Antenna Modeling for Beginners - Supplemental Information
The following material supports the book "Antenna Modeling for Beginners". It contains supplementary information including references and tutorials.
The author's presentations at the 2013 Dayton Hamvention may be downloaded as PDF files by clicking the following links:
Antenna Modeling - Getting Started (basic guidelines)
Antennas 101 - The Basics (fundamental terms and concepts)
Note: For questions about how to use EZNEC in support of the book's exercises and instructions, first review the information on this web page. If you do not see the answer to your question here, contact firstname.lastname@example.org, not the EZNEC author.
If EZNEC does not load the Backyard Dipole model when first run, switch to that model by using the Open action button and selecting Backyard Dipole from the list of available models (you will probably have to scroll up and down in the browse window to find it). With the proper model loaded into EZNEC, either exit and restart or use the Save As action button to save the file with the name LAST and you'll be ready to go as Section 2.1 expects.
Making Connections Between Wires
The Exercise that begins on page 2-6 instructs the reader to "Connect End 1 of the new Wire 2 to End 2 of the existing dipole wire by entering "W2E1" in the End 1 cell for Wire 2 and tabbing to the Y cell." First, you should enter "W1E2", not "W2E1". (Thanks to G3OUA for pointing that out!) Now, to be able to enter "W1E2", the cursor should be in the End 1 X cell for Wire 1 and not in the Conn cell. Nothing can be entered in the Conn cell - EZNEC displays information there but it can not be edited. Wire connections such as "W1E2" can be entered in any of the X, Y, or Z cells for a Wire End.
For example, after creating Wire 2, place the cursor in Wire 2's End 1 X cell and enter "W1E2". This will connect End 1 of the new wire you just added to End 2 of Wire 1.
If you are adding and connecting multiple wires, such as in the exercise at the beginning of Chapter 5 in which a square loop is made, don't be afraid to experiment - keep the View Antennas window open in order to see the effects of each action you take. Or it may be simpler to add just one wire at a time and connect it. If you don't get the results you expected, either edit the information entered for each wire or delete the wire and try again. (Thanks to Jerry KM3K for these and other suggestions)
The coordinate systems in the text are often referred to as "right-handed" in which if the fingers of the right hand are curved to point from the +X to the +Y axis, the extended thumb will point in the direction of +Z. This is also known as the "right-hand rule".
For spherical coordinates, math and physics texts use a convention in which the angle phi has a value of zero along the +Z axis (straight up) and increases in value toward the XY plane. Engineering and amateur radiation patterns use an elevation angle instead in which 0 degrees represents the XY plane (the horizon) and increases toward 90 degrees at the zenith (straight up). The inevitable confusion is regrettable but the two conventions are well-established.
- Antenna Modeling EZNEC tutorial by Greg Ordy, W8WWV for intermediate users
- Comprehensive website of LB Cebik, W4RNL (Silent Key) - requires signup to access (previously free but recently converted to a subscription services with the antennex.com online magazine), hundreds of useful tutorials, models, and antenna design notes.
- Basic Antenna Modeling: A Hands-On Tutorial - a modeling course by LB Cebik, similar to Antenna Modeling for Beginners but written assuming a higher level of background. This course might be appropriate once the material in Antenna Modeling for Beginners is understood.
- EZNEC User's Manual for version 5.0
EZNEC Model Collections
Note that most models you find online and CD-ROM will be designed for the fully-functional version of EZNEC that allows many more segments than the demonstration version. You will have to reduce the number of segments in the View Wires window, resulting in a less accurate simulation as noted in the book. Nevertheless, these models can be viewed, edited, and used as a basis for simple designs and they are good practice for learning how antenna models are constructed.
- ARRL Antenna Book - includes a collection of EZNEC models as well as EZNEC-ARRL, a limited free version of the current EZNEC software with somewhat more capability than the demo version.
- See the link to the LB Cebik website in the preceding section
- Antennex compilation of models from LB Cebik
- DF9CY collection of HF and VHF antenna models
- ARRL Antenna Book - A comprehensive handbook covering antennas, transmission lines, and equipment used in antenna systems.
- Basic Antennas by W1ZR, published by the ARRL - a good collection of articles about how antennas work and simple designs
- HF Antennas for Everyone by G1MFG, published by the Radio Society of Great Britain (RSGB) - a collection of useful and simple designs suitable for the beginning modeler
- Antenna for VHF and Above by G3YWX, published by the Radio Society of Great Britain (RSGB) - covers basic antenna designs that work well at short wavelengths through microwaves
- ARRL Antenna Classics series - a series of books containing time-tested antenna designs for HF through microwave antennas. Search for "classics" from the ARRL Store home page.
A collection of online math tutorials for various topics
An advanced Tutorial on Coordinate Systems by Associate Professor, Dan Fleisch of Wittenberg University
Reactance and Impedance - a set of tutorials on ac circuits that explain what impedance is and why complex numbers are used to describe it. The Hyperphysics web site also offers tutorials on impedance.
EZNEC creator, Roy Lewellan W7EL contributes some additional discussion on MININEC:
MININEC was written by Jim Logan and Jay Rockway. Although it uses the same general method as NEC (the method of moments), its formulation is different and it isn't a derivative of NEC. I've been through the code
of both programs in great detail, and see no commonality in any part of the programs.
> Was MININEC's ground model based upon an early version of NEC?
NEC includes three types of ground model -- perfect, reflection coefficient, and Sommerfeld. MININEC has only the first two, but with the difference that the ground is assumed perfect during impedance and current calculation. Although the reflection coefficient calculation is essentially the same in both programs, it's not at all unique or complicated.
The MININEC type ground in EZNEC imitates the ground model in MININEC -- perfect ground conductivity when calculating impedances and currents, but using user-defined conductivity and permittivity when calculating reflections to get the total field.
Page 2-4 - This part of the exercise is only to show you the Antenna Notes window and not actually enter any new text. You can view the Antenna Notes window without saving any new text by clicking the No button. This will save the model with the new filename of TestDrive. If you do wish to enter some text, use the Save button. If you click the Cancel button as instructed, the entire Save As operation will be ended without changing the filename.
Page 2-6 - The exercise instructs the reader to "Connect End 1 of the new Wire 2 to End 2 of the existing dipole wire by entering "W2E1" in the End 1 cell for Wire 2 and tabbing to the Y cell." That should be "W1E2", not "W2E1". (Thanks to G3OUA for pointing that out!) Also, the cursor should be in the End 1 X (or Y or Z) cell.
Page 2-7 - In the second full paragraph, the correct Z coordinate is 40, not 34.7.
Page 2-13 -In the paragraph beginning "The specifications for the pattern..." change the elevation angle reference from 0° to 30° in the first sentence.
Page 3-6 - In the first exercise the value used for the antenna's gain at 90 degrees should be -30 dBi, not -3.45 dBi. That results in the correct value for F/S of 7.55 dBi - (-30 dBi) = 37.55 dBi.
Page 4-8 - The value in the denominator of the equation at mid-page should be 28.25, not 28.5. This changes the amount of wire to remove from 0.61 feet to 0.59 feet. The adjusted length of the antenna then changes from 16.81 to 16.83 feet and the SWR minimum frequency will still be close to 28.3 MHz.
Page 5-2 - The SWR minimum of the loop should occur between 28.7 and 28.8 MHz, not 27.7 and 27.8 MHz.
Page 8-2 - The formulas for reactance (at the end of the exercise) and inductance (at the bottom of the page) are more clearly understood if the parentheses are inserted as follows:
Xc = 1 / (2 x pi x f x C)
L = XL / (2 x pi x f)
Page 8-12 - In the first full paragraph, the "Stepped Dia Correction in use" message may not display depending on the order in which the EZNEC action buttons have been used. If the message does not show, use the SWR action button instead.
Page 9-6 - In the first paragraph of the section Wires Too Close Together, the separation of the two wires that creates interpenetration should be 1/2 inch not 1 inch.
Figure 9.7 - The figure was created with the antenna's center at the origin instead of as shown by the data in Figure 9.8. If you start with the Inverted V model, the instructions result in the wires being arranged as in Figure 9.8 which offsets the center of the antenna 60.35 feet to the right along the X-axis.
Figure 10.2 - The value of the Frequency Step (MHz) data should 0.5 not 0.05. If 0.05 is entered, 41 patterns will be generated instead of the desired 5.
Appendix A, Figure A.1(B) - Exchange the labels X and Y and change the coordinates of the labeled point to (2,3,2). The caption should note that the axes have been rotated around the Z axis so that the positive X, Y, and Z axes are visible to the viewer.
Appendix A, Figure A.2 - Exchange the labels "YZ plane" and "XZ plane". The caption should note that the axes have been rotated around the Z axis so that the positive X, Y, and Z axes are visible to the viewer.
These two changes preserve the same "handed-ness" of the X, Y, and Z axes as is used in the rest of the book.
Page A-2 - Following the changes to Figures A.1B and A.2, the final sentence of the second full pararaph should read, "In Figure A.1B, the indicated point's location is 2 units along the X axis, 3 units along the Y axis, and 2 units along the Z axis."
Page A-3 - In the section "Azimuth-Elevation and Spherical Coordinates", delete references to the Greek letters theta and phi, including those in the caption to Figure A.5. In the context of this book and antenna modeling in general, it is only necessary to refer to azimuth and elevation angle. The spherical coordinates of a point should be shown on page A-4 as "(radius, azimuth, elevation)".
Page A-5 - In the paragraph beginning "When the CCW from X Axis convention..." exchange "clockwise" with "counterclockwise" and vice versa. Angles in the normal convention (CCW from X Axis) increase counterclockwise from the +X axis toward the +Y axis. The author regrets letting this mistake slip through and apologizes for the unnecessary confusion.
Page B-2 and B-3: to enter a negative value in the second and sixth bullet points, the key label may be either ± or +/- depending on your version of the calculator program. Similarly, the x^y and xy keys are equivalent. Where the instructions refer to pressing enter, clicking the = key is equivalent.
The directions for calculation of power are incorrect. The order of entering -0.2 as an exponent and raising 10 to that power are backwards. The correct instructions are as follows:
- Click the 1 key followed by the 0 key and press enter (or click =). The display in Figure B.1 should show a value of 10.
- Click the xy key.
- Click the 0 key followed by the . key followed by the 2 key. Then click the ± key.
- Click the = key.
The display should show 0.63095734444 and the remainder of the exercise is correct.
The formula being evaluated is: Fraction of Power Remaining = 10 (dB / 10) = 10 (-0.2) = 0.63 = 63%.