Passive devices for UWB systems 297 0 Passive devices for UWB systems Fermín Mira 1 , Antonio Mollfulleda 3 , Pavel Miˇ skovský 1 , Jordi Mateu 1,2 and José M. González-Arbesú 2 1 Centre Tecnològic de Telecomunicacions de Catalunya 2 Universitat Politècnica de Catalunya 3 Gigle Networks Spain 1. Introduction The release from the U.S. Federal Communication Commission (FCC) of the unlicensed use of the Ultra-Wide-Band (UWB) frequency range of 3.1-10.6 GHz, fed the interest for developing communication systems to be used on applications requiring high data rate transmission. The complete success and spreading of these novel applications requires inexpensive and reliable UWB communication systems and devices. The set of passive components included in these systems is definitely a key point on their full development. To this end, many efforts have been done by both the academic and industrial sectors, focusing their research activities on the development of UWB passive components. Although the design of passive components for microwave narrow band applications follows well-established procedures or even mathe- matical description, the development and design of UWB passive components is a challenge, and most of the procedures used on the synthesis of narrow band component, circuit mod- els and design procedures are not applicable for such wideband frequency ranges. In this book chapter we present the design, fabrication and measurement of most of the key passive components playing a role on an UWB communication system. To illustrate so, the following figures, Fig.1a and Fig.1b, outline the transmitter and receiver architecture of the constructed demonstrator at CTTC (Mollfulleda et al., 2006). Although we will not go into details on the design of the whole transmitter and receiver it would allow us to identify the passive compo- nents and their role and requirements from a system perspective. In both, transmitter and receiver architectures we identify as a first and second component of the system chain an antenna and an UWB frontend preselected filter (Mira et al., 2009). The following passive component is a power combiner/splitter for the transmitter/receiver, respectively. The transmitter side also includes a pulse shaping network in the pulse generator box (see Fig.1a) and a pulse inverter necessary in certain modulation schemes. Finally as can be seen in the receiver outlined in Fig. 1b a filter bank will be used on the signal detection. 2. Antennas for Optimum UWB System Performance According to the definition of the FCC (FCC, 2002) an "UWB antenna" is an antenna that po- tentially uses all its bandwidth all the time, and its properties are stable across the operational band: impedance match, radiation pattern, gain, polarization, etc. Several types of UWB an- tennas have thoroughly been described in literature. Generally they have smooth shapes such 13 www.intechopen.com