A New Phase Shifter-less Delay Line Method for Phase Noise Measurement of Microwave Oscillators

In this paper a new method for measuring phase noise of microwave oscillators based on delay line frequency discriminator is proposed. Elimination of phase shifter is the major advantage of this technique over the traditional delay line technique. By using this new technique, manual or electronic tuning of phase shifter to reach phase quadrature at the phase detector input ports is not needed anymore. A 90-degree hybrid is used in this technique and another path including a phase detector and LNA is added. Finally by using a dual channel FFT analyzer and performing some processing over the sampled data of the two channels, the phase noise of the oscillator will be extracted. A setup based on the proposed method was constructed and the phase noise of a 3 GHz phase locked oscillator was measured via three methods; the traditional delay line method, the phase shifter-less method and direct spectrum reading from spectrum analyzer. Comparison of the measured data of the three methods shows the validity of the proposed method.