LAUSR

This article summarizes theoretical and technical limitations when applying carrier-suppression interferometer (CSI) methods for precision phase-noise measurements at attosecond resolution. The CSI setup reported here outperforms conventional down-mixing methods by more than two orders of magnitude. For phase noise measurements at 1.3 GHz operation frequency, a detection floor of $\mathscr {L}={-205}\,\,{\text {dBc/Hz}}$ and an excellent time resolution of 10.76 as within an offset frequency range from 40 Hz to 1 MHz have been achieved without the usage of cross correlation or power recycling techniques. Measurement setup resolution limits, calibration methods, and effects of transmission line group delays are reported. Phase shifters and attenuators in the CSI were identified as key components. Different phase shifter technologies based on passive switches, varactor diodes, and capacitors were investigated. The presented research can be used in future in combination with conventional receiver techniques and enhances the state of the art of phase noise measurements to attosecond resolution and above.