Extremely Miniaturized Free-Space Measurement System for RF Metamaterial Composite Based on Beam Focusing Transmitarray

This letter proposes a near-field beam focusing transmitarray-based (TA-based) free space measurement system that is extremely miniaturized rather than horn-to-horn and dielectric lens-based measurement systems for radio frequency (RF) metamaterial composites. Reducing the size of the measurement setup is limited due to the natural phenomenon of conventional systems. Contrastively, TA-based system could overcome the limitation because of its phase-shifting ability to maintain the planar appearance. A device-under-test (DUT) was measured without any distortion utilizing the beam focusing characteristic of the proposed TA, which produces a uniform wavefront phase without diffraction over the DUT aperture. The proposed TA could focus the EM wave within a distance of 2 cm from the horn antenna while maintaining the phase error under $14.5^\circ$ , resulting in a plane wave-like phase. Consequently, the RF metamaterial composites could be measured at a short focal distance of 21.7% of the distance required by the conventional free-space system without additional absorbers. Further, the frequency response of DUT (i.e., $|S_{21}|$ and $\angle S_{21}$ ) could be obtained adequately compared to the full-wave simulation. The difference of transmission zero frequency between simulation and measurement was less than 1.6%.