David, Simulation will not help too much. A good simulation can be 50% away from the crude reality and that one is good simulation! Workaround: - separate the antenna area to the rest of your circuit with an air gap in the PCB. However this will not help if your antenna is too close from your circuit, preserve at least a lambda/4 (better more) open space around your antenna. You didn't say what type of antenna do you have... a 0dBi or a -xdBi SMD antenna is actually not an antenna... - check if your ground area is below or intersect some active path of the antenna, this usually will not help. - check the delay of you feeding line, on the antenna you should usually have the max. RF voltage - is your antenna impedance matched with the PCB feeder and with the amplifier output? On Thu, Jul 31, 2014 at 6:44 PM, David VanHorn wrote: > I am doing a lot of PCB trace antenna design lately, and I am seeing > another occurence of something that I had seen before, where a given > antenna design that should be workable, simply won't tune in a given > design. > > Previously all I had to address this was renting some time on a VNA and > hacking a physical prototype. > > Today I am working with XFdtd simulating the entire PCB, plus all the > surrounding materials. That makes the tuning process one of time on a GPU > instead of rental lab time and X-acto knives. > > It seems that there is some other structure on the PCB that is resonating > in some way that interferes with the antenna. I've done some > investigation with stitching vias and definitely things are a lot more > stable with those in place, but it's not affecting the main problem that = I > am seeing. > > I am wondering if others have hit this, and if so what they did to isolat= e > and get rid of the problem? > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .