Microwave amplifier device

A microwave amplifier for amplifying a microwave signal using an active element comprising:

• a bias circuit including,
• a line having an electric length one quarter a wavelength at a frequency configured to be amplified by the microwave amplifier and being connected between an output terminal of the active element and a bias voltage source, and
• a first capacitor element connected between a terminal where the line is connected to the bias voltage source and a ground that defines a reference potential of the microwave amplifier;
• and
• a resonant circuit including a resistor and a second capacitor element connected in series between the ground and the terminal where the line is connected to the bias voltage source,
• wherein
• the first capacitor element has a reactance regarded as being short-circuited at the frequency configured to be amplified,
• the resistor has a resistance value lower than an absolute value of an impedance of the first capacitor element at a frequency of a beat signal generated between a lowest frequency and a highest frequency in a communication band of the microwave amplifier,
• an inductance of the line, the resistor, and the second capacitor element constitute a resonant circuit at a frequency of the beat signal generated between the lowest frequency and the highest frequency in the communication band of the microwave amplifier, and
• the second capacitor element has a reactance in which the impedance of the line, the resistor, and the second capacitor element is positioned in a vicinity of a real axis inside a circumference of a Smith chart at a maximum frequency of the beat signal generated between the lowest frequency and the highest frequency in the communication band of the microwave amplifier.