Phase-Noise Measurement of Microwave Oscillators Using Phase-Shifterless Delay-Line Discriminator

In this paper, a modified method based on the frequency discriminator technique for measuring phase noise of microwave oscillators is presented. In the proposed method, the phase shifter is omitted. In contrast, a 90° hybrid with one more channel containing a phase detector, and a low-noise amplifier is added to the measurement setup. It can be said that an in-phase/quadrature phase-noise detection has been developed. With the proposed method, tuning of the variable phase shifter is not needed anymore. Therefore, the measurement is done automatically, and as a result, the measurement time is decreased. Another considerable advantage of this method is that the method is theoretically self-calibrated. For verifying the accuracy of the method, a measurement setup based on the proposed method was established. Two relatively low phase-noise phase-locked oscillators at frequencies of 2.8 and 4.9 GHz were designed. Their phase noise was measured by the proposed method, the conventional delay-line method, and the two-oscillator technique. Comparison of the measured data of the three methods shows the validity of the proposed method.