Testing phase noise of Ultra Low Phase Noise OCXO — Challenges and solutions

Modern instrumentation equipment, commercial & defense communication systems, and radar equipment require excellent stability, extremely low phase noise frequency sources. Testing devices that exhibit phase noise of -120 dBc/Hz at 1 Hz offset from the carrier and better than -180 dBc/Hz on the noise floor is a challenge using existing test equipment and methods. It is especially pertinent to production environment, where measurement time and accuracy of each measurement becomes critical. The purpose of this work was to investigate different test methods, evaluate different phase noise measurement equipment, and find acceptable solutions for both low frequency (around 10 MHz) Ultra Low Phase Noise (ULPN) reference, and HF/UHF ULPN OCXO. Several test methods and test instruments were investigated. There´s no “one size fits all” solution, but for each frequency range the optimum solutions were proposed.