The document contains 3 projects that were developed followed by the concentration area of The High-Frequency Design of Electronics Circuits. These projects were: The 1st project is the Band-stop filter with a microstrip line, developed during the subject of High-Frequency Electronics Design. The 2nd project is the Modeling a strain gauge and conditioning circuit for a Natural Vacuum leak detection system. Developed during the subject Methods of Simulation of Electronic Circuits. The 3rd project is the Output capacitor optimization for a Low voltage Drop-Out (LDO) regulator using the space mapping method. Developed during the subject Modeling and Design of Circuits Based on Optimization.