Abstract-A novel Ultra-wideband Willis-Sinha Tapered Slot antenna for landmine detection using Ground Penetrating Radar (GPR) system with enhanced gain and directivity is presented. The structure is constructed on a 235 × 270 mm 2 FR4 dielectric substrate. The antenna is fed by a novel tapered coplanar waveguide (CPW) to coplanar stripline (CPS) transition feed. The antenna's impedance bandwidth is extended by adding an antenna arm constructing parabola shape with the antenna element. The antenna has a corrugated structure along the antenna outer edges to improve radiation efficiency and get higher directivity. Also, a mushroom-like circular EBG structure is used in the lower side of the antenna arm to reduce interference and enhance front-to-back ratio (F/B ratio). A partial substrate removal, like circular cylinders inside the substrate, is aligned with the antenna tapered profile to obtain better radiation efficiency and enhance antenna gain. The operational bandwidth of this antenna extends from 0.18 to 6.2 GHz. The minimum return loss reaches 60 dB. The average directivity reaches 12.2 dBi while the gain and radiation efficiency are 11.8 dBi and 92%, respectively with gain enhancement of 195% due to using corrugated structure and air cavities. The front-to-back ratio (F/B ratio) is 23 dB. Also, a size reduction of 48% is achieved due to using extended arm. The antenna performance was simulated and measured. Good agreement was found between numerical and experimental results. The proposed antenna is suitable for various ultra-wideband applications especially in landmine detection. The design of the proposed antenna is given in very simple five design steps.
Abstract-A novel ultra-wideband CPW to CPS transition for TSA in landmine detection by GPR system is proposed. The structure is constructed on a 140 × 140 mm 2 FR4 dielectric substrate. It is composed of 2 sections. The first is nonuniform tapered asymmetric coplanar waveguide (TACPW), and the second section is nonuniform Tapered Asymmetric Coplanar Strips (TACPS). Electromagnetic Band Gap (EBG) structure of coplanar circular patches exists near the transition open slot and aligned with the outer edge of the CPW ground to act as a capacitive loading. The design of the proposed transition is given in very simple four design steps. The CPW to CPS transition is analyzed theoretically and experimentally. To characterize this transition, back to back transition is constructed; besides, the equivalent-circuit model that consists of nonuniform transmission lines is established. The equivalent circuit is constructed by dividing both sections TACPW and TACPS into 35 sections and using ABCD parameters to characterize each section, and conversion to S-parameters is done using MATLAB Program. The selection criterion of the section length is to maintain a linear change in the characteristic impedance with the distance. The results based on equivalent-circuit model, CST simulation (CST studio ver. 15), and measurements are compared. Several parameters are studied through simulations and experiments which are used to derive some design guidelines. The operational bandwidth for the CPW to CPS transition covers from 0 (DC) to almost 10 GHz with minimum return loss reaches −50 dB. For the GPR application (landmine detection) which extends from 0.4 to 3 GHz, the insertion loss of the proposed transition reaches almost −0.5 dB which satisfies the design requirements. The back to back transition performance was simulated and measured. Good agreement is found between numerical and experimental results especially for the GPR ranges of frequencies. The proposed transition has the advantages of compact size, ultra-wide bandwidth, and straightforward design procedure.
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