The rapid evolution of wireless communication has led to greater demands on higher data rates and wider spectrum. Being the final stage of the transmitter chain, power amplifiers are driven to adopt signals with high peak-to-average power ratio. Therefore, they play a crucial role and encounter more stringent challenges in terms of achieving wide operational bandwidth and high efficiency at output power back- off. This thesis presents the analysis, design and implementation of an RF-input sequential Load Modulated Balanced Amplifier (LMBA). This architecture is able to modulate the impedance seen by a pair of power amplifiers in a quadrature balanced configuration, by modifying the amplitude and the phase of an external control signal injected into the isolation port of the output coupler.