Flat panel antennas for satcom terminals. Martin Shelley. Name. Date The most important thing we build is trust. DEFENCE SYSTEMS Defence Electronics

Transcription

1 Name Date The most important thing we build is trust COMMUNICATIONS AND CONNECTIVITY Antenna Systems Commercial Systems SATCOM Tactical Communications and Surveillance DEFENCE SYSTEMS Defence Electronics MISSION SYSTEMS Aviation Services Life Support Mission Equipment Flat panel antennas for satcom terminals Martin Shelley SatApps Catapult Antenna Workshop Harwell, 14 th May, 2014

2 Presentation outline Scope of the presentation Benefits and shortcomings of flat panel antennas X-Band flat panel antennas for user terminals Ka-Band flat panel antennas for user terminals Single polarised designs Dual polarised designs Ka-Band flat panel antennas the manufacturing challenge 1 Flat panel antennas for satcom terminals

3 Why flat panel arrays? Packaging Arrays for SOTM Typically only a few cm thick, providing maximum space for other components Arrays for portable terminals Typically, no assembly is needed, while reflectors need to be assembled in the field Hinged antennas can be used to create larger apertures Reflectors for SOTM Difficult to package and/or high profile Reflectors for portable terminals Multiple curved sections that need to be clipped together Segments difficult to pack efficiently 2 Flat panel antennas for satcom terminals

4 Why flat panel arrays? Radiation patterns Arrays Very low sidelobes outside principal planes Can align geostationary arc outside principal planes, while maintaining high efficiency Virtually no rear radiation Reflectors Sidelobes in all planes Rear radiation due to feed spill-over Aperture flexibility Arrays Can be designed for wide range of aspect ratios Ideal for low profile SOTM Future potential for interference cancellation and electronic steering Reflectors Generally work best when the aperture is close to circular Far-field amplitude of 75cmCPTNo25LongFeedSN117Pol1LHCP.NSI Elevation (deg) Azimuth (deg) Flat panel antennas for satcom terminals

5 Why not? Flat panel arrays are expensive Typically multi-layer PCB construction or waveguide Cannot compete with a bit of bent metal! Flat panel arrays can be lossy More efficient use of a given aperture compared to a reflector, but suffers from internal losses Particular concern for RX Flat panel arrays are single band Very difficult to design arrays that cover multiple bands (ic, C- and Ku- Band or X- and Ka-Band) Reflectors can use interchangeable feeds 4 Flat panel antennas for satcom terminals

6 Cobham s X-Band antenna technology Three designs: 24 x 24 element Diamond array with uniform excitation 48 x 32 element two panel array for Microsat terminal 32 x 8 element array with tapered excitation for SOTM Key features RHCP and LHCP ports, operating over full GHz band Unique multi-layer printed circuit construction using thin substrates and foam spacers Two suspended stripline beamformers feed dual linearly polarised elements Waveguide hybrid to generate dual circular polarisations Easy integration of filtering and LNB on rear surface Typical characteristics At about 60%, efficiency similar to front fed reflector with the same aperture area Very low sidelobes in the intercardinal planes About 30mm thick, including waveguide combiner 5 Flat panel antennas for satcom terminals

7 Ka-Band arrays Printed circuit solutions cannot be used in Ka-Band due to high losses Ka-Band is essentially a dual frequency requirement (20 and 30GHz) Ka-Band is essentially a dual polarisation requirement, using orthogonal circular polarisations in the two bands For portable terminal applications, an array which generates a single pair of circular polarisations can be used (manual reconfiguration id needed) For SOTM systems, remotely switchable polarisation pairs are required by most satellite operators Two different array approaches needed: Portable terminals: Single linear polarised broadband waveguide array and unique polariser that converts to one CP in the low band and orthogonal CP in the high band SOTM: Two interleaved slant 45 polarised waveguide arrays with a conventional broadband external CP polariser 6 Flat panel antennas for satcom terminals

8 Cobham s Single polarised Ka-Band array technology Two designs Initial 16 x 16 element prototype with uniform excitation Full size 64 x 48 element prototype (520 x 400mm) with uniform excitation Key features Operate over GHz and 29-31GHz bands Include waveguide diplexer Use single waveguide beamformer and linearly polarised elements Employs unique multi-layer printed polariser (patent pending), giving orthogonal CP polarisations in RX and TX Typical characteristics At nearly 70%, efficiency better than front fed reflector with the same aperture area Very low sidelobes in the intercardinal planes About 30mm thick, including waveguide diplexer 7 Flat panel antennas for satcom terminals

9 Gain (dbi) Cobham s Dual polarised Ka-Band array technology 790 x 200mm SOTM aperture under development Key features Operates over GHz and 29-31GHz bands Includes waveguide diplexer Uses dual waveguide beamformers and interleaved slant 45 polarised elements Uses broadband printed CP polariser Simulated Azimuth Pattern 30GHz Ideal Co-polar Real BFN Co-polar FCC on GSO Typical characteristics At nearly 70%, efficiency better than front fed reflector with the same aperture area Low sidelobes in the azimuth plane using tapered distribution About 75mm thick Angle (deg) 8 Flat panel antennas for satcom terminals

10 The manufacturing challenge for Ka-Band arrays Ka-Band arrays must be waveguide based to obtain high efficiency Arrays need to be manufactured to very tight tolerances and have very small dimensions Very expensive to manufacture CNC machined parts Complex assembly Hence For high volume applications, injection moulded metallised parts can be used Can meet tolerance requirements Very low high volume pricing Very high up-front tooling costs CTS has demonstrated this in Ku-Band 9 Flat panel antennas for satcom terminals

11 The manufacturing challenge for Ka-Band arrays 3D printing offers a potential alternative Sintering of plastics, which need to be post plated Direct sintering of metal Benefits Can meet tight tolerance requirements No high up-front tooling costs Pricing much lower than CNC, even in low volumes some processes claim costs comparable to injection moulding Shortcomings Metal parts surface roughness is much higher than CNC machining or injection moulding Problems with some geometries the overhang problem Plastic parts Limited range of plastics default plastic is Nylon Still needs to be plated, hence multiple parts often required 10 Flat panel antennas for satcom terminals

12 Summary and conclusions High performance flat panel arrays can be designed and manufactured to work well in all the key satcom bands They offer considerable flexibility to cater for a wide range of installation requirements Different technologies are needed in different frequency bands Cobham has demonstrated efficiencies close to those which can be achieved using reflectors in both X-Band and Ka-Band Regulatory changes are required to make best use of the benefits of array antennas Key challenge is manufacturing cost, where reflector solutions remain unassailable 11 Flat panel antennas for satcom terminals