I. Introduction
With the rapid development of 5G communication systems and modules, reducing the size of antennas is becoming an increasingly important issue. However, according to Chu's law, the smaller an antenna is, the narrower is its bandwidth [1]. It is also difficult to reconcile miniature antenna and broadband impedance adaptation. Dealing with these aspects through traditional antenna design techniques can quickly become a delicate and complex task. Many planar antennas are made on a substrate, which reduces their volume significantly and limits the task to minimizing their effective occupied surface. However, the presence of a lossy substrate reduces their radiation efficiency. In this work, we propose a compact, purely metallic three-dimensional (3-D) antenna that covers the entire C-band (3500–3600 MHz). It is a multi-segment monopole structure that offers many degrees of freedom, making it possible to increase the antenna's radiation resistance while maintaining a compact volume. The design of such an antenna is carried out with genetic algorithms.