Looking toward the DR from this port, the circuit appears as if it were an open circuited transmission line Resonate with the reactance of the active device input (gate) port. We know that the load must have a reactance XI = 62.5 ohms to It remains to determine the length of a 50 ohm terminated microstrip line between the coupling plane of the DRĪnd the gate terminal of the active device. Negative resistance of -40.8 ohms is sufficient to allow the transistor to build up and sustain oscillation at The resultant input impedance of the active port is Za = -40.8 -j62.5 ohms at the desired frequency. Taking etch tolerances into consideration, the length of the feedback stub is chosen as 45 degrees. On the other hand, for the active port, a shorterįeedback stub induces higher negative resistance.įinally, negative resistance is reduced if the electrical length of the feedback stub is less than 25 degrees. More rapid the port reactance change with frequency. By adjusting the electric length of the feedback stub, various port impedanceĬharacteristics for Za (?) in the band of interest (6-15 GHz) can be obtained.įrom the port reactance characteristic, we observe that the shorter the electric length of feedback stub, the The open stub (characteristic impedance of 50 ohms), which is terminated at the source end of the FET, servesĪs the feedback element. The characteristic impedance of the output transmission line, Or gate of the transistor is the negative of Za. #Watch live tv streams online free series#Schematic diagram of the series feedback DRO.ĭetermine the electrical spacing of the dielectric resonator such that the reactance it presents to the base Has the possible maximum variation near resonance in order to insure high circuit Q.įigure 1. Optimize Za (?) with the parameters in the feedbackĬircuit and in the matching network to ensure that Ra (?0) is less than or equal to -25 ohms and Xa (?) Matching network and the load as shown as figure1.
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