Variable attenuator

A variable attenuator for a frequency band of a range with a lower end of at least 10 GHz, comprising:

• an input port and an output port;
• a first transmission line connecting the input port with the output port;
• a first attenuating unit provided between the first transmission line and ground, the attenuating unit included at least one transistor having two current terminals coupled with the first transmission line and ground, respectively;
• a second transmission line connected between the two current terminals of the transistor of the first attenuating unit, the second transmission line operating as an inductor in the frequency band;
• and
• one or more other attenuating units provided in parallel between the first transmission line and the ground and between the input port and the output port, the other attenuating units each providing at least one transistor,
• wherein the transistor of the first attenuating unit and the second transmission line cause a resonance frequency formed by a capacitor between the two current terminals of the transistor of the first attenuating unit and the inductor attributed to the second transmission line, the resonance frequency being within the frequency band,
• wherein the first attenuating unit is disposed closest to the input port, and
• wherein one of the other attenuating units is disposed closest to the output port and the transistor in the attenuating unit closest to the output port has a size greater than a size of the transistor in the first attenuating unit.

A variable attenuator for a frequency band of a range with a lower end of at least 10 GHz, comprising:

• an input port and an output port;
• a first transmission line connecting the input port with the output port;
• a first attenuating unit provided between the first transmission line and ground, the attenuating unit including at least one transistor having two current terminals coupled with the first transmission line and the ground, respectively;
• a second transmission line connected between the two current terminals of the transistor of the first attenuating unit, the second transmission line operating as an inductor in the frequency band;
• and
• one or more other attenuating units each provided in parallel between the first transmission line and the ground and between the input port and the output port, the other attenuating units each providing at least one transistor,
• wherein the transistor of the first attenuating unit and the second transmission line cause a resonance frequency formed by a capacitor between the two current terminals of the transistor of the first attenuating unit and the inductor attributed to the second transmission line, the resonance frequency being within the frequency band,
• wherein one of the other attenuating units is disposed closest to the output port and provides a transistor where another second transmission line is connected between the two current terminals thereof, and
• wherein the transistor in the attenuating unit disposed closest to the output port has a size greater than a size of the transistor m the first attenuating unit.