Introduction

     The beginning of 20th century (until WW2) marks the boom in wire antenna technology (dipoles and loops) and in wireless technology as a whole, which is largely due to the invention of the DeForest triode tube, used as radio-frequency (RF) generator. Radio links are realized up to UHF (about 500 MHz) and over thousands of kilometres (1).

    The antenna is the transition between a guiding device (transmission line, waveguide) and free space (or another usually unbounded medium). Its main purpose is to convert the energy of a guided wave into the energy of a freespace wave (or vice versa) as efficiently as possible, while at the same time the radiated power has a certain desired pattern of distribution in space (1).