All the analyzers I have considered have always been to inaccurate. They
sure may work on the DC bands below 30MHz where people think an
antenna is good if the SWR is below 3.

This IC seem promising. Together with a small MCU and AD and some flash
memory you might be able to build a really good instrument that could
beat everything on the market.

Does anyone know a source for these chipts whithin the EU? I have some
directional couplers without detectors that could easily be combined
with this chip.

Your Idea to use a PC to control the radio as a source seem interesting.
The only drawback would be the size of all the stuff you need to bring
into the garden when measuring.

Perhaps a modular design.
a) Optional RF-circuit (directional couplers) different for different
bands to increase accuracy.
b) Detector device (AD-chip, small controller with calibration data)
c) Optional display for computerless operation
d) Optional signal source for rig-less operation.

/Leif