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 Ω<Re{Z_L}<109 Ω and -107 Ω<Im{Z_L}<48 Ω at 20 GHz equivalent to three quadrants of the Smith chart and loads with 3 Ω<Re{Z_L}<94 Ω and -260 Ω<Im{Z_L}<91 Ω 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.