antenna-theory.com

[JET]

Hi,

I want to make a PCB antenna for 868MHz. Assume that I make a PCB monopole with a 70 x 70 mm ground plane and a straight trace of approx. 1/4 wavelength.

I would like to first adjust the length of the antenna trace so that it becomes as most efficient at 868 MHz as possible and then add a matching network to match it to 50 Ohm.

I have a VNA, but how do I know when the antenna length is optimized?

Shall I adjust the length until the imaginary part of the impedance is zero and then add matching to get it to 50Ohm?

Or shall I adjust the length until the impedance is close to 36.5 + j21.25 and then add matching to get it to 50Ohm?

Or something else?

[admin]

I would look at VSWR (Scalar measurement). Trim the length until the vswr minimum resonance is at 868 MHz. Then if the match needs further improved do the impedance matching then.