Contents I. Introduction
Regarding the approval and allocation of the frequency band between 3.1 and 10.6 GHz by the Federal Communication Commission (FCC), ultrawideband (UWB) communication systems have become one of the most developing technologies in recent years. UWB systems have advantages such as low cost for short range communication, low propagation power, high data rate, remote sensing application, and highly secured environment. On the other hand, commercial UWB systems need compact inexpensive antennas with wide bandwidth and good radiation properties. UWB antennas have been broadly employed to wireless communications, imaging, and wireless sensor networks. With progress of wireless communication systems, more applications have been employed to mobile wireless dongles with smaller size and lighter weight. It is recently noted that small UWB antennas are needed for some medical applications such as microwave imaging for breast cancer. The sensors generally have restricted size, capability, and battery life; hence, UWB antennas are suitable for communication between the sensors due to its low-cost and low power consumption [1].
