*
`
`15 th
`ANNUAL
`Meeting and Symposium
`
`ANTENNA MEASUREMENT
`
`TECHNIQUES ASSOCIATION
`
`UB/TIB Hannover
`113 879 873
`
`89
`
`Dallas, Texas
`
`October 4-8,1993
`
`Antenna/Nonmetallics Department
`Defense Systems & Electronics Group
`Texas Instruments Incorporated
`
`TOC
`
`1
`
`

`
`Table of Contents
`
`The AMTA
`
`AMTA 1993 Officers
`
`Exhibitors
`
`Future Meetings & Hosts
`
`Distinguished Achievement Award
`
`SESSION 1: ANTENNA MEASUREMENTS
`
`Algorithm for Editing RFI from Antenna Measurements
`R.B.Dybdal, G.M.Shaw
`The Aerospace Corporation
`
`A Contrast Of VHF RCS Measurement Challenges Indoor/Outdoor
`D.Craig, J.Matis
`McDonnell Douglas Technologies Incorporated
`
`Validation Measurements of Reflector Antenna Strut Lobes
`R.C.Rudduck, Teh-Hong Lee, Jo-Yu Wu
`The Ohio State University, ElectroScience Laboratory
`
`Characterization Of Aeronautical Antennas For INMARSAT Communication
`(S.R.Mishra, J.G.Dumoulin, P.Charron, J.Smithson)1, J.Moraes2
`David Florida Laboratory, Canadian Space Agency1, International Maritime Satellite
`Organization2
`
`Infrared Imaging of Electromagnetic Radiation
`P.Tornatta, R.Baltzer
`Lockheed Missiles & Space Company, Inc.
`
`Substitution and 3-Antenna Measurements of an 8-element VHF Ocean-Buoy Antenna
`D.Farina, J.Bull, R.Flam
`Flam & Russell
`
`Dual-Frequency, Dual-Polarized Millimeter Wave Antenna Characterization
`James P. Kenney, Livio D. Poles, Edward Martin, David Mooradd
`Rome Laboratory, Electromagnetics and Reliability Directorate
`
`vii
`
`ii
`
`iii
`
`iv
`
`iv
`
`v
`
`1
`
`3
`
`7
`
`12
`
`16
`
`21
`
`26
`
`32
`
`2
`
`

`
`SESSION 2: PHASED ARRAY TESTING & MATERIAL CHARACTERIZATION
`
`The Use Of An Infrared Camera System In The Analysis Of Phased Array Boresight Errors
`R.P. Gray, J.J. Kosch
`Westinghouse Electric Corporation
`
`Inerpretation Of Near-Field Data For A Phased Array Antenna
`J.E.Friedel, R.B.Keyser*, R.E.Johnson
`USAF, SM-ALC/LXSP *LHHDEC
`
`35
`
`37
`
`42
`
`Prediction Of Phased Array Antenna Sidelobe Performance Based On Element Pattern Statistics .
`H.M.Aumann, F.G.Willwerth
`MIT, Lincoln Laboratory
`
`. 48
`
`Design Of Triad Steering Antenna Arrays for the Testing of Monopulse Antenna Seeker Systems . 54
`Jay Land
`USAF, 46th Test Wing/TFGR
`
`Free Space Characterization of Materials
`D.Blackham
`Hewlett-Packard, Microwave Instruments Division
`
`An Improved NRL Arch Technique For Broad-Band Absorber Performance Evaluations
`(K.Liu, J.M.Kilpela)1, J.Wineman2
`Ray Proof Shielding Systems Corporation1, Hewlett-Packard2
`
`SESSION 3: INSTRUMENTATION
`
`58
`
`61
`
`69
`
`High-Polarization-Purity Feeds for Anechoic Chamber, Compact, and Near-Field Test Ranges.... 71
`R.Gruner, J.Hazelwood
`Communications Satellite Corporation
`
`Remote Thickness Sensor
`Walter S. Arceneaux
`Martin Marietta Corporation
`
`High-Speed, Pulsed Antenna Measurements Using the Scientific-Atlanta Model 1795P
`O.M.Caldwell
`Scientific-Atlanta, Inc.
`
`AERSAR DT Air-to-Air Imaging System
`R.Harris, R.Redman, B.Freburger
`Metratek, Inc.
`
`,
`
`An Automated Test Sequencer for High Volume Near-Field Measurements
`G.Hindman, Dan Slater
`Nearfield Systems Incorporated
`
`76
`
`81
`
`gg
`
`87
`
`viii
`
`3
`
`

`
`New Antenna Pattern Recorder Which Reduces Test Time and Provides Advanced
`
`Data Management Capabilities
`A.R.Koster, D.Morehead
`Scientific-Atlanta, Inc.
`
`Low Frequency RCS Using the HP-8510
`Edward Ditata, Chris Wegehenkel
`Northrop Corporation
`
`Portable RCS Diagnostic System
`R.Harris, R.Redman, B.Freburger, and D. Maffei
`Metratek, Inc.
`
`Ground-To-Air RCS Diagnostic System
`R.Harris, R.Redman, B.Freburger C. Zappala, A. Strasel, M. Lewis
`Metratek, Inc.
`
`High Duty Instrumentation Radar Transmitters
`Frank A. Miller
`
`Quarterwave Corporation
`
`SESSION 4: COMPACT RANGES
`
`Evaluation Of Compact Ranges For Low Sidelobe Antenna Measurements
`I.J.Gupta, W.D.Burnside
`The Ohio State University, ElectroScience Laboratory
`
`A 585 GHz Compact Range for Scale Model RCS Measurements
`M.J.Coulombe, T.Ferdinand, T.Horgan, R.Giles, J.Waldman
`University of Massachusetts - Lowell, Submillimeter Technology Laboratory,
`Research Foundation
`
`V-Band and W-Band Upgrade for a Compact RCS Range
`Stephen Yadre
`Sikorsky Aircraft
`
`An X-Band Array For Feeding A Compact Range Reflector
`J.P.McKay, Y.Rahmat-Samii, T.J.De Vicente*, L.U.Brown*
`UCLA Dept. of Electrical Engineering,*The Aerospace Corp.
`
`Lockheed's Large Compact Range
`Alex J. Kamis
`Lockheed Missiles & Space Company, Inc.
`
`A Transportable Compact Antenna Range
`(J.H.Pape, D.R.Smith)1, C.L.DevorJr.2, J. Smiddie3
`Scientific-Atlanta1, Inc., Paul E. Lehman, Inc2., Naval Surface Warfare Center3
`
`ix
`
`90
`
`95
`
`103
`
`109
`
`115
`
`121
`
`123
`
`129
`
`135
`
`141
`
`147
`
`153
`
`4
`
`

`
`The Transverse Pattern Comparison Method For Characterizing Antenna And RCS Compact
`Ranges
`
`S.Bnimley
`Boeing Defense and Space Group
`
`Design And Measurements Of Multi-Purpose Compact Range Antenna (CRA)
`M.Winebrand, Y.Rosner, E.Katz
`Orbit Advanced Technologies Ltd.
`
`SESSION 5: NEAR FDjXD
`
`159
`
`164
`
`171
`
`Implementation of a 22' x 22' Planar Near-Field System for Satellite Antenna Measurements.... 173
`G.Hindman, G.Masters
`Nearfield Systems Incorporated
`
`Considerations for Upgrading a Pre-Existing Near-Field System
`J.Way
`Nearfield Systems Incorporated
`
`Planar Near-Field Measurements of Low-Sidelobe Antennas
`(Michael H. Francis, Allen C. Newell)1, Kenneth R. Grimm2, John Hoffman3,
`& Helmut E. Schrank
`National Institute of Standards and Technology1, Nichols Research Corp.2,
`System Engineering Corp.3
`
`A Demonstration of Bistatic Electromagnetic Scattering Measurements by Spherical
`Near-Field Scanning
`M.G.Cote, RM.Wing
`Rome Laboratory/ERCT
`
`Planar Near-Field Alignment
`(D.Kremer, A.Newell, A.Repjar)1, C.Rose2, (A.Trabelsi, M.Pinkasi)3
`NIST1, Naval Surface Warfare Center2, Orbit Advanced Technologies Inc.3
`
`An Analytic Spherical Near Field To Near/Far Field Transformation
`T.K.Sarkar, P.Petre, R.F.Harrington, A.Taaghol
`Department of Electrical and Computer Engineering, Syracuse Univesity
`
`178
`
`184
`
`191
`
`198
`
`205
`
`x
`
`5
`
`

`
`SESSION 6: MEASUREMENT TECHNIQUES
`
`Simplified Polarization Measurements
`Eldon Gordon
`
`Texas Instruments, Inc.
`
`,
`
`,
`
`Application Of Prony's Method To Software Gating
`C.W.Trueman1, (S.R.Mishra, C.L.Larose, M.Flynn)2
`Concordia University1, David Florida Laboratory, Canadian Space Agency2
`
`Plane Wave Synthesis At Fresnel Zone Distances Using Ring Arrays
`J.P.McKay, Y.Rahmat-Samii
`UCLA Dept. of Electrical Engineering
`
`RF Marking Principle and Its Application in Making Antenna Measurements
`Pradeep K. Wahi1 and Y. Boison2
`Antenna Research Associates1, ESTAR S.A.2
`
`In Flight VHF/UHF Antenna Pattern Measurement Technique for Multiple Antennas
`and Multiple Frequencies
`J.S.DeRosa, D.E.Warren
`Rome Laboratory, ERPE
`
`The Effect of Spherical Measurement Surface Size on the Accuracy of Test Zone Field
`Predictions
`D.N.Black, E.B.Joy, J.W.Epple*, M.G.Guler, R.E.Wilson
`Georgia Institute of Technology, School of Electrical Engineering, Citadel Dept.
`of Electrical Engineering*
`
`Simulation And Verification of an Anechoic Chamber. ;
`R.M.Taylor1, (E.S.Gillespie, S.R.Rengarajan)2
`Computer Sciences Corp1, CSU Northridge2
`
`.
`
`.
`
`Multipaction Analysis Utilizing Finite Element Techniques
`W.A.Caven, E.S.Gillespie
`Hughes Space & Communications Co.
`
`Measurement Speed and Accuracy in Switched Signal Measurements
`John Swanstrom, Robert Shoulders
`Hewlett-Packard Company
`
`Generation of Wideband Information From A Few Samples Of Data.
`R.Adve, T.K.Sarkar
`Department of Electrical and Computer Engineering, Syracuse Univesity
`
`Satellite and Satellite Antenna Testing With High Speed Electronics
`D.W.Hess, C.B .Brechin
`Scientific-Atlanta, Inc.
`
`xi
`
`211
`
`213
`
`217
`
`221
`
`227
`
`234
`
`239
`
`244
`
`250
`
`256
`
`261
`
`267
`
`6
`
`

`
`SESSION 7: IMAGING
`
`Ground and Airborne Calibration of the Ground to Air Imaging Radar
`Walter Nagy and E.L Johansen
`ERIM
`
`Superresolution ISAR Imaging Techniques
`E.K.Walton, I.J.Gupta
`The Ohio State University, ElectroScience Laboratory
`
`Superresolution Analysis Of Frequency-Dispersive Scattering
`A.Moghaddar, Y.Ogawa, E.K.Walton
`The Ohio State University, ElectroScience Laboratory
`
`High Resolution Radar Imaging Using Data Extrapolation
`I.J.Gupta, M.J.Beals
`The Ohio State University, ElectroScience Laboratory
`
`Breaking the Lambda/2 Resolution Limit Using Spherical Microwave Holography .
`M.G.Guler, E.BJoy, D.N.Black, R.E.Wilson, J.W.Epple
`Georgia Institute of Technology, School of Electrical Engineering
`
`SESSION 8: MEASUREMENT FACILITIES
`
`Experimental Range Facility For RCS Measurement and Imaging Research
`J.W.Burns, G.G.Fliss, D.W.Kletzli, Jr.
`Environmental Research Institute of Michigan
`
`A New Antenna Metrology and Radar Cross Section Facility At The U. S. Army Redstone
`Technical Test Center
`J.B.Johnson, Jr.1, W. Scott Albritton2
`U.S. Army Redstone Technical Test Center1, AMTEC Corp.2
`
`A Modem Facility for Test and Evaluation of Full Scale Aircraft Antenna Systems
`(A.Kvick, L.Hook, K.Johansson)1, (J.F.Aubin, D.R.Frey)2
`FFV Aerotech AB1, Flam & Russell2
`
`269
`
`271
`
`277
`
`282
`
`288
`
`296
`
`301
`
`303
`
`308
`
`312
`
`Dynamic Radar Cross Section Measurements
`J.Tuttle
`
`Naval Air Warfare Center, Aircraft Division
`
`,
`
`317
`
`Vertical Bistatic RCS Measurements in the MDTI Radar Measurement Center
`Jon Duff Weatherington
`McDonnell Douglas Technologies Incorporated
`
`322
`
`xii
`
`7
`
`

`
`The HARC/STAR Microwave Measurement Facility: Physical Description and Capabilities .... 325
`B.D.Jersak, A.J.Blanchard, W.N.Colquitt, B.D.Krenek, B.A.Williams
`Space Technology and Research Center
`
`The HARC/STAR Microwave Measurement Facility: Measurement and Calibration Results .... 331
`(B.D.Jersak, A.J.Blanchard)1, J.W.Bredow2
`Space Technology and Research Center1, Wave Scattering Research Center,
`U of Texas, Arlington2
`
`Lockheed Sanders, Inc., Antenna Measurement Facility
`Edward A. Urbanik, Donald G. LaRochelle
`Lockheed Sanders, Inc.
`
`A New Extrapolation/Spherical/Cylindrical Measurement Facility at the National Institute
`of Standards and Technology
`J.R.Guerrieri, D.P.Kremer, T. Rusyn
`NIST
`
`SESSION 9: EUROPEAN SPACE AGENCY
`
`Spherical Nearfield Measurement of a Large Deployable Multibeam Satellite Antenna
`T. Beez, J. Schneemann
`ANTNachrichtentechnik GmbH, Gerberstr
`
`Applications of Microwave Holography in Antenna Design and Development
`K. S. Farhat, N. Williams, M.W. Shelley
`ERA Technology Ltd.
`
`New Extrapolation Algorithm for High Resolution Imaging Applications
`M. R. van de Goot, A.G.H. Gerrits, V. J. Vokurka,
`Eindhoven University of Technology, Department of Electrical Engineering
`
`Edge Effect Suppression In Anechoic Absorber Evaluation
`M.Knoben1, (M.Van Craenendonck, H.Pues)2
`Eindhoven University of Technolgy1, GRACE N.V., Nijberheidsstraat f
`
`Prediction and Evaluation of Anechoic Chamber Performance
`Christian Bornkessel, E. Heidrich
`Inst. f. Hochstfrequenztechnik u. Elektronik
`
`Novel APC-Methods for Accurate Pattern Determination
`J. van Norel, V. J. Vokurka
`Eindhoven University of Technology, Department of Electrical Engineering
`
`Concept & Design of a Cylindrical Outdoor Near Field Test Range for High Precision
`RF Measurements
`H.Steiner, T. Fritzel
`Deutsche Aerospace
`
`xiii
`
`337
`
`343
`
`353
`
`355
`
`361
`
`367
`
`373
`
`379
`
`385
`
`390
`
`8
`
`

`
`High Speed Antenna Measurement Systems for S.A.R. Applications
`(P. Garreau, G. Cottard)1, J. Ch. Bolomey2
`S.A.T.I.M.O. \ SUPELEC2
`
`Advances in Near-Field Techniques: Phaseless and Truncated Data
`Tommaso Isernia1, Giovanni Leone2 Rocco Pierri3
`Universita'"Federico ii" Di Napoli1, Universita Di Salerno2, Seconda Universita'Di Napolf
`
`Polarization Grids for Applications in Compact Antenna Test Ranges
`M. A. J. van de Griendt, V. J. Vokurka
`Eindhoven University of Technology, Department of Electrical Engineering
`
`Characterization and Modelling of Conducting Polymer Composites and Their Exploitation
`in Microwave Absorbing Materials
`B.Chambers, T.C.P.Wong, A.P.Anderson, P.V.Wright
`University of Sheffield
`
`395
`
`401
`
`407
`
`413
`
`Antenna Pattern Measurement Errors Evaluation at the INTA Compensated Compact Range .... 419
`P.L. Garcia Muller, J. L. Cano
`INTA/Lab. De Antenas
`
`SESSION 10: RCS MEASUREMENTS
`
`Time-Frequency Distribution Analysis Of Frequency-Dispersive Scattering Using
`the Wavelet Transform
`
`A.Moghaddar, E.K.Walton, W.D.Burnside
`The Ohio State University, ElectroScience Laboratory
`
`Scattering by a Simplified Ship Deckhouse Model
`(B. Badipour)1, (W. Wasylkiwskyj)2, (M.J. Coulombe, T. Ferdinand)3
`Carderock Division, Naval Surface Warefare Center1, George Washington University2,
`University of Mass.(Lowell)3
`
`RCS Measurements of Circular Patch Antennas
`C.R.Birtcher, J.T.Aberle, E. R. Bonsen*
`Arizona State University, College of Engineering and Applied Sciences,
`Telecommunications Research Center, Eindhoven University*
`
`"
`
`Modeling System Reflections to Quantify RCS Measurement Errors
`A.S.Ali, B.W.Deats*
`Dept. of Electrical Engineering USAF Academy, Flam & Russell*
`
`Minimum Time For RCS Measurements
`D.Mensa, D. Wirtz
`Naval Air Warfare Center, Weapons Division
`
`425
`
`427
`
`433
`
`439
`
`445
`
`451
`
`xiv
`
`9
`
`

`
`What is RCS In an Image?
`G.Fliss, D.Mensa*, W.Nagy
`ERIM, Naval Air Warfare Center*
`
`RCS Target Non-Contact Position Measurements
`N.Panich, A.Trabelsi, M.Segal, M.Winebrand, M. Levin, I. Bryskin
`Orbit Advanced Technologies Ltd.
`
`Radar Target Measurements in Multipath Environment
`AJ.Stoyanov, W.H.Schuette, M.A.Sekellick, Y.J.Stoyanov
`Carderock Division, Naval Surface Warfare Center
`
`Rotation Of A String-Suspended Target In Conical Cuts
`P.S.P.Wei, D.CBishop
`Boeing Defense & Space Group
`
`Hughes Aircraft Company RCS/Antenna Measurement Chamber Characterization
`(AJain, C.R.Boerman)1, E.Walton2, V.J.Vokurka3
`Hughes Aircraft Company1, Ohio State University2, March Microwave Systems B.V.3
`
`High Resolution SAR/ISAR Air-To-Air RCS Imaging
`(D.A. Whelen, C.R. Boerman, B.W. Ludwick, D.P. Williams?, R.G. Immell2
`Hughes Aircraft Company1, Denmar, Inc.2
`
`Ultra Wide Band VHF/UHF Air-To-Air RCS Imaging
`(D.A. Whelen, C.R. Boerman, B.W. Ludwick, D.P. Williams/, R.G. Immell2
`Hughes Aircraft Company1, Denmar, Inc.2
`
`457
`
`463
`
`470
`
`475
`
`481
`
`487
`
`489
`
`xv
`
`10
`
`

`
`THE HARC / STAR MICROWAVE MEASUREMENT FACILITY:
`PHYSICAL DESCRIPTION AND CAPABILITIES
`
`Brian D. Jersak, Andrew J. Blanchard, Walter N. Colquitt, Brendan D. Krenek, Brett A. Williams
`
`Houston Advanced Research Center
`
`Space Technology and Research Center
`4800 Research Forest Drive
`
`Telephone: (713) 363-7922
`
`The Woodlands, TX 77381
`FAX: (713) 363-7923
`
`also capable of performing fully polariinetric measure-
`ments. Thus, monostatic, bistatic and Inultistatic
`polarimetric measurements can all be performed within
`the same measurement facility.
`
`II. PHYSICAL DESCRIPTION
`
`The actual chamber size is 30‘ wide by 30' deep by
`30'6" high. Figures 1a and lb show scale views of the
`top and side of the chamber (outside looking in), indicating
`the locations of the doors, trusses, azimuth positioner,
`pedestal, and chamber coordinate system. Note that the
`chamber phase center (focal point of the antennas and
`the target location) is at the origin of the coordinate
`system.
`
`There are two doors into the chamber. The ground level
`door is 4’ x 8’, and is located 4‘ from the side wall. The
`upper door is 4' x 13' 8", and is located 8'6" from the
`side wall and 11'9" above the floor. Eventually. an
`extendable boom will allow convenient access to the
`
`target from the upper door.
`
`receiver
`truss
`
`covering
`
`transmitter
`truss
`
`target
`azimuth
`
`positioner
`
`ABSTRACT
`
`A complete description is given of the unique radar cross-
`section (RCS) measurement facility built at the Houston
`Advanced Research Center in The Woodlands, TX. The
`uniqueness of this chamber comes from its ability to
`independently move the transmit and receive antennas,
`which can each be moved to any position within their
`respective ranges of motion to a resolution of about 005°.
`The transmit antenna is fixed in azimuth, but can be
`moved in elevation: the receive antenna is free to move
`in both azimuth and elevation. Additionally, the target
`can be rotated in azimuth by means of an azimuth
`positioner.
`
`Analysis has been performed to determine the impact of
`chamber effects on measurement accuracy- The most
`notable chamber effect comes from the two large
`aluminum truss structures, which are the mounting
`supports for
`the transmit and receive antennas.
`Fortunately, the scattering from these structures can be
`readily separated from the desired target return through
`the use of range (time) gating. Time domain results are
`presented showing the effects of these structures.
`
`Keywords: Polarimetry, bistatic, radar cross—section
`
`I. INTRODUCTION
`
`The microwave measurement facility at the Houston
`Advanced Research Center was officially dedicated on
`April 30, 1991. The chamber is a unique measurement
`facility capable of performing measurements not
`attainable anywhere else in the world.
`
`This chamber has the ability to independently move the
`transmit and receive antennas, which remain at a constant
`radial distance from the target over their respective ranges
`of motion. The target can also be independently rotated
`in azimuth. Note that the antennas can be placed at any
`arbitrary position within their respective ranges of motion,
`not merely at set intervals.
`
`This design is tailored to performing measurements
`suitable for use in microwave imaging. The chamber is
`
`Figure la. Top view of chamber.
`
`325
`
`ll
`
`11
`
`

`
`The positioner is controlled with 21 SA 4131 target azimuth
`positioner controller.
`
`The entire chamber is lined with 8" pyramidal microwave
`absorbing material. The target supporting pole is
`surrounded by an 8.5" diameter PVC pipe. which is
`covered with 8" wedge absorber. Note that when the
`target is rotated in azimuth, the PVC pipe (and hence the
`absorber coating) does not rotate.
`
`The design and assembly of the two trusses, the reqiiired
`machining of the trusses, installation of the triisses, and
`the entire motion control system were obtained for less
`than $150,000.
`
`
`
`I
`[ /'
`
`I
`
`
`
`Ky
`
`access
`dggfg
`
`
`
`antenna
`trolley
`
`I
`/’ chamber
`center
`/ phase
`./
`
`\ G‘‘‘‘‘‘‘‘fig” .}
`,
`r"“it\ absorber
`i \ coated
`pcdcsml
`i
`;
`
`Figure lb. Side View of charnber.
`
`The iargest structures in the chatnlacr are the two aluminum
`trusses. They each have an outer diameter of 29' 6", an
`inner diameter of 27‘ 2", a width of 6", and a weight of
`1505 lbs. The receiver truss is mounted on spherical
`thrust bearings, which allow it to rotate about a vertical
`axis. The transmitter truss is fixed, and has its vertical
`axis offset 16" from that of the receiver truss. This offset
`allows the receiver truss to move to 0° azimuth without
`having the two trusses come into Contact with each other.
`The transmit antennas are offset from the transmitter
`
`truss by 16". Since the transmitter truss is exactly parallel
`to the x axis, the transmit antennas remain at 0° azimuth
`throughout their entire range of elevation.
`
`The transmit (receive) antennas are mounted on the
`transmitter (receiver) trolley, which can move along the
`length of the transmitter (receiver) truss. The range in
`elevation for the antenna trolleys is from 25° to 150°,
`with 0° being directly above the target. The range in
`azimuth for the receiver truss is from 0° to 190°. The
`receiver
`truss and the antenna trolleys are all
`independently controlled using belt systems driven by
`dc stepper motors. These motors are controlled by a
`Modulynx motion control system from the Superior
`Electric Company.
`
`The target is supported by a 3.5" diameter aluminum
`pole, which is capped with a 6" diameter flange. The top
`surface of the flange is located 29.375" below the phase
`center of the chamber, which is 185" above the floor. A
`12.015" extension can be bolted onto the pole’s flange
`to place the top of the extension’s flange 17.360" below
`the chamber phase center. The pole itself is mounted
`atop aiScientific Atlanta (SA) 51050A azimuth positioner,
`which can support a 500 lb radial load and a 2000 lb
`axial load. This positioner allows the target to be rotated
`through 400° in azimuth, with an accuracy of i 0.05°.
`
`Figure 2. View of chamber from upper door
`showing target pedestal and lift
`used to access the target.
`
`The radar equipment used in the chamber can be divided
`into several functional groups:
`transmitter platform,
`receiver platform, reference mixer package, and the
`network analyzer. The chamber frequency span of 2-40
`G112 is divided into three bands: low band from 2-18
`GHz, mid band from 18-265 GHZ, and high band from
`26.5-40 GHz. The chamber currently lacks the high band
`antennas, but has all of the other necessary hardware in
`place for performing high band measurements. Low band
`mixing is accomplished using fundamental harmonic
`
`326
`
`12
`
`12
`
`

`
`mixing, mid band uses 3”’ harmonic mixing, and high
`band uses 8"’ harmonic mixing.
`
`The receiver platform consists of a General Instrument
`A6100 2-20 GHz linearly polarized conical horn antenna,
`a pair of Seavy Engineering 18-265 Gllz linearly
`polarized rectangular horn antennas, a pair of I II’ 85320/\
`2-26.5 Glvlz mixers (one for each receive polarization), a
`pair of lIP 85320A—K01 26.5-40Glelz mixers (one for
`each receive polarization), and an assortment of cabling.
`switches, and attenuators. Both vertical and horizontal
`polarizations can be simultaneously received. Note that
`mixers are located next to the receive antennas in an
`
`attempt to minimize the amount of RF cabling and its
`associated loss. All of this equipment is located on the
`receiver trolley.
`An HP 85309A LO—IF test set is attached to the center
`
`of the receiver truss. The receiver trolley is designed so
`that it is able to move past the L()—Il?‘ test set without
`them coming into contact. 'llie test set was located at the
`center of the receiver truss in an attempt to minimize R1‘
`cable length and its associated loss.
`
`Figure 3.
`
`Transmitter and receiver trusses
`
`along with target pedestal. Multiple
`exposure shows motion of both the
`receiver truss and the receiver
`
`trolley.
`
`The transmitter platform consists of a Hewlett—Packard
`(HP) 83642A 240 GHz synthesized sweeper used as
`the RF source, an HP 8349B 2-20 GHz amplifier, an
`Avantek 40058~22 18-40 GHz amplifier, an HP 0955-
`0422 1-40 GHz coupler, a General Instrument A6100
`2-20 GHz linearly polarized conical horn antenna, a pair
`of Seavy Engineering 18~26.5 GHz linearly polarized
`rectangular horn antennas, and an assortment of cabling
`and switches. There are a pair of two pole mechanical
`relay switches which allow the use of the HP amplifier
`for low band measurements and the Avantek amplifier
`for mid and high band measurements. There is also a six
`pole mechanical relay switch which selects the transmit
`antenna and polarization. The use of a six pole switch
`here ensures that only a single polarization and frequency
`band are used at any given time. Note that the RF source
`is located close to the transmit antennas in an attempt to
`minimize RF cable length and its associated loss. All of
`this equipment is located on the transmitter trolley.
`
`Figure 4. Receiver platform showing receive
`antennas and mixers.
`
`The reference mixer package consists of an HP 83622/\
`2-20 GHz synthesized sweeper used as the LO source,
`an HP 85320A 2-26.5 GHz mixer, an HP 85320B-K0]
`26.5—40 GHz mixer, and an assortment of cabling.
`
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`
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`
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`
`

`
`switches, and attenuators. Since there are mixers located
`on the receiver platform, only one flexible cable in the
`entire system must carry signals all the way to 40 GHz.
`This cable is for the reference signal coming from the
`coupler on the transmitter platform. It makes its way up
`from the transmitter trolley, through a hole in the ceiling
`of the chamber, to a 3' tall crawl space immediately
`above the chamber. The reference mixer package is
`located in this crawl space immediately above the upper
`bearing of the receiver truss.
`
`Figure 5. Receiver truss azimuth motor and
`gear reduction boxes, and receiver
`elevation motor and gear reduction
`box. Belt and gear used to drive
`the receiver truss is also visible.
`
`An HP 8510B vector network analyzer, the Modulynx
`motion control system, the SA 4341 azimuth positioner
`controller, three HP 11713A attenuator/switch drivers,
`an HP 6237B power Supply for the Avantek amplifier,
`and an HP series 9000 model 360 Unix workstation are
`located in the control room immediately adjacent to the
`chamber. The HP 8510B, the three HP 11713As, the
`Modulynx system, and the SA 4341 are all interfaced to
`the Unix workstation and controlled through software.
`The current control software has been developed using
`HP VEE.
`
`As mentioned previously, the transmitter trolley elevation
`angle, the receiver trolley elevation angle, and the receiver
`truss azimuth angle are all independently controlled
`through the use of dc stepper motors. The two trolleys
`have identical motor systems which consist of a 1/4 hp
`motor, a 30:1 gear reduction box, two 60 tooth idler
`gears, a 28 tooth gear, a 60 tooth gear, and a pair of
`kevlar belts. The motor, the gear reduction box, the 60
`tooth gear, and one of the kevlar belts for the receiver
`trolley can be seen attached to the side of the receiver
`truss in the center of figure 5. The other belt is attached
`at one end to the bottom of the trolley, runs down along
`the outside of the truss to the bottom of the truss, passes
`around an idler gear into the inside of the truss, runs up
`the inside of the truss to an idler gear at the top of the
`truss, passes to the outside of the truss, and runs along
`the outside of the truss down to the top of the trolley.
`Because of all the contact between the belt and the
`
`aluminum truss, the motion of the system is exuemely
`well damped. When the motor stops turning, the trolley
`stops moving.
`
`The stepper motors require 200 steps to spin one
`revolution. Because of the gear reduction box, the gear
`ratio of the two different sized gears, and the
`circumference of the transmitter truss, the final transmitter
`trolley elevation angle gear ratio is 1945.7 steps/deg.
`Although it has the same type of motor, gear reduction
`box, and drive gears, the slightly different circumference
`of the receiver truss gives the receiver trolly an elevation
`angle gear ratio of 1958.9 steps/deg. These gear ratios
`mean that the elevation angle of either trolley can be
`varied by as little as 0.0005°. However, the absolute
`position of either trolley is known only to within about
`dz 0.05°, which corresponds to a trolley displacement of
`about i 0.15". At the top motor speed of 10000 steps/sec,
`it would take about 25 seconds for one of the trolleys to
`move through its entire range of elevation. This is a
`speed of about 5.12 deg/sec.
`
`The receiver truss azimuth motor system, seen in figure
`5, consists of a 1/4 hp motor, a 30:1 gear reduction box,
`a 60:1 gear reduction box, a 28 tooth gear, a 224 tooth
`gear, and a kevlar belt. A spare belt can be seen in
`figure 5. The spare belt was put in place during installation
`of the system because it would actually require the removal
`of the receiver truss in order to install the replacement
`belt without cutting open the belt.
`
`One gear reduction box drives the other to produce a
`gear reduction ratio of 900:1, and the two different sized
`gears provide an addition gear reduction ratio of 8:1.
`The resulting receiver truss azimuth angle gear ratio is
`8070.0 steps/deg. This extreme amount of gear reduction
`is required to allow the receiver truss to move slowly
`enough not to oscillate when the motor stops, yet still
`have the motor spin fast enough to prevent the stepper
`motor from cogging. Unlike the trolleys, there is no
`friction to dampen the motion of the receiver truss.
`Because the receiver truss is actually driven by a belt,
`
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`
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`
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`
`

`
`when the motor is suddenly stopped the only thing to
`slow down and stop the truss is the tension in the belt on
`one side of the gear. The belt will tighten and actually
`spring the truss backward, which will cause a tension to
`develop in the belt on the other side of the gear. This
`back and forth springing action continues for several
`cycles, depending on the original speed of the truss. If
`the truss is moved slowly enough, this springing action
`is completely avoided.
`
`At the slowest motor speed of 250 steps/sec, it would
`take almost 97 minutes for the receiver truss to travel
`
`through a full 180°. This is a speed of about 0.031 deg/sec.
`At the maximum motor speed of 10000 steps/sec, it would
`take about 2.5 minutes for the receiver truss to travel
`
`through 180°. This is a speed of about 1.24 deg/sec. For
`typical multistatic measurement scenarios, receiver
`azimuth movements of between 0.25° and 0.5‘’ are
`
`required. These would take between 5 and 9 seconds at
`a motor speed of 500 steps/sec. Note that the stepper
`motor motion control system has the ability to start the
`motors at a slow speed, ramp up to a fast motor speed,
`then ramp down to a slow motor speed before stopping.
`This allows smooth starts and stops while still allowing
`faster motor speeds.
`
`D1. CHAMBER EFFECTS
`
`Figure 6 shows the uncalibrated time domain backscatter
`response of a six inch diameter aluminum sphere mounted
`on a styrofoam column. The time domain data was
`9 generated using an inverse FFT on 801 evenly spaced
`frequency points spanning from 6 to 14 GHz. Thus, the
`frequency data had a 10 MHz spacing, giving a time
`domain range of 100 ns.
`
`Background subtraction is implemented by performing
`two measurements. The first measurement is of the target
`along with its support structure. The second measurement
`is identical to the first except for the removal of the
`target. When these two measurements are subtracted from
`each other, only the difference remains. Ideally, this would
`include just the target itself without the support structure.
`
`The response between -49 and -42 ns represents antenna
`coupling, which is successfully removed through
`background subtraction. The peak located at -25 ns is
`the sphere. The response between -5 and 25 ns represents
`residual scattering from within the chamber, which is
`greatly reduced through background subtraction. The
`peak located at 2 ns is the Iirst echo of the sphere off the
`trusses. The 27 ns between the sphere and the first truss
`echo corresponds to roughly 26' 6", which is the extra
`distance traveled by energy scattering off the sphere,
`traveling to and scattering off the trusses, and then
`traveling back to and re-scattering off the sphere. The
`peak located at 4.5 ns is scattering coming from the
`back side of the trusses. Note that the semicircular shape
`of the trusses tends to focus their scattering back to the
`
`target.
`
`Even though the truss echo still remains after background
`subtraction, its effects can easily be removed from the
`measured data through the use of range (time) gating. In
`fact, time gating can remove all unwanted responses from
`the measured data except those falling in the same lil-'1”
`time bins as the target itself.
`
`Figure 7 illustrates the differences in path lengths between
`polarization channels. These differences are due to
`different cable lengths among the different polarization
`channels, and can be compensated for by introducing
`appropriate amounts of phase shift into the uncalibrated
`data. Note that most (but not all) of the calibration routines
`used by the authors automatically compensate for these
`differences.
`
`2-18 GHz
`
`18-265 Gllz
`
`vv target offset
`
`hv target offset
`
`vh target offset
`
`hh target offset
`
`0.000 ns
`
`0.479 ns
`
`0.721 ns
`
`1.195 ns
`
`0.000 ns
`
`-0.842 ns
`
`-0.769 ns
`
`—1.6l9 ns
`
`target offset
`Figure7. Amount of
`uncalibrated data of all
`
`for
`four
`
`polarization channels.
`
`IV. CONCLUSIONS
`
`The chamber has been operational for nearly three years
`and has proven to be very stable and reliable. This cham ber
`is obviously not the ultimate chamber design, but rather
`an experiment that truly advances the sL'1te—of-the—art in
`microwave measurements.
`
`ACKNOWLEDGEMENTS
`
`Joseph K. Glazner and Richard F. Schindel, who are no
`longer at HARC, both made significant contributions to
`the design and construction of this chamber.
`
`The aluminum truss design and finite element analysis
`was done by Minh Le and Walter Anthony at Pressure
`Vessel Design Pro, Corp.
`The two aluminum trusses were fabricated at Allied
`Industries in Houston, TX.
`
`The truss machining was done by Hahn and Clay in
`Houston, TX.
`
`The trusses were installed at HARC by Westheimer
`Rigging and Cranes, Inc.
`
`the Texas
`Miscellaneous machining was done at
`Accelerator Center machine shop by Garry Shot’/man,
`Troy Welch, Torn Vick, and Phil Collins.
`
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`
`15
`
`15
`
`

`
`——-——- No Background Subtraction
`
`-—— With Background Subtraction
`
`(dB) 6: O C)
`
`Magnitude
`
`-60.0
`
`-50.0
`
`-40.0
`
`-30.0
`
`-20.0
`
`-10.0
`
`0.0
`
`10.0
`
`20.0
`
`30.0
`
`40.0
`
`Time (ns)
`
`Figure 6. Uncalibrated time domain of vv
`polarized backscatter scattering cross—
`section for a six inch diameter sphere.
`
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`
`16
`
`16