A printed compact UWB Vivaldi antenna with hemi cylindrical slots and directors for microwave imaging applications

A new compact UWB (Ultra Wide Band) hemi cylindrical slotted Vivaldi antenna is proposed for microwave imaging system to detect the breast cancer. The hemi cylindrical slots are added on the edges of the Vivaldi Antenna to increase the electrical length and focus the energy towards the aperture centre. The novel combination of hemi cylindrical slots and directors are introduced to improve the performance characteristics of the antenna such as UWB impedance matching, high gain, constant E plane beam tilt, better FBR (Front to Back Ration) and Cross Polarization Discrimination (XPD). To exemplify the effectiveness of this design, a prototype of the VAHCSD (Vivaldi antenna with Hemi Cylindrical Slots and Directors) is fabricated and tested. The antenna is designed on 0.8 mm thick low cost FR4 substrate (49 x 48.5 x 0.8 mm(3)) and operates from 2.9 GHz to more than 9 GHz with S-11 < -10 dB. The gain of the antenna is more than 3 dBi for frequency (3-5 GHz) and greater than 6 dBi from 5 GHz. The FBR value greater than 15 dBi, the XPD value more than -20 dB and the stable radiation pattern are achieved. The calculated fidelity factor is 0.9557 which proves the directionality and low distortion of the transmitted UWB signal. Furthermore, the time domain study of the antenna is also carried out which shows good pulse handling ability with nearly flat group delay having a small variation of +/- 0.5 ns over operating UWB band. (C) 2019 Elsevier GmbH. All rights reserved.