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Last update
05.03.2004
A Double Quad Antenna for 1296 MHz
This antenna is a medium gain directional antenna for mobile (portable) and base station use. I have built it many years ago for mobile operation to check out how good the signal of the ATV Relais DB0SCS is received in the villages around Schwabach (the QTH of the Relais). I found a similar type for 432 MHz in the literature and decided to calculate the dimensions for 1296 MHz. For the 432 MHz antenna a gain of more then 10dBd was mentioned. This seems reasonable for the size of the antenna. I was always satisfied with the antenna and a direct comparison to other antennas of a know gain showed that it really has to a have a gain of about 10dB over a dipole.
This antenna type has a number of advantages over a yagi antenna with the same gain:
It is easy to build, the size of the driven element is not highly critical
An optimal VSWR can be achieved by varying the distance to the reflector
Due to the geometry the antenna can be handled more easily at mobile or portable operation
Just like for a quad antenna for short wave, a balun is not absolutely necessary
The antenna covers a wider frequency range than an average yagi
Now have a look at this plan. All sizes are in mm. The antenna is made of copper wire with 1mm diameter (not highly critical). I leave it to your fantasy how to fix the reflector to the driven element. (I soldered it together via two 1 Megaohms resistors and put a bunch of liquid plastic over it.) I is even ok to solder it together without insulation at the top and bottom of the driven element since this are the points of maximum current and zero voltage. But due to the fact that we are not using a balun, the current maximum is not exactly at these points so we would short circuit a little bit of the antenna signal.
