By Joseph H. Reisert
Until recently, most engineers designed antennas by experience
and a certain amount of "black magic". A basic understanding
of impedance matching and the various matching methods to accomplish
a good match over the desired frequency range were required.
A good understanding of mechanical engineering principles was
a plus as well as not minding tinkering, doing "cut-and-try",
gluing and screwing parts together until the design met the desired
However, after the prospective antenna was designed
and built, there always remained the question of
how well the gain and radiation pattern held up
over the desired bandwidth. If an antenna test
range was available (a real plus), more testing
time was spent trying to verify that all design
criteria was met. Next, if all went well on the
final testing, the prospective antenna would be
transferred to the production department. Finally,
the production antennas would be tested to verify
that the design could be duplicated. Needless to
say, this was a very expensive and time consuming
Those days are gone forever. We live in a competitive
market where time and performance are critical.
Guesswork and long design cycles are out of the
question. New state-of-the-art (SOA) antennas are
required that meet all the design criteria for
sophisticated applications that may involve large
quantities at competitive cost.
In the mid 1960's, main frame computers were finally
large and fast enough to do antenna modeling. However,
it still requires an astute antenna design engineer
with a good analytic mathematical background to
write the equations and computer programs to model
In the 1970's, the NEC (Numerical Electromagnetic
Code) program was developed by the US government.
This program was very accurate but difficult to
use and required a large main frame computer. Furthermore,
its use was restricted by the government.
This all changed in the mid 1980's when PCs (personal
computers) became widely available. Soon there
were several antenna modeling programs available.
The primary one was MININEC, a smaller program
based on NEC that runs fast on a PC. Also, a PC
version of NEC became available.
As PCs increased in speed, so did the antenna
modeling programs. At first, it was not unusual
to wait 60 seconds or more for the analysis of
an antenna. Nowadays, PCs with Pentium (RTM) processors,
can model that same antenna in just seconds.
These powerful modeling programs allow the antenna
designer to use keystrokes on a PC keyboard instead
of getting their hands dirty from hours of cutting
and testing the actual antenna. Furthermore, the
performance goals can be tested before any actual
antenna is constructed. You can now "cut-and
try" an antenna design for maximum gain, front-to-back
ratio, impedance, or a combination of the three
by changing element lengths, diameters and spacings
using only a keyboard. This significantly shortened
the design to completion of the production antenna.
Modeling programs do not design an antenna per
sé. They only "test" in software
how the inputted antenna design should perform.
Modeling programs leave it up to the ingenuity
of the antenna designer to "tweak" or
optimize the mechanical dimensions until the desired
antenna performance is attained.
In the mid 1990's, optimization programs became
available for PCs. These programs will perform
the optimization for you. All you need to do is
to input a reasonable design along with a properly
weighted trade-off or Figure-of-Merit (FOM). The
FOM weighs the relative importance of each antenna
parameter such as gain, pattern and impedance over
a set of input frequencies and out comes a design.
The above may give the impression that antenna
design is no longer a "black art". While
this may be true, it still requires a lot of knowledge
and understanding of the interrelated parameters
in an antenna design as well as the FOM. In fact,
as the antenna designs of today get more complicated,
so does the work of the antenna designer.
The antenna modeling and optimization programs
available today do not completely compensate for
all variables. The output data file must be properly
interpreted by the user. Sometimes the tolerances
of the element dimensions may be difficult to realize.
Element correction factors may still be required
to compensate for the mechanical mounting of the
antenna elements. This is where the antenna designer
comes in to play. He or she must be able to realize
what designs can and can't be built as well as
any compensations that are required.
In summary, Astron Wireless Technologies, Inc.
engineers now have better design tools with which
to work. Computer modeling and optimization software
are a very big step forward in designing SOA antennas.
In fact we utilize one of the most advanced software
programs in the industry made by Ansoft. It is
called the High Frequency Structure Similator
(HFSS) program. Regardless of the software programs, the
proper design requirements must be supplied by
the user (Ref. 1.). This is where the professional
antenna designer can step in and provide the optimum
design based on your inputs.
Wireless Technologies, Inc. and the author retain the rights
to all intellectual
This information should be used as a guideline
only to help you in the appropriate selection of an antenna.
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