Near-field and far-field investigation of miniaturized UWB antenna for imaging of wood

This article presents the design of a droplet shape ultra-wide band antenna for imaging of wood. The proposed antenna is designed on PTFE substrate with a dielectric constant of 2.55, loss tangent of 0.001- and 2.4-mm thickness. The antenna is loaded by a stub to resonate at lower band frequency, strip loading at the back, and a chamfered ground to increase the bandwidth. Despite having miniaturized dimensions of 15 mm × 15 mm, it shows better results compared to recent studies. The simulation results depict a good ultra-wide bandwidth from 3.26 GHz to 20 GHz, and 21.5-25 GHz; Besides, the proposed antenna has two bands at 1.25-1.35 GHz and 1.7-1.81 GHz. In addition to that, the antenna achieved a maximum gain of 5.69 dB and directivity of 7.3 dBi. The measurement results of S-parameters transmitted and received signals performed in air, plywood, and high-density wood show a good agreement with the simulated results. In addition, the measured results illustrate a good isolation and uniform illumination among arrays as well as the received signals' shapes do not change in different environments, but only the amplitude. Hence, the proposed antenna seems to be adequate for microwave imaging of wood.