TABLE OF CONTENTS Precision missile tracking radar, tactical fighter fire control radar, and modern communications systems require low-loss, TTD phase shifters to meet stringent performance requirements. Because a precision high power, phased array missile tracking radar deploys thousands of phase shifters to provide multitarget tracking capability with high reliability, a low-loss TTD phase shifter is best suited for this application. Here low-cost, fast response, improved tracking accuracy, and high reliability are the principal requirements. MEMS switching devices and variable capacitors or varactors are used to realize switched-time phase shifters, which suffer from high cost and complexity. A TTD phase shifter configuration using the distributed MEMS phase shifter design and requiring a small analog control voltage to vary the height of the MEMS bridge offers a limited capacitance ratio not exceeding 1.5:1. This ratio is not enough to provide a large phase shift with minimum loss.
The topology of a multi-bit digital-distributed MEMS (MDDM) phase shifter deploys a synthetic transmission line whose phase velocity can be varied by snapping down the membrane or bridge of MEMS loading capacitors in the downstate position [4].
Critical elements of the MDDM, series configuration topology for the MEMS-based capacitors and fixed capacitors, and the expression for the total capacitance are shown in Figure 6.8. Note the total capacitance is 0.01 pF for the upstate position and 0.075 pF for the downstate position...
