Introduction to Antenna Modeling Antenna analysis using the computer. Don Steinbach AE6PM

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Introduction to Antenna Modeling Antenna analysis using the computer. Don Steinbach AE6PM Santa Clara County Amateur Radio Association November 8, 2010. What is Modeling?. Using a computer program specifically designed to predict performance Not perfect Cost effective - PowerPoint PPT Presentation

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AE6PMIntro_to_Ant_Modeling_R1

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Introduction to Antenna Modeling

Antenna analysis using the computer.

Don Steinbach

AE6PM

Santa Clara County Amateur Radio Association

November 8, 2010

AE6PM 2

What is Modeling?

• Using a computer program specifically designed to predict performance– Not perfect– Cost effective

• Much cheaper than building hardware– Instant answers– Can give misleading results

• Garbage in, garage out

• Tool widely used by engineers– Spacecraft thermal– Weather– Propagation

AE6PM 3

Why Antenna Modeling?

• Predict antenna performance and electromagnetic parameters– Gain

• Far-field radiation pattern in azimuth and elevation– Impedance at the feed-point– Current distribution in the elements– Near-field E and H field intensity

• Evaluate effect of changes in configuration– Antenna

• Conductor size & type• Elevation (height above ground)

– Physical environment• Local ground characteristics

AE6PM 4

Why Antenna Modeling?

• Low cost/instant answers– No wire to buy, no beams to build– No towers to erect– All paper, no hardware

• Repeatable results– Propagation not a factor

• Independent of weather, sunspots, etc.

The average ham can’t measure anything about antenna performance except the swr and feedpoint impedance.

AE6PM 5

Software Available

• EZNEC-ARRL (Included with the ARRL Antenna Book @ $39.95)

• Antenna Model ($85)*• EZNEC v5.0 ($89)*• NEC-Win Plus ($150)*• NEC-Win Pro ($425)*• EZNEC-M Pro ($450)*• EZNEC/4 ($600, must have license)*• GNEC ($795)*

*Ref: The ARRL Antenna Book, 20th Edition, page 4-2. “Commercial Implementations of MININEC and NEC-2 Programs.”

AE6PM 6

EZNEC-ARRL

• A version of EZNEC 3.0 that’s included on the Antenna Book CD-ROM– Provided by Roy Lewallen, W7EL

• Works with the specific antenna models that are also bundled on the CD-ROM– There are about 400 of them, many based on antennas in

the book– They can be modified by the user

• Works with your user-specified inputs as well– Can’t save the input data (Description) file

AE6PM 7

EZNEC-ARRL

• User input is limited to a maximum of 20 segments– Typically enough for a dipole or a two-element beam– EZNEC 5.0 allows 500 segments (1500 in the + version,

20,000 in the Pro version)

• Antenna Book models are not constrained to 20 segments– High fidelity analysis even with user modifications

AE6PM 8

EZNEC-ARRL

• Great learning tool, especially when used with existing (provided) antenna models

– Many to choose from– Easy to modify

• Downside is not being able to save your input data (Description) files

– Not a big deal for everyone, but was for me– Data entry is time consuming and error prone– Not convenient for “what-if” or parametric analyses

AE6PM 9

Typical Program Inputs

• Three dimensional (x, y, z) description of each “wire”• Number of segments in each wire

– At least 10 per half-wavelength

• Conductor type and size• Placement and type of the driving source• Frequency• Ground/soil characteristics• Loads/loading coils• Transmission lines, transformers, networks

AE6PM 10

Typical Program Outputs

• Source (driving point) impedance• Power gain• SWR graph• Far-field azimuth and elevation plane patterns• Polarization• RF current distribution• Rotatable, zoomable 3-D views of the model

AE6PM 11

Demonstration

Launch EZNEC. The Control Center window appears. All I/O is accomplished from this screen.

AE6PM 12

Demonstration

Click on the title bar and enter a new name.

AE6PM 13

Demonstration

Change the frequency to 14 MHz.

Note that the wavelength changed as well. The program did this.

AE6PM 14

Demonstration

Change units to feet (was meters).

AE6PM 15

Demonstration

Specify the wire x, y, z coordinates and size.

One wire, 30’ high and 33.43’ long.

X is the direction I’m lookingY is to my left and rightZ is up and downXYZ are mutually orthogonal

AE6PM 16

Demonstration

Define the source. It’s in the middle of the wire.

AE6PM 17

Demonstration

Select the ground type. Was “Free Space”.

AE6PM 18

Demonstration

Select the Ground Characteristics.

AE6PM 19

Demonstration

This completes the creation of the model.

Model inputs

AE6PM 20

Demonstration

View the antenna. Rotate, zoom, etc.

AE6PM 21

Demonstration

Select the Plot Type output.

AE6PM22

Demonstration

Select the Far-Field plot output.

Cursor position

Note that the gain is in dBi. Subtract 2.15 dB to convert it to dBd.

AE6PM 23

Demonstration

But I want to know what the azimuth plot looks like at 15 degrees elevation:

AE6PM 24

Demonstration

Select the Source Data output.

Negative reactive part indicates that the antenna is too short for 14 MHz (is operating below resonance).

AE6PM 25

Demonstration

SWR plot shows that lowest SWR is at 14.45 MHz

Cursor

AE6PM 26

Real-Life Application

• Given:– Fan-dipole antenna for 40/20/10 meter bands.– Inverted V, center 30’ high. End attach points 8’-6” high, 28’-

6” and 19’-6” from center support.

• Wanted:– What’s the effect of rotating the elements downward?

• How long do the elements need to be compared to a single horizontal dipole?

– What’s the effect of the spacing of the wire ends from its neighbor?

– How does 15 meters look?

AE6PM 27

Real-Life Application

Note description of each of seven wires.

AE6PM 28

Real-Life Application

View the antenna.

AE6PM 29

Real-Life Application

Run SWR plot (7 to 35 mHz by 0.2 mHz).Wire tips spaced 4” Wire tips spaced 18”

AE6PM 30

The End