6.7: Ultrawide Band Four-Bit True-Time-Delay MEMS Phase Shifter Operating over dc-40 GHz

6.7.1 Introduction

Four-bit reflection phase shifters have been designed at X-band frequencies using MEMS capacitive switches and Lance couplers. Resonant delay line phase shifters are designed for K _a-band operations. These phase shifters have demonstrated good IL, but suffers from narrow bandwidths and higher phase offset errors which are not acceptable for certain applications. Recently distributed phase shifters have been developed using CPW transmission line with MEMS bridges to vary the phase velocity of the transmission line. In this case, higher pull-down voltage (>30 60 V) is required, which may not be acceptable in applications where compatibility with microelectronics is the principal requirement. The TTD network concept for MEMS phase shifters will overcome the above-mentioned problems and limitations to achieve good phase shift performance and bandwidth that exceed those associated with MEMS capacitive switches. However, the MEMS switches will permit fabrication of high-quality switched-line TTD networks for phase shifters operating over wide microwave and mm-wave bands. Note these switches use a movable metal shunting bar to connect two RF signal lines when a dc ES actuation is applied. Furthermore, the bits can be fabricated individually for a multi-bit phase shifter with minimum cost and complexity.

Precision-phased array tracking radar incorporating ultrawide band TTD phase shifters are capable of acquiring frequency-dependent targets under multipath environments, because the TTD phase shifters offer higher phase accuracies, lower tracking errors, and minimum group delay ripples. The TTD networks can produce flat delay...