A New Technique for the Direct Measurement of Y-Parameters at Microwave Frequencies
A technique has been developed which makes practical the direct measurement of active device two-port y-parameters at microwave frequencies. The instrumentation involved is a simple modification of a conventional s-parameter test set, and the measurement procedure is only slightly more complicated than in a conventional s parameter measurement.
Large Signal GaAs MESFET
Techniques for large signal GaAs MESFET oscillator ales.@ are described which do not require repeated large signal measurement. In tbe first techaiquej smalf signal S-parameter nmasuremerrts are used with a computer program to compute the packaged and mounted device eqniv- afent circuit. Large signal measurements are made to determine a mathe- matical relationship between ordy those parameters which vary rmder large signal conditions. These relationships are included in the computer pro- gram. Thew once the eqnivafent circuit has been computed from the small signal S-parameter measurements, those parameters varying under iarge signafa are incrementaffy aftered until iarge signal S parameters are obtained which comeapond to maximum oscillator output power. These vaiues are used to calcufate embedding element vafuea for six oscillator topoiogk. A coaxial cavity FET oscillator was bailt and tested using the large signal de&gn theory, aad it substantially verifkd the design tech- nique. The seeond design technique is baaed on the fact that S2, varied more than other S parameters under large signals. By making design calcula- tions based on S21 reduced to the point corresponding to maximum oscillator power, it was possible to get usable design information for an FET oscillator.
Modeling Coherent Backscattering Errors in Fiber Optic Gyroscopes for Sources of Arbitrary Line Width
We present a new model of the noise and drift induced by coherent backscattering in a fiber optic gyroscope (FOG) interrogated with a light source of arbitrary temporal coherence. This study is critical to understand whether a FOG driven with a laser instead of a broadband source can attain high sensitivity and stability, which would have the overwhelming benefit of improving the FOG scale factor stability by at least ten-fold and would enable the use of FOGs for inertial navigation of aircrafts. Analytical and numerical solutions bring to light two significant new predictions. First, coherent-backscattering noise can be made negligibly small by utilizing a laser with a very narrow linewidth (less than ~ 20 kHz), although in this regime the drift is high. Second, by using a laser with a broad linewidth (greater than ~ 10 MHz), both the noise and the drift are low enough for aircraft inertial navigation. The dependencies of the noise and drift on fiber loss, loop coupling coefficient, and backscattering coefficient are also presented to define the optimum mode of operation of this new class of FOGs.