Microwave and millimetre wave antipodal Vivaldi antenna with trapezoid-shaped dielectric lens for imaging of construction materials

High-quality microwave and millimetre wave imaging of construction materials and structures requires ultra-wideband (UWB) techniques to provide high-range resolution as well as a reasonable penetration depth. A modified compact microwave and millimetre wave UWB antipodal Vivaldi antenna is designed and presented in this study. First, the conventional antipodal Vivaldi antenna is designed as a reference antenna. Then, to provide the desired frequency range (3.4-40 GHz) with increased gain at its lower frequencies, the slit edge technique is applied, thus creating a periodic slit edge antipodal Vivaldi antenna (PSEAVA). Finally, a trapezoid-shaped dielectric lens (TDL) as an extension of the substrate is added and optimised to increase gain and directivity at higher frequencies of the frequency range, creating PSEAVA with a TDL (PSEAVA-TDL). The results show that the PSEAVA-TDL has the highest gain (up to 16 dB) and front-to-back ratio (up to 37.5 dB), and the narrowest half power beamwidth (down to 11.7 degrees). A prototype of the proposed PSEAVA-TDL with compact size of 40 x 90 x 0.508 mm(3) is fabricated and applied for the imaging of samples made of construction materials. High-range resolution images of the samples are obtained with this antenna by using synthetic aperture radar algorithm.