of elements carefully phased around
the structure it is possible to provide clean omnidirectional
patterns with no interference nulls between elements.
Designed for high power operation, our Butler Matrix units
provide reliable communications despite the separation of
multiple antennas around a structure.
A Butler Matrix antenna distribution unit
Roke Manor Research is a world-class electronics engineering consultancy. We enable our clients
to maximise their investments in science and technology. Trusted by government and industrial
partners worldwide, we deliver technology-based R&D services, provide independent advice, and
solve technically challenging problems.
Roke make it their business to understand their clients’ key issues to provide end-to-end tailored
solutions. With extensive experience in communications systems, electronic sensors, and
information assurance and in both the civil and military domains, we understand the technical
complexities of modern and future systems. Our team of over 350 engineering consultants
develop new concepts, capabilities and systems to protect what matters most to their clients.
Established in 1956, Roke remains a British centre of excellence for world-class innovation and
engineering, and was recently awarded a Queen’s Awards for Enterprise and Innovation. Since
October 2010 Roke has been a wholly owned subsidiary of the Chemring Group plc.
DISCUSS YOUR RF INTERFERENCE STRATEGIES TODAY
If you are suffering a radio frequency problem on existing equipment, are contemplating
a dense platform aerial layout or are not sure what frequency to use for a new system
design please contact us.
Call: Email: Visit: +44 (0)1794 833000
info@roke.co.uk
www.roke.co.uk
Roke Manor Research Ltd
Romsey, Hampshire, SO51 0ZN, UK
T: +44 (0)1794 833000 • F: +44 (0)1794 833433
www.roke.co.uk • info@roke.co.uk
© Roke Manor Research Limited 2016 • All rights reserved
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