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[dnyberg2]

Does anyone have any advice for a thin flexible polyimide PIFA design that is ground plane backed for 915 MHz? I am radiating RF (<1W) into the body to interrogate a temp pill that got swallowed idea. Not new I know but I'm using this to learn.

Thanks

[helix]

A thin PIFA may be difficult. At 915MHz, the wavelength is about 300mm. If you wanted the antenna to be 3mm thick, then that's only 1% of a wavelength. A PIFA this thin will have a narrow impedance bandwidth for sure (1% or less), and could be pretty inefficient. W.r.t. impedance bandwidth, this will lead to detuning problems. I.e., the antenna center frequency will change a lot when it's placed up against the body, and possibly depending on how and where it's placed. If you want the substrate to be flexible, this is likely to only increase detuning problems.

You might consider a dipole as an alternative.