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AIR TRAFFIC CONTROL RADAR - Military - Transportable 2AIR TRAFFIC CONTROL RADAR - Fixed Terminal Area 4AIR TRAFFIC CONTROL RADAR - Civil Terminal Area 6AIR TRAFFIC CONTROL RADAR - Secondary Surveillance 8SURFACE MOVEMENT RADAR - Linear Array 10SURFACE MOVEMENT RADAR - Reflector 12COASTAL SURVEILLANCE RADAR - 7.5 m Reflector 14COASTAL SURVEILLANCE RADAR - 5.5 m Reflector 16PORT SURVEILLANCE RADAR - EA7401 Linear Array 18SPECIALIST MILITARY APPLICATIONS 20ROTATING PEDESTALS 22
TURNKEY RADAR SYSTEMS AND PROJECT PARTNERSHIPS 24CIVIL CONSTRUCTION AND SITE ENGINEERING 26RADAR SITE SURVEY AND CONSULTANCY 28DESIGN CAPABILITY 30MANUFACTURING CAPABILITY 32TESTING AND QUALITY 34RADAR ANTENNA GUIDE - Systems Overview 36RADAR PERFORMANCE - Sea Surface Surveillance 37PERFORMANCE COMPARISON BY RADAR TYPE - Air Surveillance 38RADAR PERFORMANCE - Airport Surface Surveillance 39RF DATA 40
WAVEGUIDE DATA 41RADAR DATA 42EASAT CONTACTS 44EASAT INSTALLATIONS WORLDWIDE 45
Easat is a subsidiary of Goodwin Plc, and was incorporated into the Group in1987. The Goodwin Coat of Arms was awarded in 1983 by the London Collegeof Arms.
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1
Photograph: Easat Linear Array at Orlando Airport
This brochure illustrates radar sensors, antennas and site installations supplied by Easat to its worldwide customers. Easat is a proven supplier of commercial, off-the-shelf (COTS) and bespoke equipment. The design and manufacturing facilities featured here introduce Easats extensive capabilities.
Easat Antennas Ltd, based in Stoke-on-Trent(UK), was founded in 1987 as a specialistprovider of radar antennas and sensors. Sincethat time, Easat has established a reputation asa world-leading supplier of advanced array andreflector antennas for use in radar surveillanceof air, ground and sea targets for airport, port,border security and military applications.
With over 120 installations worldwide, Easatsreputation for supplying cost-effective, highperformance antennas with proven reliabilityhas led to many end users and consultantsspecifying Easat antennas on their projects.
With users and customers including FAA(USA),NATS (UK), Transport Canada, Government ofMalaysia, UK MOD, Lockheed Martin andRaytheon, configuring systems with Easatproducts ensures the highest confidence ofachieving performance requirements, on timeand on budget.
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Air Traffic Control Radar Military - Transportable
2
Illustrated in the main picture opposite is Easats TacticalDeployable Air Surveillance Antenna. This type of antenna canbe supplied either trailer-mounted or palletised. The antennasystem is self-contained and capable of being transported byship, aeroplane, helicopter or by being towed to site.The design provides for rapid deployment in less than 30minutes from arrival at the operating location.
The palletised version (shown on opposite page in the deployedmode) has 4-ISO corner locations on the pallet for transportation by standard road transport or purpose-builttrailer. The Trailer version shown below in the transport modehas a weight of 1954 kg.
The antenna is a dual frequency band, carbon fibre composite-based reflector which operates at S-band (2.7-2.9 GHz) andL-band (1.0-1.1 GHz). Three states of polarisation (linear horizontal, left-hand circular and right-hand circular) areprovided for S-band beam by use of polarisation-switchingcapability. At L-band, the antenna operates in IFF/SSR by useof three beams: sum, difference and omni. These featurescombine to provide leading-edge RF performance from theantenna system.
Deployment Data
Design weight of antenna/trailer system 4300 lbs
Max section weight to lift during erection 72 lbs
Assembly by 2 persons (wi thout g round anchors) 30 mins
Operational Capacity
Max operational wind speed (including gust) 60 knots
Operating temperature range -40 C to +55 C
S-Band AzimuthPattern
S-Band ElevationPattern
L-Band AzimuthPattern
Photograph Centre: Easat Trailer-mounted Tactical Antenna, in thetransport modePhotograph Opposite: Easat Pallet-mounted Tactical Antenna, in thedeployed mode
d B
d B
d B
Angle (degrees)
Angle (degrees)
Angle (degrees)
L-Band ElevationPattern
d B
Angle (degrees)
AzimuthPattern dB
MainBeam dB
Aux Beam dB
Sun Beam dBDiff Beam dB
Sun Beam dB
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The high-performance Easat EA5325 Primary Surveillanceshaped reflector radar antenna is designed to provide localor terminal area coverage, using a modified cosec 2elevation pattern to in excess of 40 elevation angle.The antenna is suitable for worldwide deployment and offersextreme versatility, being capable of operating with aco-mounted MSSR without the need for a radome, even inharsh icing conditions. This antenna can be supplied with singleor dual motor drives, and a variety of encoder and rotary jointoptions, including Inductosyn .
Photograph Centre: Easat - EA5325 Antenna and MSSR Antenna onthe ASR-E ProgrammePhotograph Opposite: Harrier Jets in low-flight training exercise, UK
The antenna operates at S-band (2.7-2.9 GHz) and provides
a dual-beam receive capability to enhance high-angleperformance, whilst minimising short range ground returns.The two beams point at different elevation angles, the mainbeam being a high-power transmit and receive beam, with theauxiliary beam used on receive only. Switchable polarisation isprovided as standard using a rotating polariser. In circular polarisation mode, a weather channel (receive only) is providedon both beams, which can be optionally selected via a fast(40 ns) PIN diode switch, or alternatively provided withseparate rotating joint channels. The antenna offers 34 dB ofgain as standard, an industry-leading performance given thehigh back-angle coverage provided.
General and Mechanical
Wei ght (i nc lu di ng Pe des ta l) 3 30 0 kg (P SR on ly )
3760 kg (PSR and MSSR)
Maximum Swept Radius 3.4 m
Rotation Rate Typically 15 rpm
Design Life 20 years
Environmental
Operational Wi nd Speed 140 km/hr wi th 10 mm ice
Survival Wind Speed 240 km/hr with 40 mm ice
Humidity 100%
O per ati on al Te mp era tu re -3 0 C t o +7 0 C i nc lu di ng 18 s ol ar
-50C to +70C (optional)
Protection Suitable for Coastal Environment
S-Band Main BeamAzimuth Pattern at 2.8 GHz, CP
S-Band ElevationPattern Main andAuxiliary Beamat 2.8 GHz, CP
Electrical
Main Auxiliary
Gain (at rotary joint) 34 dBi 32 dBi
VSWR 1.4:1
Circular Polarisation 20 dB min ICR in principal
azimuth and elevation planesAzimuth Beamwidth 1.5 0.1
Azimuth Sidelobes -26.0 dB (0 to 10)-32.5 dB (10 to 30)
-35.0 dB (30 to 180)
Elevation Beamwidth (-3 dB) 4.5 n ominal 6.0 n ominal
Vertical Beam Separation 5.5 1 betweenAux and Main beam peak
Air Traffic Control Radar Military and Civil - Fixed Terminal Area
d B
Angle (degrees)
d B
Angle (degrees)
Main BeamAux Beam
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Air Traffic Control Radar Civil Terminal Area
d B
Angle (degrees)
d B
Angle (degrees)
Main BeamAux Beam
6
Photograph Centre: Easat EA5025 Composite PSRPhotograph Opposite: Busy airport approach
The antenna operates at S-band (2.7-2.9 GHz) and provides adual-beam receive capability to enhance high-angleperformance (up to 40) whilst minimising short-range groundreturns. The two beams point at different elevation angles, themain beam being a high-power transmit and receive beam withthe auxiliary beam used on receive only. Three states ofpolarisation (linear horizontal, left-hand circular and right-handcircular) can be provided for each beam by use of a standardpolarisation-switching capability. The antenna offers 33.5 dB ofgain as standard, and has excellent beam-shaping and sidelobecontrol. A weather channel output can be made available incircular polarisation state.
General and Mechanical
Wei ght (i nc lu di ng Pe des ta l) 3 84 6 kg (P SR on ly )
4300 kg (PSR and MSSR)
Maximum Swept Radius 2.72 m
Rotation Rate Typically 15 rpm
Design Life 20 years
Environmental
Operational Wi nd Speed 157 km/hr wi th 10 mm ice
Survival Wind Speed 240 km/hr with 40 mm ice (on PSR)
Humidity 100%
O per ati on al Te mp era tu re -3 0 C t o +7 0 C i nc lu di ng 18 s ol ar
-50C to +70C (optional)
Protection Suitable for Coastal Environment
S-Band Main BeamAzimuth Pattern at 2.8 GHz, CP
S-Band ElevationPattern Main andAuxiliary Beamat 2.8 GHz, CP
Electrical
Main Auxiliary
Gain (at rotary joint) 33.5 dBi 30.5 dBi
VSWR Average 1.4:1Peaks not exceeding 1.5:1
Circular Polarisation 20 dB min ICR in principalazimuth and elevation planes
Azimuth Beamwidth 1.5 0.1
Azimuth Sidelobes -25.0 dB (0 to 10)-28.0 dB (10 to 30)
-30.0 dB (30 to 180)
Elevation Beamwidth (-3 dB) 5.0 n ominal 7.0 n ominal
Vertical Beam Separation 3.0 1 betweenMain and Aux beam peak
The high-performance carbon fibre composite Easat EA5025shaped reflector Primary Surveillance Radar antenna designprovides airport local or terminal area air surveillance to anominal 60 mile range. Retaining many of the features of thelarger Easat EA5325, the Easat EA5025 is a more compactdesign, offering a cost-effective alternative. High back-anglecoverage is retained to ensure system performance can beprovided at both short and long ranges. The antenna isextremely versatile, being capable of being operated with aco-mounted MSSR. It can be supplied with single or dual drivemotors, and a variety of encoder and rotary joint options,including Inductosyn . The use of these options ensurescompliancy to the most stringent operating standards.
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Air Traffic Control Radar Secondary Surveillance
8
Easats high-gain open planar SSR/IFF array meets theworldwide LVA antenna requirements and is offered as astand-alone version (shown below) or co-mounted onto EasatsEA5325 or EA5025 Primary Surveillance antennas, as illustratedopposite. Available in either Standard (single beam) or Monopulse configurations, the antenna offers a shapedelevation pattern, a sharp horizon rolloff and superior gain,providing excellent system performance and reduced groundillumination. This antenna is Mode S compatible (Level 2).The antenna is operational worldwide.
Photograph Centre: Portuguese Air Force MSSR, installed by EasatPhotograph Opposite: Easat EA5325 Antenna with co-mounted MSSR
Mechanically, the unit offers an open-antenna structure for lowwind loadings, encapsulated dipole columns for superior weather protection, and a turning unit capable of operations insevere environments with temperatures as low as -50 C.
The EP0409 turning unit is available in single or dual driveconfigurations, with highly accurate single or dual azimuthencoders or Inductosyn . The azimuth accuracy offered by thissystem meets or exceeds all current worldwiderecommendations for redundancy and azimuth accuracy fromthis type of equipment.
General and Mechanical
Wei ght (i nc lu di ng Pe des ta l) 1 370 kg (S in gl e D ri ve )
1540 kg (Dual Drive)
Optional Stand 450 kg
Maximum Swept Radius 4.09 m
Rotation Rate Typically 5 to15 rpm
A zi mu th M ea su re me nt 1 3- or 1 4- bi t O pti ca l S ha ft En co der (s )
Inductosyn
Redundancy Options Dual Motors; Dual Encoders
Design Life 20 years
Environmental
O per ati on al Wi nd S pee d 1 60 k m/h r w ith 12 .7 m m ra di al ic e
Survival Wind Speed 231 km/hr with 12.7 mm radial ice
Humidity 5% to 100%
O per ati on al Te mp era tu re -3 0 C t o +7 0 C i nc lu di ng 18 s ol ar -50C to +70C (optional)
Protection Suitable for Coastal Environment
Elevation Pattern
Azimuth Pattern
Electrical
Transmit Frequency 1030 3.5 MHz
Receive Frequency 1090 3.5 MHz
VSWR (all channels) 1.5:1
Impedance 50 ohms
Power Handling Capacity 10 kW peak, 100 W average
Polarisation (all channels) Vertical
Cross Polari sation (al l channels) 30 dB b elow Sum peak
Gain 27 dBi min
Azimuth Patterns
Sum Pattern 3 dB Beamwidth 2.4 0.25
Su m o r D iff Ma xi mu m S id el ob e Le ve l 2 5 d B b el ow p ea k
Sum/Diff Pattern Crossover Points -3 0.5 dB
SLS Coverage of Sum Sidelobes 4 dB min
d B
Angle (degrees)
d B
Angle (degrees)
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Surface Movement Radar Linear Array
10
Easat have designed a range of high-performance, low-costLinear Array antennas specifically for Ground MovementRadar Control at airports.
The Easat Linear Array antenna EA6501 is targeted at the SMRmarkets in the USA. The model EA7401M is targeted at theSMR markets in other parts of the world such as Canada,Europe and the Pacific Basin.
The EA6501 has been specified and used by the FAA at 24 ofthe larger commercial airport sites within the USA. TheEA 7401M antenna has higher power-handling capacity, suitablefor use with magnetron-based transceivers. This antenna hasbeen specified and used by Navcanada exclusively for all 10 major airports in Canada, and is also on many major European airportssuch as Brussels, Zurich and London Heathrow.
The Linear Array antenna design is based on cellular radiotechnology and provides high performance at low cost.The X-band Linear Array antenna offers Ku-band typeresolution with a sub 0.34 (demonstrated) beamwidth, andgives excellent range and azimuth resolution superior to thatprovided with slotted waveguides. The antenna providesoperation with 40 ns pulse width without pulse distortion, andzero squint at multiple frequency, making it ideal for use with amagnetron, solid-state, frequency-agile or FMCW system.
Photograph Centre: Easat EA7401M Linear Array for SMRPhotograph Opposite: London Heathrow Airport, where Easat havesupplied complete SMR sensor systems
General and Mechanical
Wei ght (i nc lu di ng Pe des ta l) 3 50 kg Si ng le dri ve
470 kg Dual drive
Optional Stand 100 kg
Maximum Swept Radius 3.625 m
Rotation Rate Typically 60 rpm
Elevation Beamshape Inverse cosec 2 to -40
Azi muth Measurement 13 or 14 bit Opt. Shaft Encoder(s)
Inductosyn
Redundancy Options Dual Motors; Dual Encoders
Design Life 20 years
Environmental
Operational Wind Speed 150 km/hr
Survival Wind Speed 240 km/hr
Humidity 5% to 100%
O per ati on al Te mp era tu re -3 0 C t o +7 0 C i nc lu di ng 18 s ol ar
-50C to +70C (optional)
Electrical EA7401M
Operating Frequency 9.1 to 9.5 GHz
VSWR 1.4:1 at 2 spot frequencies
Backlobes -40 dB
Azimuth Sidelobes (peak) -25 dBElevation Beamshape Inverse cosec 2 to -40
Azimuth (-3 dB) Beamwidth 0.37
Polarisation Circular
Gain 35 dBi min
ICR (principal azimuth and > 15 dB min ICRelevation planes)
ElevationPattern
AzimuthPattern
d B
Angle (degrees)
d B
Angle (degrees)
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Surface Movement Radar Reflector Antenna
12
Targeted at the SMR, ASDE and A-SMGCS markets, EasatsEA3462 High Gain Reflector is designed to provide the highestperformance available, whilst minimising the weight andloading penalties often associated with reflector antennas.This product has been chosen by several recognised NationalATC authorities for reliable detection performance in poor weather conditions, typically found in regions where monsoon-type rainfall, snow, sleet and ice are prevalent. The antenna canbe operated with or without a radome. Offering effectivelyzero squint with multiple frequency, the antenna is particularlysuitable for frequency-diverse, solid-state or agile systems.
Photograph Centre: Easat EA3462 High Gain AntennaPhotograph Opposite: Schiphol Amsterdam Airport, with EasatEA3462 Reflector Antenna monitoring surface movement
The antenna provides circular polarisation as standard for excellent weather penetration, and inverse cosec 2 beamshaping to enhance short-range detection, which minimises theeffects of rain clutter. Polarisation switching is available as anoption to provide horizontal or vertical polarisation.
General and Mechanical
Wei ght (i nc lu di ng Pe des ta l) 7 35 kg Si ng le dri ve
855 kg Dual drive
Optional Stand 240 kg
Maximum Swept Radius 6.2 m
Rotation Rate Typically 60 rpm
Azi muth Measurement 13 or 14 bit Opt. Shaft Encoder(s)
Inductosyn
Polarisation Circular or Switchable (option)Redundancy Options Dual Motors; Dual Encoders
Design Life 20 years
Environmental
Operational Wi nd Speed 180 km/hr (external )
Survival Wind Speed 240 km/hr (external)
Humidity 5% to 100%
O per ati on al Te mp era tu re -3 0 C t o +7 0 C i nc lu di ng 18 s ol ar
-50C to +70C (optional)
Protection Suitable for Coastal Environment
Electrical
Operating Frequency 9.1 to 9.5 GHz
Gain 40 dBi
Elevation (-3 dB) Beamwidth 4.0 nominal
Elevation Beamshape Inverse cosec 2
Azimuth (-3 dB) Beamwidth < 0.45
Azimuth Sidelobe Level (worst) within 15 -28 dBwithin90 -40 dB
Backlobes -38 dB
VSWR < 1.30:1
ICR (principal azimuth 17 dB minand elevation planes)
Figure 1Elevation BeamPattern
Azimuth BeamPattern
Rotation up to 60 rpm is provided by the low-noise, low-vibration EP0711 turning unit (with radome) and EP0009turning unit (without radome), available in single or dual driveconfigurations, and with highly accurate single or dual azimuthencoders or Inductosyn .
d B
Angle (degrees)
d B
Angle (degrees)
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Coastal Surveillance Radar 7.5 m Reflector
14
The Easat EA2526 is a 7.5 m, shaped reflector antenna,designed to meet the modern requirements of vessel trafficmanagement and coastal surveillance systems. The antenna isillustrated below and in the opposite main picture.
Used by governments from Malaysia to Estonia, this designoffers industry-leading radio frequency performance far superior to earlier parabolic reflectors or array designs.
The high gain of the Easat antenna provides the ultimate indetection of small targets at very long ranges.
Photograph Centre: Easat EA2526 AntennaPhotograph Opposite: Easat EA2526 Antenna at Dover Coastguard
The antenna also provides reliable performance in extendedperiods of severe weather by means of antenna polarisationswitching, and the use of dual X and S-band frequencies.
The antennas narrow azimuth beamwidth improves theresolution between adjacent targets. The narrow azimuthbeamwidth also reduces rain and sea clutter.
Available in several variants, the EA2526 antenna utilises thesame main reflector with different feed structures to satisfyvarious customers needs. The antenna variants are singleS-band, single X-band and dual S- and X-band, with variouscombinations of polarisation switching.
General and Mechanical
Type Shaped reflector
Wei ght (including Pedestal ) 3500 kg
Maximum Swept Radius 4.1 mRotation Rate 5-20 rpm
Design Life 20 years
Environmental
Operational Wind Speed 150 km/hr
Survival Wind Speed 240 km/hr
Humidity 100%
O per ati on al Te mp era tu re -3 0 C t o +7 0 C i nc lu di ng 18 s ol ar -50C to +70C (optional)
Protection Suitable for salt-laden coastalenvironment
Electrical
S-band X-band
Frequency GHz 2.9-3.2 9.1-9.5
Gain (at rotary joint) 35 dBi 45 dBi
VSWR 1.3 : 1 1.3 : 1
Polarisation Circular Switchable
Azimuth Beamwidth 1.1 0.33
Elevation Beamwidth 5.5 min 1.8 min
Vertical Beam Shape Pencil beam Pencil beamor inverse cosec 2
Typical AzimuthPattern at 9.17 GHz, HP
Typical ElevationPattern at
9.17 GHz, HP
d B
Angle (degrees)
d B
Angle (degrees)
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Coastal Surveillance Radar 5.5 m Reflector
16
The Easat EA3462 shaped reflector antenna is designed for high-performance surface surveillance.The shaped elevation beam (inverse cosec 2) is ideal for thedetection of small and large targets at both short and longranges, even when the antenna is mounted on a high tower,building or hillside.
Photograph Centre: Easat EA3462 Coastal Surveillance AntennaPhotograph Opposite: Oil tanker in inlet, Valdez, Alaska
Existing applications include vessel traffic managementsystems, law enforcement, port security, border protection andsearch and rescue.
Available in several variants, the EA3462 antenna utilises thesame main reflector with different feed structures to satisfyvarious customers needs. The antenna variants are either C- or X-band, fixed or switched polarisation.
General and Mechanical
Type Shaped reflector
Weight (including Pedestal) 1130 kg
Maximum Swept Radius 3.1 mRotation Rate 10-30 rpm
Design Life 20 years
Environmental
Operational Wind Speed 150 km/hr
Survival Wind Speed 240 km/hr
Humidity 100%
O per ati on al Te mp era tu re -3 0 C t o +7 0 C i nc lu di ng 18 s ol ar -50C to +70C (optional)
Protection Suitable for salt-laden coastalenvironment
Electrical
C-band X-band
Frequency GHz 5.4-5.9 9.1-9.5
Gain (at rotary joint) 36.5 dBi 40 dBi
VSWR < 1.3:1 < 1.3:1
Polarisation Switchable Switchable
Azimuth (-3 dB) Beamwidth 0.8 0.1 0.4 0.04
Elevation Beamwidth 7.5 nominal 4 nominal
Vertical Beam Shape Inverse cosec 2 Inverse cosec 2
Typical AzimuthPattern at 9.41 GHz, CP
Typical ElevationPattern at
9.41 GHz, CP
d B
Angle (degrees)
d B
Angle (degrees)
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Port Surveillance Radar EA7401 Linear Array
18
The Easat EA7401 linear array antenna is ideal for Vessel TrafficManagement Systems and other surveillance radars for coastaland port applications.
Operating in the marine and port X-band frequency range, thisantenna uses techniques developed from cellular radiotechnology to provide a unique cost-effective combination ofRF performance, compact size and low weight, at an attractiveprice.
Photograph Centre: Easat EA7401 Linear ArrayPhotograph Opposite: Port of Gibraltar
The Easat EA7401 antenna also offers exceptional inversecosec2 elevation beam shaping, thereby enabling both long andshort-range targets to be detected from the horizon to -40below the horizon. This antenna provides unrivalledperformance for tracking targets close to the radar location.
The antenna is offered in either fixed circular or fixed horizontalpolarisation to meet varying customer needs.
General and Mechanical
Type Printed linear array
Weight (including Pedestal) 350 kg
Maximum Swept Radius 3.7 mRotation Rate 30-60 rpm
Design Life 20 years
Environmental
Operational Wind Speed 180 km/hr
Survival Wind Speed 240 km/hr
Humidity 100%
O pe ra ti on al Tem pe rat ure - 30 C to +7 0C in cl udi ng 18 s ol ar -50C to +70C (optional)
Protection Suitable for salt-laden coastalenvironment
Typical AzimuthPattern at 9.17 GHz, CP
Typical ElevationPattern at
9.17 GHz, CP
The antenna provides an exceptional azimuth beamwidth of0.32 degrees. This tight beam allows superior azimuthresolution and helps to enhance accuracy. This is important incrowded waterways, where high resolution enables the systemto differentiate between small and large vessels. An example isin a security or border control scenario, where small vessels maytry to hide behind larger targets in busy traffic lanes. It isequally important where a traffic lane is distant from the shoreand the system is providing essential safe-passage monitoring.
Uniquely for an antenna of this cost level, the design of thearray is dispersionless that is, the antenna is equallycapable of transmitting very short (< 40 ns) pulse and longpulse without change in performance. The short-pulsecapability enables high resolution and clutter reduction onshort-range targets, a level of performance not possible withconventional large-slotted waveguide antennas.
d B
Angle (degrees)
d B
Angle (degrees)
Elevation Pattern
Electrical EA7401M
Operating Frequency 9.0 to 9.5 GHz
VSWR 1.4:1 at 2 spot frequencies
Backlobes -40 dB
Azimuth Sidelobes (peak) -27 dBElevation Beamshape Inverse cosec 2 to -40
Azimuth (-3dB) Beamwidth < 0.32 @ 9.5 GHz< 0.35 @ 9.0 GHz
Gain 36 dBi @ 9.4 GHz
ICR (principal azimuth and > 15 dB min ICRelevation planes)
Polarisation Fixed circular or horizontal
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Specialist Military Applications
20
Photograph Left: Easat Phased ArrayPhotograph Centre: Easat Airwatch Antenna UK MoD RangePhotograph Above: Easat Antennas at MoD test rangePhotograph Opposite: Easat Antennas which incorporate threeantennas, operating at eight frequencies at MoD high power test facility. Radiating at a peak power density in excess of 1MW/m 2
Easats antenna expertise has been widely used on specialistproducts for military application. We are experienced in botharray and reflector antennas for extreme environments.
The in-house radio frequency and mechanical engineeringdesigners work closely with our production engineering teamto maximise cost effectiveness. In addition to volumeproduction, we also provide one-off prototype products for demanding specialist requirements. Where appropriate, we willmodify our high-end civilian products for the militaryapplication. New designs are routinely undertaken for customer-specific requirements. For sensitive and confidentialpurposes, Easat has, and is capable of carrying out, contracts ina secure environment. Employees are subject to various levelsof security clearance.
Some examples (pictured) include passive 2D phased array andhighly-shaped radar reflector designs to meet specific radar surveillance requirements. We have also provided integratedsurveillance and IFF antennas, ship-borne surveillance radar,and land-based, rapidly deployable structures.
Easat also provide antennas for FMCW use. The requirementsfor high isolation in these structures can best be met by twoseparate, co-mounted, antennas (one for transmit, the other receive). As a lower cost, lower performance alternative, wehave provided optimised single antennas, using a high isolationcirculator to separate the transmit and receive paths.
Easat can provide product from below 1 GHz to above 90 GHz,and has a proven track record working with high-peak power systems and other specialist applications.
Easat is a member of the UKs Defence ManufacturersAssociation.
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Rotating Pedestals
22
EP0409 Pedestal
POWER (kw) 0.55 to 5.5
Motor Drive Single or Dual
Weight (kg) Without Stand 300
ROTATION RATE (rpm) 60 (variants 5-60)
DESIGN PARAMETERSRotating Mass Operational (kg) 450 (In Radome)
Shear (Drag) Load Operational (kN) 1Shear (Drag) Load Survival (kN) 29
Overturning Moment About Base Operational (kNm) 0.6Overturning Moment About Base Survival (kNm) 1.7
OPTIONAL FEATURES
Clutch Electromagnetic on Dual Drive
Motors Fan or Non-Fan
Rotary Joint To Suit Application
ARP/ACP Dual or Single Encoder
ARP/ACP Inductosyn
Slip Ring To Suit Application
Operational Temparature -30C to +70C including 18 solar -50C to+70C (optional)
Control and Monitoring Can Be Provided
Easats substantial skills and experience in microwave andmechanical design enable us to offer a wide range of pedestalssuitable for rotating antennas. As acknowledged leaders in thedesign and manufacture of pedestals renowned for their reliableand robust performance in the most extreme conditions, with therequirement of minimal maintenance Easat regularly supplypedestals for other manufacturers antennas.
Pedestals can be provided with rotation rates from 5 to 60 rpm.The design enables many variants to be provided. Theseinclude single or twin-drive, mechanical or electrical clutchesand braked drives.A wide range of azimuth position encoders, rotary joints andslip rings can be fitted to the pedestals.
The range of pedestals are designed to interface with other suppliers antennas and tower interfaces. They are ideal for either new installations or replacing pedestals that have been inservice and require renewal.These pedestals are designed to operate in the most severeenvironmental conditions and with minimal maintenance.Most designs have been operational in excess of 10 years andhave a proven track record for continuous operation.
EP0711 Pedestal
The Easat EP0711 single reduction, direct worm-drive pedestalis a lightweight, low-noise, high-specification turning unitdesigned to operate in severe environmental conditions withminimum maintenance requirements.
The pedestal is designed to rotate antennas at 60 rpm for ground movement surveillance at airports, without the need for a radome and 5.5 m reflector within a radome. Variants areavailable with rotation rates down to 5 rpm.
This direct-drive, single-reduction design ensures an extremelylow noise and vibration signature, to allow it to be used insensitive locations.
The Easat EP0409 worm-drive pedestal is a lightweight,low-noise, high-specification turning unit, designed to operatein severe environmental conditions with minimal maintenancerequirements.
The pedestal is designed to rotate SSR, MSSR antennas andreflector antennas for coastal or port and harbour surveillanceapplications, without the need for radomes. In particular, itslack of belts and reduction gears ensures low noise or vibration.This gearbox is available in several sizes to meet a variety ofload requirements, and can be provided either as single or dualdrive.
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EP1643 Pedestal
POWER (kw) 2.2 to11.0
Motor Drive Dual or Single
Weight (kg) Standard SG Iron 2000-2200Low Weight Alum 1200-1400
ROTATION RATE (rpm) 4 to 20
DESIGN PARAMETERS 6,000Rotating Mass Operational (kg)
Shear (Drag) Load Operational (kN) 50Shear (Drag) Load Survival (kN) 150
Overturning Moment About Base Operational (kNm) 144Overturning Moment About Base Survival (kNm) 470
OPTIONAL FEATURES
Clutch Electromechanical and Mechanical
Motors Fan or Non-Fan
Rotary Joint To Suit Application
ARP/ACP Single or Dual Encoder
ARP/ACP Inductosyn
Slip Ring To Suit Application
Extreme Environmental Oil Heaters ProvidedOperating Temperature Range
Control and Monitoring Can Be Provided
POWER (kw) 2.2 to11.0
Motor Drive Single or Dual
Weight (kg) Without Stand 670 kg
ROTATION RATE (rpm) 5-30
DESIGN PARAMETERS 1,500Rotating Mass Operational (kg)
Shear (Drag) Load Operational (kN) 20Shear (Drag) Load Survival (kN) 54
Overturning Moment About Base Operational (kNm) 40Overturning Moment About Base Survival (kNm) 108
OPTIONAL FEATURES
Clutch Electromagnetic on Dual Drive
Motors Fan or Non-Fan
Rotary Joint To Suit Application
ARP/ACP Single or Dual Encoder
ARP/ACP Inductosyn
Slip Ring To Suit Application
Operational Temparature -30C to +70C including 18 solar -50C to +70C (optional)
Control and Monitoring Can Be Provided
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The Easat EP1643 dual or single-drive turntable pedestal is ahigh-specification turning unit designed to operate in severeenvironmental conditions, with minimal maintenancerequirements.
The pedestal is designed to rotate S-band Air Traffic Control or air defence radar antennas, with co-mounted Large VerticalAperture (LVA) Secondary Surveillance Radar (SSR) antennas,in high winds and icing. It is also used for Coastal SurveillanceRadar and large L-band en-route radar antennas when in aradome.
Rotating Pedestals
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Turnkey Radar Systems and Project Partnerships
Easat offer a wide, experienced and successful resource inRF, mechanical and civil engineering, backed by our associatedengineering group. Easat serve both the defence and civilmarkets, fulfilling turnkey projects and providing specialistservices.
Support ranges in complexity from simple antenna installationsto full greenfield site capability to major contractors for airport,port and coastal customers.
As an example, one contract was awarded this year by the UKNational Air Traffic Services for the installation of threecomplete radar sensor systems: two at London HeathrowAirport and one at Glasgow International Airport.
The work includes radar coverage planning to select suitable
sites for the radar, geo-technical survey to check groundconditions, design of suitable foundations, design of structures,and full system design of the sensor package. The installationand commissioning of all equipment is to be carried out andmanaged by Easat personnel, who have Air Side insurance,training and CDM experience. Site Acceptance Testing is to becarried out and the equipment completed and put into service.
Easats ability to provide turnkey radar systems utilisingin-house mechanical, civil, electrical and RF resources enablesus to respond rapidly to any requirement. These services havebeen recognised by many system integrators and usersincluding Skyguide, Raytheon, Northrop Grumman, Sensis andUK MoD. Easat planned and managed all aspects of thesecontracts, utilising their project management team with manyyears of experience in controlling installations to match clientrequirements.
Long-term after-sales support is provided covering all aspectsof inspection, maintenance and calibration, both in the UK andworldwide.
Project Management
Radar Coverage Planning
Site Survey
Geo-Technical Survey
Civil Engineering
Site Planning
Structural and Foundation Design
Tower and Radome Design
Engineering
Radar System Design
Infrastructure Design
Equipment Supply
System Supply
Site Management Services
Building Services
Airside Insurance
Installation
Training
Testing
After-sales Support
Inspection Maintenance
Calibration
Photograph Centre: Easat Surface Movement Radar installed atGardermoen, NorwayPhotograph Opposite: Easat Surface Movement Radar installed atBirmingham International Airport
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Civil Construction and Site Engineering
Easat can address the complete radar installation requirementand provide a solution.All or part of the following services can be included:
Site Surveys including ground investigation reports.
Complete foundation design based on antenna/tower loadings, ground conditions and service layouts.
Complete range of foundation and civil works, including siteroadwork preparation and security fencing.
CDM management for Health and Safety Regulations.
Complete project management.
Easat have considerable experience in the preparation of civilworks, and offer the above services as part of a packageavailable to supply complete turnkey solutions whichcomplement our range of radar antennas.
Photograph Left: Ground surveyPhotograph Top Centre: Preparation of foundationsPhotograph Bottom Centre: Foundations completePhotograph Above: Erection of tower
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Radar Site Survey and Consultancy
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Easat specialise in land-based and naval radar, from fixed or mobile sites. Every radar customer has a unique radar requirement, taking into consideration the nature of the site,the radar detection task, and the available budget.
By choosing the most appropriate antenna and transmitter receiver, Easat can put forward the most suitable configurationof radar sensors and associated equipment. Easat engineershave considerable experience in modelling radar performancefor a variety of applications.
The applications include the following:
Ground-based primary and secondary surveillance radars for civilian airports.
Fixed, transportable and mobile primary and secondary air
surveillance radars, for defence.Radars for airport surface movement guidance and control;airport surface detection equipment (ASDE).
Ground-fixed or ground-mobile, or naval, interrogators for Identification Friend or Foe (IFF).
Long-range coastal radar for detection of sea surface targets or for detection of both sea and air targets.
Surveillance radars for the perimeter protection of sensitiveinstallations or borders.
The radar modelling will usually commence as a desk exerciseinvolving a specified antenna height, and an assumed set ofradar, propagation and target parameters.
This modelling will typically result in a probability of detectionplot or radar coverage diagram, an example of which follows.
The probability of detection plot as shown above is modelledwithout taking account of actual terrain features which mayaffect the radar performance, such as large buildings, or hills.These may cause radar shadows, which can seriously interferewith the radar performance. To evaluate such problems, and toselect sites where such shadows are reduced or eliminated, sitesurveying on the ground must always be undertaken.However, digital terrain modelling may be employed tominimise the time and cost, and sometimes the risks topersonnel, of undertaking extensive site surveys in distant andsometimes hostile locations. The plot on the right shows thedigital map of a coastline; the solid red colour shows the seasurface satisfactorily illuminated by the radar, whilst thein-shore shadows from hills lying between the radar site andthe sea are clearly shown (lilac).
Easat will generally undertake, free of charge, the modelling ofradar detection from a proposed site having a known height, asan aid to the correct specification of the radar sensor. Physicalsite surveys, and the combining of radar detection performancewith digital terrain modelling, may be chargeable.
Site surveys are carried out to assess foundation and tower design, equipment access, power supplies and other services,data and voice communications, buildings and cabins, fireprotection, security protection and the like.
Coverage Diagram EA2526-DF
Photograph Opposite: Site survey to establish the effects of the hillon radar coverage.
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Design Capability
Technical excellence and superior service
Even though Easat Antennas have a large range of products,we continue to improve and develop new antennas at theleading edge of technological innovation. Numerousdevelopments have made Easat a world leader. For each newtechnological change, Easat brings its experience andinnovation.
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A wide experience in system integration and design enables the
company to carry out contracts for turnkey projects. The designskills enable projects to be carried out incorporating RF design,mechanical design, electrical and civil.
Easat uses the most technically advanced research, design,manufacturing and test facilities including:
Full three-dimensional electromagnetic antenna-modellingsoftware.
Full three-dimensional near-field antenna test chamber.
Finite element analysis software.
The design process is audited to BS EN ISO 9001-2000.
The provision of modern military or civil antennas requires
fusion of expertise in both RF design and mechanical design.Easat's success has in part been founded on the fact that the RFand mechanical designers work together in the samedepartment from the start of the project. This brings anefficiency to the re-iterative design process. As many of thedesign engineers have come from a manufacturingbackground, the concurrent design process is naturallyoptimised to produce world-leading, cost-effective, high-performance antennas.
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Mechanical design
This image is a typical finite element model. FE analysis is justone of the tools used in the mechanical design process.
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Mechanical Design
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Manufacturing Capability
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Manufacturing is carried out at our group engineering facility,
which is located within 10 km of Easats offices.The engineering facility covers an area of 85,000 square metresof machine shop, reflector-building department, pedestalassembly and antenna assembly areas. A 3-shift system isoperated in the works, with a workforce of 200.
The machine shop is equipped with 24 modern CNC machinetools, CNC lathes, CNC horizontal borers and CNC verticalborers.
In the reflector-build department are aluminium-forming tools,together with building and assembly jigs for the manufacture ofthe Easat range of reflector antennas.
Pedestals and antennas are finally assembled, integrated with
ancillary equipment and tested in the assembly area.The assembly area is serviced with a 20-tonne overhead crane.
The engineering facility is registered to ISO 9001(2000) andthe quality assurance department has both small and largeCMM measuring machines.
Photograph Left: S- and X-band coastal surveillance antenna withpolarisation switchingPhotograph Opposite: Easat assembly area
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Testing and Quality
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Photograph Top Left: Easat EA3462 being dimensionally checked in alarge CMM measuring machinePhotograph Bottom Left: Dimensionally checking components on aCMM machine
Quality Assured
The Easat range of antennas, pedestals and ancillary equipmentis manufactured and tested in facilities audited toBS EN ISO 9001-2000.
Production Tests
Inspection is carried out during all stages of production toensure compliance with the design quality procedures.
Together with general engineering test equipment, Easat hasalso developed a range of specialised equipment utilised to
measure reflector surfaces.Operational Testing
To ensure satisfactory operation in service, preliminary run testsare carried out on all pedestals prior to factory acceptancetesting.
Mechanical Factory Acceptance Tests
Prior to despatch, antennas, pedestals and ancillary equipmentare tested to a factory acceptance procedure and are either witnessed by the customer or Easat QA representative. Whencomplete, the equipment is prepared for despatch.
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Photograph Left: Easat EA2526 7.5 m antenna being tested in ananechoic chamber Above: Holographic images
RF Testing
Each major RF antenna component is checked to ensurecompliance with the requirements before it is assembled on theantenna. The checks include critical parameters such as:
Input VSWR and insertion loss for reflector feeds sub-arraycomponents.
Waveguide lengths and amplitude ratios for polarisationswitching networks.
Phase linearity for sub-array assemblies.
These tests are performed at Easats own laboratory, which isequipped to carry out the measurement of small to medium-sized RF components.
Every antenna manufactured by Easat is normally subjected toRF testing in an independent, ISO 9001-accredited antennatest facility.
Antenna diagnostics
Antenna holography uses the near-field measured data tocorrelate the aperture field distribution with the antennaphysical structure. This clearly identifies the areas where theradiation is originating, and helps better understanding of thephysics of antenna radiation mechanisms.
This powerful diagnostic technique allows rapid optimisationof new designs, and fault-finding when undertakingrefurbishment of existing equipment.
The technique also provides verification and validation ofEasats advanced radio frequency design tools.
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The antennas are tested in an anechoic environment to
minimise possible sources of spurious reflection. The reflectivityof the test facility is better than -50 dB, which ensuresnegligible effect on the antenna pattern caused by multipathreflections.
The antenna is measured in the near-field and the results aretransformed to the far-field; this process gives more accurateresults than far-field measurement and is also capable ofproviding pattern cuts at various points in space, should thecustomer require this.
The basic principle of near-field testing is given below:
Collect near-field dataData is collected from a known surface, which can be acylinder, sphere or a plane.
Transform to far-fieldThe collected data is transformed to a sphere of infiniteradius. This gives the far-field pattern of the antenna.
Back-transform to aperture planeThis is required to check the phase/amplitude profile of theantenna under test.
Diagnostics toolsThese simulate the result of a change before re-measuring.
Each measurement fully characterises the radiation pattern atone frequency. This includes polarisation details (linear, circular,co-polar and cross-polar), axial ratio and ICR for circular polarised antennas, and cross-polarisation level for linear polarised antennas. The data can be presented as radiationpattern plots, contour plots and also XY digital data.
RF Testing
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Radar Antenna GuideSystems Overview
36
Introduction
Radar operates by transmitting bursts of radio energy. Thesebursts hit any object within the vicinity which reflect a smallpart back towards the radar, which is then received. Providedthe returning signal is strong enough (or more strictly, thereturn is sufficiently strong with respect to the general radionoise level in the system) the return is seen by the radar.By timing the difference between when any one pulse burstis transmitted and received, the range to the reflecting object isdetermined.
In the horizontal plane, the antenna pattern is a narrow pencilbeam. By noting the direction the beam is pointing when thepeak target return is received, the radar is able to determine thebearing (or azimuth angle). This is known as two-
dimensional radar (2D). It is the fundamental method ofoperation of most surveillance radars that is, systems forminga radar map of a given area.
Where target height is required, as well as the azimuth angle,this can be determined either by scanning the antenna beam inelevation (3D-radar) or by interrogating a transponder fitted tothe target (Secondary Surveillance Radar).
Unfortunately, not all the reflections detected by the radar represent wanted targets including reflections from the land,sea and rain. These are known as clutter. Reducingsusceptibility to clutter is often the key to achieving good radar performance in practical weather conditions.
In the following pages, emphasis is put on the surveillanceradar system for different applications, such as looking for targets on the sea or in the air. Although at a fundamental level,radar operates using common principles, different aspects areof importance to different types of radar for example, coastalradar is limited in range by the curvature of the earth, whereasair coverage may not be.
Radar Antenna Features
The radar antenna is one of the critical components. Some ofthe key features of the antenna are:
Antenna gain. The ability of the radar to see a target isfundamentally linked to antenna gain. Ignoring weather andearth curvature, antenna gain determines the size of thetarget that can be seen. At a given range, the size of thetarget is the square of the antenna gain.
Azimuth beam width. In the horizontal (or azimuth) planethe antenna beamwidth sets a number of important radar parameters. The narrower the beam, the greater the abilityof the radar to distinguish between closely spaced targets.Also, the narrower the beam, the less the radar is susceptibleto clutter (unwanted reflections).
Elevation beam shape. If the vertical beam is too narrow for the application, insufficient power will be radiated at high or low elevation angles. This is a particular issue in surveillanceradar. Hence, the elevation beam shape must be chosen tomatch the application.
Sidelobes. Antenna sidelobes are unwanted subsidiary lobesradiated away from the antenna main beam. Low sidelobes,particularly backlobes, reduce unwanted returns fromclose-by structures such as buildings or cliffs.
Polarisation. In general, targets tend to provide larger radar return in linear polarisation. Aircraft tend to be moresensitive to horizontal polarisation; sailing boats to vertical.
However, either linear state is highly susceptible toreflections from rain. These are reduced using circular polarisation.
The ability of the radar to locate a target in angle andrange.
Normally expressed in dBi, a measure of theantenna to amplify the power of radiated and received signals,compared to using an omni-directional antenna. Strictly, thisshould be stated at a given angle with respect to the antennamain beam; if not, the peak value is stated.
The angular width of the antenna pattern,expressed in degrees. Normally taken at -3 dB down withrespect to the peak of the pattern.
Unwanted echoes received by the radar. Particularlyapplied to reflection from rain, sea or land.
A type of radar which continuously transmits andreceives. The transmitted waveform is varied in frequency toform a sawtooth. On receive, the radar signal processingtransforms the frequency sawtooth into an equivalent pulse intime. As the transmitter is continuously on, isolation betweentransmit and receive paths is critical and may involve twoantennas.
The use of two or more radar frequenciessimultaneously by a radar.
Moving Target Indicator. A special radar signal processor function which distinguishes moving targets from static returns.
A type of radar system which simulates a
short, high-power pulse by actually using a long, low-power pulse. Useful in transmitters of low peak power such as solid-state or travelling-wave tube (TWT) transmitters.
The ability of the radar to distinguish betweenclosely spaced targets. Can be split into two components:azimuth and range.
Secondary Surveillance Radar requires a transponder on the radar target (that is a cooperative target). The SSRinterrogates the target transponder and receives informationnormally including identity, height etc. Military form is calledIFF (Identify Friend or Foe).
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Radar PerformanceSea Surface Surveillance
37
Introduction
In sea surveillance applications such as coastal security, VTS andenvironmental monitoring, it is frequently necessary to detectships and boats of all sizes often close together, also often atlong and short range. Detection and tracking of the targetsmust occur during many types of environmental conditions(rain, fog, high winds etc). Key considerations are:
Radar Height
Range can clearly be limited by radar performance, so sufficientantenna gain is important. However, due to the curvature ofthe earths surface, range is necessarily ultimately limited by lineof sight considerations so long-range operation requires highsites to see the target.
Radar range is more complicated, and a good guide to clear weather performance is the transition range . This depends onradar and target height, and operational frequency, andrepresents the point where performance with range changesfrom 1/R 4 to 1/R 8 due to the presence of the earths surface.The figure below shows the transition range at X-band andS-band as a function of antenna height for a 1 m target height.
Radar Target Size
The table below shows the radar cross-section of typicalmarine targets used in radar calculation. There is considerablediscussion on the topic of radar cross section in circular polarisation. In brief, this can be summarised by saying largetargets (100 m vessels and above) exhibit relatively littlechange in RCS with polarisation. This is due to the complexnature of the scattering surfaces for example, even flat-sided ships are not flat at m icrowave frequencies! Small targets,and particularly aircraft, are much more polarisation-sensitive.In aircraft, a 2.5 dB cross section reduction is commonlyassumed in changing from linear to circular polarisation.
Resolution and Accuracy
It is critical in many radars to distinguish between small andlarge targets close together pirate detection is one example;safety monitoring of crowded waterways is another. Theantenna contributes to the azimuth resolution, which isimportant to distinguish between two targets. Likewiseaccuracy, important for ship location, is dependant on theantenna as well as other radar parameters. These factorsimportantly depend not just on antenna beamwidth, but onsignal-to-noise ratio in the radar system, so they relate totransmit power, receiver sensitivity and antenna gain.The figure shows resolution assuming typical radar parameters.
Target RCS X-band RCS S-Band Assummed Height
30 m pilot vessel 100 40 5
trawler 1,000 400 8
100,000 ton 100,000 40,000 18
R a n g e
( k m
)
Antenna Height (m)
X-Band
S-Band
Transition Range
R a n g e
( k m
)
Rainfall Rate (mm/hr)
X-BandS-Band
Range vs Rainfall rate for an antennaheight of 500m and a target height of 3m
R e s o l u t
i o n
i n M e t r e s
SNR (dB)
Azimuth Resolution 0.3 degree b/w
Azimuth Resolution 0.4 degree b/w
Azimuth resolution at 40nmDetection in Bad Weather
Rain produces unwanted echoes which look like noise to theantenna. Rain clutter can be greatly reduced by:
a narrow antenna beamwidth.
a narrow transmitter pulse.
using circular polarisation.
choice of frequency.
use of frequency diversity.
The figure below shows maximum detection range as afunction of rainfall rate for X-band and S-band, for a typicalradar scenario. The X-band performs better up to mediumrainfall rates, but the S-band takes over for medium to
extremely high rainfall rates; the reason is that rain attenuationand backscatter is much higher at X-band than at S-band.
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Performance Comparison by Radar TypeAir Surveillance
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Introduction
Air surveillance applications are normally performed by twotypes of radar systems: secondary surveillance radar (SSR) andprimary surveillance radar (PSR). SSR requires a transponder tobe fitted to any aircraft of interest. The SSR interrogates thistransponder and generates a target plot if a reply is received. Toimprove angular accuracy, many SSR systems use an additionalmonopulse beam in azimuth (termed MSSR).
The PSR detects any targets within the instrumented range,regardless of whether they have working transponders fitted.
Air surveillance radars typically operate at L-band and S-band.Operation has to be maintained under all weather conditionssuch as rain, fog, snow, high winds etc. Key factors for PSR air surveillance antennas are elevation pattern-shape to minimiseground clutter and maximise coverage, polarisation switchingcapability to counteract the effect of rain clutter, and azimuthbeamwidth for resolution and Doppler processing. For MSSRsystems, low sidelobes and backlobes are important tominimise false reply, and also the alignment between thetransmit and monopulse beam for accurate target positioning.
Radar Antenna Features
Polarisation
MSSR systems operate at L-band, and by internationalagreement, use linear vertical polarisation. PSR antennas workat S-band, and normally include capability to switchpolarisations between circular and linear. Circular polarisation is
critical to ensure proper operation in heavy rain, whilst beingable to use linear polarisation maximises system performance indry weather.
The choice of linear polarisation type is not a straightforwardmatter. Typically, helicopters give a better return whenhorizontal polarisation is used, whilst vertical polarisationgenerally gives better performance for systems installed near the sea.
Elevation beam shape
The antenna pattern in the vertical plane is key to providinggood air surveillance coverage, whilst minimising reflectionsfrom the ground. The first is important to enable detection oftargets at high altitude, and the latter is particularly importantfor low-flying targets.
The PSR system generally has two elevation beams: a main,
high-power transmit and receive beam, and an auxiliaryreceive-only beam which points above the main beam.Typically, the auxiliary beam is a lower-gain beam, but increasesthe air coverage past the main transmit beam; the advantage isan increase in the detection of targets at high altitudes.By switching between the two beams, the system can also helpreduce the effect of reflections from the ground.
As the antenna elevation beam shape is broadened, theantenna gain inevitably reduces. The antenna back-angle is theangle from the horizon to the point where the antenna patternprovides insufficient gain for detection to occur.
Azimuth Beamwidth
There are two main factors that decide the optimum azimuthbeamwidth for a PSR air surveillance antenna:
Azimuth Resolution. This is the ability of the radar toseparate two targets close together; this inherently requiresan antenna with a narrow azimuth beamwidth.
Doppler processing. All air surveillance radars use Doppler processing and as such, they require as many hits-per-target as possible. In effect, this means that an antennawith a broader azimuth beamwidth returns more hits per target and results in better performance.
Hence, choosing the optimum azimuth beamwidth is acompromise between the desired accuracy and the number of
hits per target.Radar Antenna Features - MSSR
The MSSR systems require an antenna with an accuratealignment between the peak of the transmit beam and the nullof the monopulse beam. Critically, the null position must notmove in angle under extremes of weather, such as heavywinds.
Both SSR and MSSR systems use a sidelobe blanking patternthat, coupled with the main transmit beam, ensures a reductionof false transponder replies. To further minimise such unwantedreplies, a transmit beam with low sidelobes and backlobes isbeneficial to the overall system performance.
G a i n r e
d u c t
i o n
( d B )
Antenna Back Angle (degrees)
Gain reduction vs Coverage angle
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Radar PerformanceAirport Surface Surveillance
Radar Sensor
Ground
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Key factors
Radar height is a critical factor to ensure that no shadowingoccurs. The radar antenna has to be high enough to allowline-of-sight between the antenna and the airport surface,and also to ensure that large targets do not cause blockageas shown below.
Operating frequency is also important in determining the
azimuth resolution of the radar and the performance in rain.The latest X-band systems offer the same or better azimuthresolution as the Ku-band predecessors, but with a better detection performance in rain. A typical detection curve isshown below for the case of a 1 m 2 target for an X-band anda Ku-band radar, operating in dual frequency diversitymode.
Choice of site is very important in order to minimisereflections from terminal or cargo buildings. In some cases,buildings can have a high reflectivity which would causeunwanted reflections on the radar screen; proper sitesurveying is essential to minimise such reflections.
The ground reflections are governed by the complex reflectioncoefficient of the wet ground; according to the incidence angle,the reflected wave is a mixture of co-polar and cross-polar energy, which gives the complex nature of the clutter scenarioin a SMR system. We can see that calculation of SMR detectionis a complex process. However, ignoring the ground reflectioneffects in a SMR system gives excessively optimistic resultsinappropriate for a safety critical system.
Radar Sensor
Target 1 Target 2
No Shadowing
MMWRadar Sensor
Target 1 Target 2
ShadowingTarget 2 is blocked by Target 1 Positional accuracy is a safety-critical parameter for any
airport. There are a number of unexpected factors to be
considered. For example, when multiple frequencies areused, the radar produces an azimuth beam for eachfrequency and the beams must be well aligned to avoidaccuracy errors.
Nearfield focusing is a desired feature for such a system.Most of the targets in a SMR environment are in the near-field of the antenna, and near-field focusing of the antennaimproves the detection performance. Variable focusing, onlyavailable on reflector type antennas, gives ultimateperformance improvement due to the capability of focusingover an entire area of the airport.
R a n g e m
Rainfall Rate (mm/hr)
1 m 2 X-band
1 m 2 Ku-band
Introduction
Surface movement radar (SMR) is an important safety systemat airports around the world, and such systems are used for detecting and tracking aircraft and utility vehicles on airporttaxiways. The system must operate in all weather types,particularly in rain or fog, when visibility is reduced and theradar may be the operators only means of monitoring theairport surface.
Unwanted reflections (clutter) dominate the radar performance. The rain clutter scenario consists of direct rainbackscatter and also reflections from the wet ground onto arain cloud, which then reflect back to the antenna. Two typesof reflection clutter have been identified: single-bounce clutter and double bounce. These are shown in the figure below.
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RF Data
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Circular Polarisation Purity
Circular polarisation purity can be considered as a function ofthe phase difference and amplitude ratio of two orthogonalcomponents. For simplicity, we consider the horizontal andvertical polarised components. Ideally, a phase difference of90 and the amplitude ratio of 1 (0 dB) between these givesperfect circular polarisation. However, in practice this cannot beachieved due to, for example, tolerances of micro-wavecomponents.
The axial ratio of a signal is a measurement of how circular thepolarisation is.
Figure 1 shows the axial ratio of the polarisation when thephase difference and amplitude ratio of the individual H and Vcomponents are known.
Figure 1 Axial Ratio vs Phase and Amplitude Ratio
Input VSWR and Return Loss
Figure 2 Return Loss vs Input VSWR
= Voltage reflection coefficient = E r /E iEr = reflected voltage
Ei = incident voltage
VSWR =
=
Return loss (dB) = 20 LOG 10( )
Mismatch Loss
Figure 3 Mismatch loss vs Input VSWR
1 +
1
VSWR 1VSWR + 1
Mismatch loss (dB) = 10 LOG 10(1- 2)
Electric constants
= free space permittivity = 8.854185 x 10 -12 F/m
= free space permeability = 1.256637 x 10 -6 H/m
c = speed of light = = 2.997925 x 10 8 m/s
Zi = free space impedance = =377
k = Boltzmanns constant = 1.38066 x 10 -23 J/K
1
A x i a l
R a t
i o ( d B )
Phase away from 90 degrees
R e t u r n
L o s s
( d B )
Input VSWR
M i s m a t c h
L o s s
( d B )
Input VSWR
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Waveguide Data
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Frequency Cut-off Waveguide Designation DimensionsRange Frequency inner cross-section
GHz GHz British U.S. 153 -IEC Width a (mm) Height b (mm)
1.12-1.70 0.908 WG6 WR650 R14 165.10 82.55
1.45-2.20 1.158 WG7 WR510 R18 129.54 64.77
1.70-2.60 1.375 WG8 WR430 R22 109.22 54.61
2.20-3.30 1.737 WG9A WR340 R26 86.36 43.18
2.60-3.95 2.080 WG10 WR284 R32 72.14 30.04
3.30-4.90 2.579 WG11A WR229 R40 58.17 29.08
3.95-5.85 3.155 WG12 WR187 R48 47.55 22.15
4.90-7.05 3.714 WG13 WR159 R58 40.39 20.19
5.85-8.20 4.285 WG14 WR137 R70 34.85 15.87.05-10.00 5.260 WG15 WR112 R84 28.50 12.62
7.00-11.00 5.790 - WR102 - 25.90 12.95
8.20-12.40 6.560 WG16 WR90 R100 22.86 10.16
10.00-15.00 7.873 WG17 WR75 R120 19.05 9.53
12.40-18.00 9.490 WG18 WR62 R140 15.80 7.90
15.00-22.00 11.578 WG19 WR51 R180 12.95 6.48
18.00-26.50 14.080 WG20 WR42 R220 10.67 4.32
22.00-33.00 17.368 WG21 WR34 R260 8.64 4.32
26.50-40.00 21.100 WG22 WR28 R320 7.11 3.56
Standard Rectangular Waveguide
X-band (GHz) g (mm) S-band (GHz) g (mm)(WR90 assumed) (WR284 assumed)
9.0 48.70 2.60 192.19
9.1 47.58 2.65 182.61
9.2 46.52 2.70 174.18
9.3 45.52 2.75 166.69
9.4 44.57 2.80 159.98
9.5 43.67 2.85 153.92
9.6 42.81 2.90 148.40
Wavelength
Free space wavelength o =
Coaxial line wavelength =
= dielectric constant of coaxial insulating core material
Rectangular waveguide wavelength g =
Figure 4 Rectangular waveguide cross-section
b
a
c = = cut-off wavelength for TE10 mode
a = waveguide width (see figure 4)
c
f
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Radar Data
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Frequency band designation
NATO Band Designation Civilian Band Designation Frequency (GHz)
E S 2.0-3.0
F S 3.0-4.0
G C 4.0-6.0
H C 6.0-8.0
I X 8.0-10.0
J X-Ku 10.0-20.0
Minimum pulse width for slotted waveguide arrays
Due to the dispersive nature of slotted waveguide antennas,there is a limitation to the minimum pulse width that can beused for a given aperture size. This is a very important consid-eration when considering slotted waveguide antennas in radar systems which use very short pulses, such as surface movementradars at airports.
Figure 5 - Pulse width vs aperture size
Radar Targets: Swerling cases
Radar targets are classified according to their variation andstatistical properties into various Swerling type targets.
Swerling case 0 is a target that gives constant RCS and showsno variation.
Swerling Case 1 and 2 are targets composed of severalscatterers, each with nearly equal RCS.
Case 1 varies scan-to-scan (constant pulse-to-pulse) and Case2 varies pulse-to-pulse.
Swerling Case 3 and 4 are targets composed of one largescatterer, with several small ones.
Case 3 varies scan-to-scan (constant pulse-to-pulse) and Case4 varies pulse-to-pulse.
Radar Detection and Frequency diversity
A radar system which operates with a given probability ofdetection (Pd) and probability of false alarm (Pfa) will detect atarget, if a minimum signal-to-noise and clutter ratio isachieved at the receiver.
Frequency diversity (use of two or more frequencies separatedby at least the inverse of pulsewidth) converts a Swerling 1target into a Swerling 2 target, and also allows multiple-pulseintegration. This increases the detection performance becausethe required signal-to-noise and clutter ratio is lower; this canbe seen in the graphs on the right, which give the detectionrequirement for three common receiver operating cases.
M i n i m u m p u
l s e w
i d t h ( n s )
Slotted waveguide aperture size (m)
S i g n a l
t o n o
i s e a n
d c l u t
t e r r a t i o
( d B )
Number of de-correlated pulses integrated
Pd = 90%, Pfa = 10 -4
Pd = 90%, Pfa = 10 -6
S i g n a l
t o n o
i s e a n
d c l u t
t e r r a
t i o ( d B )
Number of de-correlated pulses integrated
Pd = 95%, Pfa = 10-6
S i g n a l
t o n o
i s e a n
d c l u t
t e r r a
t i o ( d B )
Number of de-correlated pulses integrated
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Members of:
EEZING (Exclusive Economic Zone Industry Group)
DMA (Defence Manufacturers Association)
BAG (British Airports Group, a member of The Society ofBritish Aerospace Companies)
AcknowledgementsInductosyn is a registered trademark
Picture CreditsPage 5: Getty Images/StonePage 7: M. Wagner/aviation-images.comPage 11: www.baa.com/photolibraryPage 13: M. Wagner/aviation-images.comPage 17: Getty Images/Martin Rogers
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Easat Contacts
44
Chairman Professor Tony Brown
[email protected] Director Mr Jeff Dyer
Export Sales Manager, Air Traffic Mr Tony [email protected]
Sales Engineer, Coastal and VTS Dr Vladimir [email protected]
Easat Antennas LtdGoodwin HouseLeek Road, Hanley
Stoke-on-Trent ST1 3NRUnited KingdomTel: +44(0) 1782 208028Fax: +44(0) 1782 208060Email: [email protected]: www.easat.co.uk
Easat is easily accessible from the M6 motorway at J15or J16, and then along the A500.
From the M1 motorway, take J24a and then the A50to Stoke-on-Trent.
This brochure is the property of Easat Antennas Ltd and must not be modified, reproduced or copied without Easats permission.
While every effort has been made to ensure accuracy, no guarantees are given and it is theresponsibility ofthe user to verify all information prior to usage.
Given the need for continuous competitive improvement, we reserve the right to modify our scope of supply as outlinedin this brochure as is considered appropriate to each marketplace.
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Easat Antennas Ltd
Goodwin House,Leek Road, HanleyStoke-on-Trent, ST1 3NR, EnglandTel: +44 (0)1782 208028Fax: +44 (0)1782 208060
Email: [email protected]: www.easat.co.uk