A frequency-tunable amplifier with a simple tunable admittance inverter

This paper proposes a frequency-tunable amplifier with a simple frequency-tunable admittance inverter. The admittance inverter consists of a fixed-length transmission-line and only a single shunt variable capacitor connected in the midst of the line. The inverter can maintain the 90-degree phase-shift property while tuning its operating frequency, and is suitable for a general-purpose circuit section for frequency-tunable RF circuits. The fabricated tunable amplifier employs the inverter as a matching circuit, and has obtained its frequency-tuning range of 13-15 GHz.