2 Meter Antennas with Different Radiantion Patterns and Why
So what you are seeing here are two handheld 2 meter 3 element yagi antennas, and although they are for working on the 2 meter band, ,I designed and built them for different purposes.
The yagi on the left (ANTENNA 1) is a tape-measure yagi with a break-down fiberglass boom, and the yagi on the right (ANTENNA 2) is built from high tensile anodized aluminum tubing that is assembled by the use of double-start threads on the elements and the boom.
Both these antennas have similarities, and they both can be used for the same purposes, although they both have different strengths and weaknesses depending on the application.
ANTENNA 1 was designed and built to be a direction-finding antenna with the use of an HT and attenuator, and the tape-measure elements allow you to push your way through brush and what-not without any damage occurring to the antenna.
ANTENNA 2 was designed and built for staying connected at maximum range while in the back-country or mountain-topping with the use of an HT or other QRP transceiver.
I have built many different take-down 2 meter 3 element yagi designs over the past 20 years to allow me to connect to my mobile when I am fly-fishing on a mountain stream, and on most days your typical HT with its rubber-duck antenna will not allow this to happen due to the terrain or the distance from my mobile or a distant repeater.
ANTENNA 1 trades a bit of forward gain in exchange for a deep notch in the pattern toward the rear.
This characteristic allows this antenna to easily get a fix on a hidden transmitter off the front of the antenna, and ignores any signals potentially being heard off the back of the antenna adding confusion as to the direction of the target.
ANTENNA 2 has more gain than ANTENNA 1, but this antenna hears more signals coming in on the back side of the antenna, that could lead to confusion as to the direction of the hidden transmitter if the antenna was used for direction finding.
What I'm saying is both these antennas have different front to back ratios, and you may be asking how the two antennas allow for this.
Expand the photo and look close at the two antennas pictured here, and you will notice the distance between the director at the front of either antenna, and the reflector at the rear of either antenna are the same distance apart.
Where the difference comes in is the placement of the driven elements of either antenna.
ANTENNA 1 has its driven element placed closer to the reflector at the rear of the antenna, while ANTENNA 2 has its driven element placed further away from the reflector and closer to the director at the front of the antenna.
Both designs were modeled with EZNEC antenna modeling software to arrive at the required dimensions for their intended purposes.
If you were to look at a 2 meter handheld Arrow antenna (not pictured here), very popular with those of us that like working satellites, you would find that it has measurements that closely mirror ANTENNA 2.
That is because the Arrow antenna was designed to work satellites coming up over the horizon with an HT, and maximum gain is required to make this happen.
Still any of the 3 antennas can be used for purposes other that their entended purposes, just not as efficiently.
Click on the photo for a closer look.....