Microwave interferometry: Application to precision measurements and noise reduction techniques

A concept of interferometric measurements has been applied to the developme nt of ultra-sensitive microwave noise measurement systems. These systems ar e capable of reaching a noise performance limited only by the thermal fluct uations in their lossy components. The noise floor of a real time microwave measurement system has been measured to be equal to -193 dBc/Hz at Fourier frequencies above 1 kHz. This performance is 40 dB better than that of con ventional systems and has allowed the first experimental evidences of the i ntrinsic phase fluctuations in microwave isolators and circulators. Microwa ve frequency discriminators with interferometric signal processing have pro ved to be extremely effective for measuring and cancelling the phase noise in oscillators. This technique has allowed the design of X-band microwave o scillators with a phase noise spectral density of order -150 dBc/Hz at 1 kH z Fourier frequency, without the use of cryogenics. Another possible applic ation of the interferometric noise measurements systems include "flicker no ise-free" microwave amplifiers and advanced two oscillator noise measuremen t systems.