Page 170 - MEMS and Microstructures in Aerospace Applications

Osiander / MEMS and microstructures in Aerospace applications DK3181_c008 Final Proof page 160 1.9.2005 12:05pm

160 MEMS and Microstructures in Aerospace Applications

FIGURE 8.5 Photograph of a 2-bit switched-line phase shifter developed by the University
of Michigan and Rockwell Scientific. (Courtesy of Rockwell Scientific Company.)

element, easily implemented in microstrip, which separates the input signal into two
signals that are 908 out of phase. The two switches are tied together. If the switches
are closed, the signal is reflected back into the quadrature hybrid, where the two
reflected waves will add constructively at one port and destructively at another port.
If the switches are open, a total phase shift of Df will be added to the signal. If the
switches are perfectly matched and lossless, and the quadrature hybrid is lossless,
these phase shifters should have little insertion loss. Like the switched-line phase
shifter, several bits with a binary sequence of phase delays can be combined for
digital phase control.
In a MEMS implementation of a reflection phase shifter, MEMS switches
control the reflection stub length. There are fewer MEM reflection phase shifters

Signal in Signal out

FIGURE 8.6 Schematic of a loaded-line phase shifter. Varying the capacitance alters the
phase shift between the input and output.

© 2006 by Taylor & Francis Group, LLC