Compact and Spherical Range Design, Application and Evaluation Walter D. Burnside and Inder J. Gupta The Ohio State University ElectroScience Laboratory 1320 Kinnear Road Columbus, Ohio 43212 (614) 292-5747 and (614) 292-5951 Presented on September 21-22, 2005 for Raytheon (Tucson, AZ).

Course Outline First Full Day Second Half Day Basic Range Design Guidelines (Burnside) Compact Range Reflector Design (Gupta) Absorber Design and Layout (Burnside) Critical Range Evaluation (Gupta) Second Half Day R-Card Fences for Outdoor Ranges (Gupta) Summary of Range Design Issues (Burnside)

R-card Fences to Suppress Ground Bounce Term in Outdoor Facilities Inder (Jiti) Gupta ElectroScience Laboratory Dept. of Electrical and Computer Engineering The Ohio State University 1320 Kinnear Road, Columbus, OH 43212 Phone: (614) 292-5951 Fax: (614) 292-7297 Email: gupta.11@osu.edu

Introduction(1) In outdoor facilities, the ground bounce term can be a limiting factor. The ground bounce term can destructively interfere with the direct path term reducing the signal level in the quiet zone.

Introduction(2) The transmit antenna height is adjusted so that the direct ray and the ground bounce term add in phase. Narrowband solution Alternatively, metallic fences are used to steer the ground bounce term away from the quiet zone.

R-card Fences R-card fences have varying resistance where the resistance varies smoothly from a very low value (purely conductor) to very high values. Metallic fence can be replaced with a R-card fence. Transmit signal through the fence can end up in the quiet zone.

Outdoor Facility with R-card Fences Multiple R-card fences can be used to eliminate the ground bounce term in the quiet zone. OSU-ESL has designed and built R-card fences for outdoor facilities.

Experimental Outdoor Test Range 30 meters long Radar antenna height is 60 cm Center of target zone is 3 meters above ground 6-18 GHz frequency band Six R-card fences Fences are tilted 20° towards the feed.

30 Meter Outdoor Test Range

30 Meter Outdoor Test Range

R-card Fences Each fence is 60 cm tall. Bottom one third of a fence is pure metal. Resistance increases smoothly from pure metal to 1150 ohms. Built using ten layers of flat resistively coated thin films. Resistive taper on both sides, too.

An R-card Fence

Field Probe Data Radar – HP8510 network analyzer Radar Antenna – SA 8-12 GHz standard gain horn Probe Antenna – AEL 2-18 GHz horn LNA behind the AEL horn to compensate for the cable loss Horizontal and vertical polarization A vertical scan (center 3 meters above ground) A horizontal scan (3meters above ground)

Range with Linear Scanner

Field Probe Data - Horizontal Scan Vertical Pol No fences With fences

Field Probe Data - Horizontal Scan Horizontal Pol No fences With fences

Field Probe Data - Vertical Scan Vertical Pol No fences With fences

Field Probe Data - Vertical Scan Horizontal Pol No fences With fences

Field Probe Data - Vertical Scan Horizontal Pol 8 GHz 12 GHz

Calibrated Field Probe Data – Vertical Scan Horizontal Pol No fences With fences

Backscatter Measurements 1-foot corner reflector Backscattered fields along the boradside direction Corner reflector at various heights 8.5 GHz to 12.5 GHz frequency band in 2 MHz steps Two separate antennas for transmit and receive to perform S12 measurements Time gating (25 point smoothing) to isolate the corner reflector return

Measured Backscattered Fields – Corner Reflector Horizontal Pol No fences With fences

Measured Backscattered Fields – Corner Reflector Horizontal Pol 6 R-card fences

Multilayered R-card Fences The R-card fences discussed until now have strong reflected field term. In some applications, the reflection term is also undesired. Multilayered R-card fences have been designed and built for these applications

The R-card Layout: Layer 1

The R-card Layout: Layer 2

The R-card Layout: Layer 3

The R-card Layout: Layer 4

The R-card Layout: Layer 5

Near Field Data for Single Layer R-Card Fence Design Total Field at Receiver Site Reflected Field at Transmitter Site 3 Fences Plot Convention: #L#C# #L: number of layers per R-Card Fence #C: number of R-Card Fences #: Separation between two adjacent R-Card Fences

Near Field Data for 3 Layer R-Card Fence Design Total Field at Receiver Site Reflected Field at Transmitter Site 3 Fences Plot Convention: #L#C# #L: number of layers per R-Card Fence #C: number of R-Card Fences #: Separation between two adjacent R-Card Fences

Near Field Data for 5 Layer R-Card Fence Design Total Field at Receiver Site Reflected Field at Transmitter Site 3 Fences Plot Convention: #L#C# #L: number of layers per R-Card Fence #C: number of R-Card Fences #: Separation between two adjacent R-Card Fences

Near Field Data for 5 Layer R-Card Fence Design Total Field at Receiver Site Reflected Field at Transmitter Site 1.0” Foam Plot Convention: #L#C# #L: number of layers per R-Card Fence #C: number of R-Card Fences #: Separation between two adjacent R-Card Fences 3 Fences

Near Field Data for 5 Layer R-Card Fence Design Total Field at Receiver Site Reflected Field at Transmitter Site 1.0” Foam Plot Convention: #L#C# #L: number of layers per R-Card Fence #C: number of R-Card Fences #: Separation between two adjacent R-Card Fences 2 Fences

Measurement Setup

Measurement Setup Behind ESL Transmit Antenna Receive Antenna R-card Fences

Measurement Setup Behind ESL Receiving Antenna Transmit Antenna

Probe Field at 1575 MHz

Summary R-card fences can be used for performance enhancement of outdoor facilities. Multi-layered R-card fences can be designed to act like absorber (low-level transmission and reflection).

References Y. Kim and E.K. Walton, “Ground bounce reduction using a tapered resistive sheet fence,” AMTA2000, pp. 222-227, Philadelphia, PA, October 2000. I.J. Gupta and W.D. Burnside, ”Performance of an experimental outdoor RCS range with R-card fences,” AMTA2001, pp.400-405, Denver, CO, October 2001. T.-H. Lee and W.D. Burnside, “Applications of multilayer resistive strips (R-card) in EM measurements,” AMTA2003, pp 420-425, Irvine, CA, October 2003.