Introduction to Antenna Modeling Antenna analysis using the computer. Don Steinbach AE6PM AE6PM Intro_to_Ant_Modeling_R1

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

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

Why Antenna Modeling? Low cost/instant answers Repeatable results 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

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

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

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

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

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

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

Demonstration Launch EZNEC. The Control Center window appears. All I/O is accomplished from this screen. AE6PM

Demonstration Click on the title bar and enter a new name. AE6PM

Demonstration Change the frequency to 14 MHz. Note that the wavelength changed as well. The program did this. AE6PM

Demonstration Change units to feet (was meters). AE6PM

Demonstration Specify the wire x, y, z coordinates and size. X is the direction I’m looking Y is to my left and right Z is up and down XYZ are mutually orthogonal One wire, 30’ high and 33.43’ long. AE6PM

Demonstration Define the source. It’s in the middle of the wire. AE6PM

Demonstration Select the ground type. Was “Free Space”. AE6PM

Demonstration Select the Ground Characteristics. AE6PM

Demonstration This completes the creation of the model. Model inputs AE6PM

Demonstration View the antenna. Rotate, zoom, etc. AE6PM

Demonstration Select the Plot Type output. AE6PM

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

Demonstration But I want to know what the azimuth plot looks like at 15 degrees elevation: AE6PM

Demonstration Select the Source Data output. Negative reactive part indicates that the antenna is too short for 14 MHz (is operating below resonance). AE6PM

Demonstration SWR plot shows that lowest SWR is at 14.45 MHz Cursor AE6PM

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

Real-Life Application Note description of each of seven wires. AE6PM

Real-Life Application View the antenna. AE6PM

Real-Life Application Run SWR plot (7 to 35 mHz by 0.2 mHz). Wire tips spaced 4” Wire tips spaced 18” AE6PM

The End AE6PM