**10. Tapered composite right/left-handed transmission-line (CRLH-TL) leakywave antennas (LWAs)**

Recently composite right/left-handed (CRLH) leaky-wave antennas (LWAs) have been shown as one of the applications of the CRLH transmission line (TL) metamaterials thanks to their advantages of fabrication simplicity and frequency/electrically scanning capability without any complex feeding network. Neverthless the fixed geometrical size of a unit cell of the CRLH-TL Leaky-wave antennas, prevents the possibility to improve the antenna bandwidth "tapering" the geometrical size of unit cell.

It is well known as a composite right/left-handed transmission-line (CRLH-TL) metamaterials, used for the leaky-wave antennas (LWAs) allow to obtain a superior frequency scanning ability than its conventional counterpart [26-27]. The leaky-wave antennas possess the advantages of low-profile, easy matching, fabrication simplicity, and frequency/electrically scanning capability without any complex feeding network.

However, the conventional leaky-wave antennas suffer from major limitations in their scanning capabilities. In fact the radiation pattern is restricted to strictly positive for uniform configurations, or to a discontinuous range of negative or positive excluding broadside direction, for periodic configurations. The CRLH LWAs have essentially suppressed these limitations, being able to scans the entire space from = -90° to = +90° and thereby paved the way for novel perspectives for leaky-wave antennas.

Although actually the designs of CRLH-TL for LWAs available in the literature, are developed as a different number of unit cell with a fixed geometrical size for all the unit cells of the entire antenna.

These design prevents the possibility to improve the antenna bandwidth "tapering" the geometrical size of unit cell. In order to obtain an improvement of the antenna bandwidth a novel design of CRLH LWAs was used in our work. The simulation results of the the CRLH unit-cell with different size, obtained by a commercial 3D EM simulator has shown the good performance of this antenna compared with the performance of the uniform CRLH TL LWA antenna.

The good performance of this composite right/left-handed LWA are also demonstrated by measured results, which shown a good agreement with simulation results paving the way for the future applications of the antenna.
