LibreCAL

LibreCAL is a 4-port, 9kHz to 6GHz eCal module for LibreVNA.

LibreCAL is open source hardware, we have published all the production files, you can also make your own, but you need a professional metrology calibration and VNA for calibration. The LibreCAL we sell has been calibrated with metrology grade calibrators, and the S11 directivity is better than 50dB within 3GHz and better than 40dB above 3GHz, which is better than some mechanical calibrators that cannot provide calibration parameters, but it is important to note that even after rigorous calibration. Due to leaks inside the electronic calibrator, the electronic calibration cannot be performed and can be manually added using the mechanical calibration if necessary. Since LibreCAL is specifically designed for LibreVNA, internally stored calibration parameters can currently only be recalled by LibreVNA, and LibreCAL cannot currently be used for other VNA calibrations.

You can purchase factory calibrated libreCALs at the following stores.
AliExpress Zeenko Store
Eleshop B.V. in EU countries
Taobao in China