Electronics-Based Free-Space Terahertz Measurement using Hemispherical Lens Antennas

This paper introduces a novel free-space terahertz (THz) characterisation setup featuring an electronic-based technique and miniature additive-manufactured hemispherical lens antennas. By using in-house custom-made hemispherical lenses, radiation characteristics of the electromagnetic (EM) wave of the measurement setup, e.g. the radiation pattern as well as the collimated and focused beam size of the THz beam, can be precisely predicted and synthesized by appropriately selecting the radius size of the lenses. This technique eases design and measurement setup complexity as compared to the existing conventional THz measurement setups without compromising the measurement accuracy and reliability. To demonstrate the THz measurement setup developed in this paper, an asymptotically single-mode hollow Bragg fibre operating from 0.246 to 0.276 THz was characterised for its EM transmission properties. The measurement results characterised by this setup are in good agreements with the results obtained from the analytical study and a conventional free-space THz measurement system. The novel THz measurement technique was also characterised for its critical properties, e.g. reliability, repeatability, sensitivity, and accuracy, indicating that the setup can achieve highly accurate measurement quality whilst still offers various advantages compared to all other existing THz measurement setups such as ease of measurement that allows non-THz expert to setup, setup flexibility, cost-effectiveness, smaller required measurement space, less sensitivity to measurement environments and etc.