Design of an Ultra-Wideband Log-Period Antenna for a Vacuum Transistor THz Source

In this paper, an ultra-wideband log-period antenna for a vacuum transistor THz source is presented. The two arms of the proposed antenna are positioned on opposite sides of the substrate, with one arm connected to the photocathode and the other to the anode, ensuring compatibility with semiconductor fabrication processes. The angles of the center conductor and the arm teeth are individually optimized to enhance performance. The simulation result shows that the reflection coefficient is less than -10 dB, and the radiation resistance averages approximately 90Ω over the bandwidth of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.33-2 \text{THz}$</tex>. The gains at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\theta=0^{\circ} / 180^{\circ}$</tex> are in the range of 2.25-5.11 dBi across the bandwidth of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.4-2 \text{THz}$</tex>.