1 nec features input geometry wires & patches environment free space perfect ground real earth...

11

NEC Features NEC Features

INPUTINPUT

GeometryGeometryWires & PatchesWires & Patches

EnvironmentEnvironmentFree SpaceFree Space Perfect GroundPerfect GroundReal EarthReal Earth

SourcesSourcesVoltage & CurrentVoltage & CurrentPlane WavePlane Wave

DD I I

CC SSUU TTRR RRRR

IIEE BBNN UUTT TT

I IOONN

OUTPUTOUTPUT

I & Q DistributionsI & Q DistributionsZIN YIN PIN

Power BudgetPower BudgetPIN PRAD PLOSS

EfficiencyEfficiency

FieldsFieldsNear & FarNear & Far

GainGainPower, Directive, Power, Directive, AverageAverage

22

NEC Features (Continued)NEC Features (Continued)

INPUTINPUT

LOADINGLOADING

Lumped ImpedanceLumped ImpedanceNetworksNetworksTransmission LinesTransmission Lines

OUTPUTOUTPUT

PatternsPatternsTransmitting & Transmitting & ReceivingReceiving

Port CurrentsPort Currents

Network VoltagesNetwork Voltages

Coupling InformationCoupling Information

Scattered FieldsScattered Fields

33

NEC Input OptionsNEC Input Options

TitlesTitles Group of Comments andGroup of Comments and CM CECM CE

descriptionsdescriptions

Structure SpecificationsStructure Specifications WiresWires GWGW GAGA GCGC Surface PatchesSurface Patches SPSP SMSM SCSC

Geometry Moves & ReplicationsGeometry Moves & Replications Move, Rotate, DuplicateMove, Rotate, Duplicate GMGM Rotate, Duplicate (Z-Axis)(w/Symm)Rotate, Duplicate (Z-Axis)(w/Symm) GRGR Reflect in Coordinate Planes (w/Symm)Reflect in Coordinate Planes (w/Symm) GXGX Scale DimensionsScale Dimensions GSGS

44

NEC Input OptionsNEC Input Options

Performance ParametersPerformance Parameters Alters MatrixAlters Matrix

Frequency Stepping (Linear, Multipl.)Frequency Stepping (Linear, Multipl.) FRFR Ground Conditions (P.G., R.C., SOMM)Ground Conditions (P.G., R.C., SOMM) GNGN Structure Loading (Lumped, Distrib.)Structure Loading (Lumped, Distrib.) LDLD

Alters CurrentsAlters Currents Excitations (XMT or RCV)Excitations (XMT or RCV) EXEX Networks (Non-Radiative)Networks (Non-Radiative) NTNT Transmission Lines (Balanced)Transmission Lines (Balanced) TLTL

55

NEC Input OptionsNEC Input Options Performance SelectionPerformance Selection

Radiation Patterns/Far Fields/GainRadiation Patterns/Far Fields/Gain RPRP Near FieldsNear Fields NENE NHNH CouplingCoupling CPCP Additional Ground Conditions (Patterns)Additional Ground Conditions (Patterns) GDGD Receive CurrentsReceive Currents PTPT ChargesCharges PQPQ

Repetitive Use of Matrix and Exploit Partial SymmetryRepetitive Use of Matrix and Exploit Partial Symmetry Create Numerical Greens FunctionCreate Numerical Greens Function WGWG Use Numerical Green’s FunctionUse Numerical Green’s Function GFGF

66

NEC Output FeaturesNEC Output Features

CommentsComments Structure Specifications (Wires and Patches)Structure Specifications (Wires and Patches) Segmentation DataSegmentation Data FrequencyFrequency Structure Impedance LoadingStructure Impedance Loading Network DataNetwork Data

Excitation at Network Connection PointsExcitation at Network Connection Points Antenna EnvironmentAntenna Environment Matrix TimingMatrix Timing Currents and LocationCurrents and Location Power BudgetPower Budget

77

NEC Output FeaturesNEC Output Features

Charge DensitiesCharge Densities Near Fields Near Fields Input Impedance DataInput Impedance Data Radiation PatternsRadiation Patterns Average Power GainAverage Power Gain Scattering Cross SectionScattering Cross Section Radiated Fields Near GroundRadiated Fields Near Ground Normalized GainNormalized Gain Coupling DataCoupling Data Plane Wave ExcitationPlane Wave Excitation Receive PatternReceive Pattern

88

NEC2 Ground ConditionsNEC2 Ground Conditions

Perfectly conducting ground-imagePerfectly conducting ground-image Reflection coefficient approximationReflection coefficient approximation

(wire height > 0.1 (wire height > 0.1 )) Sommerfeld solution for wire over lossy earthSommerfeld solution for wire over lossy earth Wire ground screen approximationWire ground screen approximation Cliff approximations for radiated fieldsCliff approximations for radiated fields Ground wave calculationsGround wave calculations

99

Space Wave and Surface Wave

Space Wave and Surface Wave

Direct waveDirect wave follows free space attenuationfollows free space attenuation Reflected waveReflected wave path slightly longer + path slightly longer +

suffers some loss at reflection pointsuffers some loss at reflection point Surface waveSurface wave hugs the interface and hugs the interface and

decays rapidlydecays rapidly

ObservationObservationPointPoint

Direct WaveDirect Wave

SurfaceSurface WaveWaveWaveWave

ReflectedReflected

Lossy EarthLossy EarthRR, ,

xx

1010

Wire SpecificationsWire Specifications

Example:Example:

TAG No SegsTAG No Segs X1 Y1 Z1 X2 Y2 Z2 Radius X1 Y1 Z1 X2 Y2 Z2 Radius

GWGW 1 5 0, 0, 0 .5, 0, 0 .0011 5 0, 0, 0 .5, 0, 0 .001 Default is equal segment lengths Default is equal segment lengths ) and uniform radius, but) and uniform radius, but tapered tapered

radii (radii (aa) and) and variablevariable segmentation is an option.segmentation is an option.

ArcsArcs are formed as sections ofare formed as sections of polygons polygons

Wire ModelingWire Modeling

1111


Tag & Segment numbers help locate loads & sources Segment connections are described by integer arrays

For automatic segment connection:Separation of segment ends Segment length < 10-3

“+” Current Ref.

1 2

End 1 Seg# End 2

G.P. 1 1 2

1 2 3

-4 3 0 Free e nd

-5 4 10003 Patch

2 5 0

Ex.

1212


Wire Modeling GuidelinesWire Modeling Guidelines Segment Length

relative to wavelength

is a key parameter

< 0.1 for accuracy in most cases

< 0.05 in critical regions

< 0.2 on long, straight segments

Avoid extremely short segments ( < 10-4 )

a

1313


a a Must be small relative to bothand

awith thin wire kernel

a with extended T.W. kernel

a since no transverse current & no

variations around the wire are

included

1414


Avoid:Avoid: Large changes in radius (especially on short (especially on short

segments)segments)

Sharp bends in thick wires

Wires that are connectedconnected must contact at segment ends

Connection Separation/Length

No Connection< 10-3

1515

Wire Modeling Wire Modeling

* *

~

Use equal length segment lengths next to sourcesUse equal length segment lengths next to sources

No voltage sources or loads at a wire open endNo voltage sources or loads at a wire open end

~

1616


Source Modeling GuidelinesSource Modeling Guidelines

Balanced:Balanced: Source “gap” is a Source “gap” is a segment with E-field on itsegment with E-field on it

Unbalanced:Unbalanced:

Coax FeedCoax Feed

Multiple:Multiple:

YYININ Y Y IN IN = Y= Y11+Y+Y22+Y+Y33

1717


Computational Checks for RIN & GainComputational Checks for RIN & Gain

Find Radiated PowerRadiated Power by integrating the far field:

Input Power:Input Power:

For a Lossless Antenna PIN = PRAD

NEC prints “Average Power Gain”NEC prints “Average Power Gain”

Pr E

d

r

P VI

RAD

IN

2

42

1

2

*

G G dP

PwhenAVE P

RAD

IN

1

4

E2

1818


For a loss-free antenna, average gain is a check on solution For a loss-free antenna, average gain is a check on solution accuracyaccuracy

Source voltage Vo

NEC solves for current I (s) Input power

PPININ is sensitive to errors in I(s) is sensitive to errors in I(s)

Integrate radiated power over sphere in far fieldIntegrate radiated power over sphere in far field

PRAD is a stationary function of I (s) PRAD is a stationary function of I (s)

For Loss-Free Antenna PRAD = PIN

Vo S

P V IIN 1

200Re ( )*

1919


Average Power GainAverage Power Gain

Corrected PCorrected PININ = = Computed PIN x (GAVE/k)

Corrected Input Resistance = Corrected Input Resistance = 2 GAVE PIN

k | I (0)| 2

= Computed RIN x (GAVE/k)

Corrected Gain = Corrected Gain = Computed Gain x (k/GAVE)

G

G d

G E x H P

G kP P k for free space

for perfect ground

AVE

P

P IN

AVE RAD IN

41

21

2

Re /

/

*

2020


Wires near lossy earthWires near lossy earth Reflection coefficient approximation is reasonable for:Reflection coefficient approximation is reasonable for:

vertical wires at least 0.1 vertical wires at least 0.1 to 0.2 to 0.2 above the ground above the ground horizontal wires at least 0.4 horizontal wires at least 0.4 above earth above earth

Sommerfeld/Norton works for:Sommerfeld/Norton works for: wires as close as 10wires as close as 10-6 -6 height should be several time radius height should be several time radius

{h{h22 + a + a22} } 1/2 1/2 10 10-6 -6 , h , h3a3a

2121

Surface ModelingSurface Modeling

Surface SpecificationsSurface Specifications

Input data: Coordinates of patch center, , , Area

Other Options: Rectangular 3 corners (RHR) Triangular “ Quadrilateral 4 corners

Arbitrary Shape Patch has area & normal direction

Area A

Center

of Patch

2222


AreaArea should be less thanshould be less than 0.04 0.04 22 (.2(.2x .2 x .2 ))

Since no defined shape, avoid long, thin patchesSince no defined shape, avoid long, thin patches SinceSince currentscurrents defined at center only, not good for edge defined at center only, not good for edge

currentscurrents Where radius of curvature is small, use smaller patchesWhere radius of curvature is small, use smaller patches Surface must beSurface must be closedclosed and not tooand not too thin (no plates, no thin (no plates, no

fins or wings)fins or wings) WiresWires must connect at patch centersmust connect at patch centers Increase definition at connection pointsIncrease definition at connection points

2323


Wire Grid ModelingWire Grid Modeling

Use wire grids whereUse wire grids where edge connections are needededge connections are needed Wire grid = surfaceWire grid = surface if mesh is “small enough”if mesh is “small enough”

Problem:Problem: - can’t afford real fine meshes - can’t afford real fine meshes - sparse meshes have too much - sparse meshes have too much L, not enough C L, not enough C

PossiblePossible Solutions: Solutions: - negative L distributed loading - negative L distributed loading - fat, rod-like wires- fat, rod-like wires

2424


Wire gridding is acceptable for Wire gridding is acceptable for thin structures, plates, thin structures, plates, wings, etcwings, etc.. and for far field responses / not for surface and for far field responses / not for surface charge or currentscharge or currents

Grid size not too criticalGrid size not too critical (~ 0.1 (~ 0.1 at midband) at midband)

/a not critical /a not critical (10< (10< /a < 30/a < 30 good forgood for wires attaching to wires attaching to surface)surface)

UseUse equal radii and segmentationequal radii and segmentation at junctionsat junctions

2525

Patch vs. Wire Grid/ResourcesPatch vs. Wire

Grid/Resources

Patch:Patch: 2LW2LW Grid:Grid: 2LW + L + W2LW + L + W

But Patch can be .2But Patch can be .2 on a side … on a side …

Ex: 4x2 grid 20x20 gridEx: 4x2 grid 20x20 grid

Patch:Patch: 44 Grid:Grid: 2222 Patch:Patch: 200200 Grid: Grid: 840840

Usually find patch model will save about 40% on Usually find patch model will save about 40% on computational resourcescomputational resources

LL

WW

2LG

2

WG

2LW2( )x

2626

GC -- Wire Radius/Segment Tapering

GC -- Wire Radius/Segment Tapering

SetSet radius = 0radius = 0 on theon the GWGW card > follow with acard > follow with a GCGC cardcard

RDEL -- RDEL -- Ratio of adjacent segment lengthsRatio of adjacent segment lengths

RAD 1, RAD 2 -- RAD 1, RAD 2 -- Radius of 1st segment, radiusRadius of 1st segment, radiusof last segmentof last segment

MakeMake RDEL < 2 RDEL < 2 andand adjacent segmentsadjacent segments radiiradiiratio < 2ratio < 2

2727

GE -- Geometry End(Gound Plane Options)

GE -- Geometry End(Gound Plane Options)

Options Options (sets symmetry w.r.t. ground plane)(sets symmetry w.r.t. ground plane) 0 -- No ground plane (free space)0 -- No ground plane (free space) 1 -- Ground plane present1 -- Ground plane present

“touch” wires connected“touch” wires connected 1 -- Ground plane present1 -- Ground plane present

“touch” wires insulated “touch” wires insulated

GE 1GE 1 GE-1GE-1currentcurrent currentcurrent

2828

GX -- Reflections GX -- Reflections

Exploit Exploit symmetrysymmetry for faster solutionsfor faster solutions Tag number incrementTag number increment GW1GW1 Tag Tag GW5GW5

GW2GW2 Increment Increment GW6GW6GW3GW3 by 4 by 4 GW7GW7GW4GW4 GW8GW8

Reflection controlReflection control

xx in y-z plane in y-z planeReflect along Reflect along y Axis in x-z plane y Axis in x-z plane

z z in x-y plane in x-y plane

2929

GX -- Reflection ExamplesGX -- Reflection Examples

C

B

A

ZOne Corner Right, Upper, Front

Y

X

3 Basic WiresX, Y, Z Directed from (A, B, C)

C

C2B

A

A

GX 100

Right Upper

Y

X

Z

CC

C2B

2A

2A

2B

Z GX 110

Upper

Y

X

2A

2C2C

2C

2C

2B

2A

2A

2A

2B

2B

X

Y

Z GX 111

3030

RP - Radiation Patterns RP - Radiation Patterns

RP 0: RP 0: Space wave =Space wave = direct + reflecteddirect + reflected RP 1 : RP 1 : Ground wave = spacewave +Ground wave = spacewave + surface surface

wave.wave. Must specify observation point(s)Must specify observation point(s) Space wave (or sky wave) dominates inSpace wave (or sky wave) dominates in

ionospheric propagationionospheric propagation Surface wave decays rapidly withSurface wave decays rapidly with

distancedistance andand frequencyfrequency

3131

NT -- NetworksNT -- Networks

Connection between 2 segments containing Connection between 2 segments containing admittances (impedances)admittances (impedances)

Segments do not have to be nearbySegments do not have to be nearby(not so in real life)(not so in real life)

2-port Y-parameters2-port Y-parameters

R

V2

V1

++ ++

Y11

Y12

Y22

I2I1 Y V Y V I

Y V Y V I11 1 12 2 1

12 1 22 2 2

Y YR

YR

11 22

12

1

1

Series ResistorSeries Resistor

Example:Example:

3232

TL -- Transmission Lines TL -- Transmission Lines

NEC’s transmission lines areNEC’s transmission lines are equations, equations, not wiresnot wires If If transmission line (TL)transmission line (TL), , load (LD)load (LD), , andand voltage voltage

source (Ex)source (Ex) are on the same segmentare on the same segment …

ZL = load on LD

ZT = load on TL

Transmission LineTransmission Line

VSegmentSegment

ZT ZL

3333

Transmission Line Application

Transmission Line Application

Transmission line equations are forTransmission line equations are for balancedbalanced conditions only!conditions only!

OK!OK! NOT BALANCED!NOT BALANCED!

3434

Crossed Feeds Crossed Feeds

Turnstile radiators Turnstile radiators present a challenge at the feed present a challenge at the feed pointpoint

Slight Slight VerticalVerticalDisplacementDisplacement

Dipoles Co-PlanarDipoles Co-PlanarFeeds DisplacedFeeds Displaced

4 Feeds, Centers Connected4 Feeds, Centers Connected

jVV

j V/2

V/2j V/2

V/2

3535

Current DirectionsCurrent Directions

X1, Y1 , Z1

I

X2, Y2 , Z2

Positive current flows from Positive current flows from END 1END 1 to to END 2END 2

3636

Current DirectionsCurrent Directions

Ex: Ex: VEE dipole, fed at cornerVEE dipole, fed at corner

GW X Y Z X Y Z a

GW X Y Z X Y Z aC C C B B B

C C C A A A

1 4

2 4

, , , , , , , ,

, , , , , , , ,

GW X Y Z X Y Z a

GW X Y Z X Y Z aC C C B B B

A A A C C C

1 4

2 4

, , , , , , , ,

, , , , , , , ,

11BB

22AA

CC

++++

11

22AA

11BB

CC

++

++

3737

E- and H-Fields for a Desired Power

E- and H-Fields for a Desired Power

NECNEC usesuses peak valuespeak values for for voltage, current, and fieldsvoltage, current, and fields

We usually apply 1 volt to an unknownWe usually apply 1 volt to an unknown Zin

E Erms NEC 1 voltsource

Desired Power

2NEC Power for

1 volt source

E Erms peak / 2

38382323

NEC User Notes - Feeding of ArraysNEC User Notes - Feeding of Arrays

Problem:Problem: Array excitations are in terms of feed point Array excitations are in terms of feed point currents (amplitude currents (amplitude

& phase)& phase) NECNEC does not allow does not allow current drives,current drives, only voltage only voltage (amplitude (amplitude

& phase)& phase) at feed points at feed points You can’t drive a feed with a specified You can’t drive a feed with a specified current current unless you unless you

know the driving point impedance. But the driving point know the driving point impedance. But the driving point impedance depends on the impedance depends on the current drivecurrent drive and, of course, the and, of course, the physical arrangement of the array elements.physical arrangement of the array elements.

You could possibly “iterate” yourself to an approximate You could possibly “iterate” yourself to an approximate solution by twiddling voltage drivessolution by twiddling voltage drives

3939

NEC User Notes -Feeding of ArraysNEC User Notes -Feeding of Arrays

Solution:Solution: Current generators Current generators are realizable by high impedance, high voltage are realizable by high impedance, high voltage

series source:series source:

If you use in NEC, the large numbers used will swamp out theIf you use in NEC, the large numbers used will swamp out the drive segment voltage drive segment voltage and you won’t be able to use the resultsand you won’t be able to use the results

Can overcome this problem by replacing theCan overcome this problem by replacing the series resistor series resistor by an by an appropriate network but there is an easier method…..appropriate network but there is an easier method…..

AMP into circuits whose input impedance is <104

40404343


Details:Details:

TheThe NT NT card(s) are used thusly:card(s) are used thusly:

Cards:Cards:

NT (Tag,NT (Tag, Seg Seg), 901, 1, 0, 0 ), 901, 1, 0, 0 0, 1 0, 0 0, 1 0, 0EX 0, 901, 1, 0, (j x FEED PT. CURRENT)EX 0, 901, 1, 0, (j x FEED PT. CURRENT)

GW 901, 1, 10GW 901, 1, 1033, 0, 0, (10, 0, 0, (1033 + slightly more), 0, 0, (RADIUS) + slightly more), 0, 0, (RADIUS)

Make sure these GW900’s do not interact with each other / squirt them off in all directionsMake sure these GW900’s do not interact with each other / squirt them off in all directions

(LATEST VIEWER ALLOWS YOU TO ELIMINATE A RANGE OF SEGMENTS FROM THE VIEW!)(LATEST VIEWER ALLOWS YOU TO ELIMINATE A RANGE OF SEGMENTS FROM THE VIEW!)

Far-WayFar-WaySegmentSegment }

Onesetperfeed

One feedOne feedsegmentsegmentof arrayof array

“Extra” added“Extra” addedsegment to supportsegment to supportthe generator. Usethe generator. UseGW 901, 1, …, orGW 901, 1, …, orsimilar large tagsimilar large tagnumber.number.

Set: Y11 = YA + YC = Y22 = 0

Y12 = YC = j I = I1 = jV

I1

VYA YB

YCI2

I

V1

V2

~

4141


Process:Process: Set up enoughSet up enough GW900 GW900 cards for far-out feed segments, one for cards for far-out feed segments, one for

each array element. Make them very short w.r.t a wavelength so each array element. Make them very short w.r.t a wavelength so they will not radiate. Put them after any they will not radiate. Put them after any GS GS scaling to maximizescaling to maximizethe distance between dummy and actual geometry.the distance between dummy and actual geometry.

Add anAdd an NTNT card for connection between eachcard for connection between each GW900GW900 and its and its companioncompanion feed point segment.feed point segment.

Put the correctPut the correct current values current values on theon the EX0, 900 EX0, 900 cards to match the cards to match the array design.array design.

The input impedance at the feed points is in the The input impedance at the feed points is in the Network Excitation Network Excitation TableTable instead of under antenna input impedance. instead of under antenna input impedance.

Choose the dummies to be just one segment and set the radius so Choose the dummies to be just one segment and set the radius so /a /a 10 or more. 10 or more.

Process:Process: Set up enoughSet up enough GW900 GW900 cards for far-out feed segments, one for cards for far-out feed segments, one for

each array element. Make them very short w.r.t a wavelength so each array element. Make them very short w.r.t a wavelength so they will not radiate. Put them after any they will not radiate. Put them after any GS GS scaling to maximizescaling to maximizethe distance between dummy and actual geometry.the distance between dummy and actual geometry.

Add anAdd an NTNT card for connection between eachcard for connection between each GW900GW900 and its and its companioncompanion feed point segment.feed point segment.

Put the correctPut the correct current values current values on theon the EX0, 900 EX0, 900 cards to match the cards to match the array design.array design.

The input impedance at the feed points is in the The input impedance at the feed points is in the Network Excitation Network Excitation TableTable instead of under antenna input impedance. instead of under antenna input impedance.

Choose the dummies to be just one segment and set the radius so Choose the dummies to be just one segment and set the radius so /a /a 10 or more. 10 or more.

42424747

Equivalent Radius for Non-Circular Cross-Sections


4747

CE 2 Phased Verticals -- Current Source FedCE 2 Phased Verticals -- Current Source FedGW 1, 5, 0, 0, 0, 0, 0, 0.25, .001GW 1, 5, 0, 0, 0, 0, 0, 0.25, .001GW 2, 5, 0.25, 0, 0, 0.25, 0, 0.25, .001GW 2, 5, 0.25, 0, 0, 0.25, 0, 0.25, .001GW 901, 1, 999, 999, 999, 999, 999.001, 999, .0001 Dummy 1GW 901, 1, 999, 999, 999, 999, 999.001, 999, .0001 Dummy 1GW 902, 1, GW 902, 1, 999, 999, 999, 999, 999, 999, 999, 999.001, 999, .0001 Dummy 2999, 999.001, 999, .0001 Dummy 2GE 1GE 1GN 1GN 1NT 901, 1, 1, 1, 0, 0, 0, 1, 0, 0NT 901, 1, 1, 1, 0, 0, 0, 1, 0, 0NT 902, 1, 1, 1, 0, 0, 0, 1, 0, 0NT 902, 1, 1, 1, 0, 0, 0, 1, 0, 0EX 0, 901, 1, 0, 0, 1EX 0, 901, 1, 0, 0, 1EX 0, 902, 1, 0, 0, EX 0, 902, 1, 0, 0, 11

~~ ~~I1 = 1 I2 = j

/4/4

NEC User Notes -- Feeding of Arrays (Example)

43434747



NT 1, 4, 1, 6, 0.02, 0, 0, 0, 1e10, 0NT 1, 4, 1, 6, 0.02, 0, 0, 0, 1e10, 0

XQXQ

NT 1, 4, 1, 6, .00333, 0, 0, 0 1e10, 0NT 1, 4, 1, 6, .00333, 0, 0, 0 1e10, 0

XQXQ

EN EN

NEC User Notes -- Using NT as Loads

1 64

NT

Y11 = 1/R

Y22 =

1 74R

Place load here(50 , 300 )

4444

4747



NEC User Notes -- Minimum Segment Lengths

at Bent Wire Junctions

• Match points for both wires must lie outside the volumes

• Set a segment length limit to enforce this

5.0EK,with2or8and2or8

tansin2and

sintan2

2

2

1

1

212

211

aa

aaaa

:ALSO

:THUS

2/2

1/2

Wire 2 (Radius a2) = angle between wires

Match points from each wire atintersection

Wire 1 (Radius a1)

4545



Equivalent radiusEquivalent radius must lie between must lie between inscribedinscribed andand circumscribedcircumscribed circles which circles which bound the conductor boundary.bound the conductor boundary.

Best fit:Best fit: CirclesCircles formed with sameformed with same areaarea and and perimeterperimeter as the conductor boundary.as the conductor boundary.

Inner circle : Inner circle : Outer circle :Outer circle :

a Ai /

a P0 2 /

4646



Choose the mean:Choose the mean:

Aa

Pe

2

a

A P

e

22

47474747



• TRIANGLE:TRIANGLE: aaee = 0.425 = 0.425

• SQUARE:SQUARE: aaee = 0.65 = 0.65

• RECTANGLE OR STRIP:RECTANGLE OR STRIP: W/TW/T aaee

11 0.6 w0.6 w 2 2 0.44 w0.44 w 3 3 0.37 w0.37 w 5 5 0.32 w0.32 w 10 10 0.26 w0.26 w100100

S S

S

S

S

SS

T

W

PAae ..

4848

Modeling Guidelines Modeling Guidelines

Estimate runtimeEstimate runtime Accuracy checksAccuracy checks

Vary segmentation -- check Vary segmentation -- check convergenceconvergence CheckCheck reciprocityreciprocity Test for Test for average gainaverage gain Check grids vs.Check grids vs. patchespatches

SizeSize problem in wavelengthsproblem in wavelengths LocateLocate functional partsfunctional parts before modelingbefore modeling

Don’t forget the coupling toDon’t forget the coupling to baluns, etc.baluns, etc. bybynear fieldsnear fields

4949


Always exploitAlways exploit symmetrysymmetry for large problemsfor large problems Model theModel the radiatorsradiators firstfirst

Check the literatureCheck the literature Duplicate literature before approaching the full Duplicate literature before approaching the full

problemproblem Strip out details/simplify structureStrip out details/simplify structure

Transmission lines and connectionsTransmission lines and connections Supporting structuresSupporting structures Environmental interactionsEnvironmental interactions

5050


Wire grid modelingWire grid modeling Outline cornersOutline corners Grid size approximately 0.1 Grid size approximately 0.1 nominal nominal Try “equal area” ruleTry “equal area” rule Try two segments/sideTry two segments/side Minimize Minimize and and aa changes (< 2:1) at key changes (< 2:1) at key

junctions (near feedpoints)junctions (near feedpoints) Use denser gridding (2x) at connection points Use denser gridding (2x) at connection points

of of wireswires and and surfacessurfaces

5151


Surface patch modelingSurface patch modeling Make sure surface is Make sure surface is closedclosed MaximumMaximum patch sizepatch size: (0.2 : (0.2 0.2 0.2 )) AvoidAvoid long narrow patches long narrow patches UseUse large patcheslarge patches on smooth surfaces:on smooth surfaces:

smaller patchessmaller patches on curved areason curved areas

5252


Vary Vary segmentation, grid size, patch sizesegmentation, grid size, patch size and noteand note results -- look forresults -- look for convergenceconvergence

Consider possible problem areasConsider possible problem areas Sharp bends in thick wiresSharp bends in thick wires Changes in wire radiusChanges in wire radius Wires connected to lossy groundWires connected to lossy ground Wires too thick?Wires too thick?

5353


DetermineDetermine number of segmentsnumber of segments neededneeded < 0.1 in most cases< 0.1 in most cases too small? Low frequency limittoo small? Low frequency limit too small? Pencil lead vs. poker chipstoo small? Pencil lead vs. poker chips

““Thin Wire”Thin Wire”

““Tuna Can”Tuna Can”

“Poker Chip”“Poker Chip”

( ( aa << << ))

( ( aa ))

( ( aa >> >> ) )

1 nec features input geometry wires & patches environment free space perfect ground real earth...

Documents

cases d

surface wave direct

wire modelingavoid

equal segment lengths

short segments d

key parameter d

critical regions d

reflection pointsurface