Graduate Student: Egor Alekseev
Professor Dimitris Pavlidis
Support: URI DAAL03-92-G-0109, MURI DAAH04-96-1-0001, and Daimler Benz
The 90 degrees loaded line phase shifter employs two 5um-diameter InGaAs PIN diodes connected on the ends of the through section to change the loading of the section and therefore its impedance. The MMIC is implemented in microstrip transmission line technology on semi-insulating InP substrate using InGaAs PIN layers grown by MOCVD at the University of Michigan and by MBE at Daimler Benz. The microwave probes and biasing networks are integrated on-chip. The photograph of the fabricated phase shifter is shown in figure below.
When the diodes are in the OFF-state, there is an additional capacitive loading of the central section of the phase-shifter. The capacitive loading of the diodes combined with inductive loading of the quarter-wave vertical sections presents a short to the injected signal. The effective impedance of the central section is increased and the signal is slowed down.
Another way to look at it is: the signal leaking across OFF-state diode capacitance to ground is slowed down in the resonator formed by the diodes and central section as could be seen in the animation accessible below. Therefore a slower propagation of the signal is observed.
When the diodes are in the ON-state the central section is loaded with the shunted quarter-wave sections which present an open to the injected signal. The effective impednace of the central section is increased and the signal passed faster. The animation of the operation is also accessible below.
