Single-Transistor Impedance Matching Circuit for Over-Hundred-Octave Active Antennas

In this article, a novel active impedance matching circuit with a single transistor is studied for antennas to cover over a hundred-octave bandwidth. In the proposed matching circuit, only one field effect transistor (FET) is utilized and biased in the ohmic region. The FET is integrated with a dipole antenna at the gate, and connected with a $50~\Omega $ transmission line at the drain. With small dimensions, this active antenna performs as a receiver with a wide impedance bandwidth of 10 MHz–1.9 GHz, in which the reflection coefficient is lower than −10 dB, covering 190 octave bandwidth. An equivalent circuit model of the ohmic-biased FET is built to analyze this unusual wideband performance, which exhibits promising applications in ultrawideband (UWB) electromagnetic sensing systems with extremely restricted volume.