I am making the Printed Yagi-Uda Dipole Array with Balun (that is the full name). I used Antenna Magus to calculate dimensions. I am not sure how to properly connect it to coaxial cable.
Here is what the antenna looks like:

Printed Yagi-Uda Dipole Array with Balun

In the Feed Method it states:

Feed Method

The printed Yagi structure requires a balanced feed. Typically, however the antenna is fed using an unbalanced coaxial cable and a balun is required to provide the required balanced feed.

An integrated balun structure is taken into consideration in the Antenna Magus design procedure and the Antenna Magus export models include a co-planar quarter-wave balun construction. If a coaxial cable is used, the outer conductor is simply soldered along the one line of the balun from the reflector element all the way to the driven element. At this point the inner conductor is extended across the gap of the driven element and soldered onto the opposite arm.

The antenna could be fed using a balanced source or a different balun construction. (Note that for these cases, the balun design will need to be done independently of Antenna Magus, and the co-planar balun structure may need to be removed from the export models for simulation purposes.)

Does the image below show the correct way of connecting coax to the antenna?
Orange dots are solder spots.
Printed Yagi-Uda Dipole Array with Balun Feed method
I do not have much experience making antennas.


1 Answer 1


I'm no expert on balun designs, but I think they mean to construct a folded balun, as follows. The coax's outer conductor is soldered to the same part of the antenna, but it is left on the coax, not peeled away, so the final balun structure includes a length of the coax.

(The interpretation you proposed in your question is unlikely because if the outer conductor is separated from the coax, attaching it along the length of the trace won't function any differently from a single-point junction.)

When soldering, make sure not to melt the dielectric in the coax:

  • Perform the soldering quickly, so the heat does not spread.
  • Do not use foam-dielectric coax.
  • $\begingroup$ @PhilFrost Thanks for the confirmation. I actually considered that that was what was going on, but that very site confused me with the “cylindrical tube” part (I thought they were poorly describing something more like a sleeve balun). Which isn't exactly what is going on here, but presumably close enough. $\endgroup$
    – Kevin Reid AG6YO
    Feb 8, 2015 at 17:35
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    $\begingroup$ They say that because for this balun to work, the impedance of the two vertical bits must be equal, so they can have equal magnitude but opposite currents, so they can cancel. If the shapes of the vertical bits aren't identical, then the impedances will be unequal. In this case it could probably be made better by adding another piece of coax parallel to the feedline to give them the same shape, but then you are kinda missing the point of a printed balun: simple fabrication. $\endgroup$ Feb 8, 2015 at 17:38
  • $\begingroup$ In other words, it's a tradeoff between fabrication complexity and performance. As long as the coax is small in size compared to the width of the printed traces, it shouldn't make too much difference. $\endgroup$ Feb 8, 2015 at 17:41
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    $\begingroup$ Use thin PTFE coax like RG316 for this, it doesn't melt at soldering temperatures. Put in a dummy coax if you're worried about balance, and also, make a last zigzag and exit the antenna in the centre, not offset to one side. $\endgroup$
    – tomnexus
    Feb 8, 2015 at 19:48

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