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This paper presents novel planar dynamically reconfigurable double-stub tuners that utilize electrostatically activated microelectromechanical system (MEMS) switches. The tuners operate in the 10-20-GHz frequency range and have stubs that consist of a digital capacitor bank. Each bank has a predetermined number of capacitors that can be selected through the activation of appropriate MEMS switches. The value and number of capacitors is dictated by the range of loads that needs to be matched. Simulated and measured results from several designs are presented. A 4 bit 4 bit tuner that can match loads with 1 5 Re 109 and 107 Im 48 at 20 GHz equivalent to three quadrants of the Smith chart and loads with 3 Re 94 and 260 Im 91 at 10 GHz is demonstrated for the first time, as well as other designs. The demonstrated tuners provide real-time reconfiguration and matching for RF loads that change values during system operation. Applications include the development of several novel highly integrated microwave/millimeter-wave circuits such as ultra-wide-band high output power and increased power-added-efficiency amplifiers, ultra-wide-band multipliers, and very broad-band antenna arrays. It is expected that these circuits will be part of future low-cost and low-power intelligent RF front-end microsystems and systems-on-a-chip. Index Terms-Intelligent RF front-ends, reconfigurable tuner, RF microelectromechanical system (MEMS) switches. I. INTRODUCTION M ICROWAVE and millimeter-wave technology that offers high-performance, low cost, small size, low power, and wide tunability is essential for today's cost-driven commercial and military industries. In order to meet the above requirements, the research community over the last ten years has been focusing on entire system-on-a-chip solutions, where different components (e.g., passive, active) are integrated on the same substrate. To enhance the performance of planar microwave circuits and address associated problems, researchers have been using micromachining techniques and microelectromechanical system (MEMS) devices [1].

Two and four-bit wideband distributed microstrip phase shifters have been developed on a 21 mil (533 pn) silicon substrate for DC-18 GHz operation. Presented here is the first demonstration of microstrip distributed MEMS transmission line (DMTL) designs, periodically loaded by MEMS varactors in series with a fixed value microstrip radial stub. The two-bit design results in a reflection coefficient less than -10 dB, an average insertion loss of -2.8 dB, and a maximum phase shift of 262' at 16 GHz. The four-bit design results in a reflection coefficient. less than -9 dB, an average insertion loss of -3.0 dB, and a maximum phase shift of 333" at 16 GHz.

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