High-frequency semiconductor amplifier

A high-frequency semiconductor amplifier comprising:

• an input terminal inputted with a fundamental signal having a first frequency band and a first center frequency in the first frequency band;
• an input matching circuit including an input end and an output end, the input end of the input matching circuit being connected to the input terminal;
• a high-frequency semiconductor amplifying element including an input end and an output end, the input end of the high-frequency semiconductor amplifying element being connected to the output end of the input matching circuit, and the high-frequency semiconductor amplifying element being configured to amplify the fundamental signal;
• an output matching circuit including an input end and an output end, the input end of the output matching circuit being connected to the output end of the high-frequency semiconductor amplifying element;
• and
• an output terminal connected to the output end of the output matching circuit,
• the output matching circuit including:
• a first transmission line including an input end and an output end, the output end of the first transmission line being connected to the output end of the output matching circuit, the first transmission line having an electrical length of 72 degrees or more and 108 degrees or less at the first center frequency, and a characteristic impedance of the first transmission line being lower than 50Ω, which is a load impedance of an external load connected to the output terminal;
• a second transmission line including an input end and an output end, the output end of the second transmission line being connected to the input end of the first transmission line, the second transmission line having an electrical length of 18 degrees or more and 27 degrees or less at the first center frequency, and a characteristic impedance of the second transmission line being lower than the characteristic impedance of the first transmission line;
• a third transmission line including an input end and an output end, the output end of the third transmission line being connected to the input end of the second transmission line, the third transmission line having an electrical length of 18 degrees or more and 27 degrees or less at the first center frequency, a characteristic impedance of the third transmission line being lower than the characteristic impedance of the first transmission line and higher than the characteristic impedance of the second transmission line and a resistance of a desired load impedance provided to the high-frequency semiconductor amplifying element for fundamental frequency, and a line width along a second direction of the third transmission line being 0.8 times or more and 1.2 times or less of a line width along the second direction of the second transmission line;
• a fourth transmission line including an input end and an output end, the output end of the fourth transmission line being connected to the input end of the third transmission line, the fourth transmission line having an electrical length of 5 degrees or more and 10 degrees or less at the first center frequency, and a characteristic impedance of the fourth transmission line being equal to the resistance of the desired load impedance provided to the high-frequency semiconductor amplifying element for fundamental frequency;
• and
• a wire part including an input end and an output end, the output end of the wire part being connected to the input end of the fourth transmission line, and the input end of the wire part being connected to the input end of the output matching circuit.