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Electromagnetic Modelling
To meet the demands of the defence and aerospace business, the ATC has developed the highest quality EM simulation and modelling capability ranging across the spectrum from microwave and radio frequency systems to infra red signature prediction.
The Electromagnetics Group of the Advanced Technology Centre (ATC, Great Baddow) has many years’ experience covering ELF, HF, VHF, UHF, microwave and millimetre wave frequencies. Radar Cross-Section (RCS) reduction, antenna design, installed antenna performance prediction and measurements have been undertaken for aircraft, marine, land and space applications.
An extensive range of electromagnetic (EM) modelling techniques are available including full-wave and high frequency asymptotic codes. We maintain a strong focus on increasing our computational ability through development of hybrid codes (using combinations of EM techniques), increasing the computational efficiency of existing codes and a rolling programme of hardware improvements. EM modelling is performed on networks of high-performance Work Stations and dedicated, secure Work Stations for classified programmes. Computationally intensive tasks use supercomputers located at Universities and commercial facilities within the UK.
Air
Future aircraft will function in an increasingly demanding EM environment. Installation of multiple systems on aircraft (e.g. radar, GPS, EW, communications) requires accurate prediction of installed antenna performance. Finite-Difference Time-Domain (FDTD) calculations of radiation from installed antennas enables the effect of fuselage, radomes and co-sited antennas to be assessed. The example shows radiation from a fuselage-mounted, starboard-looking antenna scattering off wing-mounted engines below the wing. Similarly, Method of Moment calculations and practical verification using scale models enable independent validation of computed performance predictions.
Low Observable (LO or ‘stealth’) aircraft, missiles and UAVs require accurate RCS prediction for both the wholeplatform and individual vehicle components. Without careful design, the contribution to RCS of individual components, including resonant antennas, can exceed the RCS of the host platform. ATC has modelled a variety of LO antennas, and is investigating RCS reduction using broadband Vivaldi phased array antennas. The array shown operates over an octave bandwidth, can scan up to 60º from
boresight in any direction and is being designed for future LO ‘common aperture’ antenna systems. Alternative array geometries, including multi-faceted arrays, arrays with elements conformal to fuselage surfaces and incorporating radar absorbing material (RAM) blending components are being investigated for LO applications.
Optical beamformers, using True-Time Delay techniques, are being investigated for future highperformance phased array antennas. The time-evolution of fields within the Vivaldi aperture are calculated using FDTD and Finite Element techniques.
EM models include a complete description of complex, lossy materials used in RAM. Our close links with ATC (Towcester), where RAM materials have been manufactured for many years, enables a synergy of material design, manufacture, EM modelling and measurements (including RCS imaging) to provide a comprehensive microwave stealth capability for both platforms and sensors.
FDTD has been applied to modelling broadband spiral EW antennas, plasmas and seeker antennas for future missiles. The seeker antenna shown features a fixed feed / reflector and a gimballed main reflector surface. Diffraction effects and interactions between the antenna and radome surfaces are clearly visible.
Antennas at millimetric frequencies are being investigated for covert, high data-rate airborne communications links using switched beams and low sidelobe levels.
Space
The economics of commercial spacecraft for global communications systems requires increasingly complex antennas designed within short timescales. The EM Group at ATC has participated in designing antennas for three generations of INMARSAT spacecraft and on
the space segment of UMTS. By 2005 INMARSAT 4 will provide high data-rate services throughout the World using an array-fed reflector generating over 200 simultaneous antenna beams illuminating many Continents. Mass reduction is important for antennas
for future spacecraft and UAVs. EM Group has designed and manufactured lightweight, dual-polar printed antennas using multilayer aperture-coupling to provide close control of radiation pattern characteristics.
Calculated antenna footprints over South America for INMARSAT 4 spacecraft
Sea
Future Naval vessels will require signature management across the entire EM spectrum and increased sensor performance.
ATC is participating in the design of ‘integrated’ masts where sensors are embedded in the RAM and dielectric panels comprising the mast surfaces.
FDTD has been used to calculate propagation of radiated fields across the mast.
The example shows calculation of coupling between an EW sensor and a surveillance radar aperture.
Integrated Technology Mast
Land
High data-rate secure communication between ground based vehicles requires millimetre-wave antennas and antennas with
ultra-low sidelobe levels. ATC is extending this technology by investigating millimetre wave antennas with switched beams that
exploit micromachining techniques. Similar antennas are expected to find applications in future automotive radar and telematic
systems for civilian use.
ATC also has extensive in-house manufacturing and antenna / RCS measurement facilities, including a large near-field anechoic
test facility (NFTF) for antenna pattern measurements, diagnostic imaging and radar cross section measurements.
