Just to be precise: it is NOT resonant!! Resonance requires that there
be a zero value for the j term. The +j10.3 indicates your antenna DE is
a little long for the measured frequency.

Richard wrote:

The yagi is centered on 159 Mhz with a bandwidth of 6 Mhz.

The feed is 50ohm coax.

The DE is a simple hertz dipole. It's electrical parameters at the resonant
frequency are R 50.9 J + 10.3.

What kind of balun would you use? TIA.