I'm going public with an open hardware microwave vector network analyzer (VNA) project that I've been developing as a hobby on and off for the past 20 months. 

I'm trying to develop a reasonably priced (for a network analyzer..) microwave VNA that could be useful for hobbyist RF/microwave projects. VNAs can be quite expensive (~$3000 for a decades old HP boat anchor useful up to maybe 6 GHz, new ones cost between the price of a car and a house), so I'm building one for my lab.

All project files are hosted on GitHub. Documentation on GitHub currently reflects an earlier 2 GHz to 10 GHz one-port (isolation wasn't good enough to call it two-port..) revision of the project. For some more information on the previous revision, here is a presentation on that stage of the project.

Anyone who wants to try and replicate an open hardware VNA right now might want to look at Henrik Forstén's design. He scooped my project by a few months and has a more cost effective and polished project. My VNA has a similar topology, but I'm throwing more money at the problem in the hopes of achieving better dynamic range and higher frequencies.

I am currently testing the next revision of the VNA hardware. My previous revision lacked isolation and it was quite expensive because it was too modular. (Each microwave RF connection between modules  costs about $30 from the two SMA connectors and a SMA cable...)

My current revision is split into just three (down from over a dozen) modules.

• A BeagleBone cape with IO headers, power rails, and an AD9577 PLL/VCO for IF, synthesizer reference, and ADC clock generation. 
• A RF synthesizer with filtering and a (hopefully) high isolation port-switch board, to provide a signal to the device under test.
• A four channel demodulator board which synthesizes microwave a LO signal (shout out to the TI LMX2594) to mix down signals (LTC5548) to a ~45 MHz IF, simultaneously sample all channels (AD9864).

I'm currently using ebay-ed directional couplers. I'll look into designing my own once I have a working network analyzer to test them with..

Testing of the BeagleBone cape and RF synthesizer boards is in progress. They don't fry themselves and look like they could work, but I don't recommend that anyone try building them yet. I'll post updates to the log as I finish testing of these modules.