The development of many standards in telecommunications (GSM, UMTS, Bluetooth, etc.), with different central frequencies and frequency bandwidths, increases the interest for multi frequency band or ultra wide band applications. At the same time, these applications need specific radiation patterns. So, the design of antennas for such applications constitutes an important technological problem. We aim to develop a methodology to design antennas by controlling, at the same time, their frequency bandwidth and their radiation pattern by identifying the neutral and active zones on an antenna. It has been applied to two kinds of antennas, a monopole and a patch antenna. The intention of this work is to develop a library of techniques to enlarge or reduce frequency bandwidth, or control radiation pattern.