Modified three-stage doherty amplifier

A three-stage Doherty amplifier, comprising:

• a three-way splitter that splits an input signal evenly into three portions;
• a carrier amplifier that receives one of the portions of the input signal split by the three-way splitter, the carrier amplifier always turning on for the input signal;
• a first and second peak amplifiers each receiving the respective portions of the input signal split by the three-way splitter, the first peak amplifier turning on when the input signal in power thereof becomes greater than a first back-off point, the second peak amplifier turning on when the input signal in the power thereof becomes greater than a second back-off point greater than the first back-off point;
• and
• an output combiner that includes
• a first output transmission line set in a downstream side of the carrier amplifier,
• a second output transmission line set in a downstream side of the first peak amplifier,
• a third output transmission line sets in a downstream side of the second peak amplifier,
• a fourth output transmission line set in a downstream side of the second output transmission line and the third output transmission line, and
• a fifth output transmission line set in a downstream side of the first output transmission line and the fourth output transmission line,
• wherein the first to fifth output transmission lines except for third output transmission line have an electrical length of a quarter-wavelength (λ/4) and the third output transmission line has an electrical length of a half-wavelength (λ/2), where λ is a wavelength of the input signal.