HF range could be implemented for example with a switch and DDS chip. MAX2871 might be a better choice for the source if you want to extend the frequency range downwards and it wouldn't even increase cost. Make sure that the source switch has >100 dB isolation if you go this route, but it shouldn't be too hard at these frequencies. Some commercial VNAs also use this method to reduce costs. Sharing reference receiver is not a bad idea since during normal operation the non-active port reference is not needed. Hardware shouldn't need that many changes, just switch after the source and fourth receiver or switch before the reference receiver.

Especially the TRL calibration is very useful for calibrating out the connectors on the test boards. Eight term calibrations like TRL, unknown thru are hard to implement on one direction VNA. It has advantage of supporting more advanced calibrations. I would make a full two port VNA instead of one direction only. Nice to see more open source VNA projects. I'm thinking about doing a kickstarter (after redesign for manufacturability) and wanted to know if people would be interested in a ~$200 140MHz to 2.5GHz T/R VNA. The usb interface is implemented using a usb PHY and a usb virtual serial port core it can transfer up to 20MB/s but that's not utilized here since we are only transferring a few numbers (already averaged by the fpga logic). It uses 3 receivers, 20MSPS ADCs, and all DSP is done on a spartan 6 FPGA.

It covers the major useful ISM bands, and I was more interested in the lower bands because they propagate much better. EDIT: The kickstarter has now been launched: - I've been working on a low cost 140MHz - 2.5GHz 2-port VNA and got reasonable results with my first iteration: Measured vs simulated graphs (simulations done using RFSim99): Measuring a 900MHz power amplifier: More details (block diagrams, schematics, pcb designs, software, etc) are on github: Some inspirations I got from the hforsten and loxodes VNA Mine is designed to be cheap and accurate, and forgoes 6GHz support because parts get extremely expensive above about 3GHz.

Minivna tiny