Dynamic reconfiguration of antenna devices is becoming a prime need in emerging telecommunication and remote sensing systems operating in the portion of the electromagnetic (EM) spectrum spanning from millimeter-wave (MMW) to terahertz. Different techniques and materials are currently available for the implementation of a given EM reconfiguration in antenna systems at microwaves andMMW, such as semiconductors, RF-MEMS, Liquid Crystal, and ferroelectrics. However, a common feature to all these technologies is the significant increased loss and complexity with regard to the devices fixed counterpart. Both loss and complexity further increase when high-performance reconfiguration capabilities are addressed atMMWand above, constituting a major limitation to the future deployment of dynamically controllable systems. Advanced performance, low-complexity and low-cost are, therefore, the cornerstones in the development of new technologies for antenna reconfiguration. In this framework, the main objective of this thesis is to contribute to the advancement of low-cost and efficient technologies enabling antenna reconfiguration capabilities fromMMWto THz frequencies. Within this scope, it is proposed the analysis, design and implementation of mechanically reconfigurable devices using dielectric elastomer actuators (DEAs). DEAs are an emerging technology that possesses unique properties, and represents a potential alternative to conventionalmechanical reconfiguration schemes. DEAs are especially attractive for their large strain combined with low-costmaterials and fabrication, analog control and near-zero DC power consumption. These characteristics make them particularly suited to the realization of low-cost and low-loss reconfigurable antennas. The high potential of DEAs for the realization of adaptive devices is experimentally validated by the development of different prototypes operating atMMWand THz frequencies: i) a very low-loss true-time-delay phase shifter operating at Ka-band; ii) a Ka-band reconfigurable reflectarray with 1-D beam-scanning capability; iii) a stretchable and beam-scanning THz reflectarray exhibiting the uncommon potential for the implementation of conformal or reconfigurable devices based on mechanical stretching. The designs and concepts demonstrated in this thesis pave the way for the evolution of new DEA-based reconfigurable devices resulting in low-cost, low loss and compact structures.