1. INAOE, Santa Maria Tonantzintla, Puebla, Mexico
2. Departament d’Enginyeria Electrònica, Escola d’Enginyeria, Universitat Autònoma de Barcelona, Bellaterra, Spain
3. Department of Microtechnology and Nanoscience, Microwave Electronics Laboratory, Chalmers University of Technology, Gothenburg, Sweden
4. Department of Physics, L-NESS, Politecnico di Milan, Como, Italy
5. Departamento de Electrónica y Tecnología de Computadores, Pervasive Electronics Advanced Research Laboratory (PEARL), Universidad de Granada, Granada, Spain