This document provides an overview and instructions for using Yagicad, a software program for designing Yagi, quad, and quagy aerial antennas. It describes the key features of Yagicad, including entering or modifying antenna designs, optimizing designs, estimating matching units, and analyzing performance characteristics. The document also cautions that Yagicad results should be validated experimentally and notes limitations of the theoretical models used.

1. YAGI COMPUTER AIDED DESIGN
by Paul McMahon VK3DIP
Version 6.0 December 2009
Copyright Paul McMahon 1991,1992,2003,2007,2008,2009.
This file is in rich text format in YC60HLP.rtf and may be printed if required.
WHAT IS YAGICAD?
Yagicad is a fully integrated analysis and design package for Yagi, quad, and quagy,
aerials.
WHAT CAN YAGICAD DO?
With Yagicad it is possible to enter a base design from scratch or use one of a number of
saved well known designs. This design can then be optimised or scaled to suit particular
requirements. Once this has been done a matching unit can be estimated and overall
performance characteristics can be calculated and displayed graphically. Also available are
radiation patterns and hardcopy print-out of results. Allowances in an analysis can also be
made for element cross sections other than simple circular ones, as well as boom mounting
techniques.
DEFAULTS AND SUGGESTIONS.
Whenever YAGICAD prompts you for some value it will suggest a value that based on past
experience may be suitable. These values can be over written if required.
AN EXAMPLE.
The operation of YAGICAD can be most easily understood by studying an example.
Suppose you are interested in a Yagi for two metres.
1. Get the base design by either typing it in using the Add Element menu item under the
Edit menu or use one of the saved designs and choose a design that is close to your
requirements.
2. Say you choose to use the saved NBS 6 element design. So, you load (using File,
Open) the NBS6.YAG file.
3. If, as in this case, the saved frequency is not what is required then you can quickly scale
the design roughly to the new frequency say 147 MHZ using the SCALE function under
the Toolbox menu. You could also have changed the element diameters to some new
value if desired also using the SCALE function, or even allowed for non-circular cross
section elements by using an EFFECTIVE DIAMETER. These also are found under the
Toolbox menu. CALCULATION options are "L" shaped, rectangular, or folded dipole.
You could have also edited the saved data using either the EDIT menu Functions, or
just double clicked on the item to be changed or to add or delete an element etc.
4. You could then do a BASIC calculation (Calculation Menu) to determine the gain, front
to back, etc., for this new design. Graphs of pattern and other features are also available
under the Calculation menu.

2. 5. The design could now be optimised for MAXIMUM FORWARD GAIN, (FRONT TO
BACK, RESONANCE of the DRIVEN ELEMENT, or MINIMISE LARGEST SIDELOBE
could also have be chosen). This is done by selecting the appropriate entry from the
AUTO area under the CALCULATION menu and selecting the value to be varied, i.e. a
spacing, or a length. A powerful genetic multi parameter optimization option is also
available for say wideband optimisation. i.e. OWA of the design to say optimise several
attributes at once over a range
6. Steps 4 and 5 are repeated as many times as is necessary. When satisfied you could do
a SWEPT FREQUENCY RESPONSE to see how the design performs over a range of
frequencies.
7. Assuming all is OK you could now proceed to calculate a matching network for your
design. You select MATCH from the TOOLBOX and say decide to use a FOLDED
DIPOLE. (GAMMA, or TEE matches, or many others could also have been used). Let us
say you are going to use a 4 to 1 coaxial balun with 50-ohm coax i.e. the required input
impedance to be matched is 200 ohms. The program gives you the required diameter of
the folded part of the element. If you had chosen to use a gamma match, then it may
have been appropriate to RESONATE the driven element to some negative (Capacitive)
reactance. A figure of say -15 to -20 Ohms has been found to give better results than a
true resonance i.e. 0 Ohms.
8. You could now get an OVERALL RESPONSE of the design including the effect of the
matching network, but it would be best to allow for the folded dipole by first
CALCULATING its EFFECTIVE DIAMETER and EDITING in the new effective diameter
of the driven element. Steps 6,7, and 8 could then be repeated to ensure that nothing
untoward has happened. The final resultant plot as with all other graphics can be either
printed out (File, Print) or copied to the clipboard for pasting into some other program.
The option is also given to save the numerical results of the plot to a .CSV file (File,
Export) if you wish to say use a spreadsheet graphing capability instead.
9. You may now wish to allow for a metallic boom. This is done using the BOOM item in
the TOOLBOX. The values suggested by YAGICAD allow for the element being
mounted though the centre of a circular cross section metal boom with good electrical
contact. (Classic option) or insulated through boom using the G3SEK formula. You can
allow for non-circular booms with the EFFECTIVE DIAM's tool.
10.It would be a good idea to investigate the effects of varying the parameters and type of
the mathematical model used to calculate the Yagi's performance. A large number of
variations are available via the Options menu. In general, the SX model is probably the
least accurate (but fastest) and increasing the number of segments used on the NEC2
model should produce a better result. Please however note the caveats and warnings
below.
11.When satisfied the results can be printed out using the File, Print function.
12.Finally, the new design can be saved to disk for possible future use using the File, Save
option. In fact, if you come up with some particularly good design why not send the data
file to a friend using packet or put it on the web.

3. You could now build the Yagi feeling reasonably sure that it will behave at least close to the
calculations.
WHAT YAGICAD WILL NOT DO.
THIS PROGRAM IS BASED ON A THEORETICAL MODEL OF A YAGI ANTENNA, MANY
ASSUMPTIONS AND SIMPLIFICATIONS HAVE BEEN MADE. THE RESULTS OBTAINED
WITH THIS PROGRAM MUST THEREFORE BE TAKEN WITH SOME CAUTION. IN
OTHER WORDS, IF YOU BUILD AN ANTENNA THAT HAS BEEN DESIGNED WITH
YAGICAD DON'T EXPECT TO GET IT WORKING EXACTLY AS CALCULATED
WITHOUT AT LEAST SOME EXPERIMENTAL ITERATIONS. IE. YAGICAD IS NO
SUBSTITUTE FOR A VSWR METER ETC., AND AT LEAST SOME TRIAL AND ERROR.
ANYONE WHO DOESN'T AT LEAST USE A VARIABLE CAPACITOR OR HAVE SOME
MEANS OF VARYING A GAMMA ARM LENGTH IS EXPECTING TOO MUCH FROM
THIS OR ANY OTHER ANTENNA PROGRAM.
Some common sense should also be exercised when optimising designs once you are in
the area where YAGICAD is varying lengths or spacings by less than a millimetre. Sure,
extra gain is being obtained but you will have to fine tune your final antenna with a nailfile,
so be practical and you will get results that are close to calculations.
YAGICAD is limited to Yagi’s with less than 24 elements.
EXPERIMENTAL VALIDATION
Notwithstanding the very important caution above, YAGICAD has been around in various
versions for some 14 or so years. In this time, I (VK3DIP) alone have built dozens of
different yagis as designed by the various versions of this program. Others have built many
more. In all cases known to me the antennas did work more or less as designed. Adding
NEC2 to the program can only make this agreement closer and give more indication of
what is likely to happen.
My original motivation for the program was to be able to design antennas that would be
good for Two Metre Fox Hunting, as opposed to the maximal gain type usually detailed in
books etc. So, I have also had quite a bit of testing of patterns and there is no doubt that
the Yagis designed with this program have patterns much like those calculated.
TESTING THE MODEL WITHOUT BUILDING IT
One way of getting more confidence in the results given by YAGICAD is to check for
variation of those results as you vary the Model Options, or even just the element lengths. If
for example there is a wide difference between the result given by the Classic Model verses
NEC2, then while NEC2 is probably much closer to the truth (assuming you have sufficient
segments selected) the chances are that the design is going to be more difficult to realise in
practice and is probably not for the novice builder. In a similar way as mentioned before,
designs where fractions of millimetres in lengths or spacings make dB's of difference, will
not perform as predicted in a real world with things like weather, birds, and common
materials and construction techniques.

4. If however your design does not have a great sensitivity to small changes then you can
probably build it with more confidence that it will come out as expected.
DISCLAIMER
In no event or way will the Author be responsible or liable for any damages, including any
lost profits, lost savings or other incidental or consequential damages arising out of the use
of or inability to use these programs, even if the Author has been advised of the
possibility of such damages, or for any claim by any other party.
YAGICAD 6.0 is FREE
Unlike the very early versions of YAGICAD which were released under a shareware banner
(not that I ever made any money out of them) version 5.0 and on are presented free. I offer
it to the worldwide community of antenna experimenters in part repayment for the advice
and invaluable input I have received from them over the years. It is my hope that it will be
useful to them and also help to introduce new people (and especially radio amateurs) to the
joys of antenna experimentation. I do however retain the copyright, and if someone wanted
to include this program in some book or software collection I would appreciate being at
least asked first. I can be contacted at the addresses below. Similarly, if you have any
comments or feedback please feel free to email me. I can't guarantee a speedy reply, but I
probably will get there eventually
PAUL McMahon VK3DIP
47 PARK AVENUE WATTLE GLEN
VICTORIA AUSTRALIA 3096
EMAIL - vk3dip@yagicad.com <mailto:vk3dip@yagicad.com>
WEB - <http://yagicad.com>
CREDITS
This program could not have been what it is without the following:
Ham Radio Magazine
A sadly missed source of things technical. Over the years I have never missed a May issue.
In particular the articles by Lawson in the early 1980's. Joe Reisert, and Bill Orr for the
many snippets here and there.
YAGICAD Users.
The feedback from users is always appreciated.
73 and good designing PAUL McMahon VK3DIP.