TABLE OF CONTENTS The input and output scattering parameters for the cascade, C 11 and C 22, are plotted on the Smith chart in Figure 2-2. Marker 7 is at the phase zero crossing frequency of 100 MHz. C 11 is 0.24 at 133 and C 22 is 0.23 at 40 . When the cascade input and output impedances are not equal to Z o, the mismatch results in an analyzed gain that differs from the maximum available gain. If the input and output impedances are equal to each other and real, but not equal to Z o, then in the analysis, Z o may be readjusted to obtain a correct analysis. The gain and phase are then accurately modeled. To simplify measurement of the Bode response, it is generally desirable to design the oscillator network so that the input and output impedances are equal to the impedance of available measurement equipment, typically 50 or 75 ohms.
For this first example, C 22 is not exactly equal to Z o, and the calculated and displayed loop gain is less than it would be if the output were matched [2]. When the output of this cascade is connected to the input to form the oscillator, the mismatch will reduce the loop gain below the maximum available value.
If the amplifier reverse isolation is adequate, C 12 may be assumed zero. The loop gain, with the output driving the input, may then be derived...
