Ping Pong Resilient Thz-Vna Measurements

This paper presents an experimental investigation into mitigating unwanted ping pong reflections that occur when transmitted waves interact with the surface of the receiver, specifically the casing of the VNA extender or the VNA radio head, as they are not efficiently received. THz-VNA measurements were conducted in the frequency range of 275 GHz to 325 GHz through free-space transmission, encompassing three distinct scenarios. The study observed fifth order ping pong reflections spanning a total distance of approximately 12.8 meters within the dynamic range of the THz-VNA system. Furthermore, the results demonstrate that applying gel absorbers (or ice packs) to the collars of both the transmitter (TX) and receiver (RX) significantly reduces ping pong reflections, achieving an attenuation of up to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{3 9. 2 8} \mathbf{~ d B}$</tex>. Moreover, when gel absorbers are combined with foam absorbers, they effectively eliminate ping pong reflections, including those of the first order.