Klopfenstein-Tapered Vlasov Antenna for THz Mode Conversion: Design and Comparative Study

This paper presents the design and simulation of a Klopfenstein-tapered Vlasov antenna for efficient mode conversion and radiation in the terahertz (THz) frequency range. The proposed structure facilitates the transition from a coaxially guided TEM mode to the TM<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</inf>mode, followed by smooth radiation into free space through a geometrically tapered aperture based on the Klopfenstein impedance profile. Full-wave CST simulations are performed over the 0.6-0.7 THz band and compared with conventional step-cut and bevel-cut profiles. The Klopfenstein taper achieves superior reflection performance, maintaining <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$S_{11} &lt; -18$</tex> dB across the entire band, while the step and bevel cuts exhibit higher reflection levels. In the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\phi=90^{\circ}$</tex> plane, the Klopfenstein profile offers a main lobe gain of 13.8 dB and significantly reduced side-lobe level of −24.7 dB, compared to −16.8 dB and −17.5 dB for the step and bevel cuts, respectively.