A Doherty power amplifier (DPA) is an effective structure born in 1936 which, after a scarce revival around year 2000), had been strengthened from 2005 because its capability to combine linear amplification with power efficiency. Despite the conceptual simplicity of its basic operation, a lot of practical drawbacks shrink the theoretical behavior, thus leading a significant number of research works to overcome them. The main objective in DPA research is to increase efficiency while maintaining linearity and filling the specified bandwidth. This paper presents a survey of the state of the art of DPA advanced design aspects. After a short review of the DPA operation principles, aspects regarding improvements for linearity, power efficiency and amplification bandwidth are introduced. Besides, some alternative structures and technologies, as well as practical design aspects and some trade-offs which the designer usually has to face are also presented.