The Importance of Dirt in Radio-Frequency Testing and

The Importance of Dirt in Radio-Frequency Testing and Spectrum Management

Jeffrey Schleher, PE and James R. Duffey, PhD

American Systems Leidos

2015 ITEA DEPS Directed Energy Symposium May 12-15, 2015 Las Vegas, NV

Distribution Statement A: Approved for public release; distribution is unlimited

Approved for public release

Topics

• RF Propagation Considerations

• Ground Reflection

• Impact

• Modeling and Simulation

• Reflection Measurement

• Ground Propagation Needs

• Conclusions

2


Topic Test Importance To:

• Remote Sensing

• RF Communication

– All wireless activity

• RF Electronic Warfare

• Trafficability

• HPEM Directed Energy

3


RF Propagation Considerations

• Direct Propagation

• Propagation Through Foliage, Walls and Buildings (Urban and Rural Environment)

• Multiple Reflections

• Diffraction Around Buildings and Hills

• Ground

– Propagation Into Ground

4


Reflection Coefficient

5

ReflectionCoefficient

= D R

GroundElectrical

Properties

DispersionCurvature

GroundRoughness

Long, Radar Reflectivity of Land and Sea, Artech, 1983This and next slide complex equations in El-Shenawee and Miller:“Multiple-Incidence and Multifrequency for Profile Reconstruction of Random Rough Surfaces Using the 3-D Electrometric Fast Multipole Model, IEEE Geo and Remote Sensingv42,#11 Nov 2004

Penetration of the ground, with loss, and then reflection is not addressed here or in most modelsThe challenge, then, is to know ground electrical properties with depth.

• Simplified RF Reflection Equation


Ground Reflectionor absorption, or penetration, and reflection

2 2 2

2 2 2

sin cos

sin cos

i i

TM

i i

n n

n n

2 2

2 2

sin cos

sin cos

i i

TE

i i

n

n

sin

sin

cos

cos

x y z

x y z

x y z

x y z

j t j k x j k y j k zinc

x i

j t j k x j k y j k zref

x TE i


y i


y TE i

E e

E e

E e

E e

sin cos

sin cos

sin sin

sin sin

cos

cos

x y z

x y z

x y z

x y z

x y z

x


x i i


x TM i i


y i i


y TM i i


z i

j t j kref

z TM i

E e

E e

E e

E e

E e

E e

y zx j k y j k z

R, R,

2 (1 )R

o R

n j

INCEINCH

TE CaseTM Case REF INC

TEH H REF INC

TME E

i i

Einc

Eref

Etrans

Free Space

Vertical

z

x

2

r

o

n j

i i

Einc

Eref

Etrans

Free Space

Vertical

z

x

2

r

o

n j

i i

HincHref

Htrans

Free SpaceX X

X

Horizontal

2

r

o

n j

i i

HincHref

Htrans

Free SpaceX X

X

Horizontal

2

r

o

n j

R, R,

ETRHTR

rr

(1 )TR INC r

TME E e (1 )TR INC r

TEH H e

o o Rj j

For Vertical and Horizontal Polarization

6

Long, Radar Reflectivity of Land and Sea, Artech, 1983 Assuming dirt not magnetic, = 1Olhoeft, Elec. Mag. And Geo Properties for GPR, 7th Int’l Conf on GPR, 1998

• Complete Equations Including Polarization

Field Into slide

Field out of slide


Relative Electrical Properties

7Kerr, Propagation of Short Radio Waves, MIT Radiation Laboratory Series, vol 13, 1951, p. 398

Medium ’ ”

Sea water

Distilled water

Fresh-water lake

Very dry sandy loam

Very wet sandy loam

Very dry ground

Moist ground

Arizona sand

Austin TX Soilvery dry

3 m- 20 cm

3.2 cm

1 m

9 cm

9 cm

1 m

1 m

3.2 cm

3.2 cm

4.3

12

10-3 - 10-2

0.03

0.6

10—4

10-2

0.10

0.0074

S/m

80

67

80

2

24

4

30

3.2

2.8

774

23

0.06 – 0.6

1.62

32.4

0.006

0.6

0.19

0.014

wavelengthReal

Dielectric constantconductivity

ImaginaryDielectric constant


Ground RoughnessRough Surfaces

Flat Surface Subsurface Electrical Properties Variation

White Sands Desert Pavement Moisture Intrusion Channels

8Rule of Thumb: If Δh < λ/8 sin φ, the surface is “flat” (ibid, Long, p.37)

Δh


Soil Roughness Calculations

9

• Diagram used in accounting for roughness

El-Shenawee and Miller:“Multiple-Incidence and Multifrequency for Profile Reconstruction of Random Rough Surfaces Using the 3-D Electrometric Fast Multipole Model, IEEE Geo and Remote Sensing, v42,#11 Nov 2004

• Referenced paper addresses a Government model (NSF) which helps determine if roughness matters in any particular test

Computing conductivity from dielectric constant

0 ” 2pfConductivity

Permittivity of free space Imaginary part ofdielectric constant

Frequency

0 = 8.854187817620... × 10−12 farads per meter


Why Ground Bounce Matters

• Constructive & Destructive Interference of Direct and Ground Scattered Wave• Unexpected high fields

• Energy goes to unexpected locations• Safety issue in test – Fratricide issue in operations

Modeling in THP -5 is less loss than expected with out ground: Fast, REMCOM, SDRL A001:Dielectric Sensitivity Analysis v1.0, DETEC 12 SEP 0610

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

1000

900

800

700

600

500

400

300

200

100

0

Range (meters)

Height (meters)

-5 0 5 10 15 20 25

Excess Loss above Free Space (dB)

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

1000

900

800

700

600

500

400

300

200

100

0

Range (meters)

Height (meters)

-5 0 5 10 15 20 25

Excess Loss above Free Space (dB)

Very Dry Ground, 1000 MHz, Antenna Height 3m, APMSea Water 1000 MHz, Antenna Height 3m, APM


Wave Interaction

• Diagram of RF constructive and destructive interference

-1.5

-1

-0.5

0

0.5

1

1.5

Direct

Scatter

Interferance

Direct

Scatter

40%

11


Interference StructuresIn theory and field

Field Strength Differences WithDifferent Soil Types at 100m

Ground Reflection

SoilTypesEffectsIn THP

Field Test of W-band Wave InteractionHeating of Carbon Loaded Kapton

Ground Roughness Scattering

THP Calculations, Ground Dielectric Sensitivity Study IEEE-AP, Vol . 48, No. 2, April 2006, pg 45

ModelField Test

12


25 GW Wide Band Source

13

Note Rails


Theory and Field Response

10 m

6 m

Narrow Band Threat Source – A’Pretest analysis with RF-PROTEC

Could use for the application slidePlacement of targets and sensors

Could use to show Reflection? InField Test

Direct Pulse Ground Close Rail Far Rail

Off Boresight Vertically Polarized B-dot

14


Directed Energy Test and Evaluation Capability

DETEC

Propagation Environment Measurement (PEM)

• Recognized Ground Electrical Properties were a Requirement– Could not find a commercial

approach with promise and Reasonable cost

• Science and Technology Was Necessary– Reflection (Done with HSEP)

– Propagation Through Ground (To go)

• PEM Acquired (Done)– Atmospheric Measurement

Equipment for Refraction

– Sea Measurement Equipment for Roughness

15


Measuring Soil Electrical Properties

• Dielectric Constant

• Conductivity

• Magnetic Permeability ( is = 1 ?)

• Roughness (somewhere > 10GHz dominates)

16


Core Sample & 3-Months Method

Fort A.P. Hill Soil Permittivity and Conductivity Measurements for the Wide Area Airborne Minefield Detection Program, Adelphi MD, paper 2002

17

Approach used by Corp of Engineers in Iraq and Afghanistan


DET S&T Approach

• HPM Soil Electrical Properties (HSEP) Science and Technology Project

• Purpose was to quickly and accurately obtain the electromagnetic properties of test range soils before, during, and after HPM testing

• To address these problems by conventional approach:– 3 to 6 months elapse between time samples are taken and time they are

measured, need to shorten this time to minutes or hours

– Sample can change physically and electrically from time sample is taken until it is measured; needs to be representative of soil at time HPM test is conducted

– in-field testing accomplishes this

– Quality of HPM testing suffers if properties of environment are unknown at time of testing – up to x3 changes in power density on target

– Quality of input to Test Hazard Prediction (THP) program forces “worst case” exclusion zones resulting in excessive test monitoring costs

18


HPM Soil Electrical Properties (HSEP) S&T

• Phase I– Selected and demonstrated two

soil electrical property measurement technique• Micro-strip Resonators

• Time Domain Reflectometry

• Phase II– Calibrated resonators to known

standards

– Made measurements in field

• Kirtland

• Utah Test and Training Range

• WSMR

– ≈ 3 minutes/measurement at one resonant frequency

– Technique works on urban building material

19

Microstrip ring resonators:400 MHz, 900 MHz, 2500 MHz


HSEP Testing and Application

20

442 MHz

1020 MHz

2.975 GHz

(front and back)

HSEP is used in the field at • WSMR• AFRL• Redstone TC• China Lake NAWC• NRL (CREW)

Frequency (Hz)

S 11

(dB

)


How do I use Soil Electrical Properties?

• Calculate safety zones with real soil electrical property values using THP or Builder

• Frequency management input• Plan tests with predicted field

– Optimum placement of targets and sensors

• Assess when EW or HPM targets will be “shielded” by environment

• Application to counter mine operations– HSEP only reports first few cm of depth, depending on

frequency and soil moisture– Reflection but not propagation

21

10 m

6 m


Models

• Test Hazard Prediction

– EMPIRE

• APM, RPO, TIREM, VTRPE, etc.

– RF-PROTEC

• Builder

– EMPIRE

• APM, RPO, TIREM, VTRPE, etc.

22


Builder EW Planning

CREW Modeling from interactive scenario Builder NRL Promotional23

CIED Applications


Shortfall: Propagation Through Soil

24

• Also CIED and Counter Mine applications


Solution ConsiderationsAnalysis of Alternatives

25

Criteria• Frequency Resolution 100MHz• Frequency range 50MHz-2GHz• Vertical resolution 10cm• Horizontal resolution 1m• mS resolution undetermined

Geophex Ltd, Raleigh NC

Three Months Again2-3 m Horizontal Resolution

100cm vertical resolution

Core Samples + Q Cell Differential Transmission

Ground Penetrating Radar

• Other Approaches


Conclusions

• Understanding radio-frequency propagation issues in military testing in E3, EW, spectrum management, communications, DE, and safety is essential

• Ground propagation effects are important to understanding overall propagation issues

• Understanding the ground electrical properties are critical in accounting for radio-frequency waves attenuated by, scattering from or adsorption in penetrated soil

• Determining ground electrical properties is difficult and time consuming leading DET S&T to establish an instrumentation program to quickly obtain these properties– Properties for surface reflection have been met– Propagation through soil remain a shortfall

26

Documents

The Importance of Dirt in Radio-Frequency Testing and