Basic characteristics of wideband sleeve antenna

Sleeve antenna is one typical antenna type that has a possibility of wideband characteristic. Until now, several types of sleeve antenna are introduced and investigated for obtaining a wider bandwidth than their original versions [1-5]. The most fundamental feature of sleeve antenna is that, a part of the exterior conductor with the length of λ/4 is removed from the coaxial cable, and only the thin interior conductor of this part is remained. With a sleeve added to the remained exterior surface of the coaxial cable. The operation bandwidth of a fundamental sleeve antenna is relatively narrow. In this study, we propose an effective impedance improvement technique for obtaining wideband characteristic of the fundamental sleeve antenna.