In advanced wireless communication systems, a rapid increase in the mobile data traffic and broad information bandwidth requirement can lead to the use of complex spectrally efficient modulation schemes such as Orthogonal Frequency Division Multiplexing (OFDM). Generally, complex non-constant envelope modulated signals have very high peak-to-average ratios (PAPR). Doherty Power Amplifier (DPA) is the most commonly used power amplifier (PA) architecture for meeting high efficiency requirement in advanced communication systems, in the presence of high PAPR signals. However, limited bandwidth of the conventional DPA is often identified as a bottleneck for widespread deployment in base-station application for multi-standard communication signals. This thesis focuses on the development of new designs to overcome the bandwidth limitations of a conventional PA. In particular, the bandwidth limitation factors of a conventional DPA architecture are studied. Moreover, a novel design technique is proposed for DPA’s bandwidth extension.