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ARRAY MODELING USING ESP5

BRIDGE PROJECT UPDATE

By: ERIC WALTON

The Ohio State University

8/26/04

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GETTING STARTED WITH A MOM MODEL OF THE FSS ARRAYS

The most accurate modeling of the finite-sized tri-band FSS array antenna set is to use the “Method of Moments (MOM)

The model must use realistic finite sized geometry, not an assumed infinite array as computed last year using the periodic moment method (PMM) code

Prof. Ed Newman of the ESL has created a general-purpose MOM code called ESP5 that uses collections of interconnected wires (some with attached “generators”) to describe an antenna geometry.

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One must produce a Matlab code which defines the following for the wire geometry:

Nwrs = the total number of wiresSw(j,i,n) = the x,y,z coor for i=1:3 of endpoint j=1:2 of wire n=1:Nwrs

Nfds = no. of wire feed points (i.e., number of generators)Nfd_wr(nf) = wire for feed nf = 1,2,...,NfdsIfd_end(nf) = end of wire that has feed = 1 or 2Vfd_wr(nf) = mag. of voltage at wire feed nf (volts)phs_wr(nf) = phase (deg.) of voltage at wire feed nf

Note that positive polarity always defined from End j=1 to End j=2.

Initially, we will generate these arrays for a relatively simple geometry.

Prof. Edward H. Newman comments

On generation of FSS array for ESP5

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INITIAL CODE TO GENERATEWIRE SEGMENTS AND GENERATORS

Dr. Walton has begun the process of writing a MATLAB code that defines the 100’s of wire segments that constitute the FSS array antenna.

The first version of that program is done and can be used to create FSS antenna arrays of arbitrary sizes.

The wire segment commands will be used as input to the ESP5 program.

This code will be used to create models of the FSS tri-band antennas and to test:– Antenna Gain Patterns– Transparent Qualities of the array to arrays lower down on

the “stack”– Small (9x9 etc.) arrays will be tested first.

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Initial Testing of the MATLAB code

to generate wire segment geometry

(note the numbered ends of each wire segment)

The red wires are active dipole elements (1/4 λ above FSS ground plane)

cm

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Initial Testing of the MATLAB code

To check the phase of the generators.

Phase (deg) for the driven elements (the generator is at the center of the dipole).

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Initial Testing of the MATLAB code

To check the elevation of the driven elements.

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Use of the ESP5 “Workbench” to generate initial test geometry

The ESP5 Workbench uses a Graphical User Interface (GUI) – Drag and Drop– Select and Click– Quick-look geometry– Automatic interface to ESP5– It is a good place to do a quick test of concepts

BUT:– It is very labor inefficient for an FSS array with 1000’s of

elements

(we are working with Dr. Frank Paynter, the original author of the Workbench)

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Backscatter from 3x3 FSS Array @1690MHz (some initial results)

G:\EricsArray\3x3FSSBackscatter-1690MHz_pat.plt

0 45 90 135 180Theta

-40

-30

-20

-10

0

10

Ma

gn

itud

e (

dB

)Theta-Theta'Phi-Phi'Theta-Phi'Phi-Theta'

Maximum = 3.040000

BASIC GEOMETRY(NOTE SMALL GAPS)

Note (1) the polarization insensitivity to polarization near broadside (Theta = 0)

(2) Cross polarization “too low to see”

polarization

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G:\EricsArray\9x9FSSBackscatter-1690MHz.esp_pat.plt

0 45 90 135 180Theta

-20

-10

0

10

20

30

Ma

gn

itud

e (

dB

)Theta-Theta'Phi-Phi'Theta-Phi'Phi-Theta'

Maximum = 22.090000

Backscatter from 9x9 FSS Array @1690MHz (some initial results)

BASIC GEOMETRY(NOTE SMALL GAPS)

Note

(1) the polarization insensitivity to polarization near broadside (Theta = 0)

(2) Cross polarization “too low to see”

polarization

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The Initial Effort:Generation of a large array using the ToolBox GUI is very difficult. •Frank Paynter is implementing a new command for the ESP Workbench

•to generate a simple FSS •with active layer using parameters input by the user.

•The basic command and dialog box code are implemented (that was the easy part), •Now working on actually generating the wire commands based on the input (that's the hard part).•This command is used to generate the required WRR ESP commands for the basic repeating element

•including the active element•With wire Radius•And with WRC (Wire Coordinates)• used to generate the full array and run the ESP

If this works out we may wish to generalize the effort into a 'FSS Wizard' for the ESP Workbench.The command assumes a crossed-dipole FSS layer with a repeating structure •contains exactly 1/each active element (crossed dipole with generators)•The active element center position is defined relative to the repeating structure center (X, Y & Z). •The active element can be rotated about its center in the X-Y plane. •Dimensions can be meters or free-space wavelengths at the nominal design frequency

Generalized 'FSS Wizard‘ for the ESP Workbench

A new option for Dr. Paynter’s “ESP Toolbox”

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Screen Shot of Dr. Paynter’s Array/FSS Generation Tool

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Screen Shot of Dr. Paynter’s FSS ESP5 Design Tool